"In areas not overlain by ice, [permafrost] exists beneath a layer of soil, rock or sediment, which freezes and thaws annually and is called the "active layer". [...] Active layer thickness varies with the season, but is 0.3 to 4 meters thick (shallow along the Arctic coast; deep in southern Siberia and the Qinghai-Tibetan Plateau)"
So I guess the freeze/thaw may allow heavier object to sink in over time, and there may be rivers, earth movement (related to permafrost, or unrelated - like landslides- (see https://en.wikipedia.org/wiki/Permafrost#Landforms for examples), and other processes that deposit earth.
I don't know though.
BTW stunning picture of block of ice in permafrost https://en.wikipedia.org/wiki/File:Permafrost_-_Massive_buri... It looks like the mcGuffin for a horror/sci-fi film.