OCR A Level GL - 8 OCR A Level GL 2.2b EROSIONAL Landforms

Question 1

What is a corrie?

Answer 1

arm-chair-shaped rock basins with a steep back wall and a rock lip cut into mountains.

Question 2

What is the Welsh term for a corrie?

Answer 2

cwm

Question 3

What is the French and Swiss term for a corrie?

Answer 3

cirque

Question 4

What are the stages of the formation of corries?

Answer 4

1. accumulation of snow on slopes with an aspect facing away from the sun.
2. over time, snow thickness increases and compacts
3. a mountainside hollow forms through nivation processes
4. After several years, freeze-thaw weathering above the glacier provides debris, which reaches the base and is used in abrasion, deepening the hollow.
5. Plucking on the steep back wall adds further debris and retreats the back wall further.
6. Meltwater flows down the bergschrund, providing lubrication and aiding movement
7. This encourages rotational flow in the glacier, deepening the hollow.
8. At the outlet of the basin, ice movement is upwards and so there is less erosion and a rock lip forms.
9. When the glacier retreats, meltwater fills the hollow and forms a tarn.

Question 5

Give a named example of a corrie/cwm in the UK

Answer 5

1. Cwm Idwal (below Snowdonia in Wales) 2. Grisedale Tarn (Lake District)

Question 6

What is an arete?

Answer 6

narrow, steep-sided ridge found between two corries

Question 7

Give a named example of an arete in the Lake District

Answer 7

Striding Edge

Question 8

What is a pyramidal peak?

Answer 8

A pointed mountain peak with at least three sides

Question 9

How does a pyramidal peak form?

Answer 9

Where 3 or more corries develop around a mountain top, their back walls retreat. The remaining mass will be itself steepened to form a pyramidal peak

Question 10

Give a named example of a pyramidal peak

Answer 10

1. Pen-y-Fan, Brecon Beacons, Wales
2. Matterhorn, Switzerland

Question 11

What is a glacial trough also known as?

Answer 11

U-shaped valley

Question 12

How is a glacial trough formed?

Answer 12

1. As corrie glaciers descend down old river valleys they alter V shape valleys into a U shape, by creating a steep sided, flat-bottomed, wide valley.
2. As the glacier moves down the valley it plucks the rock from beneath and those rocks then rub against the bed of the valley (abrasion), eroding it further. This deepens and widens the valley.
3. Interlocking spurs in the original river valley become truncated spurs,
4. Lateral moraines and ground moraines also play an integral role, as this material is used as a tool to abrade the valley sides and floor further.
5. Melt water at the glacier base also plays a role, and where pressure melting point is exceeded the glacier can basally slide ​encouraging even more erosion.
6. These processes are not even however, and extending ​and compressing flow and variable amounts of basal ​material can cause DIFFERENTIAL erosion to occur. This ​means that some part of the valley floor are over deepened creating ​Ribbon Lakes.

Question 13

Give a named example of a ribbon lake in the Lake District, UK

Answer 13

1. Ullswater
2. Lake Windermere

Question 14

What is a roche moutonnée?

Answer 14

a small bare outcrop of rock shaped by glacial erosion, with one side smooth and gently sloping and the other steep, rough, and irregular.

Question 15

What do roche moutonnées tell us about past glaciers?

Answer 15

the patterns of ice flow as they are aligned roughly parallel to ice flow direction.

Question 16

How do roche moutonnées form?

Answer 16

1. Roches mountonnées develop beneath a sliding glacier.
2. On the stoss side of bedrock there is a zone of high pressure and particles embedded in the ice are moved across the underlying surface where they carry out abrasion.
3. The evidence of such abrasion is the common occurrence of striations (i.e. scores and scratches on bedrock) on the sloping upper surface and flanks of roches moutonnées. It also leaves a smooth up-ice side.
4. On the lee side of the bedrock there is a zone of lower pressure, which allows a cavity to form.
5. This low pressure promotes plucking (quarrying) of bedrock along lines of existing weakness (e.g. bedrock joints), resulting in a rough, plucked and cliff-girt surface on the down-ice side.

Question 17

Why are roches moutonnées useful landforms?

Answer 17

The orientation of roches moutonnées is proof of the direction of glacier flow which are useful to glaciologists aiming to reconstruct the flow direction of former glaciers.

Question 18

What are striations?

Answer 18

scratches or gouges cut into bedrock by glacial abrasion

Question 19

Why are striations useful?

Answer 19

They run parallel to the direction of ice movements and therefore can be used to calculate the direction of ice movement once a glacier has retreated.