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

The high altitude-induced permafrost of the Tibet Plateau reflects a g eothermal 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 segrega tion and thermal contraction cracking, are not widespread, and pattern ed ground phenomena (circles and nets) are restricted to sites of loca lly high moisture and variable grain size. Ice-rich sediments on north -facing slopes occur mainly as silty colluviums derived from local arg illaceous bedrock. Mean annual ground temperatures are usually warmer than -3.5 degrees C. Temperatures at 20 m depth have increased by an a verage of 0.2 to 0.3 degrees C during the past 15 years. If one assume s continued warming, permafrost is likely to become relict within the next 200 years, and an increase in degradation (i.e. thermokarst proce sses) is to be expected.