Thermokarst
Thermokarst is known as the forming of a landscape due to melting of permafrost ground. It can be caused by human activity or nature itself. Agriculture, deforestation or the construction of buildings as well as natural erosion most commonly lead to thermokarst, since the insulating layer of vegetation is being removed. The size of the formed landscape is inevitably connected with the amount of ice beneath the surface.
Thermokarst is an indicator of a warming climate since rising temperatures cause the permafrost ground to thaw. Between 1954 and 2003 the annual average temperature in the arctic regions has risen about 1 °C. The recorded average temperature in the wintertime show an increase of about 2 to 4 °C. The warmer the temperatures get the deeper the soil thaws and the active layer thickens. Thus the integrity of the soil is no longer guaranteed and can therefore lead to detachment slides on slopes.
Along with rising temperatures comes an increase of precipitation. The melting water of the thawing permafrost and the rainwater start pooling in small sinks or valleys. The presence of warmer water on the surface compared to the temperature of the underlying ground causes melting of the ice and the process of thermokarst begins.
Small ponds and later larger lakes form out of the melting water on the surface as the water cannot drain away through the deeper frozen ground. Sometimes this accumulation of water takes place in caverns under the surface. Since the caverns are not stable the peril of collapse is immense. Once collapsed the everything on the surface is being absorbed by the water.
The landscape which remains after this process is characterized by chaoticly arranged sinkholes, tunnels, caverns and hummocks (small hills). This landscape is called thaw settlement or thermokarst terrain.
The movement of heavy gear on thawed permafrost ground or an increase of ground-temperature resulting from buildings might cause thermokarst with negative effects on the local infrastructure.
To avoid greater damage the knowledge of the geoglogical circumstances is inevitable. In Alaska for example it is common to build houses on stilts to prevent a melting of the ice.
Map of permafrost area:
Sources:
Nikolas Sellheim, Jan Banneitz
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