Corrie, cirque, cwm – hollow where a glacier formed

Armchair shaped hollow – usually northerly aspect in UK and N. Hemisphere.

Steep back wall

e.g. Llyn Cau on Cader Idris

Llyn Cau -Corrie lake - Or tarn

Back wall of corrie – plucking

Overdeepening of hollow – abrasion

Rotational slip at base of glacier

Corrie lip at front edge

Looking down into a tarn

From high up on the backwall

Backwall subject to freeze thaw weathering in post-glacial – periglacial times

An arete

A knife edge ridge formed where two cories developed back to back

This example is Striding Edge on Helvellyn in the Lake District.

A pyramidal peak or horn

e.g. Matterhorn

Where 3 or more corries form back to back

A glacial trough or U shaped valley.

Steep sides are truncated spurs prexisting river valley profile altered by glacial erosion

Ice more effective at eroding by

Plucking and abrasion

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 90*.

A fjord is a drowned glaciated valley.

The ice did not use present day sea level as its base level

The ice could erode much deeper than today’s sea level.

So after the Ice Age the sea enter and drowned glaciated valleys.

Many examples in Norway

Wastwater

In some areas the glaciated valley can be overdeepened by glacial erosion. Perhaps the rocks locally were less resistant.

Alluvial fans may be formed where a post glacial stream flows into the lake. The lake may be split into two.

Keswick lies between Derwentwater and Bassenthwaite. Interlaken is another example.

Lakes are temporary features – they fill up with sediment or the post glacial reiver cuts down through the dam blocking the lake so that all the water drains away.

These striations are on rocks in the Indian Peaks Wilderness, Utah. They were formed as individual particles carried at the base of a glacier moved across the bedrock and scratched the rock.

The striations provide important clues to the orientation of ice flow, particularly important if we were not around to observe the glacier when it existed.

Definition: rock hills shaped by the passage of ice to give  a smooth up-ice side and a rough, plucked and cliffed surface on the down-ice side. The upstream surface is often marked with striations.