206
Climatic Geomorphology
The most common landforms are the thaw lakes. They are shallow lakes enclosed in
basins that result from subsidence due to the thawing of frozen ground, up to 4 m deep
and 2 km wide (French, 1996). The thaw lakes develop primarily in flat areas and are
silted up quite rapidly by peat and fine-grained sediments rarely exceeding 3000 years
old. Where they form groupings with parallel alignment, they are called oriented lakes.
I Y r T I v
lb
II
Ilia
y
-/
~,d. d..k _1 _1 ,~. y
IIIc ~_
~~~_~
~V V V
y
y
IVa
2L.
Figure 8.38. Main development stages of the alasas. (la) Original surface with syngenetic ice wedges;
(lb) initial stage of thermokarst-baydjarakhs; (II) dujoda; (IIIa) youthful alas; (IIIb) mature alas; (IIIc)
senile alas; (IVa) khonu with pingo; (IVb) khonu with depression resulting from the collapse of the pingo.
1, collapsed wedges; 2: pines and grass; 3, water; 4, slope movements; 5, alas deposits; 6, epigenetic
ice veins; 7, pingo; 8, upper limit of the permafrost (Czudek and Demek, 1970b, based on Soloviev
publications).