Soil temperature measurements from the Mongolian Altai as indicators for periglacial geomorphodynamics in continental mountain areas

In the continental areas of Central Asia periglacial features and processes are mainly determined through existence of soil humidity during the freeze -thaw cycles. Hourly measurements of the soil temperatures of different dep ths at distinct geoecological sites were carried out in two measuring cycle s 1995/96 and 1997/98 lasting almost 11 month. The detailed studies focusse d on mountain areas of the northern Mongolian Altai (Turgen-Kharkhiraa moun tains) in elevations between 1775 and 2760 m a. s.l. The main difference in the intensity of periglacial processes in the basins and mountains areas, respectively, can be seen in the freeze-thaw cycles in spring time, mainly in April. In this time the precipitation in the mountains is still snow fall and mois ture can infiltrate into the soils. Due to higher temperature the precipita tion (mainly min) in the basins evaporate and rapid drying out of the soils occurs. The main controlling factor for the cryogenic processes in the mou ntains (especially of solifluction) therefore is the amount of precipitatio n during spring time. The freeze-thaw cycles during the relatively dry autu mn season are subordinated factor for the geomorphological activity. At sit es with low radiation, as caused e. g. through shading effects in relief, t he freeze-thaw cycles displace towards the summer with more precipitation. Therefore, periglacial processes on low-radiation sites are laced to the st rength of the summer precipitation. On the other hand, the frequent freeze- thaw cycles at sites with high radiation drop towards the dry winter season and therefore, the periglacial activity is low at such sites. Accumulation of snow (e. g, in nivation hollows) and/or the occurrence of frozen ground could guarantees sufficient soil humidity apart from the distribution of p recipitation during the highest freeze-thaw cycles in the spring and autumn seasons and determines cryogenic processes and periglacial forms (e.g.eart h hummocks, patterned grounds). This local influence can be reinforced by e ffects of radiation, In the Larix forests at northern slopes a cooler local climate with reduced transpiration in the summer allows the preservation o f frozen ground and/or permafrost.