Cryogenic Landslides in the West-Siberian Plain of Russia: Classification, Mechanisms, and Landforms

Cryogenic landslides are the main relief-forming process on the Northern part of West Siberian Plain. This chapter discusses the theory of cryogenic landslides and suggests classification method based on mechanisms, specific landforms—manifestations of various landslide processes. The study is based on the long-term field observations at Research station “Vaskiny Dachi” in Central Yamal, as well as occasional observations in other areas. Two main types of cryogenic landslides were distinguished based on mechanism and mode of displacement. They are (1) earth/mud flows (retrogressive thaw slumps) and (2) translational landslides (active-layer detachments). The first type results from thawing of massive ground ice within permafrost layers, while the second type is caused by the thawing of ice lenses in the active-layer base (transient layer). Distinguished are specific landforms: (1) thermocirques, and (2) landslide cirques. Landslide cirques are considered to start at a subsequent stage of thermocirque after the massive ground ice layer is exhausted or buried by landslide masses. The thermocirque changes are noted within years and decades, while new landslides within landslide cirques are separated by several centuries. As landslide masses bury organic material of soil and vegetative canopy, it is possible to use radiocarbon dating method to know the age of the landslides. Shear surfaces of ancient landslides are overgrown by abnormally high willow shrubs which allow the use of dendrochronologic method in the analysis of landslide cirque development.