Freezing and thawing of water can cause creep, which is

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

Iread this book last year so take this with a grain of salt.gene jumps from the tree to compete with finny due to the fact that gene is always trying to do better than finny. he is put under the grasp of peer pressure due to finny almost forcing him to do this. ever since he first jumped finny kept pressuring him to jump since he thought gene enjoyed jumping.rather than uses this answer you should probably just reread chapters 3-4