Glaciation Key Terms
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
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
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
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
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 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
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
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
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
Truncated Spur: a former river valley spur which has been sliced off by
a valley glacier