Aufeis ( ) ( German for "ice on top") is a sheet-like mass of layered

ice Ice is water that is frozen into a solid state, typically forming at or below temperatures of 0 ° C, 32 ° F, or 273.15 K. It occurs naturally on Earth, on other planets, in Oort cloud objects, and as interstellar ice. As a naturally oc ...

that forms from successive flows of ground or river water during freezing temperatures. This form of ice is also called overflow, icings, or the Russian term, naled (). The term "Aufeis" was first used in 1859 by

Alexander von Middendorff Alexander Theodor von Middendorff (; 18 August 1815 – 24 January 1894) was a Russian zoologist and explorer of Baltic German and Estonian extraction. He was known for his expedition in 1843–45 to the extreme north and east of Siberia, des ...

following his observations of the phenomenon in northern

Siberia Siberia ( ; , ) is an extensive geographical region comprising all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has formed a part of the sovereign territory of Russia and its predecessor states ...

. When thawed, ''aufeis'' leave footprints in the form of ''aufeis'' glades or, perhaps more accurately in tundra habitats, ''aufeis'' barrens, because of the near absence of

vascular plant Vascular plants (), also called tracheophytes (, ) or collectively tracheophyta (; ), are plants that have lignin, lignified tissues (the xylem) for conducting water and minerals throughout the plant. They also have a specialized non-lignified Ti ...

s due to ice cover during much of the growing season.

Etymology

Aufeis literally translates from German to “on-ice”. In 1859 the Baltic German scientist and explorer

used this term to describe his observations of the phenomenon in northern

.Ashton, George D. 1986. River and lake ice engineering. Chelsea, Michigan, USA: Book Crafters, Inc.

Formation

Aufeis accumulates during winter along

stream A stream is a continuous body of water, body of surface water Current (stream), flowing within the stream bed, bed and bank (geography), banks of a channel (geography), channel. Depending on its location or certain characteristics, a strea ...

and

river A river is a natural stream of fresh water that flows on land or inside Subterranean river, caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of ...

valleys in

arctic The Arctic (; . ) is the polar regions of Earth, polar region of Earth that surrounds the North Pole, lying within the Arctic Circle. The Arctic region, from the IERS Reference Meridian travelling east, consists of parts of northern Norway ( ...

and

subarctic The subarctic zone is a region in the Northern Hemisphere immediately south of the true Arctic, north of hemiboreal regions and covering much of Alaska, Canada, Iceland, the north of Fennoscandia, Northwestern Russia, Siberia, and the Cair ...

environments. 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. Ground-water discharge is blocked by ice, perturbing the steady-state condition and causing a small incremental rise in the local

water table The water table is the upper surface of the phreatic zone or zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with groundwater, which may be fresh, saline, or brackish, depending on the loc ...

until discharge occurs along the bank and over the top of the previously formed ice. Successive ice layers can grow and expand, attaining areas of ~25+ km² and thicknesses of 6+ m. Aufeis typically melts out during summer and will often form in the same place year after year. River ''aufeis'' form when the cross-sectional area of a stream channel becomes locally restricted as ice accumulates during winter. Such restrictions or “choke-points” result in bulk overflow and local increases in hydrostatic pressure, causing water to move upward through fissures onto the original ice layer. This overflowing water subsequently freezes to produce additional ice layers, thus explaining the origin of the term ''aufeis''. This process, repeated through the long arctic winter, can generate large volumes of ice, with some ''aufeis'' in arctic Alaska—where they are also known as “icings”—attaining areas of 20+ km² and localized thicknesses of 6+ m. The cumulative area of late-winter ''aufeis'' in the Sagavanirktok River drainage alone, for example, ranges from 102 to 103 km².

Impact

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 (e.g. blocking drainages and causing flooding of roads). Aufeis can present an extreme danger to recreational boaters even during summer months, who can find themselves trapped between walls of ice or pulled under aufeis by the current of the river. Breaking dams of aufeis can cause flash floods downriver. When thawed, ''aufeis'' leave footprints in the form of “''aufeis'' glades” or more accurately in

tundra In physical geography, a tundra () is a type of biome where tree growth is hindered by frigid temperatures and short growing seasons. There are three regions and associated types of tundra: #Arctic, Arctic, Alpine tundra, Alpine, and #Antarctic ...

habitats, ''aufeis'' barrens, because of the near absence of

s due to ice cover during much of the growing season. ''Aufeis'' barrens are distinctive landscape features of the arctic tundra and provide reliable indicators of ''aufeis'' locations".

City cooling

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, and reducing the use of energy-intensive

air conditioning Air conditioning, often abbreviated as A/C (US) or air con (UK), is the process of removing heat from an enclosed space to achieve a more comfortable interior temperature, and in some cases, also controlling the humidity of internal air. Air c ...

Occurrence

River ''aufeis'' are common and widespread features of the arctic cryosphere, particularly in northern Alaska and Siberia. In eastern Siberia, where ''aufeis'' are known as ''naleds'', 10,000 ''aufeis'' with a cumulative area of ~ 50,000 km² containing 30 km³ of water have been documented in 2015. Sheets of aufeis have been observed in Alaska,

Arctic Canada Northern Canada (), colloquially the North or the Territories, is the vast northernmost region of Canada, variously defined by geography and politics. Politically, the term refers to the three territories of Canada: Yukon, Northwest Territories a ...

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 ...

, and

Mongolia Mongolia is a landlocked country in East Asia, bordered by Russia to the north and China to the south and southeast. It covers an area of , with a population of 3.5 million, making it the world's List of countries and dependencies by po ...

. Analysis of satellite imagery from 2000 to 2015 has shown that the extent and duration of many Alaskan river icings has decreased due to

climate change Present-day climate change includes both global warming—the ongoing increase in Global surface temperature, global average temperature—and its wider effects on Earth's climate system. Climate variability and change, Climate change in ...

References

External links

* {{Glaciers Earth sciences Water ice Glaciology Geography of the Arctic Lithosphere