Thaw Lakes and Thaw Sinks in the Imuruk Lake Area, Seward Peninsula, Alaska

Certain lakes and depressions in the Imuruk Lake area, Alaska, are ascribed to subsidence following the thawing of perennially frozen ground. The frozen, silty soils of the region contain large quantities of clear ice, which in volume greatly exceed the natural porosity of the unfrozen material. Melting of the clear ice results in surface subsidence; water accumulates in the resulting depressions. Thaw lakes are described, and mechanisms of enlargement and eventual drainage are discussed. The origins of drained thaw lakes and of thaw sinks are compared. Evidence is presented to show that the present climate in the Imuruk Lake area is sufficiently cold to form a small thickness of perennially frozen ground in previously unfrozen deposits but that the present large thickness of frozen ground probably is unstable under existing climatic conditions.