Glossary of Glacier Terminology - Text Version
Types of Glaciers:·Calving GlacierA glacier with a terminus that ends in a body of water (river, lake, ocean) into which it calves icebergs. ·Cirque glacierA small glacier that forms within a cirque basin, generally high on the side of a mountain. ·Hanging glacierA glacier that originates high on the wall of a glacier valley and descends only part of the way to the surface of the main glacier. Avalanching and icefalls are the mechanisms for ice and snow transfer to the valley floor below. ·Ice CapA dome-shaped accumulation of glacier ice and perennial snow that completely covers a mountainous area or island, so that no peaks or Nunataks poke through. ·Ice FieldA continuous accumulation of snow and glacier ice that completely fills a mountain basin or covers a low-relief mountain plateau to a substantial depth. When the thickness become great enough, tongues of ice overflow the basins or plateaus as Valley Glaciers. ·Ice SheetA thick, subcontinental to continental-scale accumulation of glacier ice and perennial snow that spreads from a center of accumulation, typically in all directions. Also called a Continental Glacier. ·Piedmont glacierA fan or lobe-shaped glacier, located at the front of a mountain range. It forms when one or more valley glaciers flow from a confined valley onto a plain where it expands. The 30-mile wide Malaspina is the largest in Alaska. ·Polar GlacierA glacier with a thermal or temperature regime in which ice temperatures always remain below the freezing point. ·Reconstituted GlacierA glacier formed below the terminus of a hanging glacier by the accumulation, and reconstitution by pressure melting (regelation), of ice blocks that have fallen and/or avalanched from the terminus of the hanging glacier. Also called Glacier Remaniè. ·Rock GlacierA glacier-like landform that often heads in a cirque and consists of a valley-filling accumulation of angular rock blocks. Rock glaciers have little or no visible ice at the surface. Ice may fill the spaces between rock blocks. Some rock glaciers move, although very slowly. ·Temperate GlacierA glacier with a or temperature-regime in which liquid water coexists with frozen water (glacier ice) during part or even all of the year. ·Tidewater GlacierA glacier with a terminus that ends in a body of water influenced by tides, such as the ocean or a large lake. Typically, tidewater glaciers calve ice to produce icebergs. ·Valley Glacier A glacier that flows for all or most of its length within
the walls of a mountain valley. Also called an Alpine Glacier
or a Mountain Glacier. AAblationThe loss of ice and snow from a glacier system. This occurs through a variety of processes including melting and runoff, sublimation, evaporation, calving, and wind transportation of snow out of a glacier basin. AccumulationThe addition of ice and snow into a glacier system. This occurs through a variety of processes including precipitation, firnification, and wind transportation of snow into a glacier basin from an adjacent area. Accumulation AreaThe part of a glacier that is perennially covered with snow. Also called Névé. AdvanceAn increase in the length of a glacier compared to a previous point in time. As ice in a glacier is always moving forward, a glacier's terminus advances when less ice is lost due to melting and/or calving than the amount of yearly advance. Arete
A jagged, narrow ridge that separates two adjacent glacier
valleys or cirques. The ridge frequently resembles the blade
of a serrated knife. A French term referring to the bones
in a fish backbone.
BBarren ZoneAn area of fresh, vegetation-free bedrock around the margin of a retreating glacier that documents the recent loss of ice. BergschrundA single large crevasse or series of sub-parallel crevasses that develop at the head of a glacier. The location where ice pulls away from the bedrock wall of the cirque against which it accumulated. In winter, the crevasse fills with snow. In spring or summer, it reopens. (Originally a German term). Bergy SeltzerA crackling or sizzling similar to that made by soft drinks or seltzer water but louder. The sound made as air bubbles formed at many atmospheres of pressure are released during the melting of glacier ice. Also called Ice Sizzle. Braided Stream (Anastomizing Stream)
A stream that is characterized by a complex network of branches
that continuously separate and reunite. Streams braid when
they have a much greater sediment load than they can carry.
Also called an Anastomosing Stream/.
The process by which pieces of ice break away from the terminus
of a glacier that ends in a body of water or from the edge
of a floating ice shelf that ends in the ocean. Once they
enter the water, the pieces are called icebergs.
A series of small, closely spaced, crescentic grooves or scars
formed in bedrock by rocks frozen in basal ice as they move
along and chip the glacier's bed. The horns of the crescent
generally point down glacier.
A bowl-shaped, amphitheater-like depression eroded into the
head or the side of a glacier valley. Typically, a cirque
has a lip at its lower end. The term is French and is derived
from the Latin word circus.
Any curved mark or fracture produced by plucking or chipping of the
glacier's bed. Larger than chatter marks,typically the horns of these
gouges point up glacier. Also called Lunate Fracture or Crescentic
Mark.
A crack or series of cracks that open in the surface of a
moving glacier in response to differential stresses caused
by glacier flow. They range in shape from linear to arcuate,
in length from feet to miles. Their orientation may be in
any direction with respect to the glacier flow. The deepest
crevasses may exceed 100 feet.
A cone or mound of debris-covered ice, with a thick enough
sediment cover to protect the ice from melting.
The study of tree rings and subfossil wood to provide information
about the glacial and climatic history of an area.
Disarticulation is the process through which large blocks
of ice, sometimes greater than .5 miles in width, detach from
the thinning and retreating terminus of a glacier that ends
in a body of water. Disarticulation occurs as the terminus
thins to where its buoyandcy no longer permits it to remain
in contact with its bed. As the glacier begins to float free
and rises off the bottom it rapidly comes apart along old
fracture scars and crevasses. For example, at Bering Glacier,
in the Chugach Mountains, Alaska, a single observed disarticulation
event resulted in nearly 2/3 of a mile of terminus retreat
in a single day. As many as 100 discrete, tabular pieces of
glacier ice have been observed separating from the glacier's
terminus in a single event. Bering Glacier flows through Wrangell-St.
Elias National Park, Alaska.
A tongue of glacier ice that flows away from the main trunk
of the glacier. This may result from differential melting
changing the gradient of part of a glacier.
The thinning of a glacier due to the melting of ice. This
loss of thickness may occur in both moving and stagnant ice.
Also called Thinning.
A collective term used to describe all types of glacier sedimentary
deposits, regardless of the size or amount of sorting. The
term includes all sediment that is transported by a glacier,
whether it is deposited directly by a glacier or indirectly
by running water that originates from a glacier.
An elongated ridge of glacial sediment sculpted by ice moving
over the bed of a glacier. Generally, the down-glacier end
is oval or rounded and the up-glacier end tapers. The shape
is often compared to an inverted, blunt-ended canoe. Although
not common in Alaska, drumlins cover parts of the Eastern
and Midwestern United States (Irish).
A rock of unspecified shape and size, transported a significant
distance from its origin by a glacier or iceberg and deposited
by melting of the ice. Erratics range from pebble-size to
larger than a house and usually are of a different composition
that the bedrock or sediment on which they are deposited.
A meandering, water-deposited, generally steep-sided sediment
ridge that forms within a subglacial or englacial stream channel.
Its floor can be bedrock, sediment, or ice. Subsequent melting
of the glacier exposes the deposit. Generally composed of
stratified sand and gravel, eskers can range from feet to
miles in length and may exceed 100 feet in height.
Fluctuations in the worldwide sea-level regime caused by changes
in the quantity of seawater available. The greatest changes
are caused by water being added to, or removed from, glaciers.
An intermediate stage in the transformation of snow to glacier
ice. Snow becomes firn when it has been compressed so that
no pore space remains between flakes or crystals, a process
that takes less than a year.
A line across the glacier, from edge to edge, that marks the
transition between exposed glacier ice (below) and the snow-covered
surface of a glacier (right). During the summer melt season,
this line migrates up-glacier. At the end of the melt season
the firn line separates the accumulation zone from the ablation
zone.
A glacially eroded or modified U-shaped valley that extends
below sea level and connects to the ocean. Filled with seawater,
depths may reach more than 1,000 feet below sea level. The
largest Alaskan fiords are more than 100 miles long and more
than 5 miles wide. Also spelled Fiord.
The layering or banding that develops in a glacier during
the process of transformation of snow to glacier ice. Individual
layers, called folia, are visible because of differences in
crystal or grain size, alternation of clear ice and bubbly
ice, or because of entrained sediment.
A glacial spring, generally discharging supercooled water
with a significant hydrostatic head.
A linear depression, inches to miles in length, produced by
the removal of rock or sediment by the erosive action of a
glacier.
An accumulation of standing liquid water on (supraglacial),
in (englacial), or under (subglacial) a glacier.
A channelized accumulation of liquid water on (supraglacial),
in (englacial), or under (subglacial) a glacier, moving under
the influence of gravity.
A large, perennial accumulation of ice, snow, rock, sediment
and liquid water originating on land and moving down slope
under the influence of its own weight and gravity; a dynamic
river of ice. Glaciers are classified by their size, location,
and thermal regime.
A cave formed in or under a glacier, typically by running
water. Steam or high heat flow can also form glacier caves.
Also called Ice Cave.
The movement of ice in a glacier, typically in a downward
and outward direction, caused by the force of gravity. 'Normal'
flow rates are in feet per day. 'Rapid' flow rates (i.e. surge)
are in 10s or 100s of feet per day.
A mono-mineralic type of rock, composed of crystals of the
mineral ice, formed through metamorphism of snowflakes. Metamorphism
results in recrystallization, increased density, and the growth
of hexagonal crystals. This ice comprises the majority of
the mass of a glacier. Intermediate stages include Firn and
Neve.
A rock that is balanced on a pedestal of ice, and elevated
above the surface of a glacier. The rock protects the pedestal
of ice from melting by insulating it from the sun.
A former tributary glacier valley that is incised into the
upper part of a U-shaped glacier valley, higher than the floor
of the main valley. Hanging valley streams often enter the
main valley as waterfalls.
The current part of geologic time. The Holocene epoch began
~12,000 years ago, at the end of the Pleistocene epoch.
A pointed, mountain peak, typically pyramidal in shape, bounded
by the walls of three or more cirques. Headward erosion has
cut prominent faces and ridges into the peak. When a peak
has four symmetrical faces, it is called a Matterhorn.
The transportation of glacier sediment away from the ice margin
by icebergs. Sediment transported by floating ice and deposited
in the ocean is called glacial-marine sediment. Deposited
in lakes, it is called glacial-lacustrine sediment.
The floating terminus of a glacier, typically formed when
a terrestrial glacier flow into a deep water basin, such as
in Antarctica and the Canadian Arctic.
A block of ice that has broken or calved from the face of
a glacier and is floating in a body of marine of fresh water.
Alaskan icebergs rarely exceed 500 feet in maximum dimension.
In order of increasing size, the following names are used:
Brash Ice, Growler, Bergy Bit.
A lake that exists because its water is restricted from flowing
by an ice dam. Sometimes these lakes form because an advancing
glacier had blocked a valley.
Part of a glacier where the ice flows over a bed with a very
steep gradient, typically at a higher rate than both above
and below. As a result the surface is fractured and heavily
crevassed. In a river system, this would be a waterfall.
A lake that is located adjacent to the terminus of a glacier.
Typically, these lakes form in bedrock basins scoured by the
glacier. They enlarge as the glacier retreats. Sometimes they
are dammed by an End or Recessional Moraine.
The balance between changes within the Earth's crust and mantle,
where material is displaced in response to an increase (isostatic
depression) or decrease (isostatic rebound) in mass at any
point on the Earth's surface above. Such changes are frequently
caused by advances or retreats of glaciers.
A glacier outburst flood resulting from the failure of a glacier-ice-dam,
glacier-sediment-dam, or from the melting of glacier ice by
a volcanic eruption (Icelandic).
A sand and gravel deposit formed by running water on stagnant
or moving-glacier ice. Crevasse fills or crevasse ridges form
within crevasses. Kames form on flat or inclined ice, in holes,
or in cracks. A kame terrace forms between the glacier and
the adjacent land surface. Shapes include hills, mounds, knobs,
hummocks, or ridges.
A depression that forms in an outwash plain or other glacial
deposit by the melting of an in-situ block of glacier ice
that was separated from the retreating glacier-margin and
subsequently buried by glacier sedimentation. As the buried
ice melts, the depression enlarges.
The most recent interval of temperate glacier expansion and
advance on Earth. It began ~650 years ago and continued into
the 20th century in many locations. Temperate glaciers in
North America, South America, Africa, Europe, and Asia were
affected.
A measure of the change in mass of a glacier at a certain
point for a specific period of time. The balance between accumulation
and ablation. Also called Mass Budget.
A general term for unstratified and unsorted deposits of sediment
that form through the direct action of, or contact with, glacier
ice. Many different varieties are recognized on the basis
of their position with respect to a glacier.
An irregular-shaped layer or pile of glacier sediment formed
by the melting of a block of stagnant ice. Ultimately, ablationa
moraine is deposited on the former bed of the glacier. Also
called Ablation Till.
A blanket of glacier till deposited on all of the surfaces
over which a glacier moves, typically by moving ice.
A moraine ridge consisting of a drape of sediment overlying
a mass of stagnant ice.
A sediment ridge, located on a glacier's surface adjacent
to the valley walls, extending down glacier to the terminus.
It forms by the accumulation of rock material falling onto
the glacier from the valley wall, rather than by water deposition.
A sediment ridge, located on a glacier's exposed ice
surface, away from its valley walls, extending down glacier
to the terminus. It forms by the joining of two lateral moraines
when two glaciers merge.
A ridge or pile of unstratified glacial sediment that is formed
in front of the ice margin by the terminus of an advancing
glacier, bulldozing sediment in its path.
A ridge of glacial sediment that forms when the terminus of
a retreating glacier remains at or near a single location
for a period of time sufficient for a cross-valley accumulation
to form.
A cross-valley, ridge-like accumulation of glacial sediment
that forms at the farthest point reached by the terminus of
an advancing glacier. Also called an End Moraine.
A narrow, tubular chute or crevasse through which water enters
a glacier from the surface. Occasionally, the lower end of
a moulin may be exposed in the face of a glacier or at the
edge of a stagnant block of ice.
A mountain peak or ridge that pokes through the surface of
an Ice Field or a Glacier. It may separate adjacent Valley
Glaciers (Greenlandic).
An arcuate, convex, down-glacier-pointing band or undulation
that forms on the surface of a glacier at the base of an icefall.
Two types of ogives occur: wave ogives, which are undulations
of varying height and band ogives, which are alternating light-
and dark-colored bands.
A broad, low-slope angle alluvial plain composed of glacially
eroded, sorted sediment (termed outwash), that has been transported
by meltwater. The alluvial plain begins at the foot of a glacier
and may extend for miles. Typically, the sediment becomes
finer grained with increasing distance from the glacier terminus.
A depression in an outwash plain by the melting of a block
of ice floated to its depositional site by meltwater and subsequently
buried by sediment. As it melts, a depression in the surface
of the outwash plain develops.
The epoch of geologic time, informally called the 'The Great
Ice Age' or the 'Glacial Epoch', that began ~1.8 million years
ago and ended ~8,000 years ago (see the CVO's Geologic Time
Scale). During this interval continental glaciers repeatedly
formed and covered significant parts of the Earth's surface.
Together, the Holocene and Pleistocene epochs comprise the
Quaternary Period.
The mechanical removal of pieces of rock from a bedrock face
that is in contact with glacier ice. Blocks are quarried and
prepared for removal by the freezing and thawing of water
in cracks, joints, and fractures. The resulting pieces are
frozen into the glacier ice and transported.
An isolated melting mass of glacier ice, that has become detached
from its source and the remainder of the glacier. Some remnants
cover many square miles.
A decrease in the length of a glacier compared to a previous
point in time. As ice in a glacier is always moving forward,
its terminus retreats when more ice is lost at the terminus
to melting and/or calving than reaches the terminus. During
retreat, ice in a glacier does not move back up the valley.
An elongated, rounded, asymmetrical, bedrock knob produced
by glacier erosion. It has a gentle slope on its up-glacier
side and a steep- to vertical-face on the down-glacier side.
Several landslides generated by the Great Alaskan Earthquake,
Good Friday 1964, fell onto the surface of the so-named glacierin
the Chugach Mountains, Alaska.
Fine-grained, silt-size sediment formed by the mechanical
erosion of bedrock at the base and sides of a glacier by moving
ice. When it enters a stream, it turns the stream's color
brown, gray, iridescent blue-green, or milky white. Also called
Glacier Flour or Glacier Milk.
A jagged pinnacle or tower of glacier ice located on the surface
of a glacier, formed as a glacier flows down an icefall or
by the intersection of crevasses. Frequently, large areas
of a glacier will be covered by séracs.
A mass of snow that has accumulated in the top of an open
crevasse, masking the existence of the crevasse. Frequently,
a large void exists below the snowbridge.
The in-situ melting of glacier ice. Many glaciers have stagnant
termini, covered by thick sediment debris. Some support vegetation,
including mature forests.
Multiple, generally parallel, linear grooves, carved by rocks
frozen in the bed of a glacier into the bedrock over which
it flows.
A series of bowl-like depression melted into a snow or ice
surface, separated by a network of connected ridges. Individual
suncups may be more than three feet deep and ten feet in diameter.
Suncups form during warm, sunny conditions.
A short-lived, frequently large-scale, increase in the rate
of movement of the ice within a glacier. Ice velocities may
increase 10 to 100 times above normal flow rates. In some
surges, the terminus of a glacier rapidly advances. Although
not all glaciers surge, those that do often surge with some
sort of a periodicity.
A lake that develops in the basin of a cirque, generally after
the melting of the glacier.
The lower-most margin, end, or extremity of a glacier. Also
called Toe, End or Snout.
An unsorted and unstratified accumulation of glacial sediment,
deposited directly by glacier ice. Till is a heterogeneous
mixture of different sized material deposited by moving ice
(lodgement till) or by the melting in-place of stagnant ice
(ablation till). After deposition, some tills are reworked
by water.
A clear boundary line on the wall of a glacier valley that
delineates the maximum recent thickness of a glacier. It may
be a change in the color of the bedrock, indicating the separation
of weathered from unweathered bedrock; the limit of a former
lateral moraine or other sediment deposit; or the boundary
between vegetated and bare bedrock.
A valley with a parabolic or "U" shaped cross-section,
steep walls and generally a broad and flat floor. Formed by
glacier erosion, a U-shaped valley results when a glacier
widens and over-steepens a V-shaped stream valley.
A varve is a pair of sedimentary layers, a couplet, that form
in an annual cycle as the result of seasonal weather changes.
Typically formed in glacial lakes a varve couplet consists
of a coarser grained summer layer formed during open-water
conditions, and a finer grained winter layer formed from deposition
from suspension during a period of winter ice cover. Many
varve deposits contain hundreds of couplets. |
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