Crevasse in the context of Huayna Potosí

A glacier (US: /ˈɡleɪʃər/; UK: /ˈɡlæsiə/ or /ˈɡleɪsiə/) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires distinguishing features, such as crevasses and seracs, as it slowly flows and deforms under stresses induced by its weight. As it moves, it abrades rock and debris from its substrate to create landforms such as cirques, moraines, or fjords. Although a glacier may flow into a body of water, it forms only on land and is distinct from the much thinner sea ice and lake ice that form on the surface of bodies of water.

On Earth, 99% of glacial ice is contained within vast ice sheets (also known as "continental glaciers") in the polar regions, but glaciers may be found in mountain ranges on every continent other than the Australian mainland, including Oceania's high-latitude oceanic island countries such as New Zealand. Between latitudes 35°N and 35°S, glaciers occur only in the Himalayas, Andes, and a few high mountains in East Africa, Mexico, New Guinea and on Zard-Kuh in Iran. With more than 7,000 known glaciers, Pakistan has more glacial ice than any other country outside the polar regions. Glaciers cover about 10% of Earth's land surface. Continental glaciers cover nearly 13 million km (5 million sq mi) or about 98% of Antarctica's 13.2 million km (5.1 million sq mi), with an average thickness of ice 2,100 m (7,000 ft). Greenland and Patagonia also have huge expanses of continental glaciers. The volume of glaciers, not including the ice sheets of Antarctica and Greenland, has been estimated at 170,000 km.

A glacier (US: /ˈɡleɪʃər/ GLAY-shər) 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. Because glacial mass is affected by long-term climate changes, e.g., precipitation, mean temperature, and cloud cover, glacial mass changes are considered among the most sensitive indicators of climate change. There are about 198,000 to 200,000 glaciers in the world.

A serac (/səˈræk, ˈsɛræk/; from Swiss French sérac [seʁak], a type of cheese) is a block or column of glacial ice, often formed by intersecting crevasses on a glacier. Commonly house-sized or larger, they are dangerous to mountaineers, since they may topple with little warning. Even when stabilized by persistent cold weather, they can be an impediment to glacier travel.

Seracs are found within an icefall, often in large numbers, or on ice faces on the lower edge of a hanging glacier. Notable examples of the overhanging glacier edge type are well-known obstacles on some of the world's highest mountains, including K2 at "The Bottleneck" and Kanchenjunga on the border of India and Nepal. Significant seracs in the Alps are found on the northeast face of Piz Roseg, the north face of the Dent d'Hérens, and the north face of Lyskamm.

Ski touring is skiing in the backcountry on unmarked or unpatrolled areas. Touring is typically done off-piste and outside of ski resorts, and may extend over a period of more than one day. It is similar to backcountry skiing but excludes the use of a ski lift or transport.

Ski touring combines elements of Nordic and alpine skiing and embraces such sub-disciplines as Telemark and randonnée. A defining characteristic is that the skier's heels are "free" – i.e. not bound to the skis – in order to allow a natural gliding motion while traversing and ascending terrain which may range from perfectly flat to extremely steep.

Mountain warfare or alpine warfare is warfare in mountains or similarly rough terrain. The term encompasses military operations affected by the terrain, hazards, and factors of combat and movement through rough terrain, as well as the strategies and tactics used by military forces in these situations and environments.

Mountain ranges are of strategic importance since they often act as a natural border and may also be the origin of a water source such as the Golan Heights. Attacking a prepared enemy position in mountain terrain generally requires a greater ratio of attacking soldiers to defending soldiers than a war conducted on level ground. Mountains present natural hazards such as lightning, strong gusts of wind, rockfalls, avalanches, snowpacks, ice, extreme cold, and glaciers with their crevasses; in these ways, it can be similar to cold-weather warfare. The generally uneven terrain and the slow pace of troop and material movements are additional threats to combatants. Movement, reinforcements, and medical evacuation up and down steep slopes and areas in which even pack animals cannot reach involves an enormous exertion of energy.

Ice calving, also known as glacier calving or iceberg calving, is the breaking of ice chunks from the edge of a glacier. It is a form of ice ablation or ice disruption. It is the sudden release and breaking away of a mass of ice from a glacier, iceberg, ice front, ice shelf, or crevasse. The ice that breaks away can be classified as an iceberg, but may also be a growler, bergy bit, or a crevasse wall breakaway.

Calving of glaciers is often accompanied by a loud cracking or booming sound before blocks of ice up to 60 metres (200 ft) high break loose and crash into the water. The entry of the ice into the water causes large, and often hazardous waves. The waves formed in locations like Johns Hopkins Glacier can be so large that boats cannot approach closer than three kilometres (1+1⁄2 nautical miles). These events have become major tourist attractions in locations such as Alaska.