Cold environments

Some glacial processes and

landforms

Glacial Erosion ProcessesGlacial Erosion ProcessesAll 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 The rocks in the previous picture have been broken picture have been broken

down by:down by:Erosion

ProcessesInvolve

movement

Weathering Processes

happen in situ (one place)

Frost ShatteringFrost Shattering Happens in mountainous or hilly Happens in mountainous or hilly

areas where the temperature areas where the temperature regular rises above and falls regular rises above and falls below freezing. below freezing.

Water collects in cracks in Water collects in cracks in rocks.rocks.

Overnight the water freezes and Overnight the water freezes and expands.expands.

This expansion puts stresses This expansion puts stresses and pressure on the sides of the and pressure on the sides of the crack.crack.

During the day when the During the day when the temperature rises the ice temperature rises the ice thaws/melts and contracts thaws/melts and contracts releasing the pressure on the releasing the pressure on the crack.crack.

This happens over and over This happens over and over again and eventually the rock again and eventually the rock cracks open. cracks open.

The rocks that break off are The rocks that break off are jagged and angular - scree. jagged and angular - scree.

If they are on a slope they roll If they are on a slope they roll down hill and collect on what down hill and collect on what are known as scree slopes.are known as scree slopes.

Jagged, angular rocks

of different sizes

PluckingPlucking• 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

AbrasionAbrasionAs 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.

StriationsStriations

Bedrock surfaces, such as this, commonly bear polished and scratched (‘striated’) surfaces, as well as various gouge-marks.

Ossian Sarsfjellet in NW Spitsbergen

Erosional landformsErosional landforms

Corries, cirques or Corries, cirques or cwmscwms

ArêtesArêtes Pyramidal Peaks or Pyramidal Peaks or

hornshorns Glacial TroughsGlacial Troughs and other and other

associated associated landformslandforms

CorrieCorrie [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.

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.

Corrie formationCorrie formation

BergschrundBergschrund 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.

Coire Mhic Fearchair, Torridon, Northwest Highlands.

Corrie

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 Formation of corrie, of corrie, arête and arête and pyramidal pyramidal peakpeak

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 troughGlacial 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.

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

Truncated SpurTruncated Spur

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. 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 moutonnéeA 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.

Roche moutonnée in front of Steilimmigletscher, Bernese Alps, Switzerland.

Ice flow was from right to left

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

Field sketch of Geiranger Fjord

A glaciated valley: a 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.