Lithosphere (glaciation)

Question 1

Glacial erosion

Answer 1

• The glacier freezes on to bedrock and, as it moves downhill due to gravity, it pulls away large chunks of rock from the backwall - a process known as plucking.
• This allows meltwater and rock fragments to get to the base of the glacier increasing erosive power.
• Abrasion occurs when the angular rock embedded in the ice grinds the hollow.
• Frost shattering/freeze thaw weathering occurs when water in cracks in the rock freezes, expands and contracts weakening the rock until fragments break off.

Question 2

Corrie

Answer 2

• Corries are north-facing, away from the sun which stops the ice from melting.
  1. Plucking, abrasion
  2. The weight of the glacier pushes down, causing rotational sliding, which further deepens the hollow.
  3. Bergschrund crevasse opens up at the back of the hollow.
  4. Friction causes the ice to slow down at the front edge of the corrie, allowing a rock lip to form, which traps water as ice melts, leaving a lochan or tarn.
  5. Freeze-thaw weathering.
  6. This abrasion, over time, scours out a basin shape on the mountain.
  7. This process leaves behind a corrie - a deep basin with high, steep sides.
• An example of a corrie is Stirling Ridge in the Lake District.

Question 3

U-shaped valleys

Answer 3

1. U-shaped valleys are created through glaciation.
2. Gravity and the weight of the glaciers causes them to flow downhill, following existing V-shaped valleys.
3. Glacial erosion
4. As glaciers move through a landscape, the processes of plucking and abrasion widen, steepen, deepen and smooth valleys into a ‘U’ shape.
5. Former interlocking spurs may be cut off by the glacier as it flows downhill leaving truncated spurs and steep valley sides.
6. Tributary valleys have smaller less powerful glaciers which result in less deep U-shaped valleys ‘hanging’ about the main valley.
7. After glaciation, freeze-thaw action continues with the warming and cooling of temperatures, as well as other agents of weathering. This causes rocks to weaken and fall to the valley floor as scree.
   * For example, Glen Falloch.

Question 4

Arête

Answer 4

1. An arête is a narrow ridge of rock - like a ‘knife edge’ - which separates two valleys.
2. It is typically formed when two glaciers erode parallel U-shaped valleys.
3. U-shaped valleys 2-5
4. As each glacier erodes either side of the ridge, the edge becomes steeper and the ridge becomes narrower.
5. An arête has steep sides formed by the collapse of unsupported rock, undercut by continual freezing and thawing.
6. Two opposing glaciers meeting at an arête will carve a low, smooth gap, or col.
   * For example, Inglis Clark Arête

Question 5

Pyramidal peak

Answer 5

1. A pyramidal peak is formed where three or more corries and arêtes meet.
2. Glaciers erode backwards towards each other, carving out the rocks by plucking and abrasion.
3. Freeze thaw weathers the top of the mountain, creating a sharply pointed summit.
4. A pyramidal peak has steep, triangular faces divided by sharp ridges or arêtes.
5. Erosion over time may culminate in a high triangular peak or horn formed by three or more glaciers eroding toward each other.
   * For example, the Matterhorn.

Question 6

Hanging valley

Answer 6

1. Hanging valleys are created through glaciation.
2. Gravity and the weight of the glaciers causes them to flow downhill, following existing V-shaped valleys.
3. Glacial erosion
4. The degree to which glaciers can erode down into the landscape is dictated by their size: the larger the glacier, the deeper the valley it can erode.
5. A hanging valley is a shallow valley carved by a small glacier and thus the elevation of the valley floor is ‘hanging’ high above the elevation of the valley floor carved out by the larger glacier.
   * For example, Stank Glen

Question 7

Ribbon lake

Answer 7

1. A ribbon lake is a long and deep, finger-shaped lake, usually found in a U-shaped valley.
2. U-shaped valley 2-5.
3. As a glacier flows over the land, it flows over hard rock and softer rock.
4. Softer rock is less resistant, so a glacier will carve a deeper trough.
5. When the glacier has retreated, (melted) water will collect in the deeper area and create a long, thin lake called a ribbon lake.
6. A ribbon forms in a hollow when a glacier has more deeply eroded less resistant rock or it may fill up a valley behind a wall of moraine across the valley.
7. The areas of harder rock left behind are called rock steps.
   * For example, Lake Windermere.

Question 8

Drumlins

Answer 8

1. Drumlins are elongated, oval shaped hills made up of unsorted glacial deposits, comprising till, boulder or clay.
2. Drumlins are formed as the glacier becomes overloaded with sediment and deposits it, streamlining the sediment as it flows over it.
3. The steep ‘stoss’ slope faces up-valley and the more gently-sloping ‘lee’ slope faces down-valley.
4. Drumlins are found in groups or swarms, with the tapered end of each hill pointing in the direction of glacier flow.
5. Each drumlin is a small hill, tending towards an egg shape, with its steepest slopes and summit at the up-ice end.
6. Although they come in a variety of shapes, the glacier side is always high and steep, while the lee side is smooth and tapers gently in the direction of ice movement.
   * For example, Buchlyvie

Question 9

Esker

Answer 9

1. Eskers are meandering ridges of layered sand and gravel.
2. They are made up of meltwater sands and gravel streams in or underneath a glacier.
3. These are sorted by size with large stones at the base because larger stones are dropped first by flowing water.
4. The stones also tend to be more rounded than glacial deposits, because of the action of flowing water rounding the edges by erosion.
5. As the glacier melts, sub-glacial streams flow through tunnels and the load is deposited on the channel bed.
   * For example, Kildrummie Kames

Question 10

Terminal moraine

Answer 10

1. Terminal moraine is a ridge across the valley and made up of glacial deposits/till/boulder clay; which is unsorted.
2. As the glacier moves downhill it acts like a bulldozer, pushing sediment in front of its snout as it goes.
3. On reaching lower altitudes and when temperatures rise, the glacier melts, losing power and depositing the moraine.
4. Terminal moraine marks the furthest point that the glacier reaches.
5. The longer the ice continues to melt at the same place, the higher the terminal moraine.
6. Once the ice has retreated, the terminal moraine can often form a natural dam, creating a ribbon lake.