What causes thermokarst?
Thermokarst, land-surface configuration that results from the melting of ground ice in a region underlain by permafrost. In areas that have appreciable amounts of ice, small pits, valleys, and hummocks are formed when the ice melts and the ground settles unevenly.
What is thermokarst in geography?
Periglacial Processes in Glacial Environments Thermokarst is an erosional process unique to permafrost with excess ice; it is defined as ‘the process by which characteristic landforms result from the thawing of ice-rich permafrost and/or melting of massive ice’ (van Everdingen, 1998).
Does permafrost thaw in summer?
In permafrost regions, the topmost layer of the soil—the active layer—thaws enough in summer to sustain plants and feed animals. When conditions are too cold for microbes to carry out these functions, frozen ground can hold the undecomposed remains of plants and animals for hundreds or even thousands of years.
How do oriented lakes form?
[1] In the classic model for oriented thaw lakes, sublittoral shelves form by wind-driven circulation near shorelines oriented perpendicular to the wind, protecting the adjacent banks from thaw and wave cut erosion.
How do ice wedge polygons form?
The frozen water forms wedges of ice in the soil. In summer, the active layer and the tops of the ice wedges melt. until the soil above the wedges is pushed up, forming ridges. If you look down from above, these ridges create a blocky pattern on the ground, called polygons.
What is a retrogressive thaw slump?
Retrogressive thaw slumps (RTS) are spectacular lateral thermokarst features occurring in ice-rich permafrost regions. They develop along streams or coastlines and expand inland to form landslide-like U-shaped scars exceeding a kilometer size in selected locations.
Does thawed mean unfrozen?
to cause to change from a frozen to a liquid or semiliquid state; melt. to free from the physical effect of frost or extreme cold; bring to a more normal temperature, especially to room temperature: I took the steaks out of the freezer and thawed them. to make less cold, formal, or reserved.
What does fully thawed mean?
thaw verb (BECOME NOT FROZEN) to (cause to) change from a solid, frozen state to a liquid or soft one, because of an increase in temperature: Allow the meat to thaw completely before cooking it.
What kind of Lake is a thermokarst lake?
A thermokarst lake, also called a thaw lake, tundra lake, thaw depression, or tundra pond, refers to a body of freshwater, usually shallow, that is formed in a depression formed by thawing ice-rich permafrost.
What are the effects of thermokarst in Alaska?
Thermokarst has been observed to result in the partial or complete destruction of some ecosystems and their conversion to other types of ecosystems. In one lowland area in central Alaska, permafrost degradation is widespread and rapid, causing large shifts in ecosystems from birch forests to fens and bogs ( Figure 14 ).
How is thermokarst related to permafrost thaw?
In addition to direct climate warming and permafrost thaw, thermokarst can be induced by active layer slope erosion, slumping, soil creep, and deflation, which lead to a thinning of the active layer and a new thermal equilibrium ( Koster, 1994 ). Thermokarst subsidence results in the formation of thaw depression alases, and thaw lakes.
How does thermokarst affect the Little Ice Age?
Thermokarst subsidence results in the formation of thaw depression alases and thaw lakes. Since the Little Ice Age over 40% of the permafrost region has been affected by thermokarst subsidence, and new thermokarst terrain is currently forming ( Osterkamp et al., 2000; Osterkamp, 2007 ).