PERMAFROST ON THE TIBET PLATEAU, CHINA

The Tibet Plateau represents a unique permafrost environment, being a result of high elevation caused by land uplift in the order of 3000 m over the last 2 million years. Under present climatic conditions, the lower altitudinal limit of permafrost in the north is at approximate t o 4200 m a.s.l., which means that if the Plateau were 1000 m lower tha n present, there would be hardly any permafrost. The permafrost is ice -poor, because during the Quaternary, the area was unglaciated and lit tle water was available for the formation of massive ground ice. Furth ermore, today's climate is arid and little moisture is available for s egregated and pore ice formation. As a result, mid-portion desiccation of the active layer does not occur to the same extent as in high lati tudes. Permafrost temperature on the Plateau depends mainly upon altit ude and varies irregularly with latitude. Permafrost is warm and thin compared with high latitude (polar) permafrost in both North America a nd Russia, and thus more sensitive to changes in climate and surface c onditions. A recent warming trend in ground temperature has been monit ored, and, if maintained, permafrost will become relict within the nex t ca. 150 years. Permafrost features are few due to the arid environme nt. Many of the pingos on the Plateau are genetically associated with faults, and therefore of the open-system type. Faults are the most pow erful factor disturbing the thermal regime of the plateau permafrost.