Geology Reference
In-Depth Information
8
Thermokarst
Thermokarst processes achieve their greatest importance in terrain underlain by ice-
rich and unconsolidated sediments. In alpine regions, in areas underlain by consoli-
dated and resistant bedrock, and in the extremely arid polar deserts, thermokarst
modifi cation is less apparent. Thermokarst-affected landscapes occur on a regional
level in central and northern Siberia and the western North American Arctic.
The thaw of permafrost, consequent upon climate warming, poses special problems
at the southern fringes of discontinuous permafrost. Human-induced thermokarst
continues to present problems as regards settlement and resource development in per-
mafrost regions.
An understanding of thermokarst is essential to the correct interpretation of struc-
tures and sediments that resulted from the degradation of permafrost in mid-latitudes
during the Pleistocene.
8.1. INTRODUCTION
The term “thermokarst” was fi rst used by M. M. Ermolaev (1932a, b) to describe irregular,
hummocky terrain due to the melt and thermal abrasion of “ice-complex” sediments
exposed along the coastal lowlands of the Laptev Sea, northern Siberia. Subsequently, the
term has been applied to the processes associated with the thaw of permafrost that lead
to local or widespread collapse, subsidence, erosion, and instability of the ground surface.
Although J. Dylik (1968) argued that the term should be reserved for the melt of under-
ground ice as opposed to buried glacier or surface ice, it is now accepted that the term
applies generally to the thaw of icy permafrost, irrespective of the origin of the ice con-
tained within it. In fact, the term “thermokarst” now encompasses the whole range of
geomorphic effects resulting from subsurface water on landforms in permafrost regions.
Thermokarst is not a variety of karst. The latter is a term which is applicable to lime-
stone areas where the dominant process, solution, is a chemical one. Underlying the
development of thermokarst is a physical, i.e. thermal, process, namely, that of ground ice
melting. Thermokarst is peculiar to regions underlain by permafrost.
There is a large Russian literature on thermokarst processes and phenomena (Grave
and Nekrasov, 1961; Kachurin, 1938, 1955, 1962; Popov, 1956; Popov et al., 1966
Romanovskii, 1977a; Romanovskii et al., 2000; Shamanova, 1971; Shur, 1977, 1988a, b;
Tolstov, 1961). In parts of central and eastern Siberia, it is thought that over 40% of the
land surface has been affected, at some time or another, by thermokarst processes (Are,
1973; Czudek and Demek, 1970; Soloviev, 1962, 1973b). In the permafrost regions of
North America, thermokarst phenomena were fi rst described from central Alaska
(Hopkins, 1949; Péwé, 1954) and then from the lowlands of northwestern Arctic Canada
