Serac in the context of "List of glaciers"

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.

Over 405 people have died attempting to reach—or return from—the summit of Mount Everest which, at 8,848.86 m (29,031 ft 8+1⁄2 in), is Earth's highest mountain and a particularly desirable peak for mountaineers. This makes Everest the mountain with the most deaths, although it does not have the highest death rate which is defined as the number of deaths for each person who successfully summits the mountain. The most recent years without known deaths on the mountain are 1977, in which only two people reached the summit, and 2020, when permits were suspended by Nepal because of the COVID-19 pandemic.

Deaths have been attributed to avalanches, falls, serac collapse, exposure, frostbite, or health problems related to conditions on the mountain. Not all bodies have been located, so details on those deaths are not available.

Expedition climbing (or expedition-style or pejoratively siege climbing) is a type of mountaineering that uses a series of well-stocked camps on the mountain leading to the summit (e.g. Base Camp, Camp 1, Camp 2, etc.), that are supplied by teams of mountain porters. In addition, expedition climbing can also employ multiple 'climbing teams' to work on the climbing route—not all of whom are expected to make the summit—and allows the use of supports such as fixed ropes, aluminum ladders, supplementary oxygen, and sherpa climbers. By its nature, expedition climbing often requires weeks to complete a given climbing route, and months of planning given the greater scale of people and equipment that need to be coordinated for the climb.

'Expedition style' climbing is in direct contrast to 'alpine style' climbing, which involves a single small fast-moving summit climbing team that carries all their supplies and equipment (e.g. no mountain porters or sherpas) and makes little use of support (e.g. no supplementary oxygen or fixed ropes). As a result of having less equipment and supplies, alpine-style teams need to complete their climbing route in days and it is thus considered a riskier form of mountaineering (e.g. if they get trapped in a storm, they have no supplies to wait for the storm to pass). Some argue that this risk is balanced by the fact that alpine-style teams spend less time on the mountain, thus reducing their exposure to other serious risks such as from avalanches and seracs.

An icefall is a portion of certain glaciers characterized by relatively rapid flow and chaotic crevassed surface, caused in part by gravity. The term icefall is formed by analogy with the word waterfall, which is a similar phenomenon of the liquid phase but at a more spectacular speed. When ice movement of a glacier is faster than elsewhere, because the glacier bed steepens or narrows, and the flow cannot be accommodated by plastic deformation, the ice fractures, forming crevasses. Where two fractures meet, seracs (or ice towers) can be formed. When the movement of the ice slows down, the crevasses can coalesce, resulting in the surface of the glacier becoming smoother.

The Bottleneck is a location along the South-East Spur (also known as Abruzzi Spur), the most-used route to the summit of K2, the second-highest mountain in the world, in the Karakoram, on the border of Pakistan and China.

The Bottleneck is a narrow couloir, which is overhung by seracs from the ice field east of the summit. The couloir is located only 400 m (1,300 ft) below the summit, and climbers have to traverse about 100 m (330 ft) exposed to the seracs to pass it. Due to the height of 8,200 m (26,900 ft), and the steepness of 50 to 60 degrees, this stretch is the most dangerous part of the route. According to AdventureStats, 13 out of the last 14 fatalities on K2 have occurred at or near the Bottleneck.