Activation of Cryogenic Earth Flows and Formation of Thermocirques on Central Yamal as a Result of Climate Fluctuations

Study area in continuous permafrost zone, characterized by tabular ground ice distribution, is known for active slope processes. In 90-s main attention was paid to translational landslides (active layer detachments). Due to climate trends summer temperature became warmer, active layer depth increased. As a result, active-layer base ice thawed and stopped development of translational landslides. At the same time, tabular ground ice table got involved into seasonal thaw and triggered earth flows at the lake shores, the second known type of cryogenic landslides found previously mainly at the sea coasts. Earth flows are the main process in thermal denudation: a complex of processes responsible for formation of thermocirques. Thermocirques are semi-circle shaped depressions resulting from massive ground ice thaw and removal of detached material downslope. Monitoring of thermocirque activation and development allows analyzing climatic controls of thermal denudation, and rates of thermocirque enlargement. At present in the Yamal Peninsula tundra predominance of processes associated with tabular ground ice thaw (cryogenic earth flows) over the processes associated with the ice formation at the bottom of the active layer (cryogenic translational landslides) is observed. This is caused by deepening of the active layer and exposure of the massive ground ice (tabular ground ice or ice-wedges) within permafrost to first seasonal and then perennial thaw. Activation of thermal denudation which started on Yamal Peninsula in summer 2012, is associated with extremely warm spring and summer of this year, and the warmest July of 2013. By the end of the warm season thawing of the top of icy permafrost and tabular ground ice on some slopes resulted in cryogenic landsliding in the form of earth flows and further thermocirque development. Thermocirques may form on slopes of various aspects but develop faster on south-facing slopes.