CLIMATE CONTROLS AND HIGH-ALTITUDE PERMAFROST, QINGHAI-XIZANG (TIBET) PLATEAU, CHINA

The high altitude-induced permafrost of the Tibet Plateau reflects a geothermal regime characterized by a strong diurnal pattern, high solar radiation inputs at the surface, and a high geothermal gradient. As a result, the permafrost is relatively 'warm' and sensitive to thermal disturbance. Typical permafrost-related processes, such as ice segregation and thermal contraction cracking, are not widespread, and patterned ground phenomena (circles and nets) are restricted to sites of locally high moisture and variable grain size. Ice-rich sediments on north-facing slopes occur mainly as silty colluviums derived from local argillaceous bedrock. Mean annual ground temperatures are usually warmer than -3.5 degrees C. Temperatures at 20 m depth have increased by an average of 0.2 to 0.3 degrees C during the past 15 years. If one assumes continued warming, permafrost is likely to become relict within the next 200 years, and an increase in degradation (i.e. thermokarst processes) is to be expected.