A thaw slump.
Thaw slumps are the Arctic's version of landslides. They are usually found on steep slopes above bodies of water. Slumping occurs when slopes are undercut by wave or stream action and the soft soil collapses, creating a "thaw slump". This slumping may continue for a long period of time as the insulating layer of soil and peat is steadily stripped away. Melting can continue into the permafrost as the summer sun causes even more soil to slump. One measured slump has been observed slowly eating into the landscape at a rate of 1 km per decade!
Natural processes are not the only trigger for thaw slumps. Mini slumps may occur where vehicle tracks have dug into the fragile tundra landscape. This damage may take many years to heal.