A kettle (kettle hole) is a shallow, sediment-filled body of water formed by retreating glaciers or draining floodwaters.

[edit] Overview

Kettle lakes in Siberia, adjacent to the Gulf of Ob (image right). The lake colors indicate amounts of sediment or depth; the deeper or clearer the water, the bluer the lake.

Kettles are fluvioglacial landform occurring as the result of blocks of ice calving from the front of a receding glacier and becoming buried partially to wholly by glacial outwash. Glacial outwash is generated when streams of meltwater flow away from the glacier and deposit sediment to form broad outwash plains called sandurs. When the ice blocks melt, kettle holes are left in the sandur. When the development of numerous kettle holes disrupt sandur surfaces, a jumbled array of ridges and mounds form, resembling kame and kettle topography.^[1] Kettle holes can also occur in ridge shaped deposits of loose rock fragments called till.^[2]

Kettle holes can 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 depends on the concentration of rock fragments contained in the melted ice block and on how deeply the block was buried by sediment.^[3]

Most kettle holes are less than two kilometers in diameter, although some in the U.S. Midwest exceed ten kilometers. Puslinch Lake in Ontario, Canada, is the largest kettle lake in Canada spanning 160 hectares (380 acres). Fish Lake in the North Central Cascade Mountains of Washington State, U.S.A., is 200 hectares (~550 acres).^[4]

A kettle in the Isunngua highland, central-western Greenland.

The depth of most kettles is less than ten meters.^[5] In most cases kettle holes eventually fill with water, sediment, or vegetation. If the kettle is fed by surface or underground rivers or streams it becomes a kettle lake. If the kettle receives its water from precipitation, the groundwater table, or a combination of the two, it is termed a kettle pond or kettle wetland, if vegetated. Kettle ponds that are not affected by the groundwater table will usually become dry during the warm summer months, in which case they are deemed ephemeral.[1]

If water in a kettle becomes acidic due to decomposing organic plant matter, it becomes a kettle bog or kettle peatland, if underlying soils are lime-based and neutralize the acidic conditions somewhat. Kettle bogs are closed ecosystems 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].

A kettle pond in the Hossa hiking area, Suomussalmi, Finland.

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 (61 m) 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. These lakes are monitored to study climate change. Science reported 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.

In September 2008 workers preparing a new foundation at the World Trade Center site discovered a deep pothole. ^[6]

[edit] Examples of kettle lakes

Numerous kettle lakes border the Denali Highway in Alaska.

[edit] See also

• Glacial landforms

[edit] References

[edit] External links

• 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. http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=17099. Retrieved 2006-05-02.