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U.S. Geological Survey Open-File Report 2011-1015

Quaternary Geophysical Framework of the Northeastern North Carolina Coastal System


Methods

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Click on figures for larger images.
Thumbnail image of and link to larger figure.  Map showing  inner shelf geophysical data coverage from False Cape, VA to west of Cape Lookout, NC

Figure 2. Map showing extent of inner shelf geophysical data coverage (False Cape, Virginia, to west of Cape Lookout, North Carolina).

Thumbnail image of and link to larger figure. Map showing nearshore geophysical data coverage from north of Oregon Inlet to Cape Hatteras

Figure 3. Map showing extent of nearshore geophysical data coverage (north of Oregon Inlet to Cape Hatteras).

 

Thumbnail image of and link to larger figure.  Map showing ground penetrating GPR and SWASH on barrier islands

Figure 4. Map showing extent of ground-penetrating radar (GPR) and SWASH shoreline position surveys on barrier islands.

 

Thumbnail image of and link to larger image. Map showing back barrier geophysical trackline data.

Figure 5. Map showing extent of back-barrier geophysical trackline data (Albemarle, Pamlico, and Core Sounds and tributaries).

 

Thumbnail image of and link to larger figure. Map showing locations of USGS Van Veen sediment grab samples on the inner continental shelf

Figure 6. Map showing locations of USGS Van Veen sediment grab samples on the inner continental shelf.

The geophysical datasets presented in this report were collected from numerous sources and multiple research endeavors.  Various research cruises and surveys were undertaken to collect the seismic and acoustic datasets provided. 

Inner Shelf

From 1999 to 2004 the USGS conducted six research cruises that acquired over 8,700 kilometers (km) of seismic, sidescan sonar, and bathymetric data along the inner shelf of North Carolina from False Cape, Virginia, to west of Cape Lookout, North Carolina (fig. 2).  The inner shelf and lower shoreface were mapped using high-resolution sidescan sonar (100% coverage), interferometric swath bathymetry, subbottom profilers (Compressed High Intensity Radar Pulse or “chirp” and boomer systems), fathometer, and sediment grab sampler. The total surveyed area is 2,600 square kilometers (km2) and ranges in water depth from 7 meters (m) (mid-shoreface) to 28 m (inner shelf).

Nearshore

In 2002 and 2005 a detailed bathymetric and geologic mapping study was done by project collaborators at VIMS in the nearshore region (1-8 m water depths) from 3 km north of Duck to Cape Hatteras (fig. 3). A Submetrix interferometric sidescan/bathymetry system and Edgetech Chirp 216 (2002) and 512i (2005) subbottom systems were used to collect 64 km2 of survey data.

Objectives of this study were to (1) measure the thickness of modern sand, (2) map the surface sediment distribution, and (3) map the shoreface morphology (for example, large-scale sandbars) across the nearshore and the relation with regions in which large areas of underlying geology are exposed on the sea floor.

Barrier Islands

Two separate survey methods were used along the barrier islands of the North Carolina Outer Banks. Ground-penetrating radar was collected by researchers at ECU, and shoreline positions were surveyed using the USGS's SWASH (Surveying Wide-Area Shorelines) system (fig. 4).

Ground-Penetrating Radar
Ground-penetrating radar (GPR) data were collected from 2002 to 2005 by researchers at ECU. Surveys were run lengthwise along each of the barrier islands. Cross-sectional island transects were collected along existing roads. Approximately 114 km of GPR trackline data were collected. These data were used to characterize the shallow subsurface beneath the Outer Banks barrier islands. This includes documenting former inlet locations, dune ridge deposition, and locations of washover and peat deposits.

SWASH
A high-resolution set of large-scale shoreline change observations was collected from 1997 to 2005 using the ground-based SWASH system (http://woodshole.er.usgs.gov/operations/swash/).  The coastal change observations collected provide a shoreline change signal of unprecedented resolution, revealing patterns of shoreline change along 130 km of coast at an inter-annual (5-year) time scale. Offshore geologic framework observations reveal features in the bathymetry and near-surface sediment distribution that suggest ties to the observed shoreline response. Since 1999, the shoreline position was surveyed 61 times over 130 km of coast from Corolla, near the Virginia-North Carolina border, to the tip of Cape Hatteras. This represents a unique time series for quantifying large-scale coastal evolution.

Back-barrier Coastal System

High-resolution chirp and boomer subbottom profiling systems were used to map Albemarle and Pamlico Sounds (fig. 5). Mapping of the area was conducted in multiple research cruises from 2000 to 2004. The back-barrier study area includes over 3,400 km of boomer and 2,600 km of chirp seismic data. The back-barrier sounds and adjacent tributary estuaries were surveyed using the USGS research vessel, R/V Rafael and a pontoon vessel from East Carolina University referred to as the Doghouse.  The Rafael platform provides rapid access to remote study areas and provides high-quality seismic data in a format that is directly compatible with data collected for the rest of the project.

Geologic Samples

Grab samples were collected at 202 stations using a Van Veen grab sampler on many of the USGS inner shelf cruises to aid in the interpretation of acoustic datasets (fig. 6). The locations of all vibracores used in the interpretation and integration steps of the seismic datasets described above are provided in this report. The cores were collected by various agencies; most were not funded through this research project. Further information on the vibracore datasets can be found in separate publications listed in the metadata.

Additional Bathymetry

The National Geophysical Data Center (NGDC) assembled a gridded database referred to as the Coastal Relief Model (CRM) by merging USGS 3-arc-second digital elevation models with a compilation of hydrographic soundings covering the U.S. East Coast. The CRM extends from the coastal State boundaries to as far offshore as the data will support a continuous view of the sea floor at 3-arc-second resolution.

The National Elevation Dataset (NED) is a seamless dataset maintained by the U.S. Geological Survey and comprised of the best available raster elevation data for the United States. The first priority of source data is quality, high-resolution data, typically derived from lidar or digital photogrammetry. Source data are selected from an expanding inventory of standard production USGS Digital Elevation Model (DEM’s), and also from an increasing number of datasets that are project- or agency-specific.  Further information on the NED can be found at http://ned.usgs.gov/.

The topography and bathymetry depicted in the GeoTIFF raster dataset provided in this report are a compilation and integration of the following data sources:

1) NGDC CRM 90 meter topo/bathy data;
2) Shoaling Waves Experiment (SHOWEX) 900-m bathymetry data;
3) bathymetry data collected as part of this research program; and
4) NED 3 meter topography (elevation) data.

Two gridding errors in the NGDC data south of Cape Hatteras and north of Cape Lookout were corrected during data compilation.  Further information on the NGDC CRM can be found at http://www.ngdc.noaa.gov/mgg/coastal/model.html.

The SHOWEX experiment took place off of Duck, North Carolina in 1999. Further information on the SHOWEX experiment can be found at http://www.mmm.ucar.edu/abl/showex/.

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