Cold environments

Some glacial processes and landforms

Glacial Erosion Processes All of the rocks below have been broken down into smaller, angular pieces by erosion by the glacier and frost shattering. Note the different sizes Note the angular shapes

The rocks in the previous picture have been broken down by: Erosion Processes Involve movement Abrasion Plucking Frost shattering Weathering Processes happen in situ (one place)

Jagged, angular rocks of different sizes Frost Shattering Happens in mountainous or hilly areas where the temperature regular rises above and falls below freezing. Water collects in cracks in rocks. Overnight the water freezes and expands. This expansion puts stresses and pressure on the sides of the crack. During the day when the temperature rises the ice thaws/melts and contracts releasing the pressure on the crack. This happens over and over again and eventually the rock cracks open. The rocks that break off are jagged and angular - scree. If they are on a slope they roll down hill and collect on what are known as scree slopes. Jagged, angular rocks of different sizes

Plucking The water at the bottom of the glacier freezes onto rock on the valley base. As the glacier moves the rock is pulled away from the valley base. Plucking mainly occurs when the rock is well-jointed. Well-jointed rock

Rocks carried by the glacier grind at the base and sides of valley Abrasion As a glacier slides over its bed, it picks up rock fragments that act like sandpaper, on a giant scale, rubbing against and wearing away the sides and floor of the valley. This leads to the valley getting steeper, deeper and wider. Rocks carried by the glacier grind at the base and sides of valley Rock fragments and ground-up bedrock incorporated into the base of a glacier.

Striations Bedrock surfaces, such as this, commonly bear polished and scratched (‘striated’) surfaces, as well as various gouge-marks. Ossian Sarsfjellet in NW Spitsbergen

Erosional landforms Corries, cirques or cwms Arêtes Pyramidal Peaks or horns Glacial Troughs and other associated landforms

Corrie [also known as cwm or corrie] An armchair-shaped hollow with steep sides and back wall, formed as a result of glacial erosion high on a mountainside, and often containing a rock basin with a tarn. Cwm Cau on the peak of Cadair Idris, Snowdonia National Park, Wales.

Corrie formation Snow collects in a natural hollow on the side of a mountain. Over time, further snow collects. This extra weight compresses the snow underneath, turning it into ice. The hollow is deepened and widened by the corrie glacier through the processes of abrasion and plucking. This overdeepening leads to the characteristic ‘armchair’ shape of a corrie and causes a ‘rock lip’ to be formed.

Bergschrund An irregular crevasse, usually running across an ice slope in the accumulation area, where active glacier ice pulls away from ice adhering to the steep mountainside.

Corrie Coire Mhic Fearchair, Torridon, Northwest Highlands.

Tarn A small lake occupying a hollow eroded out by ice or dammed by a moraine; especially common in corries Two tarns on the Glyderau range, Snowdonia, North Wales, both occupying cirques. The tarn on the left is Llyn Bochllwyd and that in the centre is Llyn Llyn Idwal ("llyn" is Welsh for "lake").

Arête (from the French) A sharp, narrow, often pinnacled ridge, formed as a result of glacial erosion from both sides. Nevado Jirishanca, Cordillera Huayhuash, Peru.

Formation of corrie, arête and pyramidal peak

Pyramidal peak A steep-sided, pyramid-shaped peak, formed as a result of the backward erosion of corrie glaciers on three or more sides. Matterhorn, on Swiss/Italian border.

U shaped valley formation Water formed valley Ice-formed valley

Glacial trough A glaciated valley or fjord, often characterised by steep sides and a flat bottom, resulting primarily from erosion by strongly channelled ice. Valley of Lauterbrunnen, Switzerland. The extremely steep valley sides result in impressive waterfalls, such as Staubbachfall.

Truncated Spur Former spur eroded away in its lower part by the power of a valley glacier

Hanging valley A tributary valley whose mouth ends abruptly part way up the side of the main valley, as a result of the greater amount of glacial down-cutting of the latter Hanging valley below Mitre Peak, Milford Sound, New Zealand.

A hanging valley and waterfall called Bird Woman Falls near Mt A hanging valley and waterfall called Bird Woman Falls near Mt. Oberlin, Canadian Rockies. A smaller tributary glacier could not erode the base of its valley as deep as the main valley glacier. Thus after the ice melts the smaller valley is left hanging above the main valley floor and enters it at up to 90º.

Roche moutonnée A rocky hillock with a gently inclined, smooth up-valley facing slope resulting from glacial abrasion, and a steep, rough down-valley facing slope resulting from glacial plucking. Ice flow was from right to left Roche moutonnée in front of Steilimmigletscher, Bernese Alps, Switzerland.

Fjord A fjord is a long, narrow arm of the sea, formed as a result of erosion by a valley glacier. Kejser Franz Josef Fjord in East Greenland, looking east towards the peak of Teufelschloss and the edge of the Greenland Ice Sheet, from which the icebergs were derived

A glaciated valley: a fjord Field sketch of Geiranger Fjord

Fjord Visible light satellite image of Scoresby Sund, the largest fjord system on Greenland’s east coast. On the left is the (white) Greenland ice sheet. The grey area on the right is low cloud. Note the many icebergs.