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Glacier morphology, or the form a
glacier A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...
takes, is influenced by
temperature Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...
,
precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwe ...
,
topography Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the landforms and features themselves, or a description or depiction in maps. Topography is a field of geoscience and planetary sci ...
, and other factors. The goal of glacial morphology is to gain a better understanding of glaciated landscapes and the way they are shaped. Types of glaciers can range from massive
ice sheet In glaciology, an ice sheet, also known as a continental glacier, is a mass of glacier, glacial ice that covers surrounding terrain and is greater than . The only current ice sheets are the Antarctic ice sheet and the Greenland ice sheet. Ice s ...
s, such as the
Greenland ice sheet The Greenland ice sheet is an ice sheet which forms the second largest body of ice in the world. It is an average of thick and over thick at its maximum. It is almost long in a north–south direction, with a maximum width of at a latitude ...
, to small cirque glaciers found perched on mountain tops. Glaciers can be grouped into two main categories: * Ice flow is constrained by the underlying
bedrock In geology, bedrock is solid rock that lies under loose material ( regolith) within the crust of Earth or another terrestrial planet. Definition Bedrock is the solid rock that underlies looser surface material. An exposed portion of bed ...
topography Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the landforms and features themselves, or a description or depiction in maps. Topography is a field of geoscience and planetary sci ...
* Ice flow is unrestricted by surrounding topography


Unconstrained Glaciers


Ice sheets and ice caps

Ice sheet In glaciology, an ice sheet, also known as a continental glacier, is a mass of glacier, glacial ice that covers surrounding terrain and is greater than . The only current ice sheets are the Antarctic ice sheet and the Greenland ice sheet. Ice s ...
s and
ice cap In glaciology, an ice cap is a mass of ice that covers less than of land area (usually covering a highland area). Larger ice masses covering more than are termed ice sheets. Description By definition, ice caps are not constrained by topogra ...
s cover the largest areas of land in comparison to other glaciers, and their ice is unconstrained by the underlying topography. They are the largest glacial ice formations and hold the vast majority of the world's fresh water.


Ice sheets

Ice sheets are the largest form of glacial formation. They are continent-sized ice masses that span areas over . They are dome-shaped and, like ice caps, exhibit radial flow. As ice sheets expand over the ocean, they become
ice shelves An ice shelf is a large platform of glacial ice floating on the ocean, fed by one or multiple tributary glaciers. Ice shelves form along coastlines where the ice thickness is insufficient to Displacement (fluid), displace the more dense surround ...
. Ice sheets contain 99% of all the freshwater ice found on Earth, and form as layers of snowfall accumulate and slowly start to compact into ice. There are only two ice sheets present on Earth today: the
Antarctic ice sheet The Antarctic ice sheet is a continental glacier covering 98% of the Antarctic continent, with an area of and an average thickness of over . It is the largest of Earth's two current ice sheets, containing of ice, which is equivalent to 61% of ...
and the
Greenland ice sheet The Greenland ice sheet is an ice sheet which forms the second largest body of ice in the world. It is an average of thick and over thick at its maximum. It is almost long in a north–south direction, with a maximum width of at a latitude ...
. Although only a tenth of modern Earth is covered by ice sheets, the
Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...
epoch was characterized by ice sheets that covered a third of the planet. This was also known as the
Last Glacial Maximum The Last Glacial Maximum (LGM), also referred to as the Last Glacial Coldest Period, was the most recent time during the Last Glacial Period where ice sheets were at their greatest extent between 26,000 and 20,000 years ago. Ice sheets covered m ...
.


Ice caps

An ice cap can be defined as a dome-shaped mass of ice that exhibits a radial flow. They are often easily confused with ice sheets, but these ice structures are smaller than 50,000 km2, and obscure the entirety of the topography they span. They mainly form in polar and sub-polar regions with particularly high elevation but flat ground. Ice caps can be round, circular, or irregular in shape. Ice caps often gradually merge into ice sheets making them difficult to track and document. Examples include: * Jostedal Glacier, Norway *
Devon Ice Cap The Devon Ice Cap is an ice cap on eastern Devon Island, Nunavut, Canada, covering an area of over . The highest point on Devon Island is found at the summit of the ice cap, with an elevation of . The ice cap has a maximum thickness of , and has ...
, Canada *
Barnes Ice Cap The Barnes Ice Cap is an ice cap located in central Baffin Island, Nunavut, Canada. Geography It covers close to in the area of the Baffin Mountains. It has been thinning due to regional warming. Between 2004 and 2006, the ice cap was thinning ...
, Canada *
Vatnajökull Vatnajökull ( Icelandic pronunciation: , literally "Glacier of Lakes"; sometimes translated as Vatna Glacier in English) is the largest and most voluminous ice cap in Iceland, and the second largest in area in Europe after the Severny Island i ...
, Iceland * Flade Isblink, Greenland


Ice domes

An ice dome is a part of an ice cap or ice sheet that is characterized by upstanding ice surface located in the
accumulation zone On a glacier, the accumulation zone is the area above the firn line, where snowfall accumulates and exceeds the losses from ablation, ( melting, evaporation, and sublimation). The annual equilibrium line separates the accumulation and ablation ...
. Ice domes are nearly symmetrical, with a convex or parabolic surface shape. They tend to develop evenly over a land mass that may be either a topographic height or a depression, often reflecting the sub-glacial topography. In ice sheets, domes may reach a thickness that may exceed . However, in ice caps, the thickness of the dome is much smaller, measuring roughly up to several hundred metres in comparison. In glaciated islands, ice domes are usually the highest point of the ice cap. An example of an ice dome is Kupol Vostok Pervyy in Alger Island,
Franz Josef Land Franz Josef Land () is a Russian archipelago in the Arctic Ocean. It is inhabited only by military personnel. It constitutes the northernmost part of Arkhangelsk Oblast and consists of 192 islands, which cover an area of , stretching from east ...
,
Russia Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...
.


Ice streams

Ice stream An ice stream is a region of fast-moving ice within an ice sheet. It is a type of glacier, a body of ice that moves under its own weight. They can move upwards of a year, and can be up to in width, and hundreds of kilometers in length. They t ...
s rapidly channel ice flow out to the sea, ocean, or an ice shelf. For this reason, they are commonly referred to as the "arteries" of an ice sheet. Ice from continental sheets is drained into the ocean by a complex network of ice streams, and their activity is greatly affected by oceanic and atmospheric processes. They feature a higher velocity in the centre of the stream, and are bounded by slow-moving ice on either side. Periods of greater ice stream flow result in more ice transfer from ice sheets to the ocean, raising sea level. At the margin between glacial ice and water,
ice calving Ice calving, also known as glacier calving or iceberg calving, is the breaking of ice chunks from the edge of a glacier.Essentials of Geology, 3rd edition, Stephen Marshak It is a form of ice ablation or ice disruption. It is the sudden release ...
takes place as glaciers begin to fracture, and
iceberg An iceberg is a piece of fresh water ice more than long that has broken off a glacier or an ice shelf and is floating freely in open water. Smaller chunks of floating glacially derived ice are called "growlers" or "bergy bits". Much of an i ...
s break off from the large masses of ice. Iceberg calving is a major contributor to
sea level rise The sea level has been rising from the end of the last ice age, which was around 20,000 years ago. Between 1901 and 2018, the average sea level rose by , with an increase of per year since the 1970s. This was faster than the sea level had e ...
, but the ocean is not the only place that can experience ice calving. Calving can also take place in lakes,
fjord In physical geography, a fjord (also spelled fiord in New Zealand English; ) is a long, narrow sea inlet with steep sides or cliffs, created by a glacier. Fjords exist on the coasts of Antarctica, the Arctic, and surrounding landmasses of the n ...
s, and continental ice cliffs.


Constrained glaciers


Icefields

An
icefield An ice field (also spelled icefield) is a mass of interconnected valley glaciers (also called mountain glaciers or alpine glaciers) on a mountain mass with protruding rock ridges or summits. They are often found in the colder climates and high ...
is an example of glacier structure that covers a relatively large area, and is usually located in mountain terrain. Icefields are quite similar to ice caps; however, their morphology is much more influenced by the underlying mountainous topography. The rock formations found under the icefields are variable, and rocky mountain peaks known as
nunatak A nunatak (from Inuit language, Inuit ) is the summit or ridge of a mountain that protrudes from an ice field or glacier that otherwise covers most of the mountain or ridge. They often form natural pyramidal peaks. Isolated nunataks are also cal ...
s tend to jut out from under the surface of icefields. Examples include: * Columbia Icefield, Canada *
Juneau Icefield The Juneau Icefield is an ice field located just north of Juneau, Alaska, Juneau, Alaska, continuing north through the border with British Columbia, extending through an area of in the Coast Mountains, Coast Range ranging north to south and east ...
, Canada * Southern Patagonian Ice Field, Chile and Argentina * Harding Icefield, Alaska, United States


Outlet glaciers

Outlet glaciers are often found in valleys, and they originate from major ice sheets and ice caps. They move in a singular direction that is determined by the underlying landscape. Outlet glaciers drain inland glaciers through gaps found in the surrounding topography. A higher amount of inland glacial melt ultimately increases the amount of outlet glacier output. Studies predict that outlet glaciers found in Greenland can increase the global sea level considerably following an increase in global temperature, and a subsequently higher drainage output. Examples include: * Helheim Glacier, Greenland *
Kangerlussuaq Glacier Kangerlussuaq Glacier (, meaning 'large fjord'; old spelling ''Kangerdlugssuaq'') is the largest glacier on the east coast of the Greenland ice sheet. It flows into the head of the Kangerlussuaq Fjord, the second largest fjord in East Greenland. ...
, Greenland * Jakobshavn Glacier, Greenland *
Petermann Glacier Petermann Glacier () is a large glacier located in North-West Greenland to the east of Nares Strait. It connects the Greenland ice sheet to the Arctic Ocean at 81°10' north latitude, near Hans Island. The glacier and its fjord are named after Ge ...
, Greenland


Valley glaciers

Valley glaciers are outlet glaciers that provide drainage for ice fields, icecaps or ice sheets. The flow of these glaciers is confined by the walls of the valley they are found in; but they may also form in mountain ranges as gathering snow turns to ice. The formation of valley glaciers is restricted by formations such as terminal
moraine A moraine is any accumulation of unconsolidated debris (regolith and Rock (geology), rock), sometimes referred to as glacial till, that occurs in both currently and formerly glaciated regions, and that has been previously carried along by a gla ...
s, which are collections of
till image:Geschiebemergel.JPG, Closeup of glacial till. Note that the larger grains (pebbles and gravel) in the till are completely surrounded by the matrix of finer material (silt and sand), and this characteristic, known as ''matrix support'', is d ...
(unconsolidated rock material) deposited by the terminus of the glacier. Ice-free exposed bedrock and slopes often surround valley glaciers, providing a route for snow and ice to accumulate on the glacier via
avalanche An avalanche is a rapid flow of snow down a Grade (slope), slope, such as a hill or mountain. Avalanches can be triggered spontaneously, by factors such as increased precipitation or snowpack weakening, or by external means such as humans, othe ...
s. Examples include: * Sermilik Glacier, Canada * Fláajökull, Iceland * Tviberi Glacier, Georgia


Valley-head glaciers

Valley head glaciers are types of valley glaciers that are only limited to the valley head. An example of this type of valley glacier is Bægisárjökull, found in Iceland, which does not markedly extend into the valley below it.


Fjords

True
fjords In physical geography, a fjord (also spelled fiord in New Zealand English; ) is a long, narrow sea inlet with steep sides or cliffs, created by a glacier. Fjords exist on the coasts of Antarctica, the Arctic, and surrounding landmasses of the no ...
are formed when valley glaciers retreat and seawater fills the now empty valley. They can be found in mountainous, glaciation-affected terrain. Examples include: *
Hvalfjörður Hvalfjörður (, "whale fjord") is situated in the west of Iceland between Mosfellsbær and Akranes. The fjord is approximately long and wide. The origin of the name Hvalfjörður is uncertain. Certainly today there is no presence of whales i ...
, Iceland * Hornsund, Svalbard *
Sognefjord The Sognefjord or Sognefjorden (, ), nicknamed the King of the Fjords (), is the list of Norwegian fjords, longest and deepest fjord in Norway. Located in Vestland county in Western Norway, it stretches inland from the ocean to the small village ...
, Norway * An existing valley glacier of this type is Jakobshavn Glacier in Greenland


Piedmont glaciers

Piedmont glaciers are a sub-type of valley glaciers which have flowed out onto lowland plains, where they spread out into a fan-like shape. Examples include: * Malaspina Glacier, Alaska, United States * Endeavor Piedmont Glacier, Antarctica


Cirque glaciers

Cirque glaciers are glaciers that appear in bowl-shaped valley hollows. Snow easily settles in the topographic structure; it is turned to ice as more snow falls and is subsequently compressed. When the glacier melts, a
cirque A (; from the Latin word ) is an amphitheatre-like valley formed by Glacier#Erosion, glacial erosion. Alternative names for this landform are corrie (from , meaning a pot or cauldron) and ; ). A cirque may also be a similarly shaped landform a ...
structure is left in its place. Examples include: * Lower Curtis Glacier, Washington, United States * Eel Glacier, Washington, United States


Hanging glacier

A hanging glacier appears in a hanging valley, and has the potential to break off from the side of the mountain it is attached to. As bits and pieces of hanging glaciers break off and begin to fall, avalanches can be triggered. Examples include: * Eiger Glacier, Switzerland * Angel Glacier, Canada


References


Sources

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External links

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