Freezing and thawing of water can cause creep, which is

slow downhill movement

Creep:

(of a thing) move very slowly at an inexorably steady pace.

"the fog was creeping up from the marsh"

(of a plant) grow along the ground or other surface by means of extending stems or branches.

"tufts of fine leaves grow on creeping rhizomes"

(of a plastic solid) undergo gradual deformation under stress.

Source: Google definitions