Permafrost Landscape Features

Abstract Permafrost underlies the tundra of the circumpolar North. The landforms of permafrost regions are formed from the development or thawing of ground ice. The most ubiquitous features in tundra lowlands are ice-wedge polygons, the irregular nets of three- to seven-sided units at the surface of the landscape. The boundaries of the polygons are ice wedges, developed in cracks that open at temperatures below − 10 °C as the ground contracts in winter. The little, conical, ice-cored hills that occur in some tundra landscapes, pingos, are the iconic landforms of permafrost terrain. They develop as growing ice deforms the overlying permafrost, either in drained lake basins, as the unfrozen ground in the former lake bottom freezes back, or at the base of hillslopes where hydraulic pressure may supply water to maintain ice growth. Landforms associated with thawing permafrost are also prevalent in the tundra because permafrost degradation may be initiated by local disturbance as well as climate warming. Thermokarst (thaw) lakes are common features of ice-rich terrain. They commonly expand laterally at a relatively steady rate, but the rate of deepening reduces over time. Retrogressive thaw slumps form where ice-rich permafrost is exposed by erosion of lake shores, riverbanks, and at the coast. These slumps develop rapidly and have become especially prominent in landscapes that contain buried glacier ice remnant from the last glaciation. Development of all these features has been affected by climate change enhancing the probability of near-surface permafrost thaw.