Glacier

A glacier (US: /ˈɡleɪʃər/ or UK: /ˈɡlæsiər/) 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 water.

On Earth, 99% of glacial ice is contained within vast ice sheets (also known as "continental glaciers") in the polar regions, but glaciers may be found in mountain ranges on every continent including Oceania's high-latitude oceanic island countries such as 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.[1] Glaciers cover about 10 percent of Earth's land surface. Continental glaciers cover nearly 13 million km2 (5 million sq mi) or about 98 percent of Antarctica's 13.2 million km2 (5.1 million sq mi), with an average thickness of 2,100 m (7,000 ft). Greenland and Patagonia also have huge expanses of continental glaciers.[2]

Glacial ice is the largest reservoir of fresh water on Earth.[3] 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.

Since 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.

Baltoro glacier from air
The Baltoro Glacier in northern India. At 62 kilometres (39 mi) in length, it is one of the longest alpine glaciers on earth.
Kangchenjunga East Face from Zemu Glacier
Eastern face of Kangchenjunga, the third highest mountain in the world, near the Zemu Glacier, in the Himalayan region of Sikkim, India.
Parque estatal Chugach, Alaska, Estados Unidos, 2017-08-22, DD 92
Aerial view of a glacier in Chugach State Park, Alaska, United States.
Perito Moreno Glacier Patagonia Argentina Luca Galuzzi 2005
Ice calving from the terminus of the Perito Moreno Glacier in western Patagonia, Argentina
Grosser Aletschgletscher 3178
The Aletsch Glacier, the largest glacier of the Alps, in Switzerland
Quelccaya Glacier
The Quelccaya Ice Cap is the second largest glaciated area in the tropics, in Peru

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".[4] 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 cryosphere.

Types

Classification by size, shape and behavior

Glacier mouth
Mouth of the Schlatenkees Glacier near Innergschlöß, Austria

Glaciers are categorized by their morphology, thermal characteristics, and behavior. 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.[5] A large body of glacial ice astride a mountain, mountain range, or volcano is termed an ice cap or ice field.[6] 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.[7] Several kilometers deep, they obscure the underlying topography. Only nunataks protrude from their surfaces. The only extant ice sheets are the two that cover most of Antarctica and Greenland.[8] They contain vast quantities of fresh water, enough that if both melted, global sea levels would rise by over 70 m (230 ft).[9] 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.[10] Narrow, fast-moving sections of an ice sheet are called ice streams.[11][12] In Antarctica, many ice streams drain into large ice shelves. Some drain directly into the sea, often with an ice tongue, like Mertz Glacier.

GrottaGelo
The Grotta del Gelo is a cave of Etna volcano, the southernmost glacier in Europe
Fjordsglacier
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 Patagonian 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.[13]

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.[14] 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.[15] Glaciers which are partly cold-based and partly warm-based are known as polythermal.[14]

Formation

GornerGlacier 002
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.

Packrafting at Spencer Glacier. Chugach National Forest, Alaska
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 bubbles.

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.[16]

153 - Glacier Perito Moreno - Grotte glaciaire - Janvier 2010
A glacier cave located on the Perito Moreno Glacier in Argentina

Structure

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.[17] 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 like the Great Lakes to smaller mountain depressions known as cirques.

The accumulation zone can be subdivided based on its melt conditions.

  1. The dry snow zone is a region where no melt occurs, even in the summer, and the snowpack remains dry.
  2. 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.
  3. 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.
  4. 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 ubiquitous.[18][19][20]

Motion

Chevron Crevasses 00
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.

Glaciers move, or flow, downhill due to gravity and the internal deformation of ice.[21] 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 below.[22]

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.[23]

Pexels-photo-25416
Perito Moreno glacier

Fracture zone and cracks

TitlisIceCracks
Ice cracks in the Titlis Glacier

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.

Glaciereaston
Crossing a crevasse on the Easton Glacier, Mount Baker, in the North Cascades, United States

Below the equilibrium line, glacial meltwater is concentrated in stream channels. 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.[24]

Speed

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.[25] 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.[26] These surges may be caused by failure of the underlying bedrock, the pooling of meltwater at the base of the glacier[27] — perhaps delivered from a supraglacial lake — or the simple accumulation of mass beyond a critical "tipping point".[28] 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.[29][30] The number of glacial earthquakes in Greenland peaks every year in July, August and September and increased rapidly in the 1990s and 2000s. 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.[30]

Ogives

Ogives (or Forbes bands)[31] 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.[32] Sometimes ogives consist only of undulations or color bands and are described as wave ogives or band ogives.[33]

Geography

Black-Glacier
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, Greenland and Iceland. 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.[34] In New Guinea, small, rapidly diminishing, glaciers are located on its highest summit massif of Puncak Jaya.[35] Africa has glaciers on Mount Kilimanjaro in Tanzania, on Mount Kenya and in the Rwenzori Mountains. Oceanic islands with glaciers include Iceland, several of the islands off the coast of Norway including Svalbard and 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[36] and Tenerife also had large alpine glaciers, while the Faroe and Crozet Islands[37] were completely glaciated.

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 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,[38] and central and northern Alaska,[39] though extraordinarily cold, had such light snowfall that glaciers could not form.[40][41]

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 Atacama Desert.

Glacial geology

Arranque glaciar-en
Diagram of glacial plucking and abrasion
PluckedGraniteAlandIslands
Glacially plucked granitic bedrock near Mariehamn, Åland Islands

Glaciers erode terrain through two principal processes: abrasion and plucking.

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.[42]

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.[43]

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.

Moraines

MorainesLakeLouise
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.

Drumlins

Drumlins LMB
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 glaciers.

Glacial valleys, cirques, arêtes, and pyramidal peaks

Glacial landscape
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.[44] 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.

Roches moutonnées

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.[45] 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.

Alluvial stratification

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.[46]

Glacial deposits

Receding glacier-en
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.

Loess deposits

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.

Isostatic rebound

Glacier weight effects LMB
Isostatic pressure by a glacier on the Earth's crust

Large masses, such as ice sheets or glaciers, can depress the crust of the Earth into the mantle.[47] 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 parts of Iceland and Cumbria.

On Mars

Mars north pole
Northern polar ice cap 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.[48] Topographical features and computer models indicate the existence of more glaciers in Mars' past.[49]

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 the Mars Reconnaissance Orbiter found ice under a thin layer of rocks in formations called lobate debris aprons (LDAs).[50][51][52][53][54]

The pictures below illustrate how landscape features on Mars closely resemble those on the Earth.

Wikielephantglacier

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 Foot Glacier.

Glacier as seen by ctx

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.

Wide view of glacier showing image field

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 top. 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.

Glacier close up with hirise

Enlargement of area in rectangle of the previous image. On Earth the ridge would be called the terminal moraine of an alpine glacier. Picture taken with HiRISE under the HiWish program. Image from Ismenius Lacus quadrangle.

See also

Notes

  1. ^ Post, Austin; LaChapelle, Edward R (2000). Glacier ice. Seattle: University of Washington Press. ISBN 978-0-295-97910-6.
  2. ^ National Geographic Almanac of Geography, 2005, ISBN 0-7922-3877-X, p. 149.
  3. ^ Brown, Molly Elizabeth; Ouyang, Hua; Habib, Shahid; Shrestha, Basanta; Shrestha, Mandira; Panday, Prajjwal; Tzortziou, Maria; Policelli, Frederick; Artan, Guleid; Giriraj, Amarnath; Bajracharya, Sagar R.; Racoviteanu, Adina. "HIMALA: Climate Impacts on Glaciers, Snow, and Hydrology in the Himalayan Region". Mountain Research and Development. International Mountain Society. hdl:2060/20110015312.
  4. ^ Simpson, D.P. (1979). Cassell's Latin Dictionary (5 ed.). London: Cassell Ltd. p. 883. ISBN 978-0-304-52257-6.
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References

  • This article draws heavily on the corresponding article in the Spanish-language Wikipedia, which was accessed in the version of 24 July 2005.
  • Hambrey, Michael; Alean, Jürg (2004). Glaciers (2nd ed.). Cambridge University Press. ISBN 978-0-521-82808-6. 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: Glaciers-online)
  • Benn, Douglas I.; Evans, David J.A. (1999). Glaciers and Glaciation. Arnold. ISBN 978-0-470-23651-2. OCLC 38329570.
  • Bennett, M.R.; Glasser, N.F. (1996). Glacial Geology: Ice Sheets and Landforms. John Wiley & Sons. ISBN 978-0-471-96344-8. OCLC 33359888.
  • Hambrey, Michael (1994). Glacial Environments. University of British Columbia Press, UCL Press. ISBN 978-0-7748-0510-0. OCLC 30512475. An undergraduate-level textbook.
  • Knight, Peter G (1999). Glaciers. Cheltenham: Nelson Thornes. ISBN 978-0-7487-4000-0. 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 978-0-08-013972-2. OCLC 26188. A comprehensive reference on the physical principles underlying formation and behavior.

Further reading

External links

Altimir Glacier

Altimir Glacier (Bulgarian: ледник Алтимир, 'Lednik Altimir' \'led-nik al-ti-'mir\) is a 4.8-kilometre (3.0 mi) long and 5.5-kilometre (3.4 mi) wide glacier draining the north slopes of the Osterrieth Range on Anvers Island in the Palmer Archipelago, Antarctica. It flows northwards to enter Dalchev Cove in Fournier Bay east of Studena Point.

The glacier is named after the settlement of Altimir in northwestern Bulgaria.

Astudillo Glacier

Astudillo Glacier (64°53′S 62°51′W) is a small glacier flowing into Paradise Harbor between Leith Cove and Skontorp Cove on the Danco Coast of Graham Land. The glacier was surveyed by the Chilean Antarctic Expedition of 1950–51, which applied the name, probably after an expedition member.

Bartlett Glacier

Bartlett Glacier (86°15′S 152°0′W) is a tributary glacier, about 30 nautical miles (60 km) long and 5 nautical miles (10 km) wide at its terminus, flowing northeast from Nilsen Plateau and joining Scott Glacier close north of Mount Gardiner. It was discovered in December 1934 by the Byrd Antarctic Expedition geological party under Quin Blackburn, and named by Richard E. Byrd for Captain Robert A. Bartlett of Brigus, Newfoundland, a noted Arctic navigator and explorer who recommended that the expedition acquire the Bear, an ice-ship which was purchased and rechristened by Byrd as the Bear of Oakland.

Borchgrevink Glacier

Borchgrevink Glacier (73°4′S 168°30′E) is a large glacier in the Victory Mountains, Victoria Land, draining south between Malta Plateau and Daniell Peninsula, and thence projecting into Glacier Strait, Ross Sea, as a floating glacier tongue, the Borchgrevink Glacier Tongue, just south of Cape Jones. It was named by the New Zealand Geological Survey Antarctic Expedition, 1957–58, for Carsten Borchgrevink, leader of the British Antarctic Expedition, 1898–1900. Borchgrevink visited the area in February 1900 and first observed the seaward portion of the glacier.

The Borchgrevink Glacier has several contributing glaciers:

Ingham Glacier (72°50′S 168°38′E), a tributary glacier 3 miles (5 km) west of Humphries Glacier, flowing south into Borchgrevink Glacier; mapped by the United States Geological Survey (USGS) from surveys and U.S. Navy air photos, between 1960 and 1962. It was named by the Advisory Committee on Antarctic Names (US-ACAN) for Clayton E. Ingham, New Zealand geophysicist at Hallett Station, 1957.

Humphries Glacier (72°51′S 168°50′E), a steep tributary glacier just east of Ingham Glacier, flowing generally southwestward to join Borchgrevink Glacier northwestward of Mount Prior. It was mapped by the USGS from surveys and U.S. Navy air photos, between 1960 and 1962, and named by US-ACAN for John G. Humphries, New Zealand ionospheric scientist at Hallett Station, 1957.

Behr Glacier (72°55′S 168°5′E), a steep tributary glacier, 7 miles (11 km) long, flowing east along the north side of Clapp Ridge to join Borchgrevink Glacier. The glacier first appears on a 1960 New Zealand map compiled from U.S. Navy aerial photographs. Named by US-ACAN for Col. Robert Behr, USAF, who was of assistance in the review of U.S. policy toward Antarctica in the 1970-71 period.

Hand Glacier (72°58′S 168°5′E), a deeply entrenched valley glacier that drains the east slopes of Malta Plateau and flows east along the south side of Clapp Ridge into the Borchgrevink Glacier. It was mapped by the USGS from surveys and U.S. Navy air photos between 1960 and 64, and was named by US-ACAN for Cadet H. Hand, biologist at McMurdo Station, in 1967-68.

Line Glacier (72°59′S 167°50′E), a glacier that drains the south part of the east slopes of Malta Plateau and flows east between Collins Peak and Mount Alberts into Borchgrevink Glacier; mapped by the USGS from surveys and U.S. Navy air photos between 1960 and 1964, and named by US-ACAN for Kenneth Line, traverse engineer with the United States Antarctic Research Program (USARP) glaciological party at Roosevelt Island, 1967-68.

Bargh Glacier (73°5′S 168°46′E), a glacier 6 miles (10 km) long in the southwest part of Daniell Peninsula, 2 miles (3 km) north of Langevad Glacier, whose stream it parallels, and flows southwest to enter Borchgrevink Glacier; mapped by the USGS from surveys and U.S. Navy air photos between 1960 and 1964; named by US-ACAN for Kenneth A. Bargh, seismologist at Hallett Station, in 1958.

Langevad Glacier (73°8′S 168°50′E), located 2 miles (3 km) south of Bargh Glacier and just west of Narrow Neck, draining southwest from the Daniell Peninsula into the lower part of Borchgrevink Glacier. It was mapped by the USGS from surveys and U.S. Navy air photos, between 1960 and 1964, and named by US-ACAN for Michael W. Langevad, electronics technician at Hallett Station, 1957.

Byrd Glacier

The Byrd Glacier is a major glacier in Antarctica, about 136 km long and 24 km wide, draining an extensive area of the polar plateau and flowing eastward between the Britannia Range and Churchill Mountains to discharge into the Ross Ice Shelf at Barne Inlet. Its valley below the glacier is the lowest point not to covered by water on Earth which reaches 2,780 m (9,121 feet) below sea level. It was named by the NZ-APC after Rear Admiral Byrd, US Navy, American Antarctic explorer.

Canada Glacier

Canada Glacier is a small glacier flowing south-east into the northern side of Taylor Valley in Victoria Land, Antarctica. It is in the Ross Dependency. Its melting season is in the summer.

Crane Glacier

Crane Glacier (65°20′S 62°15′W), is a narrow glacier which flows 30 miles (50 km) in an east-northeasterly direction along the northwest side of Aristotle Mountains to enter Spillane Fjord south of Devetaki Peak, on the east coast of the Antarctic Peninsula. Sir Hubert Wilkins photographed this feature from the air in 1928 and gave it the name "Crane Channel", after C.K. Crane of Los Angeles, reporting that it appeared to be a channel cutting in an east-west direction across the peninsula. The name was altered to "Crane Inlet" following explorations along the west coast of the peninsula in 1936 by the British Graham Land Expedition, which proved that no through channel from the east coast existed as indicated by Wilkins. Comparison of Wilkins' photograph of this feature with those taken in 1947 by the Falklands Islands Dependencies Survey shows that Wilkins' "Crane Channel" is this glacier, although it lies about 75 miles (120 km) northeast of the position originally reported by Wilkins.The speed of Crane Glacier increased threefold after the collapse of the Larsen B Ice Shelf in 2002 and this is likely to be due to the removal of a buttressing effect of the ice shelf.

Edge Glacier

Edge Glacier (82°29′S 51°7′W) is a small cliff-type glacier draining northward into Davis Valley in northeast Dufek Massif, Pensacola Mountains. It was mapped by the United States Geological Survey from surveys and U.S. Navy air photos, 1956–66, and was named by the Advisory Committee on Antarctic Names for Joseph L. Edge, a photographer with U.S. Navy Squadron VX-6 on Operation Deep Freeze 1963 and 1964.

Glacier National Park (U.S.)

Glacier National Park is an American national park located in northwestern Montana, on the Canada–United States border, adjacent to the Canadian provinces of Alberta and British Columbia. The park encompasses over 1 million acres (4,000 km2) and includes parts of two mountain ranges (sub-ranges of the Rocky Mountains), over 130 named lakes, more than 1,000 different species of plants, and hundreds of species of animals. This vast pristine ecosystem is the centerpiece of what has been referred to as the "Crown of the Continent Ecosystem," a region of protected land encompassing 16,000 square miles (41,000 km2).The region that became Glacier National Park was first inhabited by Native Americans. Upon the arrival of European explorers, it was dominated by the Blackfeet in the east and the Flathead in the western regions. Under pressure, the Blackfeet ceded the mountainous parts of their treaty lands in 1895 to the federal government; it later became part of the park. Soon after the establishment of the park on May 11, 1910, a number of hotels and chalets were constructed by the Great Northern Railway. These historic hotels and chalets are listed as National Historic Landmarks and a total of 350 locations are on the National Register of Historic Places. By 1932 work was completed on the Going-to-the-Sun Road, later designated a National Historic Civil Engineering Landmark, which provided greater accessibility for automobiles into the heart of the park.

The mountains of Glacier National Park began forming 170 million years ago when ancient rocks were forced eastward up and over much younger rock strata. Known as the Lewis Overthrust, these sedimentary rocks are considered to have some of the finest examples of early life fossils on Earth. The current shapes of the Lewis and Livingston mountain ranges and positioning and size of the lakes show the telltale evidence of massive glacial action, which carved U-shaped valleys and left behind moraines which impounded water, creating lakes. Of the estimated 150 glaciers which existed in the park in the mid-19th century, only 25 active glaciers remained by 2010. Scientists studying the glaciers in the park have estimated that all the active glaciers may disappear by 2030 if current climate patterns persist.Glacier National Park has almost all its original native plant and animal species. Large mammals such as grizzly bears, moose, and mountain goats, as well as rare or endangered species like wolverines and Canadian lynxes, inhabit the park. Hundreds of species of birds, more than a dozen fish species, and a few reptile and amphibian species have been documented. The park has numerous ecosystems ranging from prairie to tundra. The easternmost forests of western redcedar and hemlock grow in the southwest portion of the park. Large forest fires are unusual in the park; however, more than 13% of the park burned in 2003.Glacier National Park borders Waterton Lakes National Park in Canada—the two parks are known as the Waterton-Glacier International Peace Park and were designated as the world's first International Peace Park in 1932. Both parks were designated by the United Nations as Biosphere Reserves in 1976, and in 1995 as World Heritage sites. In April 2017, the joint park received a provisional Gold Tier designation as Waterton-Glacier International Dark Sky Park through the International Dark Sky Association, the first transboundary dark sky park.

Institute Ice Stream

The Institute Ice Stream (82°S 75°W) is an ice stream flowing north into the Ronne Ice Shelf, Antarctica, southeast of Hercules Inlet. The feature was traversed by the United States Antarctic Research Program (USARP) Ellsworth–Byrd Seismic Party, 1958–59, and the USARP – University of Wisconsin Seismic Party, 1963–64. It was delineated by the Scott Polar Research Institute – National Science Foundation – Technical University of Denmark airborne radio echo sounding program, 1967–79, and in association with Foundation Ice Stream and Support Force Glacier, named after the Scott Polar Research Institute, Cambridge, England.

Ketchum Glacier

Ketchum Glacier (75°0′S 63°45′W) is an eastward flowing glacier at the base of Palmer Land, Antarctica, about 50 nautical miles (90 km) long, descending between the Latady Mountains and the Scaife Mountains into Gardner Inlet. It was discovered by the Ronne Antarctic Research Expedition (RARE), 1947–48, under Finn Ronne, who named it for Commander Gerald Ketchum, U.S. Navy, commander of the icebreaker USS Burton Island (AG-88) which broke the ice to free the RARE from Marguerite Bay for the return home.

List of glaciers in the Antarctic

There are many glaciers in the Antarctic. This set of lists does not include ice sheets, ice caps or ice fields, such as the Antarctic ice sheet, but includes glacial features that are defined by their flow, rather than general bodies of ice. The lists include outlet glaciers, valley glaciers, cirque glaciers, tidewater glaciers and ice streams. Ice streams are a type of glacier and many of them have "glacier" in their name, e.g. Pine Island Glacier. Ice shelves are listed separately in the List of Antarctic ice shelves. For the purposes of these lists, the Antarctic is defined as any latitude further south than 60° (the continental limit according to the Antarctic Treaty System).

MacNamara Glacier

MacNamara Glacier (84°20′S 63°40′W) is a glacier in the Patuxent Range of the Pensacola Mountains in Antarctica, draining northeastward between the Thomas Hills and Anderson Hills to Foundation Ice Stream. It was mapped by the United States Geological Survey from surveys and U.S. Navy air photos, 1956–66, and was named by the Advisory Committee on Antarctic Names for Edlen E. MacNamara, a United States Antarctic Research Program exchange scientist at Molodezhnaya Station, winter 1967.

Moraine

A moraine is any glacially formed accumulation of unconsolidated glacial debris (regolith and rock) that occurs in both currently and formerly glaciated regions on Earth (i.e. a past glacial maximum), through geomorphological processes. Moraines are formed from debris previously carried along by a glacier and normally consisting of somewhat rounded particles ranging in size from large boulders to minute glacial flour. Lateral moraines are formed at the side of the ice flow and terminal moraines at the foot, marking the maximum advance of the glacier. Other types of moraine include ground moraines, till-covered areas with irregular topography, and medial moraines which are formed where two glaciers meet.

Northeast Glacier

Northeast Glacier is a steep, heavily crevassed glacier on the west side of Hemimont Plateau, 21 km (13 mi) long and 8 km (5 mi) wide at its mouth, which flows from McLeod Hill westward and then south-westwards into Marguerite Bay between the Debenham Islands and Roman Four Promontory, on the west coast of Graham Land, Antarctica. Northeast Glacier was first surveyed in 1936 by the British Graham Land Expedition (BGLE) under John Riddoch Rymill. It was resurveyed in 1940 by members of the United States Antarctic Service (USAS), who first used the glacier as a sledging route, and so named by them because it lay on the north-eastern side of their base at Stonington Island.

Siachen Glacier

The Siachen Glacier is a glacier located in the eastern Karakoram range in the Himalayas at about 35.421226°N 77.109540°E / 35.421226; 77.109540, just northeast of the point NJ9842 where the Line of Control between India and Pakistan ends. At 76 km (47 mi) long, it is the longest glacier in the Karakoram and second-longest in the world's non-polar areas. It falls from an altitude of 5,753 m (18,875 ft) above sea level at its head at Indira Col on the China border down to 3,620 m (11,875 ft) at its terminus. The entire Siachen Glacier, with all major passes, is currently under the administration of India since 1984. Pakistan controls the region west of Saltoro Ridge, far away from the glacier, with Pakistani posts located 3,000 ft below more than 100 Indian posts on Saltoro Ridge.The Siachen Glacier lies immediately south of the great drainage divide that separates the Eurasian Plate from the Indian subcontinent in the extensively glaciated portion of the Karakoram sometimes called the "Third Pole". The glacier lies between the Saltoro Ridge immediately to the west and the main Karakoram range to the east. The Saltoro Ridge originates in the north from the Sia Kangri peak on the China border in the Karakoram range. The crest of the Saltoro Ridge's altitudes range from 5,450 to 7,720 m (17,880 to 25,330 feet). The major passes on this ridge are, from north to south, Sia La at 5,589 m (18,336 ft), Bilafond La at 5,450 m (17,880 ft), and Gyong La at 5,689 m (18,665 ft). The average winter snowfall is more than 1000 cm (35 ft) and temperatures can dip to −50 °C (−58 °F). Including all tributary glaciers, the Siachen Glacier system covers about 700 km2 (270 sq mi).

Strandzha Glacier

Strandzha Glacier (Lednik Strandzha \'led-nik 'stran-dzha\) is located on Burgas Peninsula, eastern Livingston Island in the South Shetland Islands, Antarctica northeast of Ropotamo Glacier, south of Sopot Ice Piedmont and southwest of Pautalia Glacier. It is bounded by Delchev Peak to the west, Spartacus Peak, Trigrad Gap and Yavorov Peak to the northwest, and by Elena Peak to the north, extends 1.6 km in northeast-southwest direction and 800 m in northwest-southeast direction, and flows southeastward into Bransfield Strait.

The feature is named after Strandzha Mountain, Bulgaria.

Talev Glacier

Talev Glacier (Bulgarian: Талев ледник, ‘Talev Lednik’ \'ta-lev 'led-nik\) is the 4 km long and 2.8 km wide glacier on Barison Peninsula, Graham Coast on the west side of Antarctic Peninsula, situated west of Cadman Glacier and southeast of Butamya Glacier. It drains northeastwards, and flows into Beascochea Bay.

The glacier is named after the Bulgarian writer Dimitar Talev (1898-1966).

Thwaites Glacier

Thwaites Glacier (75°30′S 106°45′W) is an unusually broad and fast Antarctic glacier flowing into Pine Island Bay, part of the Amundsen Sea, east of Mount Murphy, on the Walgreen Coast of Marie Byrd Land. Its surface speeds exceed 2 km/yr near its grounding line, and its fastest flowing grounded ice is centred between 50 and 100 km east of Mount Murphy. It was named by ACAN after Fredrik T. Thwaites, a glacial geologist, geomorphologist and professor emeritus at the University of Wisconsin–Madison. Thwaites Glacier drains into West Antarctica’s Amundsen Sea and is closely watched for its potential to raise sea levels.Along with Pine Island Glacier, Thwaites Glacier has been described as part of the "weak underbelly" of the West Antarctic Ice Sheet, due to its apparent vulnerability to significant retreat. This hypothesis is based on both theoretical studies of the stability of marine ice sheets and recent observations of large changes on both of these glaciers. In recent years, the flow of both of these glaciers has accelerated, their surfaces lowered, and the grounding lines retreated.

Glaciers
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