2.A7 Glacial erosion creates distinctive landforms and contributes to glaciated landscapes -

Question 1

Glacier erosional processes -

Answer 1

Abrasion, quarrying, plucking,
crushing and basal melting, combined with subaerial freeze
thaw and mass movement.

Question 2

Quarrying (extreme form of plucking) -

Answer 2

Creating steep and angular rock cliff faces.

Question 3

Sub-aerial processes -

Answer 3

Mass movement (rock falls and landslides) is a source of rock material which falls onto the surface of ice and is incorporated.

Question 4

Crushing -

Answer 4

Crushing is erosion caused by a sheer pressure exerted by rock fragments embedded at the base of a glacier. Caused by the weight of the glacier, produces large angular rocks.

Question 5

Basal melting -

Answer 5

Is abrasion by meltwater, acting under great pressure at the base of a glacier. Causes fluvial erosion processes.

Question 6

All these processes inevitably lead to the formation of:

Answer 6

cirque and valley glaciers (cirques/corries (5),
arêtes, pyramidal peaks, glacial troughs, truncated
spurs/hanging valleys and ribbon lakes.

Question 7

Cirque/Corrie

Answer 7

An armchair shaped-hollow on a hillside above a glacial valley. A pre-glacial hollow is enlarged by plucking and abrasion, as the ice moves under the influence of gravity can be divided into 2 processes. For example Cwm Idwal Snowdonia. Can vary NE or N

Question 8

Process 1: Corrie

Answer 8

• The hollow is initially deepened by nivation, as this ice deepens from more accumulation, this enhances abrasion on the bedrock of the glacier. Ice pulls away from the back of the wall, the plucking rocks are already loosened by freeze-thaw weathering.

Question 9

Process 2 : Corrie

Answer 9

This causes abrasion and deepens the hollow creating this distinctive arm chair shape.

Question 10

Cirque/Corrie - Macro

Answer 10

• Arm chair shaped depressions found at generally high altitude areas.
• Initial stage of formation is for snow to accumulate in a sheltered mountain side location.
• Found most commonly on the NE side of a mountain.
• Once the snow in the sheltered area has accumulated nivation begin, which enlarges the hollow by freeze-thaw weathering loosening the rock and in the summer meltwater takes the debris away from the origin enlarging it.
• Once the nivation hollow is established positive feedback occurs.
• Then the process of plucking and abrasion continue to perform to develop the hollow.
• May expand and move down the valley during a glacial period.

Question 11

Aretes - Macro

Answer 11

-The erosion of cirque headwalls backwards into the slopes behind can result in the formation of an arete.
- A steep-knife edge intersected between two cirque headwalls on either side of the slope divide. Between two cirques E.G striding edge lake district.

Question 12

Pyramidal peaks - Macro

Answer 12

If glaciers continue to erode away at the mountain from three sides or more sides the result is a pyramidal peak. Three or more cirques back to back to back.

Question 13

Glacial troughs ( U/V shaped valleys) - Macro

Answer 13

• Steep-sided, flat floored, straight valley.
  With the direction of ice movement it straightens, widens and deepens the valley changing them from V shape pre-existing valley rivers to U, it is important to know it is widened and deepened by erosional processes and the glacier itself.

Question 14

Hanging valley - Macro (Glacial troughs)

Answer 14

Occur when a small side tributary glacier meets a main valley glacier, the surface ice elevation is the same but because the erosion beneath the main valley glacier is much greater, once the glaciers have retreated the tributary valley can be left hanging valley to the main valley below.

Question 15

Ribbon lake - Macro (Glacial troughs)

Answer 15

Glacial flow is uneven and where erosion has over-deepened a section of the valley (with softer rock) it forms a rock basin, these are usually filled with water post-glaciation forming a ribbon lake.

Question 16

Truncated spur - Macro (Glacial troughs)

Answer 16

Steep sided, possible rocky section of the side of a trough. The pre-glacial interlocking spurs of the river valley are eroded by a much more powerful glacier.

Question 17

Crag and tail - Meso

Answer 17

Formed from different geology, where the glacier ice is forced around a resistant rock or obstacle, which protects the less resistant rock on the leeside causing the feature to taper into a tail in the down glacier direction. Where glacier ice is forced around a large and resistant rock obstacle, protects the lee-slide of the less resistant rock causing the feature to tapper into a tail. The crag is the resistant rock and has resisted glacier erosion

Question 18

Knoch and Lochan - Macro

Answer 18

Known as irregular landscapes from ice sculpted hills of Knocks and small lakes (lochans), result of wide spread abrasion and plucking by an ice sheet moving across hard metamorphic rock. Erosion of joints and faults has created the lochan from softer rocks and the knocks are left over from more resistant rock. Influenced highly be geology.

Question 19

Rouches moutonnees - Meso

Answer 19

Abrasion smooths the up-glacier, while glacier makes the down-glacier. Smooth on one side and jagged on the other. They often from striations from where the glacier moves over harder rock which shows the direction of movement.