Barcelona Field Studies Centre

GCSE Glaciated Valleys Glossary

Abrasion: erosion caused by rocks and boulders in the base of the glacier acting like a giant file scratching and scraping the rocks below.

Angular Rock: a rock with sharp edges.

Arête: sharp, knife-like ridge formed between two cirques cutting back.

Aspect: the direction a cirque faces; south-facing cirques tend to be larger and more eroded due to greater ice movement.

Bergschrund: a deep crevasse found at the back wall of a cirque, formed as the ice moves away downhill. This may have an important role in the processes leading to the deep erosion of the cirque basin.

Boulder Clay: an unsorted mixture of sand, clay and boulders carried by a glacier and deposited as ground moraine over a large area. Now regarded as an obsolete term.

Cirque: armchair-shaped hollow in the mountainside formed by glacial erosion and freeze-thaw weathering. This is where the valley glacier begins.

Corrie: see Cirque.

Crevasse: a deep crack on the surface of an ice sheet or valley glacier.

Erratics: rocks which have been transported and deposited by a glacier some distance from their source region.

Englacial Moraine: moraine carried within the ice itself.

Erosion: the wearing away of the land by rivers, ice sheets, waves and wind.

Fiord (or Fjord): a long, narrow, steep-sided inlet formed by glaciers and later drowned by a rise is sea level. Fjords are often over 3 kilometres deep.

Freeze-Thaw Weathering: also called frost-shattering as it occurs in cold climates when temperatures are often around freezing point and where exposed rocks contain many cracks. Water enters the cracks during the warmer day and freezes during the colder night. As the water turns into ice it expands and exerts pressure on the surrounding rock, causing pieces to break off.

Frost-Shattering: see Freeze-Thaw Weathering.

Glacial Trough: see Glaciated Valley.

Glaciated Valley a river valley widened and deepened by the action of glaciers (ice sheets); they become ‘U’-shaped instead of the normal ‘V’-shape of a river valley.

Glacier: an sheet of ice that moves slowly down a river valley under the influence of gravity. This is often described as a river of ice.

Grinding: see Abrasion.

Ground Moraine: moraine at the base of the glacier, a result of abrasion and plucking of the valley floor.

Hanging Valley: a tributary valley to the main glacier, too cold and high up for ice to be able to easily move. It therefore was not eroded as much as the lower main valley, and today is often the site for a waterfall crashing several hundred metres to the main valley floor.

Ice Age: a period of colder climate when ice sheets form on the land, causing a lowering of sea level.

Ice Movement: when under pressure, ice behaves as jelly and flows with the aid of gravity and melt water lubrication. The melting point of ice at the base of the glacier can be lower than 0ºC due to the pressure of weight.

Ice Sheet: huge mass of ice covering the landscape that moves very slowly. Only the mountain peaks protrude above the ice.

Interglacial: a warmer spell between ice ages, lasting about 10,000 years.

Lateral Moraine: a narrow band of rock debris which runs along the sides of a glacier resulting from ice erosion of the valley sides and freeze-thaw weathering on the bare rock above.

Medial Moraine: a narrow band of weathered rock debris which runs down the centre of the glacier. It forms from the merging of the lateral moraines of two glaciers.

Misfit Stream: After the ice has melted and the river returns to the valley, it often looks tiny and out-of-place in its huge U-shaped trough.

Moraines: frost-shattered rock debris and material eroded from the valley floor and sides, transported and deposited by glaciers.

Physical Weathering: the disintegration of rock into smaller pieces without any chemical change in the rock; this is most likely in areas of bare rock where there is no vegetation to protect the rock from extremes of weather e.g. freeze-thaw and exfoliation (or onion weathering).

Plucking: a type of erosion where melt water in the glacier freezes onto rocks, and as the ice moves forward it plucks or pulls out large pieces along the rock joints.

Pyramidal Peak: where several cirques cut back to meet at a central point, the mountain takes the form of a steep pyramid, e.g. the Matterhorn in the Alps.

Quarrying: see Plucking.

Ribbon lakes: long, narrow lakes found in glaciated valleys formed in locations where the glacier had more erosive power, e.g. in areas of softer rock, where the valley gradient temporarily steepened or a tributary glacier joined the main valley.

Roches Moutonnées: rocks looking like a sheep's head, one side smoothed and polished and the other plucked and jagged.

Rotational Movement: avalanches of snow collecting at the back wall of a cirque exert great pressure, forcing the ice out of the front of the hollow in a rotational movement, similar to the pushing of jelly from bowl.

Sea Level Changes: changes in the level of the sea against the land are caused by either the building up of melting of polar ice caps, or by rising and falling land levels.

Scree: a slope of loose, large angular rocks broken away from the mountainside by freeze-thaw weathering.

Snout: the end of the glacier where melting occurs.

Snowline: the altitude where permanent snow begins in mountainous regions.

Spur: a narrow neck of highland extending into a river valley, often forming the divide between two tributaries.

Tarn: a deep circular lake filling a cirque hollow.

Terminal Moraine: a prominent ridge of rock debris dumped at the end of a glacier and formed of unsorted boulders, sand, gravel and clay.

Till: also known as Boulder Clay.

Time: an important factor in glacial erosion and deposition.

Truncated Spur: a former river valley spur which has been sliced off by a valley glacier.

U-shaped Valley: see Glaciated Valley.

Valley Glacier: see Glacier.

Weathering the break-down or decomposition of rock by biological, physical or chemical processes.