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Glacial Revision Notes

These terms are the bare minimum glaciation vocabulary you should be able to use and understand when sitting the examination. You are free to download this page for your own educational use.

Ablation

The loss of ice from a glacier due to surface melting, evaporation and the calving of icebergs.

Abrasion

The wearing away of rocks by the action of water, ice or wind using moving debris.

Arête

An arete is a sharp ridge of rock formed by two cirques meeting back to back. A good example is Striding Edge in the Lake District.

Bergschrund

The crevasse which forms at the back of the glacial ice where it meets the cirque backwall. It is formed as the ice moves down and away from the rock wall.

Boulder clay

Glacial moraine consisting of thick clay with angular rocks. The exact composition will depend on the rocks eroded by the glacier. Boulder clay is sometimes called till.

Cirque

A steep armchair shaped hollow formed by the erosion of the rock by snow and ice. The rotational movement of the ice within the cirque hollows out the base creating a depression. The hollow will become a tarn once the ice retreats.

Corrie

See Cirque

Crag and tail

An erosional feature produced when ice moved over a layer of hard rock. The hard rock protected the softer rocks behind it forming an outcrop with a steep side facing the ice flow and a gentle slope on the down stream side.

Crevasse

A vertical crack in the glacial ice. It may be formed when a glacier begins to move down a steep slope, when it is forced to make a sharp turn, or when he ice has to move over undulations in the glacier bed. Crevasses can open and close and vary in their size and depth. Most are formed across the glacier but where a glacier widens they may also form parallel to the direction of flow.

Cwm

See Cirque

Drumlins

Elongated oval hills made of Boulder clay. The long axis is parallel to the flow of the original glacier with the steeper end facing towards to flow of the ice. They are a depositional feature.

Erratics

Large blocks of rock which were picked up by a glacier then deposited, sometimes hundreds of miles from their source, when the ice melted.

Esker

A long and narrow ridge of sand and glacial debris which is raised above the surrounding land. It was once the bed of a stream that flowed beneath a glacier, and was left behind after the ice melted.

Ground moraine

See Moraine

Hanging valley

A hanging valley is a tributary valley that enters the side of a U shaped glaciated valley. Originally the 'hanging' valley would have joined the main valley in a normal way, its streams or rivers flowing into the main valley at the same level. The main valley was made deeper by glaciation, but the side valleys were left at their original level. When the ice melted they were no longer level with the bottom of the valley due to the deepening which had occurred. They appear to 'hang' on the steep sides of the new valley, their streams flowing into the main valley via waterfalls.

Ice sheet

Vast areas of ice which can cover much of a continent. A modern example is Antarctica. During Ice Ages these sheets of ice advanced and covered much of Northern Europe reaching, in the UK, as far south as Bath.

Lateral moraine

See Moraine

Lip

The down slope edge of a cirque base forms a lip. As the ice rotated in the cirque it moved down at the back wall and was forced upwards as the glacier began to move out of the cirque. This creates a lip at the edge due to decreased erosion. See Cirque for further information.

Medial moraine

See Moraine

Moraine

The rock material eroded by a glacier is known as moraine. There are five main types of moraine which you need to remember.

1. Lateral Moraine : Moraine which forms along the sides of a glacier.

2. Terminal Moraine : Moraine which collects along the front of a glacier

3. Ground Moraine : Moraine underneath the glacier.

4. Medial Moraine : A band of moraine along the centre of the glacier formed when two glaciers join, their lateral moraines meeting to form the central band of debris.

5. Englacial Moraine : Moraine that is held within the glacier. Usually this is rocks that have fallen into crevasses and become trapped in the ice below the surface.

Outwash plain

Material from a terminal moraine washed down stream may be deposited as an outwash plain.

Plucking

An erosional process. Ice freezes to rocks surrounding the glacier. As the glacier moves the rocks are pulled with the ice to which they are attached. This results in the pieces of rock being tugged, or 'plucked' away from the bed and sides of the valley.

Pyramidal peak

A pyramid shaped peak formed when cirques develop all around a mountain. As the cirques erode backwards and meet each other a very sharp and jagged peak is formed.

Roches moutonnée

Translated, this means 'sheep rocks' and gives an idea of what they look like. The rocks are smooth on the upstream side and have rough, plucked surfaces on the downstream side. The upstream surface is often marked with striations.

Snout

The downstream end of a glacier.

Snowline

The snowline marks the level on a mountain above which there is ALWAYS snow. Snow which falls below this line will melt in summer.

Striations

These are scratch marks found on rocks which were eroded by glaciers. When the ice moved over large rocks, the fragments of rock held in the ice were scraped across the surface scratching it. The striations are parallel to the direction of ice movement. Striations are a good indication of past glaciation.

Tarn

The lake which forms in the hollow at the base of a cirque

Terminal moraine

See moraine

Till

See Boulder clay

Truncated spur

A river spur cut off by glaciation of a former river valley. The spur typically has an abrupt and near vertical end.

U shape valley

Glacial valleys have a U shape cross section due to downward erosion across the entire valley floor. By contrast river valleys have a V shape cross section.

Valley glacier

A glacier that originates high up a mountain and then flows down a valley. This is the usual type of glacier, also known as an Alpine glacier.

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