Esker
An esker, eskar, eschar, or os, sometimes called an asar, osar, or serpent kame,
Etymology
The term esker is derived from the
The synonym os comes from the Swedish word ås, "ridge".
Geology
Most eskers are argued to have formed within ice-walled tunnels by streams that flowed within and under glaciers. They tended to form around the time of the
Eskers may also form above glaciers by accumulation of sediment in supraglacial channels, in crevasses, in linear zones between stagnant blocks, or in narrow embayments at glacier margins. Eskers form near the terminal zone of glaciers, where the ice is not moving as fast and is relatively thin.[5]
Plastic flow and melting of the basal ice determines the size and shape of the subglacial tunnel. This in turn determines the shape, composition and structure of an esker. Eskers may exist as a single channel, or may be part of a branching system with tributary eskers. They are not often found as continuous ridges, but have gaps that separate the winding segments. The ridge crests of eskers are not usually level for very long, and are generally knobby. Eskers may be broad-crested or sharp-crested with steep sides.[5] They can reach hundreds of kilometers in length and are generally 20–30 m (66–98 ft) in height.
The path of an esker is governed by its water pressure in relation to the overlying ice. Generally, the pressure of the ice was at such a point that it would allow eskers to run in the direction of glacial flow, but force them into the lowest possible points such as valleys or river beds, which may deviate from the direct path of the glacier. This process is what produces the wide eskers upon which roads and highways can be built. Less pressure, occurring in areas closer to the
The concentration of rock debris in the ice and the rate at which sediment is delivered to the tunnel by melting and from upstream transport determines the amount of
There are various cases where inland dunes have developed next to eskers after deglaciation.[7] These dunes are often found in the leeward side of eskers, if the esker is not oriented parallel to prevailing winds.[7] Examples of dunes developed on eskers can be found in both Swedish and Finnish Lapland.[7][8]
Lakes may form within depressions in eskers. These lakes can lack surface outflows and inflows and have drastic fluctuations over time.[9]
Life on eskers
Eskers are critical to the ecology of Northern Canada. Several plants that grow on eskers, including
Examples of eskers
Europe
In Sweden, Uppsalaåsen stretches for 250 km (160 mi) and passes through Uppsala city. The Badelundaåsen esker runs for over 300 km (190 mi) from Nyköping to lake Siljan. Pispala's Pyynikki Esker in Tampere, Finland, is on an esker between two lakes carved by glaciers. A similar site is Punkaharju in Finnish Lakeland.
The village of
North America
Great Esker Park runs along the Back River in Weymouth, Massachusetts, and is home to the highest esker in North America (27 m (90 ft)).[12]
There are over 1,000 eskers in the
Esker systems in the U.S. state of Maine can be traced for up to 160 km (100 mi).[14]
Thelon Esker is almost 800 km (500 mi) long, straddling the boundary between the territories of Nunavut and Northwest Territories in Canada.[15]
Uvayuq or Mount Pelly, in Ovayok Territorial Park, the Kitikmeot Region, Nunavut is an esker.
Roads are sometimes built along eskers to save expense. Examples include the Denali Highway in Alaska, the Trans-Taiga Road in Quebec, and the "Airline" segment of Maine State Route 9 between Bangor and Calais.[16]
There are numerous long eskers in the
See also
- Eskers Provincial Park – Provincial park in British Columbia
- Glacial landform – Landform created by the action of glaciers
- Glacier morphology – Geomorphology of glaciers
- Kame – Mound formed on a retreating glacier and deposited on land
- Tunnel valley – Glacial-formed geographic feature
References
- ^ Collins English Dictionary
- ^ "McGraw-Hill Dictionary of Scientific & Technical Terms". Archived from the original on 2015-04-20. Retrieved 2015-06-30.
- ^ Gedney, Larry (August 1, 1984). "Eskers: The Upside-Down Riverbeds". Alaska Science Forum Article #674. Archived from the original on 4 April 2012. Retrieved 29 September 2011.
- ISBN 0-901714-29-1.
- ^ ISBN 0-13-860958-6.
- ^ Shreve, R.L., 1985, Esker characteristics in terms of glacier physics, Katahdin esker system, Maine: GSA Bulletin, v. 96, pp. 639–646.
- ^ ISBN 9780521564069.
- .
- ISBN 91-7333-104-X.
- ISBN 0-7922-3877-X
- ISBN 978-085272-694-5.
- ^ "Mountain And Glacial Landforms: What Is An Esker?". WorldAtlas. 2017-04-25. Retrieved 2022-07-13.
- ^ "Eskers". Archived from the original on 2013-12-03. Retrieved 2013-12-02.
- ^ "Surficial Geologic History of Maine". Explore Maine Geology. Maine Geological Survey. 6 October 2005. Retrieved 30 August 2022.
- ISBN 0-679-31220-X.
- ^ Down East Region
- ^ "Sea Serpents in the Adirondacks? You Bet!". Adirondack Almanack. 7 November 2009. Retrieved 2015-07-30.
Further reading
- Trenhaile, Alan (2007). Geomorphology: A Canadian Perspective. Don Mills, Ontario: Oxford University Press. pp. 188–191. ISBN 978-0-19-542474-4.
External links
- Oblique aerial photo of an esker in Waterford, Maine
- Esker Riada Webpage
- Diagram illustrating (i) tunnel in glacier before retreat of ice, forming (ii) meandering esker in The Ice Melts: Deposition, p. 6 of "Pennsylvania and the Ice Age" published 1999 by PA DCNR Bureau of Topographic and Geologic Survey
- The Bridgenorth Esker: geomorphology and sedimentology