The Role of Ground Ice

Abstract

The ice content of permafrost soils has a large impact on processes that occur when permafrost thaws; exposed ground ice is the primary cause of destructive abrupt thaw processes. This chapter presents the origin of common forms of ground ice: segregation ice, ice wedges and larger ground ice bodies. The presence of ground ice is expressed at the surface as geomorphological features such as ice wedge polygon networks, palsas and pingos. A processes that is important for transfer of carbon in permafrost soils is cryoturbation; it is also linked to micro-relief at the soil surface in the shape of various forms of patterned ground. The processes and landforms that result from thawing ground ice are discussed: erosional forms such as cryogenic landslides. Next, permafrost has a profound effect on the hydrology; a frozen subsurface acts as a barrier to groundwater movement. This affects also runoff and river discharge, which are further determined by water storage as snow in winter, and its sudden release in spring during snowmelt. Permafrost thaw results in hydrological changes: the development of thaw lakes and increased groundwater flow. The chapter concludes with a short presentation of geophysical methods to detect and map ground ice and permafrost in the subsurface.