Table of Contents

How to:

Navigate EEZ-View Text

Navigate EEZ-View Images

What is:

The Exclusive Economic Zone?

Plate Tectonics?

Remote Sensing with GLORIA?

Maps and Images:

Continental United States

Alaska

Pacific Islands

Additional Information:

Glossary of Terms

Advanced Features

Additional Data

Acknowledgments

Quit


Navigating EEZ-Tour
Navigating EEZ-View Text

Within the EEZ-View Text window, you can click on colored text to perform an action (on other pages).

Green text changes the page within the EEZ-View Text window.

Red text displays an image in the EEZ-View Images window.

Blue text pops up a box of text on top of the EEZ-View Text window. Click anywhere to close it.

The buttons at the top of the EEZ-View Text window perform the following actions:

  opens the Table of Contents page.

  provides a list of topics addressed in EEZ-View Text. When you select a topic, various options will appear. Select one of those options to open that page.

  returns to the previous page you were viewing.

  prints the current page of EEZ-View Text.

  jumps backward to the previous page in EEZ-View Text.

  jumps forward to the next page in EEZ-View Text.

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Navigating EEZ-View
Navigating EEZ-View Images

The buttons at the top of the EEZ-View Images window perform the following actions:

  will reset EEZ-View to the beginning of the program.

  will restore images to their original size after you use the zoom-in tool.

  will close the currently displayed image.

  allows you to click on yellow EEZ zones to display a new image within the EEZ-View Images window and change the page with the EEZ-View Text window.

  allows you to zoom in on an image. Click once on the image to center on that location. Click-drag a rectangle to fill the window with that portion of the image.

  allows you to zoom out on an image. Click once on the image to center on that

location. Click-drag a rectangle to zoom out from that portion of the image.

  allows you to move an image around on the screen. Click once on the image and drag that point in the desired direction. The image will then redisplay.

  allows you to measure distances on an image. Use single clicks to measure any shape of line, and double-click to end the measurement. The length of the last line segment and the cumulative line length will be displayed in the bar at the base of the image window. This tool is not available on all images.

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EEZ Background
Exclusive Economic Zone

EEZ Extent

(caption)

In 1879 Congress established the U. S. Geological Survey (USGS) as a scientific research organization. For more than 100 years, the USGS has examined the geological structure and resources of the nation. The information provided by the USGS is helpful in promoting the health and safety of the people, as well as in the management of our natural resources.

World War II and the development of sonar technology significantly improved our knowledge of the ocean basins. By the late 1950's, the scientific community had knowledge of the depths of the world's oceanic trenches and the existence of submarine mountain chains. In 1962, Congress extended the geologic investigations of the USGS into the marine realm. The data collected over the past 35 years have dramatically altered our perception of the sea floor.

On March 10, 1983, President Reagan formally declared the Exclusive Economic Zone (EEZ) of this nation to extend over 200 nautical miles beyond its shorelines in the Atlantic, Pacific, and Arctic Oceans, the Gulf of Mexico, and the Caribbean and Bering Seas. The EEZ includes more than 13 million square kilometers (sq km) offshore, an area surprisingly much larger than our on-shore territory! This declaration gave the United States sovereign rights to all natural resources within the EEZ and provided a mandate for reconnaissance exploration.

The EEZ, in comparison to long-studied onshore areas, clearly is a new frontier. By 1980, before the images featured on this CD-ROM were collected, the general bathymetry of the EEZ was known but the detailed geology was not well known. Only with such detailed knowledge of the sea floor could we begin to understand human impact on the oceans, appraise its resource potential, and be aware of existing geologic hazards. However, the problems encountered in mapping the sea floor are not unlike the challenges of mapping the Moon, Mars, Venus, and other planetary bodies. The environments are hostile, so scientists rely on remote-sensing techniques. Mapping the EEZ requires scientists to use geologic knowledge and intuition to synthesize information from several data sources.

The USGS designed the EEZ-SCAN program to provide reconnaissance maps of the newly declared EEZ. During 1984 through 1991 extensive deep-water portions of the EEZ were mapped systematically using sidescan sonar, a remote-sensing technology that uses sound to collect images of the ocean floor. The resulting sidescan-sonar images, shown on this CD-ROM, are no less remarkable than the first photographs from the far side of the Moon. These reconnaissance views of the sea floor provide a "road map" to aid the next generation of studies of the geologic processes and resources of our oceans' floors.

References

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Plate Tectonics

Cross-Section of Tectonic Plates

(caption)

The size of the Earth -- about 12,750 kilometers (km) in diameter -- was known by the ancient Greeks, but it was not until the turn of the 20th century that scientists determined that our planet is made up of three main layers: crust, mantle, and core [image A and caption]. This layered structure can be compared to that of a boiled egg. The crust, the outermost layer, is rigid and very thin compared with the other two. Like the shell of an egg, the Earth's crust is brittle and can break. Below the crust is the mantle (the white of a boiled egg), a dense, hot layer of semi-solid rock approximately 2,900 km thick. At the center of the Earth lies the core (yolk), which is nearly twice as dense as the mantle.

The surface of our planet has been shaped by plate-tectonic processes. In the early 1960's, the emergence of the theory of plate tectonics started a revolution in the earth sciences. Scientists now have a fairly good understanding of how the tectonic plates move and how such movements relate to earthquake activity, sea-floor topography, and almost all geologic processes active on the surface of the Earth.

In geologic terms, a plate is a large, rigid slab of solid rock. The word tectonics comes from the Greek root "to build." Putting these two words together, we get the term plate tectonics, which refers to how the Earth's surface is built of numerous plates. The theory of plate tectonics states that the Earth's outermost layer is fragmented into a dozen or more plates that are moving relative to one another [image B and caption].

The tectonic plates do not randomly drift or wander about the Earth's surface. They are driven by the slow movement of hot, softened mantle that lies below the rigid plates. The mobile rock beneath the rigid plates is believed to be moving in a circular manner somewhat like a pot of thick soup when heated to boiling. The heated soup rises to the surface, spreads and begins to cool, and then sinks back to the bottom of the pot where it is reheated and rises again. This cycle is repeated over and over to generate what scientists call a convection cell or convective flow [image C and caption]. This convection within the mantle moves the tectonic plates along the Earth's surface in much the same way as a conveyor belt.

This conveyor belt activity causes the plates to be perpetually "recycled." New crust is formed at the mid-ocean ridge spreading centers while older crust is destroyed as it sinks into subduction zones. The size of the Earth has not changed significantly during the past 600 million years, and probably not since shortly after its formation 4.6 billion years ago. The Earth's unchanging size implies that the crust must be destroyed at about the same rate as it is being created.

Because the tectonic plates are constantly in motion, the areas where they meet, boundary zones, are geologically very dynamic. The main types of plate boundaries are: divergent, convergent, and transform. Divergent boundaries occur along spreading centers (often on the ocean floor) where plates are moving apart and new crust is created by magma pushing up from the mantle. Picture two giant conveyor belts, facing each other but slowly moving in opposite directions as they transport newly formed oceanic crust away from the ridge crest. Perhaps the best known of the divergent boundaries is the Mid-Atlantic Ridge. This submerged mountain range, which extends from the Arctic ocean to beyond the southern tip of Africa, is but one segment of the global mid-ocean ridge that encircles the Earth. This immense system of submarine mountain chains -- more than 50,000 km long and, in places, more than 800 km across -- zigzags between the continents, winding its way around the globe like the seam on a baseball. Rising an average of about 4,500 meters(m) above the sea floor, the global mid-ocean ridge overshadows all the mountains in the United States except for Mount McKinley (Denali) in Alaska (6,194 m).

Convergent boundaries occur where tectonic plates collide. When two plates converge, one is usually subducted under the other, and in the process a deep sea-floor trench is formed. The plate being subducted sinks into the trench and is destroyed or recycled back into the mantle. Frequent earthquakes occur due to the stress of this plate interaction. As the subducted plate begins to melt, some of the newly formed magma rises through the overriding crust to form volcanoes. When oceanic and continental tectonic plates collide, the relatively dense oceanic crust is subducted beneath the more buoyant continental crust [image D and caption]; the trench occurs on the ocean floor along the continental margin, and the volcanoes develop along the continental borderlands. When an oceanic plate is subducted beneath another oceanic plate, volcanoes are slowly built on the ocean floor, sometimes rising above sea level to form island volcanoes [image E and caption]. Such volcanoes are typically strung out in chains called island arcs, which closely parallel the trenches. The Pacific Ocean is encircled by sea-floor trenches and active volcanoes. This is commonly known as "The Ring of Fire" [image F and caption].

Transform boundaries occur where two plates slide horizontally past one another. These large faults or fracture zones commonly offset the active spreading ridges (divergent plate boundaries), producing zigzag plate margins, and are generally defined by shallow earthquakes. Most transform faults are found on the ocean floor. However, a few occur on land, for example the San Andreas fault zone in California is a transform boundary.

The vast majority of earthquakes and volcanic eruptions occur near plate boundaries, but there are some exceptions. For example, the Hawaiian Islands, which are entirely of volcanic origin, have formed in the middle of the Pacific Ocean more than 3,200 km from the nearest plate boundary. The distinctive linear shape of the Hawaiian Island-Emperor Seamounts chain resulted from the Pacific Plate moving over a deep, stationary hot spot in the mantle, located beneath the present-day position of the Island of Hawaii [image G and caption]. Heat from this hot spot produced a persistent source of magma by partly melting the overriding Pacific Plate. The magma, which is lighter than the surrounding solid rock, then rises through the mantle and crust to erupt onto the sea floor, forming an active seamount. Over time, countless eruptions cause the seamount to grow until it finally emerges above sea level to form an island volcano. Continuing plate movement eventually carries the island beyond the stationary hot spot, cutting it off from the magma source, and volcanism ceases. As one island volcano becomes extinct, another develops over the hot spot, and the cycle is repeated. This process of volcano growth and death, over many millions of years, has left a long trail of volcanic islands and seamounts across the Pacific Ocean floor.

References

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Remote Sensing
Remote Sensing with GLORIA

Sidescan-Sonar Data Collection

(caption)

Remote-sensing technologies provide a unique view of otherwise inaccessible areas, as well as powerful analytical capabilities. Most imaging techniques that we are familiar with, such as photography or satellite imaging of the earth, use reflected light as their data source. Sonar technology uses sound waves to create images called sonographs. This technology is an essential tool in the study of the deep, dark sea floor.

The first sidescan-sonar system was developed in 1960 by the Institute of Oceanographic Sciences (IOS) in the United Kingdom for use in shallow water.  When the submarine Thresher was lost in 1963, the need for deep-water search capability became clear. In 1969 IOS introduced GLORIA (Geologic LOng Range Inclined ASDIC), the first sidescan-sonar system capable of deep-water geologic surveying. In 1977 they produced the next generation, GLORIA II, which was used to collect the imagery presented on this CD-ROM.

The GLORIA II sidescan-sonar system, used by the U.S. Geological Survey to map the U.S. Exclusive Economic Zone (EEZ), was specifically designed to map the large-scale morphology and texture of sea-floor features in the deep ocean. To map efficiently a large area such as the EEZ, some detail had to be sacrificed. GLORIA cannot resolve human debris such as pieces of shipwrecks, but it can map an area the size of New Jersey in a single day! The images shown on this CD-ROM have a pixel resolution of 500 meters (m). Higher resolution GLORIA images (50 m pixels) are available on other CD-ROMs (see Additional Data section of EEZ-View Text).

Acoustic images of the sea floor are formed by aiming sound waves at the sea floor and recording the returning sound waves. These images are graphic presentations of the interaction of acoustic energy with the sea floor, not optical views of the sea floor. The GLORIA II sonar vehicle is 8 m long, weighs 2.25 tons in air, and is neutrally buoyant in sea water. This torpedo-shaped "fish" is towed at about 50 m depth behind a ship by a heavy cable containing electrical wires that transmit the signals between the ship and the fish [image A and caption]. The electronic instruments in the fish send out a pulse of sound that travels through the water and is reflected by the sea-floor sediments. Computers aboard the ship then record the amount of energy (backscatter) that returns from the sea floor and use that data to create the image.

"Sidescan" refers to the shape of the sonar beam, which fans out to the sides and scans a wide "swath" of sea floor. The energy beam is confined to the plane perpendicular to the ship's track, forming a narrow acoustic beam in the horizontal plane and a broad beam in the vertical plane. With every sound pulse the fish emits, it images one strip of sea floor as much as 22 km wide on each side of the fish. As the ship tows the fish along its course, it insonifies successive areas of the sea floor, building a long swath of imagery pulse by pulse. The fish is towed along parallel tracklines back and forth over an area, like mowing a lawn, with a small amount of overlap between adjacent swaths. With proper navigational control, these parallel swaths of sonar imagery can be mosaicked together to produce large areas of continuous sea-floor imagery, similar to the method used in aerial photography.

The mosaic is a gray-scale image of the acoustic backscatter variations of the sea floor. The darkness or lightness of a feature on the mosaic is a function of how much sound is backscattered from the sea floor. White represents the most acoustic backscatter, and black represents the least. The amount of backscattered acoustic energy is controlled by the sea-floor topography, roughness of the sea-floor surface, and the sea-floor composition.

Sea-floor topography dramatically affects the amount of backscatter received by the sidescan fish. When viewed from the ship's trackline, a positive-relief feature, such as a volcano, usually appears as a bright zone (the slope facing the sonar beam) with a dark zone (the acoustic shadow) behind it. Conversely, a negative-relief feature, such as a canyon, usually appears as a dark zone (the near wall is shadowed) followed by a bright zone (the far wall is facing the sonar beam).

Hard rock ocean-floor substrates such as seamounts, volcanoes, and oceanic ridges reflect a lot of acoustic energy (high backscatter), and are recorded as bright areas on the sidescan image. Bright patterns also can be caused by certain sedimentation patterns and by steep sediment-covered slopes facing the sonar beam. Sea-floor materials such as soft mud tend to absorb much of the acoustic signal, returning very little energy (low backscatter), and appear on the image as dark areas. Dark patterns also have a variety of causes, but are commonly caused by acoustic shadows and certain variations in sediment type.

USGS scientists have interpreted the geology of many of the sonar images from the EEZ. In this CD-ROM we provide these geologic maps, where available, to aid you in your examination of the imagery. The first-time viewer is often distracted by the dark, narrow stripes of the ship's nadir, which are non-data areas. They indicate the path of the sidescan fish, and thus the source of sonar beams; they can be ignored.

References

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United States
Continental United States and Puerto Rico

Continental U. S.

Exclusive Economic Zone

See the images and maps for the:

East Coast of USA

Gulf of Mexico

Puerto Rico

West Coast of USA


East Coast of USA

Sidescan-Sonar Image

The Atlantic sidescan-sonar mosaic covers more than 500,000 square kilometers (sq km) of a passive continental margin. This GLORIA image reveals a vast system of canyons that disperse sediment from the continental shelf, across the continental slope and the continental rise to the deep abyssal plains seaward of the area shown in the GLORIA image. The continental slope between Long Island and the Chesapeake Bay is cut by many large submarine canyons. While several of these can be traced across the continental rise, Hudson Canyon is the most prominent [image A and caption]. It is visible on the GLORIA image as a clearly defined channel, while the others appear as more general bright stripes.

The continental rise, which constitutes much of this GLORIA image, was sculpted by mass movements, channelized flows, and contour currents. When sea level rises, as it has done during Holocene time, sediments are trapped in estuaries; during lowered sea level, rivers empty into the ocean near the edge of the continental shelf, causing large volumes of sediment to accumulate near the shelf edge and upper slope. These deposits become unstable and move downslope as slumps, slides, and debris flow, leaving dramatic scars on the sea floor. Off North Carolina are the Cape Fear and Cape Lookout slide complexes, which are visible on the GLORIA image as large bright swaths [image B and caption]. They are 30 to 70 km wide and more than 250 km long. The Cape Fear slide has removed as much as 80 vertical meters (m) of sediment from the upper rise.

The Blake Plateau is a submerged limestone plateau seaward of South Carolina, Georgia and Florida [image C and caption]. Like the modern Bahama Platform, the Blake Plateau formed at sea level. Unlike the Bahamas, the Blake Plateau has stopped growing and has subsequently been submerged to its present depth of about 1,000 m. The eroded edge of the Blake Plateau, the Blake Escarpment, is an undersea cliff nearly 4,000 m high that appears on the GLORIA image as a conspicuous white band. Most of the surface of the escarpment consists of giant steps caused by the erosion of flat-lying limestone strata by southward-flowing contour currents.

Six ancient volcanoes are visible on the GLORIA image offshore of New England [image D and caption]. They are part of a 1,200-km-long chain of sea-floor volcanoes that extends to the Mid-Atlantic Ridge, and represents the only volcanic outcrop along the U.S. Atlantic seaboard. Formed during the Cretaceous period approximately 125 million years ago, these volcanoes are now partly buried by a growing sedimentary wedge.

A full-color geologic map has been created using this sidescan-sonar mosaic. It illustrates many of the features discussed above [image E and caption].

Remove yellow boxes

Geologic Interpretation of Image

(Display/Remove)

Select any of the geologic units listed below to highlight that area on the sonar image. Map and units reprinted from Twichell and Polloni, 1993 (see References).

Continental rise, hemipelagic drape

Basement seamount

Canyon-channel complex

Channel-gather area

Current-reworked sediment

Current-scoured outcrop

Sediment waves

Mesozoic and Cenozoic carbonate outcrop

Terrigenous debris flow

Manganese pavement

Continental Shelf deposit

Clear yellow highlighting

Shaded-Relief Image

(Display/Remove)

A shaded-relief image will overlay the green land bordering the East Coast of the United States (some green may still show because the coastline has been generalized for rapid display). The image is made by computer processing of millions of elevation values derived from digitizing the elevation contours from published topographic maps. Exaggeration of the relief and illumination by a simulated sun increases the contrast between rugged and smooth topography. See reference Thelin and Pike, 1991.

References

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Gulf of Mexico

Sidescan-Sonar Image

The Gulf of Mexico is a small, geologically diverse ocean basin that can be divided into three distinct provinces: a salt deformation province underlying the continental slope in the northwest Gulf, the Mississippi Canyon and Fan system in the central Gulf, and a carbonate province along its eastern boundary. The GLORIA image of this area covers about 420,000 square kilometers (sq km) of sea floor.

The continental slope in the northwestern Gulf of Mexico, offshore of Texas and Louisiana, has a unique morphology: rather than submarine canyons crossing the slope as seen off the east or west coasts of the United States, this area is characterized by numerous circular to irregularly shaped domes and basins. These features develop as newly deposited sediments press down on the thick layer of salt that underlies the continental slope. The salt flows under the sediment load, creating a hummocky topography of salt domes and salt-withdrawal basins. These domes can be large enough to influence the downslope path of large submarine slides [image A and caption]. The 5 meter (m) high Sigsbee Escarpment marks the seaward limit of the salt [image B and caption].

The central Gulf of Mexico is dominated by the Mississippi Canyon and Fan system. During glacial times, the Mississippi River delivered a huge amount of sediment into the Gulf of Mexico: during the Pleistocene as much as 4.5 km of sediment accumulated on the Mississippi Fan, locally burying the Florida Escarpment. This sidescan-sonar mosaic provided the first complete view of the Mississippi deep-sea fan. The low-backscatter regions around the margins of the fan represent fine-grained hemipelagic deposits, while the high-backscatter regions on the fan are sandy deposits.

The Mississippi Canyon feeds sediment downslope to the Mississippi Fan. A single channel meanders for 600 km from the base of the slope across the surface of the Mississippi Fan to the basin floor [image C and caption]. Mass wasting has played a key role in redirecting channels and sites of sedimentation. New depositional lobes, visible as high-backscatter areas on the image, are created when debris flows choke the main channel, resulting in a levee breach. Sediment is then redirected through the breach out onto the surface of a new part of the fan. It is amazing that at 3,000 m water depth, the main channel shows the same meanders and over-levee deposits that the Mississippi River does on land!

In the eastern Gulf of Mexico, the Florida Escarpment rises more than 1,500 m from the sea floor and extends along the western side of Florida for about 650 km. On the main image it appears as a thin, bright feature along much of the eastern edge of the mosaic; use the magnifier tool to see it in more detail. This limestone cliff, like the Blake Escarpment off the east coast of Florida, was formed by the growth of reefs and carbonate shelf-edge banks during the Mesozoic. Erosional processes have subsequently steepened the escarpment, causing as much as 8 km of retreat along its base.

A full-color geologic map has been created using this sidescan-sonar mosaic. It illustrates many of the features discussed above [image D and caption].

Remove yellow boxes

Geologic Interpretation of Image

(Display/Remove)

Select any of the geologic units listed below to highlight that area on the sonar image. Map and units reprinted from Twichell and Polloni, 1993 (see References).

Continental slope, hemipelagic drape

Canyon-channel complex

Sediment waves

Fan depositional lobe

Fan linear stripe

Mesozoic and Cenozoic carbonate outcrop

Pleistocene carbonate mud

Carbonate debris flow

Terrigenous debris flow

Carbonate talus deposit

Salt diapir

Salt deformation province

Salt escarpment

Clear yellow highlighting

Shaded-Relief Image

(Display/Remove)

A shaded-relief image will overlay the green land bordering the Gulf of Mexico (some green may still show because the coastline has been generalized for rapid display). The image is made by computer processing of millions of elevation values derived from digitizing the elevation contours from published topographic maps. Exaggeration of the relief and illumination by a simulated sun increases the contrast between rugged and smooth topography. See reference Thelin and Pike, 1991.

References

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Puerto Rico

Sidescan-Sonar Image

The GLORIA image of the Exclusive Economic Zone (EEZ) of Puerto Rico covers about 280,000 square kilometers (sq km) of sea floor. The insular shelf north of Puerto Rico is narrow, generally less than 5 km wide. The shelf edge occurs at a depth of 100 meters (m) or less. The insular slope extends from the shelf edge to about 7,000 m depth where it ends abruptly in the Puerto Rico trench, a large, flat-floored trough that trends parallel to the Puerto Rican shoreline. Numerous canyons as much as 400 m deep have been incised into the upper slope. Scientists in research submarines have seen large boulders perched on the canyon walls, showing how strong the erosional forces were that carved the canyons. Downslope from the canyons are two amphitheater-shaped scarps created by mass wasting. The larger scarp is about 60 km wide and represents the removal of more than 1,500 cubic kilometers of sediment [image A and caption]. In addition, numerous small scarps are visible between canyons on the upper and middle slope [image B and caption].

Shelf- and slope-derived sediment that was transported through the canyons accumulated in the 80 km wide basin and ridge province on the lower part of the slope. Most sediment was trapped in the inter-ridge basins before it reached the Puerto Rico Trench floor, but some sediment did travel all the way to the trench. Within the basin and ridge province, ridges exhibit several hundred meters of local relief, and sediments are distributed irregularly in the inter-ridge areas.

The Puerto Rico Trench lies 150 km north of the island, just beyond the basin and ridge province [image C and caption]. It can be seen on the GLORIA image as a dark east-trending band south of latitude 20º N. With depths exceeding 8,000 m, the Puerto Rico Trench is the deepest part of the Atlantic Ocean! It is also part of the only active plate margin in the North Atlantic. The Caribbean-North American Plate boundary zone experiences strike-slip motion in the Puerto Rico Trench to the north, and compressional forces in the Muertos Trough to the south. Seismic activity extending to depths of at least 150 km confirms that deformation continues to the present day.

The erosional forces acting on the insular slope south of the island have not been as strong as those on the north slope. Numerous channels and areas of eroded sea floor exist, but the channels are fewer, shorter, and less deeply incised than on the north slope, and no large scarps are visible on the GLORIA image south of Puerto Rico. Use the magnifier tool to see that area in more detail.

A full-color geologic map has been created using this sidescan-sonar mosaic. It illustrates many of the features discussed above [image D and caption].

Remove yellow boxes

Geologic Interpretation of Image

(Display/Remove)

Select any of the geologic units listed below to highlight that area on the sonar image. Map and units reprinted from Twichell and Polloni, 1993 (see References).

Abyssal plain, hemipelagic drape

Basement seamount

Canyon-channel complex

Carbonate bank

Manganese nodule field

Insular slope, eroded sediment

Sediment-filled basin

Insular slope, hemipelagic drape

Tectonically deformed sediment

Inter-basin tectonic zone

Clear yellow highlighting

Shaded-Relief Image

(Display/Remove)

A shaded-relief image will overlay the green land of the island of Puerto Rico (some green may still show because the coastline has been generalized for rapid display). The image is made by computer processing of millions of elevation values derived from digitizing the elevation contours from published topographic maps. Exaggeration of the relief and illumination by a simulated sun increases the contrast between rugged and smooth topography.

References

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West Coast of USA

Sidescan-Sonar Image

The GLORIA image of the Exclusive Economic Zone (EEZ) off California, Oregon, and Washington covers about 830,000 square kilometers (sq km) of sea floor. Many geologic features visible on the imagery are representative of a tectonically active continental margin: volcanic ridges and seamounts, faults, crustal lineaments, channels, levees, slump scars, large sediment bedforms, and varying sediment types. The geologic processes active along this margin differ north and south of about latitude 40º N due to a major change in the nature of the ocean-continent plate boundary. North of latitude 40º N, the North American Plate boundary is a subduction zone; south of 40º N the plate boundary is transform.

In the north, new ocean crust forms along the Juan de Fuca spreading center, as oceanic plates move apart. This spreading center is part of the global ridge system that extends 50,000 km through all the ocean basins. The Blanco Fracture Zone accommodates the offset between the Juan de Fuca Ridge and the Gorda Ridge [image A and caption]. Cascadia Channel, a major sediment conduit, can be clearly traced from offshore central Oregon south to where it snakes through the Blanco Fracture Zone, and then heads off the mosaic to the west [image B and caption]. The channel transports sediment from the Columbia and Fraser River systems westward more than 500 km across the Juan de Fuca and Pacific Plates. The Cascadia Subduction Zone is active along the Washington, Oregon, and northern California coasts: here the North American continental plate overrides both the Gorda and the Juan de Fuca oceanic plates, causing large earthquakes and creating the string of Cascade volcanoes in Oregon and Washington. The Mendocino Fracture Zone (MFZ) is a right-lateral transform fault that forms the boundary between the young crust of the Gorda Plate to the north and the older, more sediment-covered Pacific Plate to the south [image C and caption] and accommodates the relative motion between these two tectonic plates. Use the magnifier tool to see the Gorda Ridge in more detail (bright, NE-SW trending feature between the Blanco and Mendocino Fracture Zones).

South of latitude 40º N, the transform plate boundary is located onshore near the shoreline. The geologic features most visible in the mosaic are deep-sea fans and seamounts. Perhaps the best-studied submarine fan in the area is the Monterey Fan. The continental margin off central California has a narrow shelf and steep slope. The margin extends from the shoreline to depths of 3,000 meters. Monterey Bay is a 40-km (N-S) by 10-km (E-W) reentrant of the coastline that forms a shallow, relatively broad portion of the shelf. The continental slope seaward of Monterey Bay is incised by the large Monterey Canyon system [image D and caption]. This canyon system feeds sediment to the Monterey Fan, which covers about 100,000 sq km of sea floor. The Monterey Fan, bounded on the north by the Farallon Fan and on the south by the Murray Fracture Zone, thins to the west, ending more than 400 km from the shoreline.

The large influx of sediment along the central California margin, which created the numerous deep-sea fans, diminishes to the south. A large number of seamounts are visible along the southern California margin draped with only a thin covering of sediment [image E and caption].

A full-color geologic map has been created using this sidescan-sonar mosaic. It illustrates many of the features discussed above [image F and caption].

Remove yellow boxes

Geologic Interpretation of Image

(Display/Remove)

Select any of the geologic units listed below to highlight that area on the sonar image.

Basement fracture zone

Basement ridge with sparse sediment cover

Basement ridge with thick sediment cover

Basement seamounts with sparse sediment cover

Basement seamounts with thick sediment cover

Continental margin

Sediment, basin facies

Sediment, channelized

Sediment, debris flow

Sediment, depositional lobe

Sediment, fan facies

Sediment - fan facies with large bedforms

Sediment, slump

Sediment, sea-floor-spreading texture

Individual volcano with crater

Clear yellow highlighting

Shaded-Relief Image

(Display/Remove)

A shaded-relief image will overlay the green land bordering the West Coast of the United States (some green may still show because the coastline has been generalized for rapid display). The image is made by computer processing of millions of elevation values derived from digitizing the elevation contours from published topographic maps. Exaggeration of the relief and illumination by a simulated sun increases the contrast between rugged and smooth topography. See reference Thelin and Pike, 1991.

References

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Alaska

Alaskan

Exclusive Economic Zone

See the images and maps for the:

Aleutian Arc

Bering Sea

Gulf of Alaska


Aleutian Arc

Sidescan-Sonar Image

This sidescan-sonar image of the Exclusive Economic Zone (EEZ) south of the Aleutian Islands covers about 800,000 square kilometers (sq km) of sea floor. The Aleutian Arc is a string of volcanoes that has formed along the northern boundary of the Pacific plate where the oceanic crust is subducted beneath the Bering Sea at the Aleutian Trench. Although a geologic-interpretation map of this GLORIA image is not yet available, there are some interesting features to be noted. The oceanic crust entering the Aleutian Trench is relatively old, and during its history has accumulated a thick blanket of terrigenous and hemipelagic sediment that has buried and smoothed over the original rough topography of the igneous crust [image A and caption]. Additional sediment accumulates on the plate just prior to its subduction in the bathymetric low of the Aleutian Trench. The trench acts as a conduit and site of deposition for sediment transported westward from mainland Alaska and locally derived debris from the Aleutian Arc.

Because of this sediment cover, the Aleutian Trench is not an obvious feature in the GLORIA image [image B and caption]. During subduction much of the sedimentary cover riding on the down-going oceanic crust is scraped off by the overriding plate and accreted to the front of the Aleutian Arc. During the accretionary process, this originally flat-lying sedimentary blanket is folded and stacked up, forming long, steep-sided ridges that parallel the trench [image C and caption]. This process results in a striking morphology and structure analogous to that which occurs when a rug is pushed up against a wall and rumples up into a series of parallel folds.

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Shaded-Relief Image

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A shaded-relief image will overlay the green land of Alaska and the islands of the eastern Aleutian Arc (some green may still show because the coastline has been generalized for rapid display). The image is made by computer processing of millions of elevation values derived from digitizing the elevation contours from published topographic maps. Exaggeration of the relief and illumination by a simulated sun increases the contrast between rugged and smooth topography. See reference Riehle and others, 1997.

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Bering Sea

Sidescan-Sonar Image

The Bering Sea is an isolated ocean basin with depths as great as 4,500 meters (m). It is bounded to the north and east by the Bering Sea continental shelf and to the south by the Aleutian trench. The GLORIA image of the deep Bering Sea covers some 830,000 square kilometers (sq km) of sea floor, and does not include the vast, shallow continental shelf. Before the Aleutian Arc formed, the Bering Sea was open to the Pacific Ocean. At that stage, the oceanic plate in the North Pacific was being subducted along the northern Siberian continental margin. In early Tertiary time, the subducting plate boundary jumped southward to its modern position, forming the Aleutian Arc and trapping a piece of the ancient oceanic plate within the newly-formed Bering Sea basin.

Since the formation of the Bering Sea, more than 4 km of sediment have accumulated in some parts of the basin. This influx of sediment has buried almost all traces of the igneous crust, forming a flat, largely featureless sea floor that slopes gently down to the west. Sediment is delivered to the deep Bering Sea by deep-sea channels [image A and caption] and by submarine landslides, both of which can be seen in the GLORIA imagery. Use the magnifier tool to see the Beringian Margin debris flows along the northeast edge of the image. One of the most striking patterns visible in the southern Bering Sea basin is the variations in the reflectivity of the sea floor formed by the diffuse distributional pathways traveled by sediment flowing across the basin floor [image B and caption]. Earthquakes along the Aleutian Arc trigger large submarine landslides around the margins of the Bering Basin. One clear example is a 30 by 40 km section of sediment that slid down the western flank of Umnak Plateau [image C and caption]. Pelagic sedimentation, ice-rafting and volcanic fallout also contribute significant amounts of debris to the basin.

Bowers Ridge is a large, curved fossil island arc in the southwest section of the Bering Sea [image D and caption]. An abandoned trench lies to the north and east of the ridge, and is buried by as much as 10 km of sediment. Wave action has eroded the shallower portions of Bowers Ridge, leaving it distinctly flat-topped.

A full-color geologic map has been created using this sidescan-sonar mosaic. It illustrates many of the features discussed above [image E and caption].

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Geologic Interpretation of Image

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Aleutian Arc

Beringian Margin

Basement Ridge, Sedimented

Canyon-channel complex

Plateau, sediment-covered

Sediment, basin facies with acoustic artifacts

Sediment, basin facies

Sediment, debris apron

Umnak debris flow

Beringian Margin debris flow

Bowers debris flow

Shirshov debris flow

Aleutian debris flow

Sediment, fan facies

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Shaded-Relief Image

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A shaded-relief image will overlay the green land of Alaska and the islands of the eastern Aleutian Arc (some green may still show because the coastline has been generalized for rapid display). The image is made by computer processing of millions of elevation values derived from digitizing the elevation contours from published topographic maps. Exaggeration of the relief and illumination by a simulated sun increases the contrast between rugged and smooth topography. See reference Riehle and others, 1997.

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Gulf of Alaska

Sidescan-Sonar Image

The GLORIA image of the Exclusive Economic Zone (EEZ) in the Gulf of Alaska covers over 800,000 square kilometers (sq km) of sea floor. Although a geologic-interpretation map of this sidescan-sonar image is not yet available, there are some interesting features to be noted.

The Gulf of Alaska has been the site of steadily increasing sediment accumulation for at least the last 11 million years. During the last 2.5 million years the combination of high mountains, high snowfall rates, and active glaciers in Alaska has produced an extremely high erosion rate. Large quantities of sediment have been delivered to the Gulf of Alaska where the major onshore glacial and fluvial drainage systems reach the coast. The Gulf of Alaska has a very narrow continental shelf, and a steep continental slope. This geometry insures that most of the sediment eroded from the mountain belts is rapidly transported to the deep-sea floor in the Gulf.

During the sea-level lowstands of the Pliocene and Pleistocene, glaciers extended all the way across the shelf, and sediment was delivered more or less directly to the continental slope [image A and caption]. The sediment pathways connect from the shore, across the shelf, and down the slope via submarine canyons and continue across the deep-ocean floor for thousands of kilometers. Thus, these sediment-transport pathways reach unbroken from the mountains to the deep sea. This prodigious accumulation of sediment has covered over and obscured all but the most prominent volcanic features (seamounts) resulting in a sea floor dominated by sedimentary features.

Sediment that reaches the deep-sea floor in a continuous or pulsating stream is often delivered by a dilute density-driven flow called a turbidity current. These currents are driven by gravity, tend to channelize, [image B and caption] and behave similarly to a river flowing across the land. Because the flows are gravity driven and always must go downslope, complex interactions with submarine obstacles can occur. In the southern Gulf, a deep-sea channel crosses the axis of a seamount chain in a very convoluted fashion [image C and caption]. In the central Gulf the Surveyor Channel meanders downslope, first southwestward across the Gulf, then northwestward to the deep Aleutian Trench. Click and drag the magnifier tool over the central third of the Gulf of Alaska mosaic to find the thin, wiggly, gray line of Surveyor Channel.

Along the southeastern margin of the Gulf of Alaska is a visible contact between two of the Earth's tectonic plates: the North American and the Pacific Plates. In this region, the plates are moving parallel to one another in opposite directions, forming a transform boundary. The Queen Charlotte and Fairweather faults, which together form the contact between these plates, are visible as a distinct, sharp line on the GLORIA image that can be traced for more than 600 km [image D and caption]!

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Shaded-Relief Image

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A shaded-relief image will overlay the green land bordering the Gulf of Alaska (some green may still show because the coastline has been generalized for rapid display). The image is made by computer processing of millions of elevation values derived from digitizing the elevation contours from published topographic maps. Exaggeration of the relief and illumination by a simulated sun increases the contrast between rugged and smooth topography. See reference Riehle and others, 1997.

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Pacific Islands

Pacific Islands

Exclusive Economic Zone

See the images and maps for the:

Southeastern Hawaiian Ridge

Central Hawaiian Ridge

Northwestern Hawaiian Ridge

Johnston Island

Kingman Reef and Palmyra Atoll


Southeastern Hawaiian Ridge

Sidescan-Sonar Image

The Hawaiian Islands are the southern end of a 5,000-km-long string of underwater volcanoes called the Hawaiian-Emperor Chain. Volcanoes of the Hawaiian chain form a long, discontinuous ridge called the Hawaiian Ridge. The GLORIA image of the Exclusive Economic Zone (EEZ) of the southeastern Hawaiian Ridge covers over one million square kilometers (sq km) of sea floor. In this image the Hawaiian Islands (green) top the northwest-southeast-trending ridge. Because the ridge is heavy, it pushes down the oceanic plate beneath it, as much as several kilometers. In reaction, the surrounding crust bulges upward a few hundred meters to form the Hawaiian Arch.

Over the past 80 million years, the Hawaiian-Emperor Chain developed, one volcano after another, as the Pacific Plate moved slowly northwestward over a stationary hot spot. At the hot spot, magma from the Earth's mantle continually rises through the ocean crust, and lava erupts frequently to slowly build a volcanic seamount. Many of the seamounts grow tall enough to break the surface of the water, forming the Hawaiian Islands. Because they sit on the ocean floor in water depths greater than 5 km, the Hawaiian volcanoes are some of the tallest mountains in the world!

As the Pacific Plate continues to move northwestward, it carries the once-active volcano away from the magma source. Over time the extinct volcano gradually sinks below sea level due to its weight and continued cooling of the ocean crust. Meanwhile, a new volcano develops on the adjacent area of sea floor newly moved over the hot spot. All of the Hawaiian volcanoes in this area are younger than about 8 million years, the youngest toward the southeast. Loihi Seamount is the newest volcano growing off the southeast coast of the Island of Hawaii. Although Loihi is not an obvious feature in this sonar mosaic, it does show up in the bathymetric data [image A and caption].

Extensive young lava flows are visible on the GLORIA image hundreds of kilometers from the Hawaiian volcanoes. While these flows occur in several areas north and south of the Hawaiian Islands, the most extensive field is the North Hawaiian Arch lava field, which covers an area of about 25,000 sq km north of Oahu [image B and caption]. The lava has erupted from fissures that cross the crest of the Hawaiian Arch. Thin tongues of lava more than 100 km long have flowed both southward and northward from this topographic high. The southern ends of some lava flows are interbedded with landslide debris from the Hawaiian Islands, showing that this lava field developed at the same time as the nearest Hawaiian volcanoes, apparently in response to the same hot spot. This suggests that the hot spot affects a much wider expanse of the sea floor than was suspected previously.

The Molokai Fracture Zone is visible in the eastern and southwestern sections of the GLORIA image [image C and caption]. It extends at least 2,000 km westward through the Johnston Island EEZ and more than 4,000 km eastward to offshore of central Baja California. This fracture zone consists of groups of linear faults caused by offsets in the mid-ocean ridge. The pattern of short, linear bands perpendicular to the fracture zone [image D and caption] is called spreading fabric and is composed of volcanic ridges that formed, one after another, at the spreading center of the mid-ocean ridge. The segment of the East Pacific Rise spreading center that produced both this spreading fabric and the Molokai Fracture Zone is now being overridden and disrupted by the North American continent. The spreading fabric and fracture zone developed long before the Hawaiian Islands and were locally buried by the development of the Hawaiian Ridge when this section of the Pacific Plate traveled over the hot spot.

These GLORIA images have helped scientists to understand the important role of landslides in the erosion of underwater volcanoes. Large-scale landslides are quite common throughout the Hawaiian Islands; at least 68 landslides are visible on the GLORIA images between Hawaii and Midway Island, each more than 20 km long. While various kinds of mass movement occur on the slopes of the Hawaiian Ridge, the predominant types are slumps and debris avalanches.

Slumps consist of coherent blocks that slip episodically over extended periods of time, rotating along deep faults. Sheer coastal cliffs, named "pali" in the Hawaiian language, provide some of the most dramatic scenery around the Hawaiian Islands. These cliffs are the eroded headwall scarps of large slumps. The submarine landslide deposits are visible on the imagery directly offshore of the cliffs. The Hilina Slump is offshore on the southeast flank of the active volcano Kilauea on the Island of Hawaii. It moves episodically along steep faults which extend to depths of more than 5 km. In 1975, a brief episode of slumping caused a magnitude 7.2 earthquake that was experienced quite dramatically by 32 people camping on the southeast shore of Hawaii near the head of this huge landslide.

Debris avalanches are rapidly moving, catastrophic landslides that deposit chaotic debris that can extend hundreds of kilometers from the source. They occur when large areas of solid rock break into many smaller blocks that travel along the sea floor in a great flowing mass. The Nuuanu-Wailau debris avalanches are among the largest landslides known on Earth, estimated to represent about a third of the Island of Oahu plus half of Molokai that collapsed in two or more catastrophic events [image E and caption]. The avalanche debris is strewn downslope 145 km and then continues upslope another 90 km, climbing more than 400 meters (m) in elevation! Before this imagery was available, the huge blocks in the debris avalanche deposit were thought to be separate underwater volcanoes. "Tuscaloosa Seamount", the largest such block, measures 26 km long, 14 km wide, and about 1,600 m high.

A full-color geologic map has been created using this sidescan-sonar mosaic. It illustrates many of the features discussed above [image F and caption].

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Geologic Interpretation of Image

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Apron of debris around volcanoes

Former island

Lava flow

Landslide from Ridge

Lineated sea floor

Island

Apron of sediment around Ridge

Submarine flank of Hawaiian Ridge

Volcanic edifice

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Shaded-Relief Image

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A shaded-relief image will overlay the green islands of the state of Hawaii (some green may still show because the coastline has been generalized for rapid display). Use the magnifier tool to see the topography of the islands. The image is made by computer processing of millions of elevation values derived from digitizing the elevation contours from published topographic maps. Exaggeration of the relief and illumination by a simulated sun increases the contrast between rugged and smooth topography. See reference Moore and Mark, 1992.

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Central Hawaiian Ridge

Sidescan-Sonar Image

The Hawaiian Islands are the southern end of a 5,000-km-long string of underwater volcanoes called the Hawaiian-Emperor Chain. Volcanoes of the Hawaiian chain form a long, discontinuous ridge called the Hawaiian Ridge. The GLORIA image of the Exclusive Economic Zone (EEZ) of the central Hawaiian Ridge covers over 800,000 square kilometers (sq km) of sea floor. Within this sidescan-sonar image the row of non-data areas in blue traces the axis of the northwest-southeast-trending ridge. Because the ridge is heavy, it pushes down the oceanic plate beneath it, as much as several kilometers. In reaction, the surrounding crust bulges up a few hundred meters to form the Hawaiian Arch.

Over the past 80 million years, the Hawaiian-Emperor Chain developed, one volcano after another, as the Pacific Plate moved slowly northwestward over a stationary hot spot. At the hot spot, magma from the mantle continually rises through the ocean crust, and lava erupts frequently to slowly build a volcanic seamount. Many of the seamounts grow tall enough to break the surface of the water, forming the Hawaiian Islands. As the Pacific Plate continues to move northwestward, it carries the once-active volcano away from the magma source. Over time the extinct volcano gradually sinks below sea level due to its weight and continued cooling of the ocean crust.

Although a geologic-interpretation map of this GLORIA image is not yet available, there are some interesting features to be noted. Several of the Hawaiian seamounts and small islands extending southeastward through the center of this area were large islands 10-20 million years ago. In the middle of this central segment of the Hawaiian EEZ the extensive shallow area surrounding Gardner Pinnacles is an excellent example of a former reef-ringed island. It was once as large as the present Island of Hawaii, but is now almost completely submerged [image A and caption].

In addition to the relatively young volcanoes of the Hawaiian Ridge, two groups of older volcanoes also occur in this area. The oldest group of seamounts, visible north of the Hawaiian Ridge and near the southwestern corner of this image area, occur in short north-northwest-trending rows and were produced by short-lived hot spots more than 75 million years ago; use the magnifier tool to see them in more detail. A somewhat younger group of ridges and rows of small seamounts trends east-northeast in a broad band in the southern part of the mosaic. They were produced by eruptions from deep fissures in the oceanic crust about 65 to 70 million years ago. Especially prominent among these volcanoes of intermediate age is Necker Ridge, the largest of several long ridges in this area [image B and caption].

The Murray Fracture Zone is visible in the north-central part of the GLORIA mosaic [image C and caption]. It extends both southwestward through the Hawaiian EEZ and more than 4,000 km eastward nearly to the coast of central California. The fracture zone consists of groups of linear, east-west faults caused by offsets in the mid-ocean ridge. The pattern of short, linear bands perpendicular to the fracture zone is called spreading fabric and is composed of volcanic ridges that formed, one after another, at the spreading center of the mid-ocean ridge. The segment of the East Pacific Rise spreading center that produced both this spreading fabric and the Murray Fracture Zone is no longer active, having been overridden by the North American continent. The spreading fabric and fracture zone developed long before the Hawaiian Islands and were locally buried by the development of the Hawaiian Ridge when this section of the Pacific Plate traveled over the hot spot. Also visible in the southeastern corner of the mosaic is a part of the Molokai Fracture Zone, described in the Southeastern Hawaiian Ridge text.

These GLORIA images have helped scientists to understand the important role of landslides in the erosion of underwater volcanoes. Large-scale landslides are quite common throughout the Hawaiian Islands; at least 68 landslides are visible on the GLORIA images between Hawaii and Midway Island, each more than 20 km long. While various kinds of mass movement occur on the slopes of the Hawaiian Ridge, the predominant types are slumps and debris avalanches.

Slumps consist of coherent blocks that slip episodically over extended periods of time, rotating along deep faults. Debris avalanches are rapidly moving, catastrophic landslides that deposit chaotic debris that can extend hundreds of kilometers from the source; they occur when large areas of solid rock break into many smaller blocks that travel along the sea floor in a great flowing mass. Landslide debris of both types are common near the ridge in this image. Use the magnifier tool to enlarge the area around Gardner Pinnacles (Image A yellow box) and you will see the white speckly marks characteristic of such debris.

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Northwestern Hawaiian Ridge

Sidescan-Sonar Image

The Hawaiian Islands are the southern end of a 5,000-km-long string of underwater volcanoes called the Hawaiian-Emperor Chain. Volcanoes of the Hawaiian chain form a long, discontinuous ridge called the Hawaiian Ridge. The GLORIA image of the Exclusive Economic Zone (EEZ) of the northwestern Hawaiian Ridge covers about 700,000 square kilometers (sq km) of sea floor. Within this sidescan-sonar image the row of non-data areas in blue traces the axis of the northwest-southeast-trending ridge. Over the past 80 million years, the Hawaiian-Emperor Chain developed, one volcano after another, as the Pacific Plate moved slowly northwestward over a stationary hot spot. At the hot spot, magma from the mantle continually rises through the ocean crust, and lava erupts frequently to slowly build a volcanic seamount. Many of the seamounts grow tall enough to break the surface of the water, forming the Hawaiian Islands. As the Pacific Plate continues to move northwestward, it carries the once-active volcano away from the magma source. Over time the extinct volcano gradually sinks below sea level due to its weight and continued cooling of the ocean crust. Twenty to thirty million years ago several of the Hawaiian seamounts and small islands extending southeastward through the center of this area were much larger islands.

Although a geologic-interpretation map of this GLORIA image is not yet available, there are some interesting features to be noted. Unlike the Hawaiian volcanoes farther to the southeast, most volcanoes in this segment of the chain do not form a continuous ridge. Instead, the Hawaiian volcanoes in this area occur among older seamounts (probably older than 75 million years) that are aligned in rows trending south-southeast rather than east-southeast like the rest of the Hawaiian Ridge. These older seamounts are thought to represent the traces of ancient hot spots, similar to the Hawaiian hot spot but no longer active. North of Lisianski Island, for example, are three guyots believed to have formed over such a hot spot [image A and caption].

The Murray Fracture Zone, visible north of the Hawaiian ridge in the Central Hawaiian GLORIA mosaic, can barely be seen in the southwest part of this image. This fracture zone consists of groups of linear, east-west-trending faults caused by offsets in the mid-ocean ridge. The pattern of short, linear bands perpendicular to the fracture zone is called spreading fabric and is composed of volcanic ridges that formed, one after another, at the spreading center of the mid-ocean ridge. Here the fracture zone is obscured by sediment from islands; the faint expression of the sea-floor spreading fabric gives a clue to its location. It also appears to be much wider than it is in the central Hawaiian EEZ; evidently the spreading center underwent some significant changes when this part of the sea floor formed about 110 to 130 million years ago. Additional evidence for such changes can be seen in the far northern part of the mosaic, where unusual "swirly" patterns in the spreading fabric [image B and caption] suggest that the spreading center of the East Pacific Rise spun off a series of very small tectonic plates as it "dueled" with other spreading centers at a triple junction.

Also visible in this mosaic are several large landslides from Hawaiian volcanoes and older guyots. A good example occurs near Lisianski Island [image C and caption]. Such landslides are quite common throughout the Hawaiian Islands; at least 68 landslides are visible on the GLORIA images between Hawaii and Midway Island, each more than 20 km long.

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Johnston Island

Sidescan-Sonar Image

Johnston Island marks the center of this circular Exclusive Economic Zone (EEZ) [image A and caption]. It is the northernmost of the Line Islands, a series of seamounts and linear volcanic ridges created as oceanic crust traveled over local hot spots. This 4,200-km-long island chain is bordered by the Mid-Pacific Mountains and the Molokai Fracture Zone. The GLORIA image of the Johnston Island EEZ covers about 450,000 square kilometers (sq km) of sea floor. Although a geologic-interpretation map of this sidescan-sonar image is not yet available, there are some interesting features to be noted.

Necker Ridge (top center of mosaic) is an elongate ridge that trends NE-SW from the Hawaiian EEZ to the Johnston Island EEZ. Necker Ridge is 600 km long and ranges in width from about 20 km at its northern and southern ends to more than 40 km along the central segment of the ridge. It rises as much as 3 km above the surrounding abyssal plain. Necker Ridge originally formed through volcanic processes and has been sculpted by mass movement. Numerous slumps and canyons incise the flanks of the ridge, providing sediment to the small deep-sea fans along the base. Unlike the very large deep-sea fans off the east or west coast of the North American continent, these fans are less than 10 km across.

Horizon Guyot is a flat-topped volcanic ridge running parallel to and lying southeast of Necker Ridge [image B and caption]. It is 300 km long, 70 km wide, and rises 3,500 meters (m) above the adjacent abyssal plain. The guyot has been submerged since the Late Cretaceous. Erosional processes are quite active on Horizon Guyot. Well-developed talus aprons are present along the base of the guyot. Along the western flank large-scale faulting occurs, and chaotic, slump-like features predominate. Numerous terraces expose basement rock. These terraces are visible on the GLORIA image as bright areas along the western rim of the guyot. In contrast, the eastern flank shows a predominance of rills and gullies that occur in a dendritic pattern.

Two distinct strands of the Molokai Fracture Zone (MFZ) are visible in the northeast section of the GLORIA image [image C and caption]. These bright lineations are multiple ridges and basins caused by offsets in the East Pacific Rise spreading center, now being overridden by North America. The MFZ extends from central Baja California westward across the Pacific Ocean, through the Hawaiian EEZ and into the area shown in this mosaic. While the southern strand disappears before Karin Ridge [image D and caption], the northern strand continues in the western part of the Johnston Island EEZ.

In the northeast section of the GLORIA image lies a series of low abyssal hills [image E and caption]. The mottled backscatter pattern in that area is intriguing. While it may represent recent lava flows, it is most likely a large field of manganese nodules. Known manganese nodule fields have a similar backscatter pattern, and manganese encrustations are common in this area.

The southern half of the mosaic is dominated by numerous seamounts, many previously undiscovered [image F and caption]. The geologic reason for this scattering of seamounts is not clear, but may be related to the early history of the Pacific Plate.

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Kingman Reef and Palmyra Atoll

Sidescan-Sonar Image

This GLORIA image shows about 200,000 square kilometers (sq km) of sea floor, representing the northern two-thirds of the Exclusive Economic Zone (EEZ) around Kingman Reef and Palmyra Atoll in the central Pacific Ocean [image A and caption]. The southwestern third of this EEZ has yet to be imaged. Kingman Reef and Palmyra Atoll are on the 4,200-km-long northwest-southeast-trending Line Islands Ridge. Although a geologic-interpretation map of this sidescan-sonar image is not yet available, there are some interesting features to be noted.

A broad, relatively shallower area adjoins the Line Islands Ridge northeast of Kingman and Palmyra. The escarpments that bound the north side of this area rise 1,200 meters (m) above the adjacent basin (darkest area, center of image) and are incised with large amphitheater-shaped scarps. Within the shallower region, several seamounts rise another 1,200 m for a total of 2,400 m above the deep basin. Small, bright features visible on the tops of these seamounts may be drowned reefs [image B and caption].

Numerous canyons incise the flanks of the relatively shallower area. On the southwest flank is a dendritic pattern of small channels, each channel about 3 km wide and 20 m deep. These channels coalesce into a single westward-flowing channel. The single channel plunges over the precipice at the edge of the shallower area, then broadens into a 5-km-wide constructional channel that turns northeast and continues 350 km to the edge of this EEZ [image C and caption]. It is joined by a similar-sized channel apparently derived from the eastern side of the shallower area.

The Line Islands Ridge is superimposed on a large expanse of middle-Cretaceous seamounts. Two types of volcanic edifices are visible in the GLORIA image: large guyots in the shallower area or along the ridge that once were so shallow they may have developed reefs [image D and caption], and smaller off-ridge volcanoes, whose summits were always too far below sea level to support reef-building activity.

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Glossary
Glossary of Terms

abyssal plains

A flat region of the ocean floor, usually at the base of a continental rise, whose slope is less than 1:1000 or 0.07°. It is formed by the deposition of turbidity-current and pelagic sediments that obscure the preexisting topography.

accretion

The addition of island-arc or microcontinental material to a continent by convergent and transform motion, i.e. by collision and welding or suturing.

acoustics

The study of sound, including its production, transmission, reception, and utilization, especially in fluid media such as air or water.

acoustic frequency

The rate at which the acoustic signal oscillates.

acoustic transducer

Equipment which transmits the sonar signal.

active margin

A boundary between two plates that are moving toward each other.

anamorphic ratio

The ratio of the along-track dimension to the across-track dimension of a feature.

angle of incidence

The angle that a ray of energy (optic, acoustic, or electromagnetic) makes with the normal to a boundary surface.

asthenosphere

The layer or shell of the Earth below the lithosphere, which is weak and in which isostatic adjustments take place, magmas may be generated, and seismic waves are strongly attenuated. It is a part of the upper mantle.

axis

A line that follows the trend of large landforms, such as one following the crest of a ridge or mountain range, or of the bottom or trough of a depression.

backscatter

The acoustic energy scattered back toward the sonar fish from the sea floor.

basement rock

The undifferentiated complex of rocks that underlies the rocks of interest in an area.

bathymetry

The measurement of ocean depths and the charting of the topography of the ocean floor.

bedforms

Any deviation from a flat bed, generated by the flow on the bed of an alluvial channel.

Cenozoic

An era of geologic time, from the beginning of the Tertiary period to the present.  It is characterized paleontologically by the evolution and abundance of mammals, advanced mollusks, and birds; paleobotanically, by angiosperms. The Cenozoic is considered to have begun about 65 million years ago.

channel flow

Movement of surface runoff in a long narrow trough-like depression bounded by banks or valley walls that slope toward the channel.

continental borderland

That area of the continental margin between the shoreline and the continental slope which is topographically more complex than the continental shelf. It is characterized by ridges and basins, some of which are below the depth of the continental shelf.

continental crust

That type of the Earth's crust which underlies the continents and the continental shelves; it ranges in thickness from about 35 km to as much as 60 km under mountain ranges.

continental margin

The ocean floor that is between the shoreline and the abyssal ocean floor, including various provinces: the continental shelf, continental borderland, continental slope, and the continental rise. An active continental margin is where two plates are moving toward each other; a passive margin is formed by rifting and continental rupture.

continental rise

That part of the continental margin that is between the continental slope and the abyssal plain, except in areas of an oceanic trench. It is a gentle incline with slopes of 1:40 (or 1.5°) to 1:2000 (or 0.03°), and generally smooth topography, although it may bear submarine canyons.

continental shelf

That part of the continental margin that is between the shoreline and the continental slope (or, when there is no noticeable continental slope, a depth of 200 m). It is characterized by its very gentle slope of 0.1° (or 1:600).

continental slope

That part of the continental margin that is between the continental shelf and the continental rise (or oceanic trench). It is characterized by its relatively steep slope of 3-6° (or 1:19 to 1:10).

contour current

A density current in the ocean flowing approximately parallel to the bathymetric contours, e.g. a density current flowing parallel to the slope of a continental rise, such as the Western Boundary Undercurrent in the northwest Atlantic Ocean.

convection

In tectonics, a pattern of movement of mantle material in which the central area is uprising and the outer area is down-flowing, due to heat variations.

convergent plate boundary

A boundary between two plates that are moving toward each other.

core

The central zone or nucleus of the Earth's interior, below the Gutenberg discontinuity at a depth of 2,900 km. It is divided into an inner core and an outer core,  with a transition zone between. Since only compressional waves propagate in the outer core, it is a fluid. The inner core, having a radius of approximately 1,300 km, is solid, as shear waves have been observed to propagate through it. The Earth's magnetic field originates within the core.

Cretaceous

The final period of the Mesozoic era (after the Jurassic and before the Tertiary period of the Cenozoic era), thought to have covered the span of time between 135 and 65 million years ago; also, the corresponding system of rocks. It is named after the Latin word for chalk ("creta") because of the English chalk beds of this age.

cross section

(a) A diagram or drawing that shows features transected by a given plane; specif. a vertical section drawn at right angles to the longer axis of a geologic feature, such as the trend of an ore body, the mean direction of flow of a stream, or the axis of a fossil.  (b) An actual exposure or cut that shows transected geologic features.

crust

The outermost layer or shell of the Earth, defined according to various criteria, including seismic velocity, density and composition. It represents less than 0.1% of the Earth's total volume.

debris flow

A moving mass of rock fragments, soil, and mud, more than half of the particles being larger than sand size. Slow debris flows may move less than 1 m per year; rapid ones reach 160 km per hour.

dendritic pattern

A drainage pattern in which the streams branch randomly in all directions and at almost any angle, resembling in plan the branching habit of certain trees; it is produced where a stream receives several tributaries which in turn are fed by smaller tributaries.

divergent boundary

A boundary between two tectonic plates that are moving away from each other.

EEZ

An acronym of Exclusive Economic Zone. The 200-nautical-mile-wide zone around a country's coastlines reserved for that country's economic use.

erosion

The general process or the group of processes whereby the materials of the Earth's crust are loosened, dissolved, or worn away, and simultaneously moved from one place to another, by natural agencies; specif. the mechanical destruction of the land and the removal of material (such as soil) by running water (including rainfall), waves and currents, moving ice, or wind.

estuary

(a) The seaward end or the widened funnel-shaped tidal mouth of a river valley where fresh water comes into contact with seawater and where tidal effects are evident; e.g. a tidal river, or a partially enclosed coastal body of water where the tide meets the current of a stream. (b) A portion of an ocean, as a firth or an arm of the sea, affected by fresh water; e.g. the Baltic Sea. (c) A drowned river mouth formed by the subsidence of land near the coast or by the drowning of the lower portion of a non-glaciated valley due to the rise of sea level.

facies

The aspect, appearance, and characteristics of a rock unit, usually reflecting the conditions of its origin.

fish

Any oceanographic sensing device that is towed behind a ship.

fissure

A surface fracture or crack in rock along which there is a distinct separation. It is often filled with mineral-bearing material.

fluvial

Of or pertaining to a river or rivers.

fracture zone

On the deep-sea floor, an elongate zone of unusually irregular topography that often separates regions of different depths. Such zones commonly cross and apparently displace the mid-oceanic ridge by faulting.

geophysics

Study of the Earth by quantitative physical methods. Basic divisions include solid-earth geophysics, physics of the atmosphere and hydrosphere, and solar-terrestrial physics. There are numerous specialties within the field, e.g. seismology, tectonophysics, engineering geophysics. The term is sometimes used to include instrumental study of the Moon and planets.

Global Positioning System

Computerized navigation system determining position on the surface of the Earth from multiple satellite fixes.

GLORIA

An acronym of Geologic Long Range Inclined ASDIC (where ASDIC is a British acronym for sonar), for the instrument used by the USGS to map the deep-water portions of the U.S. EEZ, i.e. from the shelf break to 200 nautical miles offshore.

gully

A very small valley, such as a small ravine in a cliff face, or a long, narrow hollow or channel worn in earth or unconsolidated material (as on a hillside).

guyot

A type of seamount that has a platform top.

headwall scarp

A line of cliffs produced by faulting or by erosion. The term is an abbreviated form of escarpment, and the two terms commonly have the same meaning, although "scarp" is more often applied to cliffs formed by faulting.

hemipelagic

Deep-sea sediment in which more than 25% of the fraction coarser than 5 microns is of terrigenous, volcanogenic, and/or neritic origin. Such deposits usually accumulate near the continental margin and its adjacent abyssal plain.

Holocene

An epoch of the Quaternary period, from the end of the Pleistocene, approximately 10,000 years ago, to the present time; also, the corresponding series of rocks and deposits.

hot spot

Stationary, localized magma source beneath a tectonic plate, not associated with a spreading center.

hummock

A rounded or conical knoll, mound, hillock, or other small elevation. Also, a slight rise of ground above a level surface.

ice-rafting

The transporting of rock fragments of all sizes on or within icebergs, ice floes, or other forms of floating ice.

igneous

Said of a rock or mineral that solidified from molten or partly molten material, i.e. from a magma. Igneous rocks constitute one of the three main classes into which rocks are divided, the others being metamorphic and sedimentary.

insonify

To suffuse a volume or surface with sound. The term is used in geophysical investigations based on acoustic properties of rocks.

insular shelf

An area of the ocean floor analogous to the continental shelf, but surrounding an island.

island arc

A generally curved linear belt of island volcanoes adjacent to a subduction zone, and the volcanic and plutonic rocks formed there. Syn: volcanic arc; magmatic arc

levee

An embankment of sediment, bordering one or both sides of a submarine canyon, fan valley, or deep-sea channel. It is similar to a river-channel levee in the subaerial environment.

lithosphere

In plate tectonics, a layer of strength relative to the underlying asthenosphere for deformation at geologic rates. It includes the crust and part of the upper mantle and is of the order of 100 km in thickness.

Loran-C

A long-range radio position-fixing system by which hyperbolic lines of position are determined by measuring the difference in arrival times of synchronized pulse signals from two or more fixed transmitting radio stations of known geographic position. Loran fixes may be obtained at a range of 1,400 nautical miles at night.

lowstand

The interval of time between one or more cycles of relative change of sea level when sea level is below the shelf edge.

Ma

Millions of years before the present.

magma

Naturally occurring molten rock material, generated within the Earth, from which igneous rocks are derived through solidification and related processes.

mantle

The zone of the Earth below the crust and above the core, which is divided into the upper mantle and the lower mantle, with a transition zone between.

mass movement

A unit movement of a portion of the land surface; specifically mass wasting or the gravitative transfer of material down a slope.

mass wasting

A general term for the dislodgement and downslope transport of soil and rock material under the direct application of gravitational body stresses. In contrast to other erosion processes, the debris removed by mass wasting is not carried within, on, or under another medium. The mass properties of the material being transported depend on the interaction of the soil and rock particles and on the moisture content. Mass wasting includes slow displacements, such as creep and solifluction, and rapid movements such as rockfalls, rockslides, and debris flows.

Mesozoic

An era of geologic time, from the end of the Paleozoic to the beginning of the Cenozoic, or from about 225 to about 65 million years ago.

mid-ocean ridge

A continuous, seismic, median mountain range extending through the North and South Atlantic Oceans, the Indian Ocean, and the South Pacific Ocean. It is a broad, fractured swell with a central rift valley and usually extremely rugged. According to the hypothesis of sea-floor spreading, the mid-oceanic ridge is the source of new crustal material.

morphology

The external structure, form, and arrangement of rocks in relation to the development of landforms.

mosaic

An assembly of remotely-sensed images whose edges have been feathered and matched to form a continuous representation of a part of the Earth's surface.

m.y.

Million years.

nadir

The point on the ground vertically beneath the sidescan-sonar vehicle.

neritic

Pertaining to the ocean environment or depth zone between low-tide level and 200 m, or between low-tide level and approximately the edge of the continental shelf; also, pertaining to the organisms living in that environment. It is called by some the sub-littoral zone, i.e. is considered to be a part of the littoral zone.

oceanic crust

That type of the Earth's crust which underlies the ocean basins. The oceanic crust is about 5 to 10 km thick.

passive margin

A continental boundary caused by rifting and continental rupture.

pelagic sedimentation

Sediment accumulated in the open ocean.

plate tectonics

A theory of global tectonics in which the lithosphere is divided into a number of plates whose pattern of horizontal movement is that of torsionally rigid bodies that interact with one another at their boundaries, causing seismic and tectonic activity along these boundaries.

Pleistocene

An epoch of the Quaternary period, after the Pliocene of the Tertiary and before the Holocene; also, the corresponding worldwide series of rocks. It began 1.6 million years ago and lasted until the start of the Holocene some 10,000 years ago.

Pliocene

An epoch of the Tertiary period, after the Miocene and before the Pleistocene; also, the corresponding worldwide series of rocks. The Pliocene epoch began 5.3 million years ago and ended 1.6 million years ago.

quadrangle

A rectangular area bounded by parallels of latitude and meridians of longitude, used as a unit in systematic mapping. The dimensions of a quadrangle are not necessarily the same in both directions, and its size and the scale at which it is mapped are determined by the prime purpose of the map.

reentrant

A prominent, generally angular indentation in a landform; e.g. an inlet between two promontories along a coastline.

right-lateral fault

A fault on which the displacement is such that, in plan view, the side opposite the observer appears displaced to the right.

rill

A dendritic channel formed by a small stream debauching onto a sand flat or a mud flat; it shows a downslope bifurcation.

seamount

An elevation of the sea floor, 1,000 m or higher, either flat-topped (called a guyot) or peaked. Seamounts may be either discrete, arranged in a linear or random grouping, or connected at their bases and aligned along a ridge or rise.

sediment facies

(a) The aspect, appearance, and characteristics of a rock unit, usually reflecting the conditions of its origin; esp. as differentiating the unit from adjacent or associated units. (b) A mappable, areally restricted part of a rock unit, differing in lithology or fossil content from other beds deposited at the same time and in lithologic continuity. (c) The environment or area in which a rock was formed, e.g. "sandy-bottom facies".

shield volcano

A volcano in the shape of a flattened dome, broad and low, built by flows of very fluid basaltic lava, or by rhyolitic ash flows.

sidescan sonar

See sonar. "Sidescan" refers to the shape of the sonar beam, which fans out to the sides and scans a wide "swath" of sea floor. The energy beam is confined to the plane perpendicular to the ship's track, forming a narrow acoustic beam in the horizontal plane and a broad beam in the vertical plane.

sonar

An acronym of SOund NAvigation and Ranging, a method used in oceanography to study the ocean floor acoustically.

sonograph

Acoustic image of the sea floor formed by bouncing sound waves off the sea floor and recording the returning acoustic energy levels.

spreading center

See mid-ocean ridge.

strike slip

In a fault, the component of the movement or slip that is parallel to the strike of the fault.

subduction

The process of one lithospheric plate descending beneath another. A subduction zone is a long, narrow belt in which subduction takes place, e.g. along the Peru-Chile trench or in the volcanic arc belts of the western Pacific Ocean.

submarine fan

A fan-shaped body of sediment typically built by deposition from repeated turbidity currents exiting from a submarine canyon where the canyon opens onto the continental rise or abyssal plain.

substrate

The composition of the sea floor.

talus

Rock fragments of any size or shape (usually coarse and angular) derived from and lying at the base of a cliff or very steep, rocky slope. Also, the outward sloping and accumulated heap or mass of such loose broken rock, considered as a unit, and formed chiefly by gravitational falling, rolling, or sliding.

tectonic plate

A torsionally rigid, thin segment of the Earth's lithosphere, which may be assumed to move horizontally and adjoins other plates along zones of seismic activity.

terrace

Any long, narrow, relatively level or gently inclined surface, generally less broad than a plain, bounded along one edge by a steeper descending slope and along the other by a steeper ascending slope; a large bench or step-like ledge breaking the continuity of a slope. A terrace commonly occurs along the margin and above the level of a body of water, marking a former water level; e.g. a stream terrace.

terrigenous

Derived from the land or continent.

Tertiary

The first period of the Cenozoic era thought to have covered the span of time between 65 million years ago and 3 to 2 million years ago.

topography

(a) The general configuration of a land surface or any part of the Earth's surface, including its relief and the position of its natural and man-made features. (b) The natural or physical surface features of a region, considered collectively as to form; the features revealed by the contour lines of a map.

transform boundary

A plate boundary that ideally shows pure strike-slip displacement.

trench

A narrow, elongate depression of the deep-sea floor, with steep sides, oriented parallel to the trend of the continent and between the continental margin and the abyssal hills. Such a trench is about 2 km deeper than the surrounding ocean floor, and may be thousands of kilometers long.

triple junction

The intersection of three active spreading centers.

turbidity current

A density current in water, air or other fluid, caused by different amounts of matter in suspension, such as a dry-snow avalanche or a descending cloud of volcanic dust; specif.  A bottom-flowing current laden with suspended sediment, moving swiftly (under the influence of gravity) down a sub-aqueous slope and spreading horizontally on the floor of the body of water, and having a density greater than that of the surrounding or overlying clear water.

volcanic arc

A generally curved linear belt of volcanoes above a subduction zone,  and the volcanic and plutonic rocks formed there. Syn: island arc; magmatic arc

volcanic fallout

Fragmental material ejected from a volcano and eventually redeposited. It may have undergone considerable atmospheric sorting before deposition.

yaw

Turning relative to the vertical axis of the vehicle.

References

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Advanced Features

Experienced ArcView users may change the GUI (Graphical User Interface) to include most of the standard ArcView capabilities. Some ArcView functionality is restricted with the Data Publisher; see 1_README.TXT for details.

Toggle the GUI between the limited set of analysis tools and the full ArcView interface. Be patient; it takes a moment to load all the files. This feature is intended only for users who are familiar with ArcView and its capabilities.

Naming conventions for views and themes are provided to assist you in accessing the data manually. All buttons and hypertext links within EEZ-View Text will remain active for automated data display if preferred.

  is provided to re-size overly small or large text you may encounter while in full-ArcView mode. Such problems may occur during manual zoom actions because text is attached to themes at a scale designed for the displays presented in this tutorial.

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Naming conventions for views and themes
Naming Conventions

Explanation of View Names:

EEZ Alaska - contains the 3 sonar mosaics for the Alaskan EEZ.

EEZ Pacific - contains the 5 sonar mosaics for the Pacific EEZ.

EEZ States - contains the 4 sonar mosaics for the Continental US EEZ.

Exclusive Economic Zone - contains an image of the globe and the EEZ zones.

graphic of... - contains a single illustration for either the Remote Sensing or Plate Tectonics sections.

zoom image... - contains a single image clipped from one of the sonar mosaics. These are snapshots, not projected images.

   AA - Aleutian Arc

   BS - Bering Sea

   GA - Gulf of Alaska

   EC - East Coast of USA

   GM - Gulf of Mexico

   PR - Puerto Rico

   WC - West Coast of USA

   HW_SE - SE Hawaiian Ridge

   HW_C - Central Hawaiian Ridge

   HW_NW - NW Hawaiian Ridge

   JI - Johnston Island

   KP - Kingman/Palmyra

Explanation of Theme Names:

Hotlink... - hotlink theme for user to jump from one area to another. Theme must be active (not visible) for hotlink tool to be enabled.

box A... - yellow box illustrating location of zoomed-in images.

Etopo5 Data - gridded bathymetry data

DEM - shaded-relief images of land (derived from Digital Elevation Model information)

EEZ Zones - extent of local EEZ

Geologic Boundaries - red outlines of units in geologic map

Geologic Map - interpretation of sonar mosaic

Quadrangles - numbered-quadrangle index maps to future CD-ROMs containing high-resolution GLORIA data

Sonar Mosaic - sidescan-sonar mosaic. Note: some of the mosaics are displayed with a linear stretch to make geologic features more visible to the untrained eye. This DN value stretch is shown in the Image Legend Editor Linear Lookup graph.

For more information about the data displayed in this project see 1_README.TXT in the top-level directory of the CD-ROM.

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Additional Data

Full-Resolution Quadrangles

Each GLORIA mosaic image presented in this CD-ROM was desampled for quick display. High-resolution sidescan-sonar images of the EEZ are available either in paper atlas form or on present or future CD-ROMs. Full-resolution digital data of each sonar mosaic are divided into multiple quadrangles (2 by 2 degree images for most areas, and 2 by 3 degree images in the Alaskan EEZ). Numbered quadrangle maps are accessible in this CD-ROM for each mosaic area; to view them, go to the Advanced Features page in the EEZ-View Text window and click the red text "Toggle the GUI". You can then manually display maps and images for any area.

Other USGS GLORIA Atlas Publications

Paper atlases and CD-ROMs of GLORIA sidescan imagery are available in many university libraries and can be purchased through USGS Information Services in Denver, CO by calling (800) 435-7627 or (303) 202-4700.

Paper atlases printed to date:

Bering Sea EEZ-SCAN Scientific Staff, 1991, Atlas of the U.S. Exclusive Economic Zone, Bering Sea: U.S. Geological Survey Miscellaneous Investigation Series I-2053, 145 p., scale 1:500,000.

EEZ-SCAN 84 Scientific Staff, 1986, Atlas of the Exclusive Economic Zone, western conterminous United States: U. S. Geological Survey Miscellaneous Investigations Series I-1792, 152 p., scale 1:500,000. (out of print)

EEZ-SCAN 85 Scientific Staff, 1987, Atlas of the U.S. Exclusive Economic Zone, Gulf of Mexico and Eastern Caribbean Areas: U.S. Geological Survey Miscellaneous Investigation Series I-1864-A,B, 160 p., scale 1:500,000.

EEZ-SCAN 87 Scientific Staff, 1991, Atlas of the Exclusive Economic Zone, Atlantic continental margin: U. S. Geological Survey Miscellaneous Investigations Series I-2054, 174 p., scale 1:500,000.

CD-ROMs published to date:

Paskevich, V., 1996, Digital mosaics of the GLORIA sidescan sonar data of the Gulf of Mexico: U.S. Geological Survey Open-File Report 96-657, 1 CD-ROM.

Paskevich, V., in press, Digital mosaics of the GLORIA sidescan sonar data of the U.S. Atlantic East Coast: U.S. Geological Survey Open-File Report 97-xxx, 2 CD-ROMs.

Twichell, D.C. and C.F. Polloni, 1993, CD-ROM atlas of the deepwater parts of the United States Exclusive Economic Zone in the Atlantic Ocean, the Gulf of Mexico, and the eastern Caribbean Sea: U. S. Geological Survey Digital Data Series DDS-15, 1 CD-ROM.

CD-ROMS planned for release in 1998 will contain full-resolution quadrangles and desampled mosaics from the West Coast, Bering Sea, Aleutian Arc, Gulf of Alaska, Hawaiian Ridge, Johnston Is., Kingman Reef and Palmyra Atoll. For more information e-mail Chris Gutmacher at cgutmacher@usgs.gov.

Web Sites

Check out the web sites for the USGS Coastal and Marine Geology Program for information on current projects and upcoming publications:

National   http://www.usgs.gov/

Western Region  http://walrus.wr.usgs.gov/

Eastern Region:

  Woods Hole  http://woodshole.er.usgs.gov/

  St. Petersburg  http://coastal.er.usgs.gov/

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Acknowledgments

This CD-ROM was developed at the U.S. Geological Survey by Molly G. Groome, Christina E. Gutmacher and Andrew J. Stevenson.

The authors gratefully acknowledge the contributions of the dedicated and talented people in the following groups:

•	Image Processing Groups of the U. S. Geological Survey in Flagstaff, Arizona, and Coastal and Marine Geology in Menlo Park, California, for their production of digital mosaics of the West Coast, Alaskan, and Pacific areas, here published for the first time.

•	GIS staff of Coastal and Marine Geology of the U. S. Geological Survey in Menlo Park, California, for invaluable assistance and advice at every stage of this project.

•	Environmental Systems Research Institute, Inc. Data Publishing Group in Redlands, California, for providing technical assistance during the development of this CD-ROM project.

•	Scientists and technicians of the Institute of Oceanographic Sciences (IOS), United Kingdom, and of the USGS who collaborated on initial collection of the GLORIA imagery and on many resulting scientific papers.

•	Captains and crews of the M/V Farnella, whose skill and years of effort in performing the GLORIA surveys resulted in an excellent and comprehensive data set.

We also deeply appreciate the efforts of Florence Wong, Guy Cochrane, Becky Cooper, Alan Cooper, and Michael Hamer for their patient testing of earlier versions of this CD-ROM and giving helpful feedback.  We thank Jane Reid for help in pulling together the glossary, and Kevin Evans for the "Mapping the U.S. EEZ" graphic.  We are especially grateful to Florence Wong for her careful text and functional review, resulting in substantial improvements to the final version.

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Welcome to EEZ-View
Atlas of GLORIA Sidescan-Sonar Imagery of the Exclusive Economic Zone of the United States:  EEZ-View

EEZ-View is an educational tour of the Exclusive Economic Zone of the United States of America. It is designed to introduce the high school or college student to the exciting worlds of marine geology and remote sensing. Click on the green text below.

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abyssal plains

A flat region of the ocean floor, usually at the base of a continental rise, whose slope is less than 1:1000 or 0.07°. It is formed by the deposition of turbidity-current and pelagic sediments that obscure the preexisting topography.


accretion

The addition of island-arc or microcontinental material to a continent by convergent and transform motion, i.e. by collision and welding or suturing.


acoustics

The study of sound, including its production, transmission, reception, and utilization, especially in fluid media such as air or water.


acoustic frequency

The rate at which the acoustic signal oscillates.


acoustic transducer

Equipment which transmits the sonar signal.


anamorphic ratio

The ratio of the along-track dimension to the across-track dimension of a feature.


angle of incidence

The angle that a ray of energy (optic, acoustic, or electromagnetic) makes with the normal to a boundary surface.


asthenosphere

The layer or shell of the Earth below the lithosphere, which is weak and in which isostatic adjustments take place, magmas may be generated, and seismic waves are strongly attenuated. It is a part of the upper mantle.


axis

A line that follows the trend of large landforms, such as one following the crest of a ridge or mountain range, or of the bottom or trough of a depression.


backscatter

The acoustic energy scattered back toward the sonar fish from the sea floor.


basement rock

The undifferentiated complex of rocks that underlies the rocks of interest in an area.


bathymetry

The measurement of ocean depths and the charting of the topography of the ocean floor.


bedforms

Any deviation from a flat bed, generated by the flow on the bed of an alluvial channel.


Cenozoic

An era of geologic time, from the beginning of the Tertiary period to the present.  It is characterized paleontologically by the evolution and abundance of mammals, advanced mollusks, and birds; paleobotanically, by angiosperms. The Cenozoic is considered to have begun about 65 million years ago.


channel flow

Movement of surface runoff in a long narrow trough-like depression bounded by banks or valley walls that slope toward the channel.


continental borderland

That area of the continental margin between the shoreline and the continental slope which is topographically more complex than the continental shelf. It is characterized by ridges and basins, some of which are below the depth of the continental shelf.


continental crust

That type of the Earth's crust which underlies the continents and the continental shelves; it ranges in thickness from about 35 km to as much as 60 km under mountain ranges.


continental margin

The ocean floor that is between the shoreline and the abyssal ocean floor, including various provinces: the continental shelf, continental borderland, continental slope, and the continental rise. An active continental margin is where two plates are moving toward each other; a passive margin is formed by rifting and continental rupture.


continental rise

That part of the continental margin that is between the continental slope and the abyssal plain, except in areas of an oceanic trench. It is a gentle incline with slopes of 1:40 (or 1.5°) to 1:2000 (or 0.03°), and generally smooth topography, although it may bear submarine canyons.


continental shelf

That part of the continental margin that is between the shoreline and the continental slope (or, when there is no noticeable continental slope, a depth of 200 m). It is characterized by its very gentle slope of 0.1° (or 1:600).


continental slope

That part of the continental margin that is between the continental shelf and the continental rise (or oceanic trench). It is characterized by its relatively steep slope of 3-6° (or 1:19 to 1:10).


contour current

A density current in the ocean flowing approximately parallel to the bathymetric contours, e.g. a density current flowing parallel to the slope of a continental rise, such as the Western Boundary Undercurrent in the northwest Atlantic Ocean.


convection

In tectonics, a pattern of movement of mantle material in which the central area is uprising and the outer area is down-flowing, due to heat variations.


convergent plate boundary

A boundary between two tectonic plates that are moving toward each other.


core

The central zone or nucleus of the Earth's interior, below the Gutenberg discontinuity at a depth of 2,900 km. It is divided into an inner core and an outer core,  with a transition zone between. Since only compressional waves propagate in the outer core, it is a fluid. The inner core, having a radius of approximately 1,300 km, is solid, as shear waves have been observed to propagate through it. The Earth's magnetic field originates within the core.


Cretaceous

The final period of the Mesozoic era (after the Jurassic and before the Tertiary period of the Cenozoic era), thought to have covered the span of time between 135 and 65 million years ago; also, the corresponding system of rocks. It is named after the Latin word for chalk ("creta") because of the English chalk beds of this age.


cross section

(a) A diagram or drawing that shows features transected by a given plane; specif. a vertical section drawn at right angles to the longer axis of a geologic feature, such as the trend of an ore body, the mean direction of flow of a stream, or the axis of a fossil.  (b) An actual exposure or cut that shows transected geologic features.


crust

The outermost layer or shell of the Earth, defined according to various criteria, including seismic velocity, density and composition. It represents less than 0.1% of the Earth's total volume.


debris flow

A moving mass of rock fragments, soil, and mud, more than half of the particles being larger than sand size. Slow debris flows may move less than 1 m per year; rapid ones reach 160 km per hour.


dendritic pattern

A drainage pattern in which the streams branch randomly in all directions and at almost any angle, resembling in plan the branching habit of certain trees; it is produced where a stream receives several tributaries which in turn are fed by smaller tributaries.


divergent boundaries

Tectonic plate boundaries where new crust is generated as the plates move away from each other.


erosion

The general process or the group of processes whereby the materials of the Earth's crust are loosened, dissolved, or worn away, and simultaneously moved from one place to another, by natural agencies; specif. the mechanical destruction of the land and the removal of material (such as soil) by running water (including rainfall), waves and currents, moving ice, or wind.


estuary

(a) The seaward end or the widened funnel-shaped tidal mouth of a river valley where fresh water comes into contact with seawater and where tidal effects are evident; e.g. a tidal river, or a partially enclosed coastal body of water where the tide meets the current of a stream. (b) A portion of an ocean, as a firth or an arm of the sea, affected by fresh water; e.g. the Baltic Sea. (c) A drowned river mouth formed by the subsidence of land near the coast or by the drowning of the lower portion of a non-glaciated valley due to the rise of sea level.


fish

Any oceanographic sensing device that is towed behind a ship.


fissures

A surface fracture or crack in rock along which there is a distinct separation. It is often filled with mineral-bearing material.


fluvial

Of or pertaining to a river or rivers.


fracture zone

On the deep-sea floor, an elongate zone of unusually irregular topography that often separates regions of different depths. Such zones commonly cross and apparently displace the mid-oceanic ridge by faulting.


geophysics

Study of the Earth by quantitative physical methods. Basic divisions include solid-earth geophysics, physics of the atmosphere and hydrosphere, and solar-terrestrial physics. There are numerous specialties within the field, e.g. seismology, tectonophysics, engineering geophysics. The term is sometimes used to include instrumental study of the Moon and planets.


Global Positioning System

Computerized navigation system determining position on the surface of the Earth from multiple satellite fixes.


GLORIA

An acronym of Geologic Long Range Inclined ASDIC (where ASDIC is a British acronym for sonar), for the instrument used by the USGS to map the deep-water portions of the U.S. EEZ, i.e. from the shelf break to 200 nautical miles offshore.


gully

A very small valley, such as a small ravine in a cliff face, or a long, narrow hollow or channel worn in earth or unconsolidated material (as on a hillside).


guyot

A type of seamount that has a platform top.


headwall scarp

A line of cliffs produced by faulting or by erosion. The term is an abbreviated form of escarpment,  and the two terms commonly have the same meaning, although "scarp" is more often applied to cliffs formed by faulting.


hemipelagic

Deep-sea sediment in which more than 25% of the fraction coarser than 5 microns is of terrigenous, volcanogenic, and/or neritic origin. Such deposits usually accumulate near the continental margin and its adjacent abyssal plain.


Holocene

An epoch of the Quaternary period, from the end of the Pleistocene, approximately 10,000 years ago, to the present time; also, the corresponding series of rocks and deposits.


hot spot

Stationary, localized magma source beneath a tectonic plate, not associated with a spreading center.


hummock

A rounded or conical knoll, mound, hillock, or other small elevation. Also, a slight rise of ground above a level surface.


ice-rafting

The transporting of rock fragments of all sizes on or within icebergs, ice floes, or other forms of floating ice.


igneous

Said of a rock or mineral that solidified from molten or partly molten material, i.e. from a magma. Igneous rocks constitute one of the three main classes into which rocks are divided, the others being metamorphic and sedimentary.


insonify

To suffuse a volume or surface with sound. The term is used in geophysical investigations based on acoustic properties of rocks.


insular shelf

An area of the ocean floor analogous to the continental shelf, but surrounding an island.


levee

An embankment of sediment, bordering one or both sides of a submarine canyon, fan valley, or deep-sea channel. It is similar to a river-channel levee in the subaerial environment.


lithosphere

In plate tectonics, a layer of strength relative to the underlying asthenosphere for deformation at geologic rates. It includes the crust and part of the upper mantle and is of the order of 100 km in thickness.


Loran-C

A long-range radio position-fixing system by which hyperbolic lines of position are determined by measuring the difference in arrival times of synchronized pulse signals from two or more fixed transmitting radio stations of known geographic position. Loran fixes may be obtained at a range of 1,400 nautical miles at night.


lowstand

The interval of time between one or more cycles of relative change of sea level when sea level is below the shelf edge.


magma

Naturally occurring molten rock material, generated within the Earth, from which igneous rocks are derived through solidification and related processes.


mantle

The zone of the Earth below the crust and above the core, which is divided into the upper mantle and the lower mantle, with a transition zone between.


mass movement

A unit movement of a portion of the land surface; specifically mass wasting or the gravitative transfer of material down a slope.


mass wasting

A general term for the dislodgement and downslope transport of soil and rock material under the direct application of gravitational body stresses. In contrast to other erosion processes, the debris removed by mass wasting is not carried within, on, or under another medium. The mass properties of the material being transported depend on the interaction of the soil and rock particles and on the moisture content. Mass wasting includes slow displacements, such as creep and solifluction, and rapid movements such as rockfalls, rockslides, and debris flows.


Mesozoic

An era of geologic time, from the end of the Paleozoic to the beginning of the Cenozoic, or from about 225 to about 65 million years ago.


mid-ocean ridge

A continuous, seismic, median mountain range extending through the North and South Atlantic Oceans, the Indian Ocean, and the South Pacific Ocean. It is a broad, fractured swell with a central rift valley and usually extremely rugged topography. According to the hypothesis of sea-floor spreading, the mid-oceanic ridge is the source of new crustal material.


morphology

The external structure, form, and arrangement of rocks in relation to the development of landforms.


mosaic

An assembly of remotely-sensed images whose edges have been feathered and matched to form a continuous representation of a part of the Earth's surface.


nadir

The point on the ground vertically beneath the sidescan-sonar vehicle.


neritic

Pertaining to the ocean environment or depth zone between low-tide level and 200 m, or between low-tide level and approximately the edge of the continental shelf; also, pertaining to the organisms living in that environment. It is called by some the sub-littoral zone, i.e. is considered to be a part of the littoral zone.


oceanic crust

That type of the Earth's crust which underlies the ocean basins. The oceanic crust is about 5 to 10 km thick.


pelagic sedimentation

Sediment accumulated in the open ocean.


plate tectonics

A theory of global tectonics in which the lithosphere is divided into a number of plates whose pattern of horizontal movement is that of torsionally rigid bodies that interact with one another at their boundaries, causing seismic and tectonic activity along these boundaries.


Pleistocene

An epoch of the Quaternary period, after the Pliocene of the Tertiary and before the Holocene; also, the corresponding worldwide series of rocks. It began 1.6 million years ago and lasted until the start of the Holocene some 10,000 years ago.


Pliocene

An epoch of the Tertiary period, after the Miocene and before the Pleistocene; also, the corresponding worldwide series of rocks. The Pliocene epoch began 5.3 million years ago and ended 1.6 million years ago.


quadrangle

A rectangular area bounded by parallels of latitude and meridians of longitude, used as a unit in systematic mapping. The dimensions of a quadrangle are not necessarily the same in both directions, and its size and the scale at which it is mapped are determined by the prime purpose of the map.


reentrant

A prominent, generally angular indentation in a landform; e.g. an inlet between two promontories along a coastline.


right-lateral fault

A fault on which the displacement is such that, in plan view, the side opposite the observer appears displaced to the right.


rill

A dendritic channel formed by a small stream debauching onto a sand flat or a mud flat; it shows a downslope bifurcation.


seamount

An elevation of the sea floor, 1,000 m or higher, either flat-topped (called a guyot) or peaked. Seamounts may be either discrete, arranged in a linear or random grouping, or connected at their bases and aligned along a ridge or rise.


sediment facies

(a) The aspect, appearance, and characteristics of a rock unit, usually reflecting the conditions of its origin; esp. as differentiating the unit from adjacent or associated units. (b) A mappable, areally restricted part of a rock unit, differing in lithology or fossil content from other beds deposited at the same time and in lithologic continuity. (c) The environment or area in which a rock was formed, e.g. "sandy-bottom facies".


sidescan sonar

Sonar is an acronym of SOund NAvigation and Ranging, a method used in oceanography to study the ocean floor acoustically. "Sidescan" refers to the shape of the sonar beam, which fans out to the sides and scans a wide "swath" of sea floor. The energy beam is confined to the plane perpendicular to the ship's track, forming a narrow acoustic beam in the horizontal plane and a broad beam in the vertical plane.


sonar

An acronym of SOund NAvigation and Ranging, a method used in oceanography to study the ocean floor acoustically.


sonograph

Acoustic image of the sea floor formed by bouncing sound waves off the sea floor and recording the returning acoustic energy levels.


strike slip

In a fault, the component of the movement or slip that is parallel to the strike of the fault.


subduction

The process of one lithospheric plate descending beneath another. A subduction zone is a long, narrow belt in which subduction takes place, e.g. along the Peru-Chile trench or in the volcanic arc belts of the western Pacific Ocean.


submarine fan

A fan-shaped body of sediment typically built by deposition from repeated turbidity currents exiting from a submarine canyon where the canyon opens onto the continental rise or abyssal plain.


substrate

The composition of the sea floor.


talus

Rock fragments of any size or shape (usually coarse and angular) derived from and lying at the base of a cliff or very steep, rocky slope. Also, the outward sloping and accumulated heap or mass of such loose broken rock, considered as a unit, and formed chiefly by gravitational falling, rolling, or sliding.


tectonic plate

A torsionally rigid, thin segment of the Earth's lithosphere, which may be assumed to move horizontally and adjoins other plates along zones of seismic activity.


terrace

Any long, narrow, relatively level or gently inclined surface, generally less broad than a plain, bounded along one edge by a steeper descending slope and along the other by a steeper ascending slope; a large bench or step-like ledge breaking the continuity of a slope. A terrace commonly occurs along the margin and above the level of a body of water, marking a former water level; e.g. a stream terrace.


terrigenous

Derived from the land or continent.


Tertiary

The first period of the Cenozoic era thought to have covered the span of time between 65 million years ago and 3 to 2 million years ago.


topography

(a) The general configuration of a land surface or any part of the Earth's surface, including its relief and the position of its natural and man-made features. (b) The natural or physical surface features of a region, considered collectively as to form; the features revealed by the contour lines of a map.


transform boundary

A plate boundary that ideally shows pure strike-slip displacement.


trench

A narrow, elongate depression of the deep-sea floor, with steep sides, oriented parallel to the trend of the continent and between the continental margin and the abyssal hills. Such a trench is about 2 km deeper than the surrounding ocean floor, and may be thousands of kilometers long.


triple junction

The intersection of three active spreading centers.


turbidity current

A density current in water, air or other fluid, caused by different amounts of matter in suspension, such as a dry-snow avalanche or a descending cloud of volcanic dust; specif.  A bottom-flowing current laden with suspended sediment, moving swiftly (under the influence of gravity) down a sub-aqueous slope and spreading horizontally on the floor of the body of water, and having a density greater than that of the surrounding or overlying clear water.


volcanic arc

A generally curved linear belt of volcanoes above a subduction zone,  and the volcanic and plutonic rocks formed there. Syn: island arc; magmatic arc


volcanic fallout

Fragmental material ejected from a volcano and eventually redeposited. It may have undergone considerable atmospheric sorting before deposition.


yaw

Turning relative to the vertical axis of the vehicle.


Exclusive Economic Zone

Data presented on this CD-ROM are from the deep-water portions of the U.S. Exclusive Economic Zone areas shown here in yellow. The full EEZ of the United States includes several more island Territories in the central and western Pacific, for which equivalent datasets have never been collected.


EEZ References

The preceding text was derived and definitions reprinted from the following sources:

Bates, R.L. and J.A. Jackson, eds., 1987, Glossary of Geology 3rd edition, American Geological Institute, 788 p.

EEZ-SCAN 84 Scientific Staff, 1986, Atlas of the Exclusive Economic Zone, western conterminous United States: U. S. Geological Survey Miscellaneous Investigations Series I-1792, 152 p., scale 1:500,000.


Plate Tectonics

Artist's cross-section illustrating the main types of plate boundaries (see text below). Graphic reprinted from Kious and Tilling, 1996, see references.


Earth cross-section

Cutaway views showing the internal structure of the Earth. The cross-section view is drawn to scale and demonstrates that the Earth's crust literally is only skin deep. The wedge view, not drawn to scale, shows the Earth's three main layers (crust, mantle, and core) in more detail. Graphic reprinted from Kious and Tilling, 1996, see references.


tectonic plates

There are more than a dozen rigid tectonic plates moving relative to each other on the surface of the Earth. Graphic reprinted from Kious and Tilling, 1996, see references.


mantle convection

Conceptual drawing of assumed convection cells in the mantle. Below a depth of about 700 km, the descending slab begins to soften and flow, losing its form. Graphic reprinted from Kious and Tilling, 1996, see references.


oceanic-continental convergence

If by magic we could pull a plug and drain the Pacific Ocean, we would see a most amazing sight -- a number of long narrow, curving trenches thousands of kilometers long and 8 to 10 km deep cutting into the ocean floor. Trenches are the deepest parts of the ocean floor and are created by subduction. Graphic reprinted from Kious and Tilling, 1996, see references.


oceanic-oceanic convergence

Subduction processes in oceanic-oceanic plate convergence result in the formation of volcanoes that may eventually become large enough to be islands. Magmas that form island arcs are produced by the partial melting of the descending plate and/or the overlying oceanic lithosphere.   Graphic reprinted from Kious and Tilling, 1996, see references.


Ring of Fire

Volcanic island arcs and oceanic trenches partly encircling the Pacific Basin form the so-called Ring of Fire, a zone of frequent earthquakes and volcanic eruptions. The trenches are shown in blue-green. The volcanic island arcs, although not labeled, are parallel to, and always landward of, the trenches. For example, the island arc associated with the Aleutian Trench is represented by the long chain of volcanoes that make up the Aleutian Islands. Graphic reprinted from Kious and Tilling, 1996, see references.


Hawaii hot spot

The distinctive linear shape of the Hawaiian Island-Emperor Seamounts chain resulted from the Pacific Plate moving over a deep, stationary hot spot in the mantle located beneath the present-day position of the Island of Hawaii. This plate movement is documented by the progression in ages from Suiko seamount (65 m.y.) to Midway Islands (27 m.y.) to present day eruptions on the Island of Hawaii. Graphic modified from original and used by courtesy of Tasa Graphic Arts, Inc., Albuquerque, New Mexico.


Plate Tectonics References

The preceding text, image captions and definitions were largely reprinted from the following sources:

Bates, R.L. and J.A. Jackson, eds., 1987, Glossary of Geology 3rd edition, American Geological Institute, 788 p.

Kious, W.J. and R.I.Tilling, 1996, This Dynamic Earth; the story of Plate Tectonics: U. S. Geological Survey General Interest Publication, 77 p.


Sidescan-sonar data collection

The image at left shows a ship towing a sidescan-sonar vehicle, the thin strip of sea floor insonified by the instrument, and the resulting sonograph. The thin red arrows link sea-floor features with their corresponding spot on the image. The ship's nadir is represented on the sonograph as a thin white line, and the two black sections adjacent to the nadir represent the water column which is removed during processing.


GLORIA fish

Here the GLORIA sidescan-sonar vehicle is being lowered into the water from the stern of a research ship.


Remote Sensing References

The preceding text was derived and definitions reprinted from the following sources:

Bates, R.L. and J.A. Jackson, eds., 1987, Glossary of Geology 3rd edition, American Geological Institute, 788 p.

EEZ-SCAN 84 Scientific Staff, 1986, Atlas of the Exclusive Economic Zone, western conterminous United States: U. S. Geological Survey Miscellaneous Investigations Series I-1792, 152 p., scale 1:500,000.

Gowen, M.H., 1992, Analysis of High-Resolution Sidescan-Sonar Data: Applications to Sea Floor Mapping and Resource Evaluation: Masters Thesis, Duke University Press, 163 p.


Image A - East Coast

Hudson Canyon (on the left) and Carstens Valley, seen here as a pair of thin wiggly bright lines, are two of the largest submarine canyons along the Atlantic Margin. Red lines represent geologic boundaries.


Image B - East Coast

Cape Fear slide (southern bright area outlined in red) and Cape Lookout Slide (central bright area outlined in red) originated near the shelf break (west) and transport sediment downslope (east) to the base of the continental slope.


Image C - East Coast

Blake Escarpment (nearly vertical bright band in center) separates the deep (4,000 m) ocean basin (east) from the Blake Plateau (west). Bright area at upper center is the Blake Spur, an extension of the Plateau. Red lines represent geologic boundaries.


Image D - East Coast

Off New England, old (125 Ma) submarine volcanoes (bright patches outlined in red) are partially buried by younger sedimentary material.


Image E - East Coast

Geologic map of the EEZ of the East Coast of the United States.


East Coast References

The preceding text was derived and definitions reprinted from the following sources:

Bates, R.L. and J.A. Jackson, eds., 1987, Glossary of Geology 3rd edition, American Geological Institute, 788 p.

EEZ-SCAN 87 Scientific Staff, 1991, Atlas of the Exclusive Economic Zone, Atlantic continental margin: U. S. Geological Survey Miscellaneous Investigations Series I-2054, 174 p., scale 1:500,000.

Schlee, J.S., W.P. Dillon, P. Popenoe, J.M. Robb, and D.W. O'Leary, 1992, GLORIA mosaic of the deep sea floor off the Atlantic Coast of the United States: U. S. Geological Survey miscellaneous field studies map MF-2211, 1 plate, scale 1:2,000,000.

More References


More East Coast References

The preceding text was derived and definitions reprinted from the following sources:

Thelin, G.P. and R.J. Pike, 1991, Landforms of the Conterminous United States - A digital shaded-relief portrayal: U.S. Geological Survey Miscellaneous Investigations Series Map I-2206.

Twichell, D.C. and C.F. Polloni, 1993, CD-ROM atlas of the deepwater parts of the United States Exclusive Economic Zone in the Atlantic Ocean, the Gulf of Mexico, and the eastern Caribbean Sea: U. S. Geological Survey Digital Data Series DDS-15, 1 CD-ROM.


Image A - Gulf of Mexico

Note the way the landslide (light streaky area) had to flow around the salt domes (dark circular shapes). Red lines represent geologic boundaries.


Image B - Gulf of Mexico

Bright east-west trending band (outlined in red) marks the Sigsbee Escarpment which separates the shallower area underlain by mobile salt (north) from the deeper area where salt is absent (south).


Image C - Gulf of Mexico

The Mississippi Channel (wiggly pair of red lines) snakes across the Mississippi Fan for 600 km. Red lines represent geologic boundaries.


Image D - Gulf of Mexico

Geologic map of the EEZ of the Gulf of Mexico.


Gulf of Mexico References

The preceding text was derived and definitions reprinted from the following sources:

Bates, R.L. and J.A. Jackson, eds., 1987, Glossary of Geology 3rd edition, American Geological Institute, 788 p.

Thelin, G.P. and R.J. Pike, 1991, Landforms of the Conterminous United States - A digital shaded-relief portrayal: U.S. Geological Survey Miscellaneous Investigations Series Map I-2206.

Twichell, D.C. and C.F. Polloni, 1993, CD-ROM atlas of the deepwater parts of the United States Exclusive Economic Zone in the Atlantic Ocean, the Gulf of Mexico, and the eastern Caribbean Sea: U. S. Geological Survey Digital Data Series DDS-15, 1 CD-ROM.

Twichell, D.C., K.M. Scanlon and W.P. Dillon, 1996, Gulf of Mexico and Caribbean EEZ, In Geology of the United States' Sea floor: the View from GLORIA, eds. J.V. Gardner, M.E. Field and D.C. Twichell, p.81-83, Cambridge University Press.


Image A - Puerto Rico

Narrow yet deeply-incised submarine canyons (bright streaks outlined in red) transport sediment from the narrow, shallow shelf (on the south) northward down the steep upper slope to the deep-sea floor. The 60-km-wide amphitheater scarp is the large bright area in the northwest quadrant of this image (A).


Image B - Puerto Rico

Scarps (bright half-rounds outlined in red across middle of image) are sites where submarine landslides have occurred. Slides constitute a major mechanism of sediment transport from the slope (on the south) northward to the deep sea.


Image C - Puerto Rico

Puerto Rico Trench (dark band, lower left to upper right) lies at a depth of more than 8,000 m, the deepest point in the Atlantic Ocean. Red lines represent geologic boundaries.


Image D - Puerto Rico

Geologic map of the EEZ of Puerto Rico.


Puerto Rico References

The preceding text was derived and definitions reprinted from the following sources:

Bates, R.L. and J.A. Jackson, eds., 1987, Glossary of Geology 3rd edition, American Geological Institute, 788 p.

Scanlon, K.M. and D.G. Masson, 1996, Sedimentary processes in a tectonically active region: Puerto Rico north insular slope, In Geology of the United States' Sea floor: the View from GLORIA, eds. J.V. Gardner, M.E. Field and D.C. Twichell, p.123-134, Cambridge University Press.

Twichell, D.C. and C.F. Polloni, 1993, CD-ROM atlas of the deepwater parts of the United States Exclusive Economic Zone in the Atlantic Ocean, the Gulf of Mexico, and the eastern Caribbean Sea: U. S. Geological Survey Digital Data Series DDS-15, 1 CD-ROM.


Image A - West Coast

The Blanco Fracture Zone (northwest-southeast trending bright linear feature) offsets the active spreading center (bright lineated areas northwest and southeast of Fracture Zone). This offset occurs as a result of different rates of spreading on the Juan de Fuca Ridge (northwest) and Gorda Ridge (southeast). Cascadia Channel is outlined by parallel red lines going due south (eastern side of image), then abruptly turning west and threading through the Blanco Fracture Zone (center image) to the edge of the image.


Image B - West Coast

Cascadia Channel (dark sinuous ribbon in center of image) is redirected from a southward course to a westward course when it encounters the topographic low of the Blanco Fracture Zone (lower right to middle left). Look again at Image A where the channel turns west.


Image C - West Coast

The Mendocino Fracture Zone (bright horizontal stripe in center) forms a transform plate boundary between the Pacific Plate on the south and the Gorda Plate on the north. Red lines represent geologic boundaries.


Image D - West Coast

Monterey Submarine Canyon and Channel (thin sinuous ribbon in mid-image) transport sediment from the shallow shelf (on the northeast) southwestward to the deep ocean. Monterey Channel and its remarkable south-looping horse-shoe bend are clearly visible in the center of this image.


Image E - West Coast

Seamounts (quasi-circular bright patches outlined in red) off the southern California coast are surrounded by sediment-covered sea floor.


Image F - West Coast

Geologic map of the EEZ of the West Coast of the United States.


West Coast References

The preceding text was derived and definitions reprinted from the following sources:

Bates, R.L. and J.A. Jackson, eds., 1987, Glossary of Geology 3rd edition, American Geological Institute, 788 p.

Cacchione, D.A., D.E. Drake and J.V. Gardner, 1996, A meandering channel at the base of the Gorda Escarpment, In Geology of the United States' Sea floor: the View from GLORIA, eds. J.V. Gardner, M.E. Field and D.C. Twichell, p.181-192, Cambridge University Press.

Gardner, J.V., R.G. Bohannon, M.E. Field and D.G. Masson, 1996, The morphology, processes, and evolution of Monterey Fan: a revisit, In Geology of the United States' Sea floor: the View from GLORIA, eds. J.V. Gardner, M.E. Field and D.C. Twichell, p.193-220, Cambridge University Press.

Thelin, G.P. and R.J. Pike, 1991, Landforms of the Conterminous United States - A digital shaded-relief portrayal: U.S. Geological Survey Miscellaneous Investigations Series Map I-2206.


Image A - Aleutian Arc

The image on the right is old, sediment-blanketed crust of the Pacific Plate south of the Aleutian Trench and shows the uniform backscatter character typical of this mosaic. The image on the left shows the highly variable backscatter typical of a younger, unsedimented spreading center from imagery off the coast of California.


Image B - Aleutian Arc

Aleutian Trench floor (between white lines) is difficult to distinguish because of the flat-lying sediment covering both it and the oceanic plate to the south.


Image C - Aleutian Arc

Ridges of off-scraped sediment form long sub-parallel streaks landward (towards top of image) of the Aleutian Trench, which can be seen as a darker band horizontally across the center of the image. Light blob in center of image is a slope failure from the outermost ridge which flowed onto the Trench floor. Sub-parallel bright streaks south of the Trench are fault breaks in the oceanic crust. These faults form as the crust bends during subduction into the Trench.


Aleutian Arc References

The preceding text was derived and definitions reprinted from the following sources:

Bates, R.L. and J.A. Jackson, eds., 1987, Glossary of Geology 3rd edition, American Geological Institute, 788 p.

Riehle, J.R., M.D. Fleming, B.F. Molnia, J.H. Dover, J.S. Kelley, M.L. Miller, W.J. Nokleberg, G. Plafker, and A.B. Till, 1997, Digital Shaded-Relief Image of Alaska:  U.S. Geological Survey Miscellaneous Investigations Series Map I-2585.

Stevenson, A.J., 1997, personal communication.


Image A - Bering Sea

Bering Channel (direction of flow shown by arrows) is fed primarily by debris shed from the eastern Aleutian Arc (southeast of this image) and Bristol Bay (northeast of this image). As the channel reaches the flat floor of the Aleutian Basin it breaks up into a series of smaller distributary channels (southwest corner of image). The bright streak in the southeast corner of the image is part of the submarine landslide shown in Image C.


Image B - Bering Sea

Variations in backscatter intensity (light vs. dark), believed to be associated with variations in sediment composition, highlight sediment transport pathways. Transport direction is from the Aleutian Arc (southeast of this image) towards the Aleutian Basin (northwest of this image).


Image C - Bering Sea

Large slope failure outlined in white on the western flank of Umnak Plateau sends a debris flow westward into the deep Bering Sea. Direction of sediment movement is indicated by arrows.


Image D - Bering Sea

Bowers Ridge (arcuate feature outlined in white), a fossil island arc, stands above the flat, sedimented (even-toned) floor of the deep Bering Sea.


Image E - Bering Sea

Geologic map of the deep-water EEZ in the Bering Sea.


Bering Sea References

The preceding text was derived and definitions reprinted from the following sources:

Bates, R.L. and J.A. Jackson, eds., 1987, Glossary of Geology 3rd edition, American Geological Institute, 788 p.

Riehle, J.R., M.D. Fleming, B.F. Molnia, J.H. Dover, J.S. Kelley, M.L. Miller, W.J. Nokleberg, G. Plafker, and A.B. Till, 1997, Digital Shaded-Relief Image of Alaska:  U.S. Geological Survey Miscellaneous Investigations Series Map I-2585.

Stevenson, A.J., 1997, personal communication.


Image A - Gulf of Alaska

Large debris fan (inside white line) deposited at the base of the slope directly seaward of the mouth of Chatham Strait, a large glacial outlet. The coarse nature of the sediment on the fan and lack of sediment on the adjacent shallow shelf indicates sediment was transported by a glacier over the shelf edge. Note the deep-sea channel (particularly visible in west side of image) which forms a moat around the edge of the fan and transports the finer grained sedimentary component farther southward offshore.


Image B - Gulf of Alaska

Deep sea channels (dark streak, center left) surrounded by levees (flanking bright bands) form important pathways for sediment transport to the deep sea. Red arrows on either side of channel show direction of sediment transport.


Image C - Gulf of Alaska

The lighter gray band wiggling from north to south through this image is Mukluk Channel as it takes a sinuous route through a string of seamounts (brighter blotches) on its way its termination in the Tufts Abyssal Plain, more than 1,000 km to the south.


Image D - Gulf of Alaska

The trace of the Queen Charlotte Transform Fault (thin bright northwest-southeast streak), which forms the Pacific - North American Plate boundary, is clear as it crosses the mouth of Dixon Entrance. Here the trace of the fault is seen to cross one of the canyons (plain gray area, center of image) which feeds sediment to Mukluk Channel. The presence of a scarp in the floor of the canyon attests to the recent activity of the fault.


Gulf of Alaska References

The preceding text was derived and definitions reprinted from the following sources:

Bates, R.L. and J.A. Jackson, eds., 1987, Glossary of Geology 3rd edition, American Geological Institute, 788 p.

Carlson, P.R., 1997, personal communication.

Riehle, J.R., M.D. Fleming, B.F. Molnia, J.H. Dover, J.S. Kelley, M.L. Miller, W.J. Nokleberg, G. Plafker, and A.B. Till, 1997, Digital Shaded-Relief Image of Alaska:  U.S. Geological Survey Miscellaneous Investigations Series Map I-2585.

Stevenson, A.J., 1997, personal communication.


Image A - SE Hawaii

This shaded-relief image of the combined bathymetry and topography of the Southeastern Hawaiian Ridge EEZ shows the newest volcano Loihi building off the southeast coast of the Island of Hawaii. Red denotes shallowest areas; blue denotes deepest areas.


Image B - SE Hawaii

The North Hawaiian Arch lava field can be clearly seen here; it is the brighter area with an outline that looks like spilled liquid. This image helped settle a scholarly dispute about whether lava erupts from the Hawaiian Arch, or only from directly over the hot spot. Red lines represent geologic boundaries.


Image C - SE Hawaii

Several strands of the Molokai Fracture Zone (MFZ) are seen here as bright nearly east-west streaks. Red lines represent geologic boundaries.


Image D - SE Hawaii

The bright, nearly north-south lineations perpendicular to the MFZ trend are remnants of sea-floor spreading fabric; they are parallel to the trend of the East Pacific Rise spreading center at the time when this area of the sea floor originated. Red lines represent geologic boundaries.


Image E - SE Hawaii

In this image of the Nuuanu-Wailau debris avalanche the bright areas near the islands of Oahu and Molokai (in white), and scattered bright spots farther away, have the characteristic pattern of a huge debris avalanche. Many examples of submarine landslides are visible in the Hawaiian EEZ mosaic: look for the scattered bright spots clustered around the base of the islands and large seamounts. Images such as this one confirmed geologists' suspicions that huge landslides have occurred offshore of the Hawaiian Islands. Red lines represent geologic boundaries.


Image F - SE Hawaii

Geologic map of the Southeastern Hawaiian Ridge EEZ.


Southeast Hawaii References

The preceding text was prepared by Robin Holcomb using the following sources:

Atwater, T., 1989, Plate tectonic history of the northeast Pacific and western North America, Geol. Soc. Amer., Geology of North America, v. N, p. 21-72.

Bates, R.L. and J.A. Jackson, eds., 1987, Glossary of Geology 3rd edition, American Geological Institute, 788 p.

Clague, D.A., and G.B. Dalrymple, 1987, The Hawaiian-Emperor Chain:  U.S.G.S. Professional Paper 1350, p. 5-54.

Clague, D.A., R.T. Holcomb, J.M. Sinton, R.S. Detrick, and M.E. Torresan, 1990, Pliocene and Pleistocene alkalic flood basalts on the seafloor north of the Hawaiian Islands:  Earth and Planet. Sci. Letters, v. 98, p. 175-191.

Hamilton, E.L., 1957, Marine geology of the southern Hawaiian Ridge:  Bull. Geol. Soc. Amer., v. 68, p. 1011-1026.

More References


More Southeast Hawaii References

The preceding text was prepared by Robin Holcomb using the following sources:

Holcomb, R.T., and R.C. Searle, 1991, Large landslides from oceanic volcanoes:  Marine Geotechnology, v. 10, p. 19-32.

Moore, J.G., 1987, Subsidence of the Hawaiian Ridge:  USGS Professional Paper 1350, p. 85-100.

Moore, J.G., D.A. Clague, R.T. Holcomb, P.W. Lipman, W.R. Normark, and M.E. Torresan, 1989, Prodigious submarine landslides on the Hawaiian Ridge:  Jour. Geophys. Res., v. 94, p. 17,465-17,484.

Moore, J.G. and R.K. Mark, 1992, Morphology of the Island of Hawaii:  GSA Today, v. 2, no. 12, p. 257-259 & 262.

Moore, J.G., W.R. Normark, and R.T. Holcomb, 1994, Giant Hawaiian landslides:  Annu. Rev. Earth Planet. Sci., v. 22, p. 119-144.

More References


More Southeast Hawaii References

The preceding text was prepared by Robin Holcomb using the following sources:

Searle, R.C., R.T Holcomb, J.B. Wilson, M.L. Holmes, R.J. Whittington, E.S. Kappel, B.A. McGregor, and A.N. Shor, 1993, The Molokai Fracture Zone near Hawaii, and the Late Cretaceous change in Pacific/Farallon spreading direction:  Amer. Geophys. Union, Geophys. Monograph 77, p. 155-169.

Tilling, R.I., R.Y. Koyanagi, P.W. Lipman, J.P. Lockwood, J.G. Moore, and D.A. Swanson, 1976, Earthquake and related catastrophic events, Island of Hawaii, November 29, 1975: A preliminary report:  USGS Circular 740, 33 p.


Image A - Central Hawaii

Gardner Pinnacles are tiny but steep islands of volcanic rock. They are all that remain of an island that was once as large as the present Island of Hawaii before the former island slowly subsided below sea level beginning about 15 million years ago. The upper flanks of the submerged island are outlined in white. The enclosed gray and black area contains no sonar imagery because it is less than 400 m deep, too shallow to be surveyed by GLORIA. The deeper flanks are marked by reefs (thin, concentric bright stripes especially visible on the west and south sides of the submerged island) that developed at successive temporary sea levels as the island subsided.


Image B - Central Hawaii

Necker Ridge, outlined here in white, and other nearby sub-parallel ridges are a set of large volcanic ridges that grew along cracks in the Earth's crust between the Molokai and Murray fracture zones about 70 million years ago. Necker Ridge continues southwestward into the Johnston Island EEZ.


Image C - Central Hawaii

The rectangular array of ridges (bright linear features) in this image are part of the Murray Fracture Zone. It was produced by a series of offsets in the East Pacific Rise as the sea floor here formed about 100 million years ago. The smaller ridges trending roughly north-south were produced successively, from west to east, by the process of sea-floor spreading along the crest of the East Pacific rise. The larger ridges and faults trending roughly east-west were produced by a series of transform fault offsets in the spreading center. This band of closely-spaced offsets, called the Murray Fracture Zone, is one of the great fracture zones of the northeast Pacific. It extends eastward across the Pacific nearly to the coast of California.


Central Hawaii References

The preceding text was prepared by Robin Holcomb using the following sources:

Atwater, T., 1989, Plate tectonic history of the northeast Pacific and western North America, Geol. Soc. Amer., Geology of North America, v. N, p. 21-72.

Bates, R.L. and J.A. Jackson, eds., 1987, Glossary of Geology 3rd edition, American Geological Institute, 788 p.

Clague, D.A., and G.B. Dalrymple, 1987, The Hawaiian-Emperor Chain:  U.S.G.S. Professional Paper 1350, p. 5-54.

Hamilton, E.L., 1957, Marine geology of the southern Hawaiian Ridge:  Bull. Geol. Soc. Amer., v. 68, p. 1011-1026.

Holcomb, R.T., and R.C. Searle, 1991, Large landslides from oceanic volcanoes:  Marine Geotechnology, v. 10, p. 19-32.

More References


More Central Hawaii References

The preceding text was prepared by Robin Holcomb using the following sources:

Moore, J.G., 1987, Subsidence of the Hawaiian Ridge:  USGS Professional Paper 1350, p. 85-100.

Moore, J.G., D.A. Clague, R.T. Holcomb, P.W. Lipman, W.R. Normark, and M.E. Torresan, 1989, Prodigious submarine landslides on the Hawaiian Ridge:  Jour. Geophys. Res., v. 94, p. 17,465-17,484.

Moore, J.G., W.R. Normark, and R.T. Holcomb, 1994, Giant Hawaiian landslides:  Annu. Rev. Earth Planet. Sci., v. 22, p. 119-144.

Pringle, M.S., 1993, Age progressive volcanism in the Musicians Seamounts: A test of the hot spot hypothesis for the Late Cretaceous Pacific, Amer. Geophys. Union, Geophys. Monograph 77, p. 187-215.


Image A - NW Hawaii

This image shows a chain of large old guyots that grew up from the sea floor to form small islands about 100 million years ago. White circles indicate the approximate locations of the summits of the guyots. These volcanoes probably were produced in succession from north to south atop a hot spot that later cooled. Other nearby seamounts never reached sea level.


Image B - NW Hawaii

A swirly pattern of numerous sea-floor ridges (seen here as short, brighter linear features) defines a series of small "microplates". About 120 million years ago, these ridges formed successively from west to east at the junction between intersecting centers of sea-floor spreading. Although it is much, much slower, the pattern of ridges resulting from this process resembles that of small water eddies spinning successively away from the blade of a canoe paddle.


Image C - NW Hawaii

Lisianski Island is a small remnant of a much larger island, larger than the present-day island of Maui. The general shape of the present shallow platform is outlined in white, and the approximate location of Lisianski itself is indicated by a white spot. Most of the island subsided below sea level about 20 million years ago after losing much of its southwest flank in a giant landslide. Landslide debris, visible here as numerous bright spots, litters the sea floor southwest of the present island.


Northwest Hawaii References

The preceding text was prepared by Robin Holcomb using the following sources:

Bates, R.L. and J.A. Jackson, eds., 1987, Glossary of Geology 3rd edition, American Geological Institute, 788 p.

Clague, D.A., and G.B. Dalrymple, 1987, The Hawaiian-Emperor Chain:  U.S.G.S. Professional Paper 1350, p. 5-54.

Holcomb, R.T., and R.C. Searle, 1991, Large landslides from oceanic volcanoes:  Marine Geotechnology, v. 10, p. 19-32.

Moore, J.G., 1987, Subsidence of the Hawaiian Ridge:  USGS Professional Paper 1350, p. 85-100.

More References


More Northwest Hawaii References

The preceding text was prepared by Robin Holcomb using the following sources:

Moore, J.G., D.A. Clague, R.T. Holcomb, P.W. Lipman, W.R. Normark, and M.E. Torresan, 1989, Prodigious submarine landslides on the Hawaiian Ridge:  Jour. Geophys. Res., v. 94, p. 17,465-17,484.

Pringle, M.S., 1993, Age progressive volcanism in the Musicians Seamounts: A test of the hot spot hypothesis for the Late Cretaceous Pacific, Amer. Geophys. Union, Geophys. Monograph 77, p. 187-215.


Image A - Johnston Island

The featureless gray area seen in this enlargement is the shallow platform surrounding Johnston Island; it is too shallow to be imaged by GLORIA. The approximate location of the island is shown as a white spot. Dashed lines indicate the center of a large chute that funnels talus shed from the bathymetric high of Johnston Island. On the right side of the image a line shows the local border between the brighter talus on the deep flank of the island edifice and the darker sediment in the basin adjacent to it.


Image B - Johnston Island

A white line encloses the relatively flat top of Horizon Guyot. The sliver of image between the northwest edge of the guyot top and the dashed line shows the bright bedrock terraces. The far edge of talus aprons on the northwest side of the guyot is marked by a white line.


Image C - Johnston Island

White line segments show the southwest-northeast trend of the ridges in this close-up of the southern strand of the Molokai Fracture Zone. The circle encloses a ridge perpendicular to the MFZ; that ridge is part of the original sea-floor spreading fabric.


Image D - Johnston Island

Close-up view of a portion of Karin Ridge, a prominent feature that trends northwest-southeast just east of Johnston Island. White lines show approximate edges of the ridge. The southern strand of the Molokai Fracture Zone does not extend into this view.


Image E - Johnston Island

Close-up of mottled-backscatter pattern that is unique in all the United States EEZ imaged to date. Manganese nodules have been dredged from areas in the mid-Atlantic that have a similar backscatter pattern. No dredging has yet been reported here.


Image F - Johnston Island

This image from the southern Johnston Island EEZ shows a group of 5 large and several smaller seamounts. Approximate locations of their summits are circled in white.


Johnston Island References

The preceding text was derived and definitions reprinted from the following sources:

Bates, R.L. and J.A. Jackson, eds., 1987, Glossary of Geology 3rd edition, American Geological Institute, 788 p.

Ryan, H. F., A.S. Davis, Q. Huggett, and D. Bishop, 1992, Cruise Report for EEZ-SCAN cruise F13-90-CP, Necker Ridge and Johnston Island: U.S. Geological Survey Open-File Report 92-433, 27p.


Image A - Kingman/Palmyra

White circles in the dark gray non-data areas show the approximate locations of Kingman Reef, northwest, and Palmyra Atoll, southeast. Note the dendritic drainage patterns on both their flanks.


Image B - Kingman/Palmyra

The 1,000-2,000-m-deep central core of the shallower area is outlined here in white. It is about 2,400 m shallower than the basin in the center of the mosaic (off this image to the northwest) through which a huge submarine channel runs. The dendritic pattern of canyons on the southwest side of this core area is the head of that huge channel; the canyons coalesce into small channels that join to become the main channel.


Image C - Kingman/Palmyra

In this close-up image white lines indicate the joining of the main channel that runs through this mosaic with another large channel from the southeast. The southwest arm heads near the highest core of the shallower area (see text) and the southeast arm heads somewhere off the southeast side of the EEZ. Once joined into one channel, it continues downslope off the mosaic on the northeast side.


Image D - Kingman/Palmyra

This bathymetric high on the Line Islands Ridge is informally named the S.P. Lee Guyot, after a U. S. Geological Survey research vessel that took dredge samples here in 1983. The summit area is outlined in white, and ranges from 1,000-1,500 m deep. The brighter features within the circle may be lava or remnants of ancient reef growth. Samples of those exact spots would be required to know for sure. Similar bright features are visible within the shallowest area east of Palmyra Atoll (in Image B).


Kingman-Palmyra References

The preceding text was derived and definitions reprinted from the following sources:

Bates, R.L. and J.A. Jackson, eds., 1987, Glossary of Geology 3rd edition, American Geological Institute, 788 p.

Gutmacher, C.E., and S.L. Ross, 1991, GLORIA side-scan images of unusual geomorphology in the Line Islands:  EOS, Transactions, American Geophysical Union, v.72, no.44, p.249.


Glossary References

The preceding terms and definitions are reprinted with some editing from:

Bates, R.L. and J.A. Jackson, eds., 1987, Glossary of Geology 3rd edition, American Geological Institute, 788 p.