Development of a thermokarst lake and its thermal effects on permafrost over nearly 10 yr in the Beiluhe Basin, Qinghai-Tibet Plateau

The thermal influence of a thermokarst lake on permafrost in the Beiluhe -Basin of the Qinghai-Tibet Plateau was examined over nearly 10 yr (2006-2014), and lake development involved both downward and lateral heat transfers. Downward heat transfer rapidly thawed 8 m of permafrost beneath the lake bottom center, forming a through talik (i. e., year-round unfrozen ground in perma-frost that is open to top and unfrozen layers beneath permafrost) by October 2008. Lateral heat transfer resulted in permafrost temperatures and permafrost table depths at the lakeshore that decreased with distance from the lake. In 2014, the maximum differences in the mean annual ground temperature and permafrost table depth within 75 m of the lake were 0.4 degrees C and 0.8 m, respectively. The horizontal extent of the talik has expanded gradually from the lake center to the lakeshore. The development of the thermokarst lake on the Qinghai-Tibet -Plateau is discussed in terms of four stages, initiation, development, stabilization, and termination, resulting from changes in the surface energy balance.