Kettle (landform)
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A kettle (or kettle hole) is a fluvioglacial landform occurring as the result of blocks of ice calving from the front of a receding glacier and becoming partially to wholly buried by glacial outwash. Glacial outwash is generated when sediment laden streams of meltwater flow away from the glacier and are deposited to form broad outwash plains called sandurs. When the ice blocks melt, holes are left in the sandur. When the development of numerous kettle holes disrupt sandur surfaces, a jumbled assemblage of ridges and mounds form, resembling kame and kettle topography.[1] Kettle holes can also occur in ridge shaped deposits of unconsolidated rock fragments called till.[2] Kettle holes can also form as the result of floods caused by the sudden drainage of an ice-dammed lake. These floods, called Jokulhlaups, often rapidly deposit large quantities of sediment onto the sandur surface. The kettle holes are formed by the melting blocks of sediment rich ice that were transported and consequently buried by the Jokulhlaups. It was found in field observations and laboratory simulations done by Maizels in 1992 that ramparts form around the edge of kettle holes that are generated by Jokulhlaups. The development of distinct types of ramparts depend on the concentration of rock fragments contained in the melted ice block and how deep the block was buried by sediment.[3]
Most kettle holes are no larger than 2 kilometers in diameter, although select kettles in the midwest of the United States have exceeded 10 kilometers. Additionally, the general depth of most kettles are less than 10 meters.[4] In most cases kettle holes eventually fill with water, sediment, or vegetation. Kettle holes are not fed by rivers or streams, so they rely on precipitation, the groundwater table, or a combination of the two. Kettles that are full of water year-round are called kettle lakes or ponds. Kettles that are not affected by the groundwater table will usually be empty during the warm summer months[1] If water in a kettle becomes acidic due to decomposing organic plant matter, it becomes a kettle bog. Kettle bogs are closed systems because they have no water source other than precipitation. Both acidic kettle bogs and fresh water kettles are important ecological niches for some symbiotic species of flora and fauna [2].
The Kettle Moraine is a region of Wisconsin, covering an area from Green Bay to south-central Wisconsin, and has numerous kettles, moraines and other glacial features. It has many kettle lakes, some of which are 100 to 200 feet deep. Kettle Point, Ontario, a First Nation community on Lake Huron in Ontario, Canada has many examples of kettles, hence the name.
Pothole lakes dot the landscape of the Northern Hemisphere in the American and Canadian prairies, the Russian steppes, and throughout northern Siberia. Some of these lakes are far from agricultural land and settled areas, so they have fairly clear and unpolluted waters. Scientists use satellite images of these glacial kettle lakes to measure water clarity and to make environmental assessments. Scientists also monitor these lakes to study climate change. Researchers reported in Science that over the past 30 years, some glacial kettle lakes in northern Siberia have drained as the region has warmed and the permafrost beneath the lakes has "cracked," allowing lake water to drain out.
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[edit] Examples of kettle lakes
[edit] See also
[edit] External links and References
- Geology of Ice Age National Scientific Reserve of Wisconsin NPS Scientific Monograph No. 2
- The genesis of the northern Kettle Moraine, Wisconsin - PDF
- Geology of the Adirondack Park
- Pothole Lakes in Siberia. NASA Earth Observatory. Retrieved on May 2, 2006.
[edit] Notes
- ^ Bennet, M and Glasser, N: Glacial Geology:Ice Sheets and Landforms, page 262. John Wiley and Sons, 1997
- ^ Tarbuck, E and Lutgens, F:Earth, page 351. Prentice Hall, 2002
- ^ Bennett, M and Glasser, N:Glacial Geology: Ice Shetts and Landforms, page 267. John Wiley and Sons, 1997
- ^ Tarbuck, E and Lutgens, F:Earth, page 351. Prentice Hall, 2002