ice has 10 percent greater volume than water, so it continues to exert pressure on the ground. thermal expansion and contraction can cause cracks to develop in the permafrost. during the thaw season in the freeze-thaw cycle, water gets into the cracks and forms veins of ice called ice wedges. ice wedges enlarge with successive seasons of freezing and thawing. some ice wedges that have been buried for centuries are revealed during excavations or landslides.