2. Erosional landforms

Question 1

What are the erosional landforms associated with glaciers?

Answer 1

Corries
Aretes and pyramidal peaks 
Troughs 
Roche moutonnées
Striations 
Ellipsoidal basins

Question 2

What are corries?

Answer 2

Bowl-shaped hollows with a steep back wall and a raised rock lip at the front

Question 3

How are corries formed?

Answer 3

1. Snow compacts and accumulate over many years to form neve
2. Hollow deepens by nivation
3. Glacier moves downhill due to mass of ice and moves by rotational slip
4. Ice freezes to back wall and plucks rocks
5. Freeze thaw above the hollow shatters rock and delivers scree to ice
6. This material is moved under the ice, abrading the hollow
7. Aided by the fact that pmp is often exceeded so lots of meltwater under glacier therefore lots of basal sliding
8. Creates a steep back wall and hollow aka corrie
9. At the front of corrie ice thins out so less erosion leaving a lip of rock
10. When ice melts a tarn is formed

Question 4

What is an arête?

Answer 4

A narrow steep-sided ridge found between two corries forming a knife-edge

Eg. Striding Edge which has almost-vertical slopes of 200-300 metres high

Question 5

How is an arête formed?

Answer 5

Formed by glacial erosion from retreating corries that are back to back

Question 6

What is a pyramidal peak?

Answer 6

Where three or more corries form back to back, can be sharpened by weathering processes
Eg. The Matterhorn, Switzerland is over 1200 metres high

Question 7

What is a trough?

Answer 7

A parabolically shaped valley that was carved out by glacier(s) that have since receded or disappeared
Eg Glen Avon, Cairngorms

Question 8

How do glacial troughs form?

Answer 8

• Glacier erodes sides and floors of valley causing it to become wider and steeper
• Previous V-shaped valley carved out by river had interlocking spurs, glacier is far more powerful an bulldozes to form truncated spurs

Over-deepened areas form ribbon lakes eg. Windermere

Question 9

Why are troughs parabolic, not U-shaped?

Answer 9

Due to weathering and mass movement of the upper valley sides which causes scree slopes to accumulate at the base which lessen the slope angle

Question 10

What are striations?

Answer 10

Scratches made by debris embedded in base of glacier that run parallel to ice movement

Question 11

What is a hanging valley?

Answer 11

A small tributary glacier high above the main valley, once the ice has melted waterfalls occur here

Question 12

What is a Roche moutonnée?

Answer 12

A mass of resistant rock with a smooth, rounded up-valley slope which faces the direction of ice flow and a jagged down slope formed by plucking.

Question 13

How are Roche moutonnées formed?

Answer 13

• When a glacier meets a resistant mass of rock the ice cannot go over the obstacle so the ice compresses
• Abrasion from rocks within the ice can cause striations on the lee side
• Compression of ice leads to a build up of pressure on the stoss side causing it to exceed the pressure melting point
• The ice melts due to increase temperature from pmp, so flows around the rock
• Once the meltwater has reached the lee side, the temperature decreases as pressure is lost so the water refreezes
• The ice then carries out plucking creating a jagged uneven side on the downwards slope

Question 14

What is an ellipsoidal basin?

Answer 14

Deep elongated lakes caused by erosion from ICE SHEETS

Eg Laurentide ice sheet of North America produced a series of ellipsoidal basins, such as Hudson Bay