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 depths at distinct geoecological sites were carried out in two measuring cycles 1995/96 and 1997/98 lasting almost 11 month. The detailed studies focussed on mountain areas of the northern Mongolian Altai (Turgen-Kharkhiraa mountains) 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 moisture can infiltrate into the soils. Due to higher temperature the precipitation (mainly min) in the basins evaporate and rapid drying out of the soils occurs. The main controlling factor for the cryogenic processes in the mountains (especially of solifluction) therefore is the amount of precipitation during spring time. The freeze-thaw cycles during the relatively dry autumn season are subordinated factor for the geomorphological activity. At sites with low radiation, as caused e. g. through shading effects in relief, the freeze-thaw cycles displace towards the summer with more precipitation. Therefore, periglacial processes on low-radiation sites are laced to the strength 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 precipitation during the highest freeze-thaw cycles in the spring and autumn seasons and determines cryogenic processes and periglacial forms (e.g.earth hummocks, patterned grounds). This local influence can be reinforced by effects of radiation, In the Larix forests at northern slopes a cooler local climate with reduced transpiration in the summer allows the preservation of frozen ground and/or permafrost.