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 to 4200 m a.s.l., which means that if the Plateau were 1000 m lower than present, there would be hardly any permafrost. The permafrost is ice-poor, because during the Quaternary, the area was unglaciated and little water was available for the formation of massive ground ice. Furthermore, today's climate is arid and little moisture is available for segregated and pore ice formation. As a result, mid-portion desiccation of the active layer does not occur to the same extent as in high latitudes. Permafrost temperature on the Plateau depends mainly upon altitude and varies irregularly with latitude. Permafrost is warm and thin compared with high latitude (polar) permafrost in both North America and Russia, and thus more sensitive to changes in climate and surface conditions. A recent warming trend in ground temperature has been monitored, and, if maintained, permafrost will become relict within the next ca. 150 years. Permafrost features are few due to the arid environment. Many of the pingos on the Plateau are genetically associated with faults, and therefore of the open-system type. Faults are the most powerful factor disturbing the thermal regime of the plateau permafrost.