Yamal Peninsula, Permafrost-related Terrain Phenomena: Tabular Ground Ice, Thermocirques and Gas Emission Craters

Leading controls of terrain development in the permafrost zone are various types of ground ice. The paper deals with the formation of specific landforms in the continuous permafrost of Yamal Peninsula with tabular ground ice in the geological section. Processes related to tabular ground ice (TGI, thick and extended ground-ice layers) thaw are triggered by climate warming. Air temperature rise in most environments results in higher ground temperature and deeper active layer (the layer in the upper part of permafrost, which thaws in summer and freezes back in winter). Warming of the last decades had caused an increase in the rate of thaw reaching the upper surface of TGI and starting thermodenudation. Climate warming may also lead to increase in ground temperature, which triggers gas-emission crater formation through decomposition of methane clathrates up to formation of high pressure under the TGI layer until it breaks. Thus, TGI serves as a source of water for saturation of slope deposits and a shear surface for movement of these deposits down slope under the action of both heat and gravity. The role of TGI in the process of gas emission crater formation is not related to its melting as in thermodenudation, but serves as an impermeable to gas, plastic layer. Gas released from decomposition of methane clathrates accumulates beneath the ice layer deforming it to form a gas-inflated mound—predecessor of the crater. Thermocirques, resulting from thermodenudation, and gas emission craters evolve with time depending on the ice extent and warming trend.