As Palsa (plural: palsas, also Palsen ), refers to a low oval ground survey in areas with permafrost, which in the ground by a core consisting of eisreichem frozen peat and ice lenses formed in bogs. A Palsa is similar to a Pingo, from a frozen core and the overlying ( raised ) floor material, in case of Palsa mostly peaty soil.
A Palsa needed to form its core (consisting of frozen peat and several ice lenses ) larger amounts of water, which is why its existence is bound to peat soils, which can store enormous amounts of water in their pore space. At the points where in a bog the winter freezing front penetrates faster ( by a thinner snow cover), the ice accumulation is in contrast preference to the surrounding moorland. Are forming ice lenses, which grow at the expense of the surrounding water, where they exercise by the volume expansion of ice during freezing pressure on the surrounding soil and thus squeeze out water from the soil pores, which in turn can freeze onto the ice lenses and causes further volume expansion. It develops a self- reinforcing mechanism. In the case of palsas the squeezing of water from the pore space, however, is not crucial, as the peaty soil is water- saturated and therefore already have enough water available for the Eiskernwachstum available.
Due to the progressive volume expansion of the freezing ice overlying the peat layer is lifted gradually up, and the more so the more the core grows. A Palsa arose. The frozen core of a Palsa shows a layering caused by the different ( winter ) freeze intervals and Eissegregation.
Palsas arise mainly in bogs and are hence its name to a certain Moor Type: the Palsamoor.
Even outside of bogs there are similar forms, which are counted because of their size to the palsas.
Palsas, as pingos, typical forms of permafrost area and therefore found in northern America, in Siberia, in northern Scandinavia, Greenland and Iceland, in the area of the Antarctic as well as in Alaska and - rarely - on Spitsbergen.
Remnants of glacial Palsen can also be found in bogs in Central Europe, such as in the High Fens in the German -Belgian border.
Differences and similarities between pingos and palsas
Palsas are very similar, but with heights of between about 0.5 and 2 meters and lengths between about 5 and 25 meters significantly smaller than pingos in their morphology and origin to the pingos. Furthermore palsas occur in contrast to Pingos not in isolation but usually in groups, along with other palsas, for example in Palsamoor.
Both palsas and Pingos caused by the freezing of water in an ice core. In palsas but not necessarily hydrostatic pressure must be present ( for water injection), as the peaty soil is saturated with water and is able to store large amounts of water, so that from the outset, first, sufficient water to form the ice lens available. For the Pingogenese authoritative (especially for Pingos the closed system ), however, water injection is due to hydrostatic pressure, which is caused by the volume expansion of the ice as a result of freezing.