<P> A glacier (US: / ˈɡleɪʃər / or UK: / ˈɡlæsiə /) is a persistent body of dense ice that is constantly moving under its own weight; it forms where the accumulation of snow exceeds its ablation (melting and sublimation) over many years, often centuries . Glaciers slowly deform and flow due to stresses induced by their weight, creating crevasses, seracs, and other distinguishing features . They also abrade rock and debris from their substrate to create landforms such as cirques and moraines . Glaciers form only on land and are distinct from the much thinner sea ice and lake ice that form on the surface of bodies of water . </P> <P> On Earth, 99% of glacial ice is contained within vast ice sheets in the polar regions, but glaciers may be found in mountain ranges on every continent including Oceania's high - latitude oceanic islands such as New Zealand and Papua New Guinea . Between 35 ° N and 35 ° S, glaciers occur only in the Himalayas, Andes, Rocky Mountains, a few high mountains in East Africa, Mexico, New Guinea and on Zard Kuh in Iran . Glaciers cover about 10 percent of Earth's land surface . Continental glaciers cover nearly 13,000,000 km (5 × 10 ^ sq mi) or about 98 percent of Antarctica's 13,200,000 km (5.1 × 10 ^ sq mi), with an average thickness of 2,100 m (7,000 ft). Greenland and Patagonia also have huge expanses of continental glaciers . </P>

When a glacial valley is partly filled by an arm of the sea this type of glacier is formed