thufur
perennial hummocks formed in either the active layer in permafrost areas, or in the seasonally frozen ground in non-permafrost areas, during freezing of the ground.
Image
These big lumps in the ground are called thufur. Thufur can form when the ground freezes and thaws. These thufur are in Iceland.
Reinhold Richter
Topic(s):
frozen ground or permafrost