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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. |
