Thermokarst
As Thermokarst or Kryokarst a land forming process is periglacial by superficial thawing permafrost called. The original derivation of the term thermokarst comes from the certain similarity of the emerging land forms with the classic carbonate karst ; however, the shaping processes differ significantly. Geomorphological processes that have arisen due to fluidity and temperature changes are called pseudokarst .
Development process
The thawing of permafrost soil melts the ground ice contained in the soil . The loss of volume gives rise to characteristic land forms through the subsidence of the land surface. The term thermokarst only includes the pure subsidence due to loss of volume, but not erosion caused by flowing water. If mechanical erosion also occurs due to flowing water, it is called thermal erosion. In a broader sense, the resulting relief structures are also referred to as thermokarst. In general, the formation of thermokarst is linked to a high ice content ( ice wedges , segregation ice ) in the soil. The higher the ice volume, the stronger the thermokarst can develop as the ice melts. The irregular subsidence of the land surface creates depressions that quickly fill with water and create so-called thermokarst lakes. Due to their higher heat capacity compared to the air and the ground, these water bodies promote the further thawing of the permafrost soil under the lake and a progressive subsidence. By expanding horizontally, thermokarst lakes can unite to form larger bodies of water.
Distribution areas
Thermokarst is widespread in the permafrost regions of the world: Siberia , Alaska, and Canada . Thermokarst also occurs to a lesser extent in sedimentary deposits in high mountain regions . Thermokarst is a typical post-glacial formation that began particularly strongly due to global warming with the beginning of the current warm period , the Holocene .
Different types
There are different forms of thermokarst: thermokarst lakes, thermokarst depressions, and thermokarst hills. Special forms are the oriented thermokarst lakes that are found in the lowlands of the Arctic coastal areas. These lakes are clearly stretched along a longitudinal axis and are therefore mostly elliptical, with the orientation of the longitudinal axis deviating only slightly from each other in all lakes. A widespread hypothesis for this phenomenon tries to explain the origin of the sea axis orientation with strongly prevailing wind directions perpendicular to the longitudinal axis of the lakes.
Impact on the environment
Thermokarst can become a highly explosive topic in the course of global warming and the warming of the permafrost. Thermokarst has been releasing frozen plant residues in the permafrost for decades to decompose, releasing the greenhouse gases methane and carbon dioxide . Such self-intensified processes of destruction would not be reversible on a short time scale of a few centuries, as the original storage dragged on for many thousands of years. This is one of the tipping points of global warming . The formation of thermokarst can also pose a threat to existing or yet to be built infrastructure in the arctic areas (pipelines, buildings, runways, etc.).
