Arête A narrow ridge between glacial valleys. It is formed when two glaciers carve out adjacent valleys.

Bergschrund A deep gap formed when a glacier pulls away from the solid, immobile wall of ice behind it.

Cirque A semicircular basin in a mountainside, from which compacted areas of snow spill out to form a glacier. Cirques are also known as cwms or corries.

Crevasse A deep crack in a glacier. A crevasse is formed when ice splits as it moves over uneven rocks or turns a corner.

Drumlin A smooth, tear-shaped hill, formed when glaciers move over soft clay or gravel that has been deposited there by previous glaciers.

Erratic Large block of rock transported far from its point of origin by a glacier or ice sheet.

Esker A narrow, winding ridge of gravel, deposited by meltwater streams running beneath a glacier.

Fjord A deep, U-shaped valley that has been gouged out by a glacier and “drowned” by rising sea levels. There are many fjords on the coast of Norway and New Zealand.

Glacial erosion The gradual wearing down of the land by the movement of glaciers. Rocks and pebbles carried on the bottom and sides of a glacier scrape along the ground, acting like sandpaper.

Glacier A glacier is a moving mass of ice that is formed when layers of snow pile up and compress. The ice then starts to move under its own weight. Some glaciers snake down mountain valleys, while others are so huge and thick they almost totally cover the land.

Hanging valley A small glacial valley that joins a larger valley. The base of the smaller valley is much higher up than that of the main valley and so “hangs” over its side. Hanging valleys are formed by small, tributary glaciers flowing into larger glaciers.

Ice sheet An ice cap that covers whole continents for a long period of time. Today the only ice sheets are in Greenland and Antarctica.

Moraine The soil and rock carried and deposited by glaciers. Lateral moraine is the debris carried at the sides of a glacier. When two glaciers join, their lateral moraines form a medial moraine in the middle of the combined glacier. A terminal moraine is the ridge deposited at the end, or snout, of a glacier when it melts.

Meltwater stream The water that comes from a melted glacier. Glacial meltwater may run under the glacier to form lakes in front of its snout.

Moulin A vertical hole through a glacier, carved out by meltwater trickling down through cracks in the surface of the ice.

Nunatak A mountain summit that pokes through the top of a glacier or ice cap.

Post-glacial rebound The rising up of land that has previously been pressed down by the weight of ice. For example, much of Scandinavia, which was covered by glaciers almost 20,000 years ago, is still rising by about 1 cm (0.4 inches) per year.

Randkluft A deep crack formed where a glacier pulls away from the wall of rock behind it.

Roche moutonnée A smooth, tear-shaped mound of bedrock formed by glacial erosion.

Serac A large block of glacial ice that forms between two crevasses. Seracs are often unstable, and prone to collapsing. For this reason, they pose a great risk to mountaineers.

Snout The lowest point, or end, of a glacier, sometimes called its terminus.

Till Sediment from the erosion carried out by a glacier. It is deposited as moraines by the ice or from glacial meltwater. Till consists mostly of clay, silt and sand, but with pebbles and boulders scattered amongst it. It is also known as boulder clay.

Tributary glacier A small glacier that leads into a larger one.

Valley A low area of land between mountains or hills. Glacial valleys, typically U-shaped, are carved out by glacial erosion, while river valleys are V-shaped.

Consultant: Ian Fairchild