A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation (melting and sublimation) over many years, often centuries. At least 0.1 km2 in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight. Crevasses, seracs, and other distinguishing features of a glacier are due to its flow. Another consequence of glacier flow is the transport of rock and debris abraded from its substrate and resultant landforms like cirques and moraines. Glaciers form on land, often elevated, and are distinct from the much thinner sea ice and lake ice that form on the surface of bodies of water.