Dead ice is the ice in a part of a
glacier
A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...
or
ice sheet
In glaciology, an ice sheet, also known as a continental glacier, is a mass of glacier, glacial ice that covers surrounding terrain and is greater than . The only current ice sheets are the Antarctic ice sheet and the Greenland ice sheet. Ice s ...
that is no longer moving. As the ice melts, it leaves behind a
hummock
In geology, a hummock is a small knoll or mound above ground.Bates, Robert L. and Julia A. Jackson, ed. (1984). "hummock." Dictionary of Geological Terms, 3rd Ed. New York: Anchor Books. p. 241. They are typically less than in height and ten ...
y terrain known as dead-ice moraine. Dead-ice
moraine
A moraine is any accumulation of unconsolidated debris (regolith and Rock (geology), rock), sometimes referred to as glacial till, that occurs in both currently and formerly glaciated regions, and that has been previously carried along by a gla ...
is produced by the accumulation of
sediment
Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...
s carried by glaciers that have been left behind from ice melting. Features of such terrain include
kettle hole
A kettle (also known as a kettle hole, kettlehole, or pothole) is a depression or hole in an outwash plain formed by retreating glaciers or draining floodwaters. The kettles are formed as a result of blocks of dead ice left behind by retreating ...
s.
Landscapes forming
Veiki moraines in northern Sweden and Canada have been attributed to the erosion of extensive bodies of
till
image:Geschiebemergel.JPG, Closeup of glacial till. Note that the larger grains (pebbles and gravel) in the till are completely surrounded by the matrix of finer material (silt and sand), and this characteristic, known as ''matrix support'', is d ...
-covered dead ice.
Formation
Dead ice is created when a glacier or ice sheet experiences an increase in melting and accumulates debris from various sediment sources. The debris seeps into the ice, effectively covering the surface area.
This leads to the affected area becoming mixed with different types of debris, ultimately slowing the glacier's melting rate.
This process continues over and over, creating layers of ice and debris, until it forms dead ice. Dead ice most commonly occurs on
surge-type glaciers that have ceased moving.
It can also be found in any stagnant or debris-filled glacier landforms.
Melting
There are two types of ways dead ice can melt: backwasting and downwasting. Backwasting is when the dead ice melts parallel to an ice-wall or ice-cored slope. Backwasting is more likely to occur when an area is fully ice-cored.
Downwasting is when dead ice melts at its top and bottom surfaces. Both dead ice melting rates depend on the climate condition of the area it is in; however downwasting has several other factors that contribute to its process.
Another factor that affects both melting rates is the type of debris that covers the dead ice.
References
Glaciology
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