A glacier (US: /ˈɡleɪʃər/ or UK: /ˈɡlæsiə/) is a persistent
body of dense ice that is constantly moving under its own weight; it
forms where the accumulation of snow exceeds its ablation (melting and
sublimation) over many years, often centuries. Glaciers slowly deform
and flow due to stresses induced by their weight, creating crevasses,
seracs, and other distinguishing features. They also abrade rock and
debris from their substrate to create landforms such as cirques and
moraines. Glaciers form only on land and are distinct from the much
thinner sea ice and lake ice that form on the surface of bodies of
On Earth, 99% of glacial ice is contained within vast ice sheets in
the polar regions, but glaciers may be found in mountain ranges on
every continent including Oceania's high-latitude oceanic islands such
New Zealand and Papua New Guinea. Between 35°N and 35°S, glaciers
occur only in the Himalayas, Andes, Rocky Mountains, a few high
mountains in East Africa, Mexico,
New Guinea and on
Zard Kuh in
Iran. Glaciers cover about 10 percent of Earth's land surface.
Continental glaciers cover nearly 13,000,000 km2
(5×10^6 sq mi) or about 98 percent of Antarctica's
13,200,000 km2 (5.1×10^6 sq mi), with an average
thickness of 2,100 m (7,000 ft).
Greenland and Patagonia
also have huge expanses of continental glaciers.
Glacial ice is the largest reservoir of fresh water on Earth. Many
glaciers from temperate, alpine and seasonal polar climates store
water as ice during the colder seasons and release it later in the
form of meltwater as warmer summer temperatures cause the glacier to
melt, creating a water source that is especially important for plants,
animals and human uses when other sources may be scant. Within
high-altitude and Antarctic environments, the seasonal temperature
difference is often not sufficient to release meltwater.
Because glacial mass is affected by long-term climatic changes, e.g.,
precipitation, mean temperature, and cloud cover, glacial mass changes
are considered among the most sensitive indicators of climate change
and are a major source of variations in sea level.
A large piece of compressed ice, or a glacier, appears blue, as large
quantities of water appear blue. This is because water molecules
absorb other colors more efficiently than blue. The other reason for
the blue color of glaciers is the lack of air bubbles. Air bubbles,
which give a white color to ice, are squeezed out by pressure
increasing the density of the created ice.
1 Etymology and related terms
2.1 Classification by size, shape, and behavior
2.2 Classification by thermal state
5.1 Fracture zone and cracks
7 Glacial geology
7.3 Glacial valleys, cirques, arêtes, and pyramidal peaks
7.4 Roches moutonnées
7.5 Alluvial stratification
7.6 Glacial deposits
8 Isostatic rebound
9 On Mars
10 See also
13 Further reading
14 External links
Etymology and related terms
The word glacier is a loanword from French and goes back, via
Franco-Provençal, to the
Vulgar Latin glaciārium, derived from the
Late Latin glacia, and ultimately
Latin glaciēs, meaning "ice".
The processes and features caused by or related to glaciers are
referred to as glacial. The process of glacier establishment, growth
and flow is called glaciation. The corresponding area of study is
called glaciology. Glaciers are important components of the global
Classification by size, shape, and behavior
Mouth of the Schlatenkees
Glacier near Innergschlöß, Austria
Glaciers are categorized by their morphology, thermal characteristics,
Cirque glaciers form on the crests and slopes of
mountains. A glacier that fills a valley is called a valley glacier,
or alternatively an alpine glacier or mountain glacier. A large
body of glacial ice astride a mountain, mountain range, or volcano is
termed an ice cap or ice field.
Ice caps have an area less than
50,000 km2 (19,000 sq mi) by definition.
Glacial bodies larger than 50,000 km2 (19,000 sq mi)
are called ice sheets or continental glaciers. Several kilometers
deep, they obscure the underlying topography. Only nunataks protrude
from their surfaces. The only extant ice sheets are the two that cover
Antarctica and Greenland. They contain vast quantities of
fresh water, enough that if both melted, global sea levels would rise
by over 70 m (230 ft). Portions of an ice sheet or cap
that extend into water are called ice shelves; they tend to be thin
with limited slopes and reduced velocities. Narrow, fast-moving
sections of an ice sheet are called ice streams. In
Antarctica, many ice streams drain into large ice shelves. Some drain
directly into the sea, often with an ice tongue, like Mertz Glacier.
The Grotta del Gelo is a cave of Etna volcano, the southernmost
glacier in Europe
Sightseeing boat in front of a tidewater glacier, Kenai Fjords
National Park, Alaska
Tidewater glaciers are glaciers that terminate in the sea, including
most glaciers flowing from Greenland, Antarctica, Baffin and Ellesmere
Islands in Canada, Southeast Alaska, and the Northern and Southern
Ice Fields. As the ice reaches the sea, pieces break off,
or calve, forming icebergs. Most tidewater glaciers calve above sea
level, which often results in a tremendous impact as the iceberg
strikes the water. Tidewater glaciers undergo centuries-long cycles of
advance and retreat that are much less affected by the climate change
than those of other glaciers.
Classification by thermal state
Thermally, a temperate glacier is at melting point throughout the
year, from its surface to its base. The ice of a polar glacier is
always below the freezing point from the surface to its base, although
the surface snowpack may experience seasonal melting. A sub-polar
glacier includes both temperate and polar ice, depending on depth
beneath the surface and position along the length of the glacier. In a
similar way, the thermal regime of a glacier is often described by its
basal temperature. A cold-based glacier is below freezing at the
ice-ground interface, and is thus frozen to the underlying substrate.
A warm-based glacier is above or at freezing at the interface, and is
able to slide at this contact. This contrast is thought to a large
extent to govern the ability of a glacier to effectively erode its
bed, as sliding ice promotes plucking at rock from the surface
below. Glaciers which are partly cold-based and partly warm-based
are known as polythermal.
Gorner Glacier in Switzerland
Glaciers form where the accumulation of snow and ice exceeds ablation.
A glacier usually originates from a landform called 'cirque' (or
corrie or cwm) – a typically armchair-shaped geological feature
(such as a depression between mountains enclosed by arêtes) – which
collects and compresses through gravity the snow that falls into it.
This snow collects and is compacted by the weight of the snow falling
above it, forming névé. Further crushing of the individual
snowflakes and squeezing the air from the snow turns it into "glacial
ice". This glacial ice will fill the cirque until it "overflows"
through a geological weakness or vacancy, such as the gap between two
mountains. When the mass of snow and ice is sufficiently thick, it
begins to move due to a combination of surface slope, gravity and
pressure. On steeper slopes, this can occur with as little as
15 m (50 ft) of snow-ice.
A packrafter passes a wall of freshly exposed blue ice on Spencer
Glacier, in Alaska. Glacial ice acts like a filter on light, and the
more time light can spend traveling through ice, the bluer it becomes.
In temperate glaciers, snow repeatedly freezes and thaws, changing
into granular ice called firn. Under the pressure of the layers of ice
and snow above it, this granular ice fuses into denser and denser
firn. Over a period of years, layers of firn undergo further
compaction and become glacial ice.
Glacier ice is slightly less dense
than ice formed from frozen water because it contains tiny trapped air
Glacial ice has a distinctive blue tint because it absorbs some red
light due to an overtone of the infrared OH stretching mode of the
water molecule. Liquid water is blue for the same reason. The blue of
glacier ice is sometimes misattributed to
Rayleigh scattering due to
bubbles in the ice.
A glacier cave located on the
Perito Moreno Glacier
Perito Moreno Glacier in Argentina
A glacier originates at a location called its glacier head and
terminates at its glacier foot, snout, or terminus.
Glaciers are broken into zones based on surface snowpack and melt
conditions. The ablation zone is the region where there is a net
loss in glacier mass. The equilibrium line separates the ablation zone
and the accumulation zone; it is the altitude where the amount of new
snow gained by accumulation is equal to the amount of ice lost through
ablation. The upper part of a glacier, where accumulation exceeds
ablation, is called the accumulation zone. In general, the
accumulation zone accounts for 60–70% of the glacier's surface area,
more if the glacier calves icebergs.
Ice in the accumulation zone is
deep enough to exert a downward force that erodes underlying rock.
After a glacier melts, it often leaves behind a bowl- or
amphitheater-shaped depression that ranges in size from large basins
Great Lakes to smaller mountain depressions known as cirques.
The accumulation zone can be subdivided based on its melt conditions.
The dry snow zone is a region where no melt occurs, even in the
summer, and the snowpack remains dry.
The percolation zone is an area with some surface melt, causing
meltwater to percolate into the snowpack. This zone is often marked by
refrozen ice lenses, glands, and layers. The snowpack also never
reaches melting point.
Near the equilibrium line on some glaciers, a superimposed ice zone
develops. This zone is where meltwater refreezes as a cold layer in
the glacier, forming a continuous mass of ice.
The wet snow zone is the region where all of the snow deposited since
the end of the previous summer has been raised to 0 °C.
The health of a glacier is usually assessed by determining the glacier
mass balance or observing terminus behavior. Healthy glaciers have
large accumulation zones, more than 60% of their area snowcovered at
the end of the melt season, and a terminus with vigorous flow.
Following the Little
Ice Age's end around 1850, glaciers around the
Earth have retreated substantially. A slight cooling led to the
advance of many alpine glaciers between 1950 and 1985, but since 1985
glacier retreat and mass loss has become larger and increasingly
Shear or herring-bone crevasses on
Emmons Glacier (Mount Rainier);
such crevasses often form near the edge of a glacier where
interactions with underlying or marginal rock impede flow. In this
case, the impediment appears to be some distance from the near margin
of the glacier.
Main article: Ice-sheet dynamics
Glaciers move, or flow, downhill due to gravity and the internal
deformation of ice.
Ice behaves like a brittle solid until its
thickness exceeds about 50 m (160 ft). The pressure on ice
deeper than 50 m causes plastic flow. At the molecular level, ice
consists of stacked layers of molecules with relatively weak bonds
between layers. When the stress on the layer above exceeds the
inter-layer binding strength, it moves faster than the layer
Glaciers also move through basal sliding. In this process, a glacier
slides over the terrain on which it sits, lubricated by the presence
of liquid water. The water is created from ice that melts under high
pressure from frictional heating.
Basal sliding is dominant in
temperate, or warm-based glaciers.
Although evidence in favour of glacial flow was known by the early
19th century, other theories of glacial motion were advanced, such as
the idea that melt water, refreezing inside glaciers, caused the
glacier to dilate and extend its length. As it became clear that
glaciers behaved to some degree as if the ice were a viscous fluid, it
was argued that "regelation", or the melting and refreezing of ice at
a temperature lowered by the pressure on the ice inside the glacier,
was what allowed the ice to deform and flow. James Forbes came up with
the essentially correct explanation in the 1840s, although it was
several decades before it was fully accepted.
Perito Moreno glacier
Fracture zone and cracks
Ice cracks in the
The top 50 m (160 ft) of a glacier are rigid because they
are under low pressure. This upper section is known as the fracture
zone and moves mostly as a single unit over the plastically flowing
lower section. When a glacier moves through irregular terrain, cracks
called crevasses develop in the fracture zone. Crevasses form due to
differences in glacier velocity. If two rigid sections of a glacier
move at different speeds and directions, shear forces cause them to
break apart, opening a crevasse. Crevasses are seldom more than
46 m (150 ft) deep but in some cases can be 300 m
(1,000 ft) or even deeper. Beneath this point, the plasticity of
the ice is too great for cracks to form. Intersecting crevasses can
create isolated peaks in the ice, called seracs.
Crevasses can form in several different ways. Transverse crevasses are
transverse to flow and form where steeper slopes cause a glacier to
accelerate. Longitudinal crevasses form semi-parallel to flow where a
glacier expands laterally. Marginal crevasses form from the edge of
the glacier, due to the reduction in speed caused by friction of the
valley walls. Marginal crevasses are usually largely transverse to
flow. Moving glacier ice can sometimes separate from stagnant ice
above, forming a bergschrund. Bergschrunds resemble crevasses but are
singular features at a glacier's margins.
Crevasses make travel over glaciers hazardous, especially when they
are hidden by fragile snow bridges.
Crossing a crevasse on the Easton Glacier, Mount Baker, in the North
Cascades, United States
Below the equilibrium line, glacial meltwater is concentrated in
Meltwater can pool in proglacial lakes on top of a
glacier or descend into the depths of a glacier via moulins. Streams
within or beneath a glacier flow in englacial or sub-glacial tunnels.
These tunnels sometimes reemerge at the glacier's surface.
The speed of glacial displacement is partly determined by friction.
Friction makes the ice at the bottom of the glacier move more slowly
than ice at the top. In alpine glaciers, friction is also generated at
the valley's side walls, which slows the edges relative to the center.
Mean speeds vary greatly, but is typically around 1 m (3 ft)
per day. There may be no motion in stagnant areas; for example, in
parts of Alaska, trees can establish themselves on surface sediment
deposits. In other cases, glaciers can move as fast as 20–30 m
(70–100 ft) per day, such as in Greenland's Jakobshavn Isbræ
(Greenlandic: Sermeq Kujalleq). Velocity increases with increasing
slope, increasing thickness, increasing snowfall, increasing
longitudinal confinement, increasing basal temperature, increasing
meltwater production and reduced bed hardness.
A few glaciers have periods of very rapid advancement called surges.
These glaciers exhibit normal movement until suddenly they accelerate,
then return to their previous state. During these surges, the glacier
may reach velocities far greater than normal speed. These surges
may be caused by failure of the underlying bedrock, the pooling of
meltwater at the base of the glacier — perhaps delivered
from a supraglacial lake — or the simple accumulation of mass
beyond a critical "tipping point". Temporary rates up to 90 m
(300 ft) per day have occurred when increased temperature or
overlying pressure caused bottom ice to melt and water to accumulate
beneath a glacier.
In glaciated areas where the glacier moves faster than one km per
year, glacial earthquakes occur. These are large scale earthquakes
that have seismic magnitudes as high as 6.1. The number of
glacial earthquakes in
Greenland peaks every year in July, August and
September and is increasing over time. In a study using data from
January 1993 through October 2005, more events were detected every
year since 2002, and twice as many events were recorded in 2005 as
there were in any other year. This increase in the numbers of glacial
Greenland may be a response to global warming.
Ogives are alternating wave crests and valleys that appear as dark and
light bands of ice on glacier surfaces. They are linked to seasonal
motion of glaciers; the width of one dark and one light band generally
equals the annual movement of the glacier. Ogives are formed when ice
from an icefall is severely broken up, increasing ablation surface
area during summer. This creates a swale and space for snow
accumulation in the winter, which in turn creates a ridge.
Sometimes ogives consist only of undulations or color bands and are
described as wave ogives or band ogives.
Further information on this topic:
List of glaciers
List of glaciers and Retreat of
glaciers since 1850
Black ice glacier near Aconcagua, Argentina
Glaciers are present on every continent and approximately fifty
countries, excluding those (Australia, South Africa) that have
glaciers only on distant subantarctic island territories. Extensive
glaciers are found in Antarctica, Chile, Canada, Alaska,
Mountain glaciers are widespread, especially in the Andes,
the Himalayas, the Rocky Mountains, the Caucasus, Scandinavian
mountains and the Alps. Mainland Australia currently contains no
glaciers, although a small glacier on
Mount Kosciuszko was present in
the last glacial period. In New Guinea, small, rapidly
diminishing, glaciers are located on its highest summit massif of
Puncak Jaya. Africa has glaciers on
Mount Kilimanjaro in Tanzania,
Mount Kenya and in the Rwenzori Mountains. Oceanic islands with
glaciers include Iceland, several of the islands off the coast of
Jan Mayen to the far North, New Zealand
and the subantarctic islands of Marion, Heard, Grande Terre
(Kerguelen) and Bouvet. During glacial periods of the Quaternary,
Taiwan, Hawaii on Mauna Kea and
Tenerife also had large alpine
glaciers, while the Faroe and Crozet Islands were completely
The permanent snow cover necessary for glacier formation is affected
by factors such as the degree of slope on the land, amount of snowfall
and the winds. Glaciers can be found in all latitudes except from 20°
to 27° north and south of the equator where the presence of the
descending limb of the
Hadley circulation lowers precipitation so much
that with high insolation snow lines reach above 6,500 m
(21,330 ft). Between 19˚N and 19˚S, however, precipitation is
higher and the mountains above 5,000 m (16,400 ft) usually
have permanent snow.
Even at high latitudes, glacier formation is not inevitable. Areas of
the Arctic, such as Banks Island, and the
McMurdo Dry Valleys
McMurdo Dry Valleys in
Antarctica are considered polar deserts where glaciers cannot form
because they receive little snowfall despite the bitter cold. Cold
air, unlike warm air, is unable to transport much water vapor. Even
during glacial periods of the Quaternary, Manchuria, lowland
Siberia, and central and northern Alaska, though
extraordinarily cold, had such light snowfall that glaciers could not
In addition to the dry, unglaciated polar regions, some mountains and
volcanoes in Bolivia, Chile and Argentina are high (4,500 to
6,900 m or 14,800 to 22,600 ft) and cold, but the relative
lack of precipitation prevents snow from accumulating into glaciers.
This is because these peaks are located near or in the hyperarid
Diagram of glacial plucking and abrasion
Glacially plucked granitic bedrock near Mariehamn, Åland Islands
Glaciers erode terrain through two principal processes: abrasion and
As glaciers flow over bedrock, they soften and lift blocks of rock
into the ice. This process, called plucking, is caused by subglacial
water that penetrates fractures in the bedrock and subsequently
freezes and expands. This expansion causes the ice to act as a lever
that loosens the rock by lifting it. Thus, sediments of all sizes
become part of the glacier's load. If a retreating glacier gains
enough debris, it may become a rock glacier, like the Timpanogos
Glacier in Utah.
Abrasion occurs when the ice and its load of rock fragments slide over
bedrock and function as sandpaper, smoothing and polishing the bedrock
below. The pulverized rock this process produces is called rock flour
and is made up of rock grains between 0.002 and 0.00625 mm in
size. Abrasion leads to steeper valley walls and mountain slopes in
alpine settings, which can cause avalanches and rock slides, which add
even more material to the glacier.
Glacial abrasion is commonly characterized by glacial striations.
Glaciers produce these when they contain large boulders that carve
long scratches in the bedrock. By mapping the direction of the
striations, researchers can determine the direction of the glacier's
movement. Similar to striations are chatter marks, lines of
crescent-shape depressions in the rock underlying a glacier. They are
formed by abrasion when boulders in the glacier are repeatedly caught
and released as they are dragged along the bedrock.
The rate of glacier erosion varies. Six factors control erosion rate:
Velocity of glacial movement
Thickness of the ice
Shape, abundance and hardness of rock fragments contained in the ice
at the bottom of the glacier
Relative ease of erosion of the surface under the glacier
Thermal conditions at the glacier base
Permeability and water pressure at the glacier base
When the bedrock has frequent fractures on the surface, glacial
erosion rates tend to increase as plucking is the main erosive force
on the surface; when the bedrock has wide gaps between sporadic
fractures, however, abrasion tends to be the dominant erosive form and
glacial erosion rates become slow.
Glaciers in lower latitudes tend to be much more erosive than glaciers
in higher latitudes, because they have more meltwater reaching the
glacial base and facilitate sediment production and transport under
the same moving speed and amount of ice.
Material that becomes incorporated in a glacier is typically carried
as far as the zone of ablation before being deposited. Glacial
deposits are of two distinct types:
Glacial till: material directly deposited from glacial ice. Till
includes a mixture of undifferentiated material ranging from clay size
to boulders, the usual composition of a moraine.
Fluvial and outwash sediments: sediments deposited by water. These
deposits are stratified by size.
Larger pieces of rock that are encrusted in till or deposited on the
surface are called "glacial erratics". They range in size from pebbles
to boulders, but as they are often moved great distances, they may be
drastically different from the material upon which they are found.
Patterns of glacial erratics hint at past glacial motions.
Glacial moraines above Lake Louise, Alberta, Canada
Glacial moraines are formed by the deposition of material from a
glacier and are exposed after the glacier has retreated. They usually
appear as linear mounds of till, a non-sorted mixture of rock, gravel
and boulders within a matrix of a fine powdery material. Terminal or
end moraines are formed at the foot or terminal end of a glacier.
Lateral moraines are formed on the sides of the glacier. Medial
moraines are formed when two different glaciers merge and the lateral
moraines of each coalesce to form a moraine in the middle of the
combined glacier. Less apparent are ground moraines, also called
glacial drift, which often blankets the surface underneath the glacier
downslope from the equilibrium line.
The term moraine is of French origin. It was coined by peasants to
describe alluvial embankments and rims found near the margins of
glaciers in the French Alps. In modern geology, the term is used more
broadly, and is applied to a series of formations, all of which are
composed of till. Moraines can also create moraine dammed lakes.
A drumlin field forms after a glacier has modified the landscape. The
teardrop-shaped formations denote the direction of the ice flow.
Drumlins are asymmetrical, canoe shaped hills made mainly of till.
Their heights vary from 15 to 50 meters and they can reach a
kilometer in length. The steepest side of the hill faces the direction
from which the ice advanced (stoss), while a longer slope is left in
the ice's direction of movement (lee).
Drumlins are found in groups called drumlin fields or drumlin camps.
One of these fields is found east of Rochester, New York; it is
estimated to contain about 10,000 drumlins.
Although the process that forms drumlins is not fully understood,
their shape implies that they are products of the plastic deformation
zone of ancient glaciers. It is believed that many drumlins were
formed when glaciers advanced over and altered the deposits of earlier
Glacial valleys, cirques, arêtes, and pyramidal peaks
Features of a glacial landscape
Before glaciation, mountain valleys have a characteristic "V" shape,
produced by eroding water. During glaciation, these valleys are often
widened, deepened and smoothed to form a "U"-shaped glacial valley or
glacial trough, as it is sometimes called. The erosion that
creates glacial valleys truncates any spurs of rock or earth that may
have earlier extended across the valley, creating broadly
triangular-shaped cliffs called truncated spurs. Within glacial
valleys, depressions created by plucking and abrasion can be filled by
lakes, called paternoster lakes. If a glacial valley runs into a large
body of water, it forms a fjord.
Typically glaciers deepen their valleys more than their smaller
tributaries. Therefore, when glaciers recede, the valleys of the
tributary glaciers remain above the main glacier's depression and are
called hanging valleys.
At the start of a classic valley glacier is a bowl-shaped cirque,
which has escarped walls on three sides but is open on the side that
descends into the valley. Cirques are where ice begins to accumulate
in a glacier. Two glacial cirques may form back to back and erode
their backwalls until only a narrow ridge, called an arête is left.
This structure may result in a mountain pass. If multiple cirques
encircle a single mountain, they create pointed pyramidal peaks;
particularly steep examples are called horns.
Passage of glacial ice over an area of bedrock may cause the rock to
be sculpted into a knoll called a roche moutonnée, or "sheepback"
rock. Roches moutonnées may be elongated, rounded and asymmetrical in
shape. They range in length from less than a meter to several hundred
meters long. Roches moutonnées have a gentle slope on their
up-glacier sides and a steep to vertical face on their down-glacier
sides. The glacier abrades the smooth slope on the upstream side as it
flows along, but tears rock fragments loose and carries them away from
the downstream side via plucking.
As the water that rises from the ablation zone moves away from the
glacier, it carries fine eroded sediments with it. As the speed of the
water decreases, so does its capacity to carry objects in suspension.
The water thus gradually deposits the sediment as it runs, creating an
alluvial plain. When this phenomenon occurs in a valley, it is called
a valley train. When the deposition is in an estuary, the sediments
are known as bay mud.
Outwash plains and valley trains are usually accompanied by basins
known as "kettles". These are small lakes formed when large ice blocks
that are trapped in alluvium melt and produce water-filled
depressions. Kettle diameters range from 5 m to 13 km, with
depths of up to 45 meters. Most are circular in shape because the
blocks of ice that formed them were rounded as they melted.
Landscape produced by a receding glacier
When a glacier's size shrinks below a critical point, its flow stops
and it becomes stationary. Meanwhile, meltwater within and beneath the
ice leaves stratified alluvial deposits. These deposits, in the forms
of columns, terraces and clusters, remain after the glacier melts and
are known as "glacial deposits".
Glacial deposits that take the shape of hills or mounds are called
kames. Some kames form when meltwater deposits sediments through
openings in the interior of the ice. Others are produced by fans or
deltas created by meltwater. When the glacial ice occupies a valley,
it can form terraces or kames along the sides of the valley.
Long, sinuous glacial deposits are called eskers.
Eskers are composed
of sand and gravel that was deposited by meltwater streams that flowed
through ice tunnels within or beneath a glacier. They remain after the
ice melts, with heights exceeding 100 meters and lengths of as
long as 100 km.
Very fine glacial sediments or rock flour is often picked up by wind
blowing over the bare surface and may be deposited great distances
from the original fluvial deposition site. These eolian loess deposits
may be very deep, even hundreds of meters, as in areas of China and
the Midwestern United States of America. Katabatic winds can be
important in this process.
Main article: Post-glacial rebound
Isostatic pressure by a glacier on the Earth's crust
Large masses, such as ice sheets or glaciers, can depress the crust of
Earth into the mantle. The depression usually totals a third
of the ice sheet or glacier's thickness. After the ice sheet or
glacier melts, the mantle begins to flow back to its original
position, pushing the crust back up. This post-glacial rebound, which
proceeds very slowly after the melting of the ice sheet or glacier, is
currently occurring in measurable amounts in
Scandinavia and the Great
Lakes region of North America.
A geomorphological feature created by the same process on a smaller
scale is known as dilation-faulting. It occurs where previously
compressed rock is allowed to return to its original shape more
rapidly than can be maintained without faulting. This leads to an
effect similar to what would be seen if the rock were hit by a large
hammer. Dilation faulting can be observed in recently de-glaciated
Iceland and Cumbria.
Northern polar ice cap on Mars
Main article: Glaciers on Mars
The polar ice caps of
Mars show geologic evidence of glacial deposits.
The south polar cap is especially comparable to glaciers on Earth.
Topographical features and computer models indicate the existence of
more glaciers in Mars' past.
At mid-latitudes, between 35° and 65° north or south, Martian
glaciers are affected by the thin Martian atmosphere. Because of the
low atmospheric pressure, ablation near the surface is solely due to
sublimation, not melting. As on Earth, many glaciers are covered with
a layer of rocks which insulates the ice. A radar instrument on board
Mars Reconnaissance Orbiter found ice under a thin layer of rocks
in formations called lobate debris aprons (LDAs).
The pictures below illustrate how landscape features on
resemble those on the Earth.
Romer Lake's Elephant Foot
Glacier in the Earth's Arctic, as seen by
Landsat 8. This picture shows several glaciers that have the same
shape as many features on
Mars that are believed to also be glaciers.
The next three images from
Mars show shapes similar to the Elephant
Mesa in Ismenius Lacus quadrangle, as seen by CTX. Mesa has several
glaciers eroding it. One of the glaciers is seen in greater detail in
the next two images from HiRISE. Image from Ismenius Lacus quadrangle.
Glacier as seen by HiRISE under the HiWish program. Area in rectangle
is enlarged in the next photo. Zone of accumulation of snow at the
Glacier is moving down valley, then spreading out on plain.
Evidence for flow comes from the many lines on surface. Location is in
Protonilus Mensae in Ismenius Lacus quadrangle.
Enlargement of area in rectangle of the previous image. On
ridge would be called the terminal moraine of an alpine glacier.
Picture taken with HiRISE under the HiWish program. Image from
Ismenius Lacus quadrangle.
Retreat of glaciers since 1850
List of glaciers
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This article draws heavily on the corresponding article in the
Spanish-language, which was accessed in the version of 24
Hambrey, Michael; Alean, Jürg (2004). Glaciers (2nd ed.). Cambridge
University Press. ISBN 0-521-82808-2. OCLC 54371738.
An excellent less-technical treatment of all aspects, with superb
photographs and firsthand accounts of glaciologists' experiences. All
images of this book can be found online (see Weblinks:
Benn, Douglas I.; Evans, David J. A. (1999). Glaciers and Glaciation.
Arnold. ISBN 0-470-23651-5. OCLC 38329570.
Bennett, M. R.; Glasser, N. F. (1996). Glacial Geology:
Ice Sheets and
Landforms. John Wiley & Sons. ISBN 0-471-96344-5.
Hambrey, Michael (1994). Glacial Environments. University of British
Columbia Press, UCL Press. ISBN 0-7748-0510-2.
OCLC 30512475. An undergraduate-level textbook.
Knight, Peter G (1999). Glaciers. Cheltenham: Nelson Thornes.
ISBN 0-7487-4000-7. OCLC 42656957. A textbook for
undergraduates avoiding mathematical complexities
Walley, Robert (1992). Introduction to Physical Geography. Wm. C.
Brown Publishers. A textbook devoted to explaining the geography
of our planet.
W. S. B. Paterson (1994). Physics of Glaciers (3rd ed.). Pergamon
Press. ISBN 0-08-013972-8. OCLC 26188. A comprehensive
reference on the physical principles underlying formation and
Moon, Twila. Saying goodbye to glaciers, Science, 12 May 2017, Vol.
356, Issue 6338, pp. 580–581, DOI: 10.1126/science.aam9625
The Wikibook Historical Geology has a page on the topic of: Glaciers
Wikimedia Commons has media related to Glacier.
Glacier Changes: Facts and Figures". United Nations
Environment Programme (UNEP). 2008. , a report in the Global
Environment Outlook (GEO) series.
Glacial structures – photo atlas
NOW on PBS "On Thin Ice"
Photo project tracks changes in Himalayan glaciers since 1921
Short radio episode California Glaciers from The Mountains of
California by John Muir, 1894. California Legacy Project
Dyanamics of Glaciers
GletscherVergleiche.ch - Before/After Images by Simon Oberli
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