An ice shelf is a thick floating platform of ice that forms where a glacier or ice sheet flows down to a coastline and onto the ocean surface. Ice shelves are only found in Antarctica, Canada, the boundary between the floating ice shelf and the grounded ice that feeds it is called the grounding line. The thickness of ice shelves ranges from about 100 to 1000 meters, in contrast, sea ice is formed on water, is much thinner, and forms throughout the Arctic Ocean. It is found in the Southern Ocean around the continent of Antarctica, Ice shelves are principally driven by gravity-driven pressure from the grounded ice. That flow continually moves ice from the line to the seaward front of the shelf. The primary mechanism of mass loss from ice shelves was thought to have been iceberg calving, typically, a shelf front will extend forward for years or decades between major calving events. Snow accumulation on the surface and melting from the lower surface are important to the mass balance of an ice shelf.
Ice may accrete onto the underside of the shelf, the density contrast between glacial ice, which is denser than normal ice, and liquid water means that only about 1/9 of the floating ice is above the ocean surface. The worlds largest ice shelves are the Ross Ice Shelf and the Filchner-Ronne Ice Shelf in Antarctica, the term captured ice shelf has been used for the ice over a subglacial lake, such as Lake Vostok. All Canadian ice shelves are attached to Ellesmere Island and lie north of 82°N, Ice shelves that are still in existence are the Alfred Ernest Ice Shelf, Milne Ice Shelf, Ward Hunt Ice Shelf and Smith Ice Shelf. The MClintock Ice Shelf broke up from 1963 to 1966, the Ayles Ice Shelf broke up in 2005, a total of 74 percent of the Antarctic coastline has ice shelves attached. Their aggregate area is over 1,550,000 km2, in the last several decades, glaciologists have observed consistent decreases in ice shelf extent through melt and complete disintegration of some shelves. The Ellesmere ice shelf reduced by 90 percent in the century, leaving the separate Alfred Ernest, Milne, Ward Hunt.
A1986 survey of Canadian ice shelves found that 48 km². of ice calved from the Milne, the Ayles Ice Shelf calved entirely on August 13,2005. The Ward Hunt Ice Shelf, the largest remaining section of thick landfast sea ice along the coastline of Ellesmere Island. It further decreased by 27% in thickness between 1967 and 1999, in summer 2002, the Ward Ice Shelf experienced another major breakup. Two sections of Antarcticas Larsen Ice Shelf broke apart into hundreds of small fragments in 1995 and 2002. The breakup events may be linked to the dramatic polar warming trends that are part of global warming, the leading ideas involve enhanced ice fracturing due to surface meltwater and enhanced bottom melting due to warmer ocean water circulating under the floating ice
A crevasse is a deep crack, or fracture, found in an ice sheet or glacier, as opposed to a crevice that forms in rock. Crevasses form as a result of the movement and resulting stress associated with the shear stress generated when two pieces above a plastic substrate have different rates of movement. The resulting intensity of the stress causes a breakage along the faces. Crevasses often have vertical or near-vertical walls, which can melt and create seracs, arches. These walls sometimes expose layers that represent the glaciers stratigraphy, Crevasse size often depends upon the amount of liquid water present in the glacier. A crevasse may be as deep as 45 metres, as wide as 20 metres, a crevasse may be covered, but not necessarily filled, by a snow bridge made of the previous years accumulation and snow drifts. The result is that crevasses are rendered invisible, and thus potentially lethal to anyone attempting to navigate their way across a glacier, occasionally a snow bridge over an old crevasse may begin to sag, providing some landscape relief, but this cannot be relied upon.
Anyone planning to travel on a glacier should be trained in crevasse rescue, the presence of water in a crevasse can significantly increase its penetration. Longitudinal crevasses form parallel to flow where the width is expanding. They develop in areas of stress, such as where a valley widens or bends. They are typically concave down and form a greater than 45° with the margin. Splashing crevasses result from shear stress from the margin of the glacier and they extend from the glaciers margin and are concave up with respect to glacier flow, making an angle less than 45° with the margin. At the centre line of the glacier, there is zero pure shear from the margins, transverse crevasses are the most common crevasse type. They form in a zone of longitudinal extension where the stresses are parallel to the direction of glacier flow. These crevasses stretch across the glacier transverse to the flow direction and they generally form where a valley becomes steeper. Bergschrund Bowie Crevasse Field Glaciology Paterson, W. S.
B,1994, The Physics of Glaciers, 3rd edition, ISBN 0-7506-4742-6. Boon, S. M. J. Sharp,2003, The role of hydrologically-driven ice fracture in drainage system evolution on an Arctic glacier, Geophysical Research Letters,30, pp.1916. Van der Veen, C. J.1998, Fracture mechanics approach to penetration of surface crevasses on glaciers, Cold Regions Science and Technology,27, pp. 31–47
Mendenhall Glacier is a glacier about 13.6 miles long located in Mendenhall Valley, about 12 miles from downtown Juneau in the southeast area of the U. S. state of Alaska. The glacier and surrounding landscape is protected as part of the 5, 815-acre Mendenhall Glacier Recreation Area, the Juneau Icefield Research Program has monitored the outlet glaciers of the Juneau Icefield since 1942, including Mendenhall Glacier. The glacier has retreated 1.75 miles since 1929, when Mendenhall Lake was created, the end of the glacier currently has a negative glacier mass balance and will continue to retreat in the foreseeable future. This is because increasing amounts of warm, moist air will be carried up to the head of the icefield, the increased amount of snow will feed the icefield, possibly enough to offset the continually increasing melting experienced at the glaciers terminus. However, this phenomenon will fade away if temperatures continue to climb. It was originally known as Sitaantaago or Aakwtaaksit, latinized as Aakwtaaksit, the glacier was named Auke Glacier by naturalist John Muir for the Tlingit Auk Kwaan band in 1888.
In 1891 it was renamed in honor of Thomas Corwin Mendenhall and it extends from the Juneau Icefield, its source, to Mendenhall Lake. The glacier has recently come to the forefront of the debate on global warming. The US Forest Service, which manages the Mendenhall Glacier, says because glaciers are a product of climate, the Mendenhall glacier has been in retreat since the end of the Little Ice Age in the 1700s. It is expected the glacier face will soon out of the lake. The retreat of the Mendenhall Glacier and other glaciers in the area is believed by some to be a result of broader retreat, the Juneau Icefield is the fifth largest icefield in North America. For many populations near glacial areas these glaciers are a source of drinking water. Once these glaciers are gone the people relying on this water will be out of their familiar fresh water source. For example, Anchorage is one of the most populated cities in Alaska, if the recession of this glacier continues they will be out of their main source of water.
Although there are many effects of the recession of the Mendenhall Glacier and glaciers in general. With the retreat of the Mendenhall Glacier, the Mendenhall Lake has formed, the lake is a result of the run-off from the glacier and is increasing in size as the glacier continues to retreat. The lake began formation in 1929 and has continued to grow since then, the lake has its own unique ecosystem and is a nursery for a variety of fish including several type of salmon, Dolly Varden char, and cutthroat trout. Recently, a new discovery has made regarding the Mendenhall Glacier
Glacial lake outburst flood
A glacial lake outburst flood is a type of outburst flood that occurs when the dam containing a glacial lake fails. An event similar to a GLOF, where a body of water contained by a glacier melts or overflows the glacier, is called a Jökulhlaup, the dam can consist of glacier ice or a terminal moraine. A glacial lake outburst flood is a type of outburst flood occurring when water dammed by a glacier or a moraine is released. A water body that is dammed by the front of a glacier is called a lake. When a marginal lake bursts, it may be called a marginal lake drainage, when a sub-glacial lake bursts, it may be called a jökulhlaup. A jökulhlaup is thus a sub-glacial outburst flood, Glacial lake volumes vary, but may hold millions to hundreds of millions of cubic metres of water. Catastrophic failure of the ice or glacial sediment can release this water over periods of minutes to days. On a downstream floodplain, it suggests a somewhat slower inundation spreading as much as 10 kilometres wide, both scenarios are significant threats to life and infrastructure.
The United Nations has a series of monitoring efforts to prevent death. The importance of this situation has magnified over the past century due to increased populations, there are a number of imminent deadly GLOFs situations that have been identified worldwide. The Tsho Rolpa glacier lake is located in the Rolwaling Valley, about 110 kilometres northeast of Kathmandu, the lake is dammed by a 150 metres high unconsolidated terminal moraine dam. The most famous are the immense jökulhlaup released from the Vatnajökull Ice Cap in Iceland and it is not by chance that the term jökulhlaup comes from Icelandic, as the south of Iceland has very often been the victim of such catastrophes. The jökulhlaup reached a rate of 50,000 cubic metres per second. The flood carried ice floes that weighed up to 5000 tons with icebergs between 100–200 tons striking the Gigjukvisl Bridge of the Ring Road, the tsunami released was up to 4 metres high and 600 metres wide. The flood carried with it 185 million tons of silt, the jökulhlaup flow made it for several days the 2nd largest river after the Amazon.
After the flooding, some icebergs 10 metres high could be seen on the banks of the river where the run had left them behind. The peak water release from a lake that develops around the Grímsvötn Volcanic Crater in the center of the Vatnajökull ice cap generates flows that exceed the volume of the Mississippi River. The outbursts have occurred in 1954,1960,1965,1972,1976,1982,1983,1986,1991 and 1996, in 1996, the eruption melted 3 cubic kilometres of ice and yielded an outburst of 6,000 cubic metres per second at peak flow
A moulin or glacier mill is a roughly circular, vertical to nearly vertical well-like shaft within a glacier or ice sheet which water enters from the surface. The term is derived from the French word for mill and they can be up to 10 meters wide and are typically found on ice sheets and flat areas of a glacier in a region of transverse crevasses. Moulins can reach the bottom of the glacier, hundreds of meters deep and they are the most typical cause for the formation of a glacier cave. Moulins are parts of the structure of glaciers, that carry meltwater from the surface down to wherever it may go. Water from moulins may help lubricate the base of the glacier, given an appropriate relationship between an ice sheet and the terrain, the head of water in a moulin can provide the power and medium with which a tunnel valley may be formed. The role of water in lubricating the base of ice sheets and glaciers is complex and it is implicated in accelerating the speed of glaciers. Firn Giants kettle Holocene glacial retreat Melt pond Sinkhole Snake coils Subglacial lake Supraglacial lake Earth Observatory page, december 2006 article about a NASA expedition to Greenland moulin
Retreat of glaciers since 1850
Studied by glaciologists, the temporal coincidence of glacier retreat with the measured increase of atmospheric greenhouse gases is often cited as an evidentiary underpinning of global warming. Glacier mass balance is the key determinant of the health of a glacier, Glaciers in retreat will have negative mass balances, and if they do not find an equilibrium between accumulation and ablation, will eventually disappear. The Little Ice Age was a period from about 1550 to 1850 when the world experienced relatively cooler temperatures compared to the present, until about 1940, glaciers around the world retreated as the climate warmed substantially. Glacial retreat slowed and even reversed temporarily, in many cases, in locations such as the Andes of South America and Himalayas in Asia, the demise of glaciers in these regions has the potential to affect water supplies in those areas. The acceleration of the rate of retreat since 1995 of key outlet glaciers of the Greenland and West Antarctic ice sheets may foreshadow a rise in sea level, the mass balance, or difference between accumulation and ablation, of a glacier is crucial to its survival.
Climate change may cause variations in temperature and snowfall, resulting in changes in mass balance. A glacier with a negative balance loses equilibrium and retreats. A sustained positive balance is out of equilibrium and will advance to reestablish equilibrium. Currently, nearly all glaciers have a mass balance and are retreating. Glacier retreat results in the loss of the region of the glacier. Since higher elevations are cooler, the disappearance of the lowest portion decreases overall ablation, thereby increasing mass balance, methods for measuring retreat include staking terminus location, global positioning mapping, aerial mapping and laser altimetry. The key symptom of disequilibrium is thinning along the length of the glacier. This indicates a diminishment of the accumulation zone, the result is marginal recession of the accumulation zone margin, not just of the terminus. In effect, the no longer has a consistent accumulation zone. However, the Grinnell Glacier in Montana, U. S. will shrink at an increasing rate until it disappears.
The difference is that the section of Easton Glacier remains healthy and snow-covered. Small glaciers with minimal altitude range are most likely to fall into disequilibrium with the climate, middle latitude glaciers are located either between the Tropic of Cancer and the Arctic Circle, or between the Tropic of Capricorn and the Antarctic Circle. Both areas support glacier ice from glaciers, valley glaciers and even smaller icecaps
Aufeis, is a sheet-like mass of layered ice that forms from successive flows of ground water during freezing temperatures. This form of ice is called overflow, icings, or the Russian term, the term was first used in 1859 by A. T. von Middendorff following his observations of the phenomenon in northern Siberia. Aufeis accumulates during winter along stream and river valleys in arctic and subarctic environments and it forms by upwelling of river water behind ice dams, or by ground-water discharge. The latter mechanism prevails in high-gradient alpine streams as they freeze solid, successive ice layers can lead to aufeis accumulations that are several meters thick. Aufeis typically melts out during summer and will form in the same place year after year. Sheets of aufeis may block stream channels and cause their flood plains to widen as spring floodwaters are forced to flow around the ice, research on aufeis has to a large extent been motivated by the variety of engineering problems the ice sheets can cause.
Culverts and pipelines can actually help to block flow and lead to the development of more extensive aufeis. Aufeis can present a danger to recreational boaters even during summer months. Breaking dams of aufeis can cause flash floods downriver, proper scouting and precautions when choosing campsites can minimize these risks. In late 2011, Mongolia planned to test the use and storage of artificial naleds as a way of cooling Ulan Bator in the hot Mongolian summer, sheets of aufeis have been observed in Alaska, Arctic Canada and Mongolia. Wang, Vohden, Jim, et al, Larry P. Day, Warren C. eds. Aufeis Accumulations in Stream Bottoms in Arctic and Subarctic Environments as an Indicator of Geologic Structure, recent U. S. Geological Survey Studies in the Tintina Gold Province, United States, and Yukon, Canada — Results of a 5-Year Project. U. S. Department of the Interior and U. S. Geological Survey, media related to Aufeis at Wikimedia Commons
A randkluft is the headwall gap between a glacier or snowfield and the adjacent rock face at the back of the cirque or, more loosely, between the rock face and the side of the glacier. It is formed by the melting of ice against warmer rock, during summer therefore, a randkluft will become wider and thus more difficult for climbers to negotiate. Randklufts are often found in relatively low-lying glaciers such as the Blaueis in the Berchtesgaden Alps or the Höllentalferner in the Wetterstein, unlike a randkluft, a bergschrund has two ice walls. Crevasse Cryosphere Glossary, National Snow and Ice Data Center Photo of the randkluft on the Höllentalferner
An icefall is a portion of certain glaciers characterized by rapid flow and a chaotic crevassed surface. The term icefall is formed by analogy with the waterfall, a similar. When ice movement is faster than elsewhere, because the glacier bed steepens or narrows, the flow cannot be accommodated by plastic deformation, where two fractures meet, seracs can be formed. When the movement of the ice slows down, the crevasses can coalesce, perhaps the most conspicuous consequence of glacier flow, icefalls occur where the glacier bed steepens and/or narrows. Most glacier ice flows at speeds of a few hundred metres per year or less, the flow of ice in an icefall may be measured in kilometres per year. Such rapid flow cannot be accommodated by deformation of the ice. Instead, the ice fractures forming crevasses, intersecting fractures form ice columns or seracs. These processes are imperceptible for the most part, however, a serac may collapse or topple abruptly and this behavior often poses the biggest risk to mountaineers climbing in an icefall.
Below the icefall, the bed flattens and/or widens and the ice flow slows. Crevasses close and the surface becomes much smoother and easier to traverse. The Roosevelt Glacier icefall, on the face of Mount Baker, is about 730 metres high. The ice cliff of the side of the ice fall. Typical of mountain glaciers, this icefall forms as the ice flows from a high plateau or basin accumulation zone to a lower valley ablation zone. Much larger icefalls may be found in the glaciers of continental ice sheets. Icefalls are climbed because of their beauty and the challenge they pose, in some cases, an icefall may provide the only feasible or the easiest route up one face of a mountain. An example is the Khumbu Icefall on the Nepalese side of Mount Everest and it is about 5,500 metres above sea level. Glacier morphology Media related to Icefalls at Wikimedia Commons
A terminal moraine, called end moraine, is a type of moraine that forms at the snout of a glacier, marking its maximum advance. At this point, debris that has accumulated by plucking and abrasion, because the glacier acts very much like a conveyor belt, the longer it stays in one place, the greater the amount of material that will be deposited. The moraine is left as the point of the terminal extent of the ice. Terminal moraines are one of the most prominent types of moraines in the Arctic, one famous terminal moraine is the Giants Wall in Norway which, according to legend, was built by giants to keep intruders out of their realm. In North America, the Outer Lands is a given to the terminal moraine archipelago of the northeastern region of the United States. Other prominent examples of terminal moraines are the Tinley Moraine and the Valparaiso Moraine and these moraines are most clearly seen southwest of Chicago. In Europe, virtually all the terrain in the central Netherlands is made up of a terminal moraine.
In New Zealand the Franz Josef Glacier on the West Coast has created the terminal called the Waiho Loop. Glacial landform Postglacial rebound Push moraine Outwash plain Trafalgar Moraine Oak Ridges Moraine List of glacial moraines
A serac is a block or column of glacial ice, often formed by intersecting crevasses on a glacier. Commonly house-sized or larger, they are dangerous to mountaineers since they may topple with little warning, even when stabilized by persistent cold weather, they can be an impediment to glacier travel. Seracs are found within an icefall, often in large numbers, notable examples of this type are well-known obstacles on some of the worlds highest mountains, including K2 at The Bottleneck or Kanchenjunga on the border of India and Nepal. Significant seracs in the Alps are found on the northeast face of Piz Roseg, the face of the Dent dHérens. The collapse of large seracs was responsible for at least 8 of the 11 deaths of the August 2008 climbing accident on K2, in April 2014, a large serac broke off and caused an avalanche on Mount Everest, which was responsible for the deaths of 16 climbers. On a 1970 Japanese expedition to Mount Everest Kyak Tsering was killed by a falling serac