EQ3 Flashcards
Landforms of glacial erosion - Corrie (cirque or cwm):
-Scale - Macro.
-Location example - Coire Mhic Fhearchair, Northwest Highlands.
-Description - An amphitheatre-shaped depression in a mountainside with a steep back wall and a rock lip at the front of the hollow, which acts as a dam to trap water and form a small lake - or tarn.
-Formation - A large rounded hollow on a mountainside is eroded and deepened by plucking and abrasion due to the rotational ice movement of a cirque glacier.
Landforms of glacial erosion - Arete:
-Scale - Macro.
-Location example - Nevada Jirishanca, Peru.
-Description - A narrow, knife-edged ridge between two cirques.
-Formation - Plucking and abrasion on the back wall of two cirques on a mountainside mean they erode backwards towards one another, creating a narrow ridge. Freeze-thaw action is also important.
Landforms of glacial erosion - Pyramidal Peak:
-Scale - Macro.
-Location example - Mont Blanc, France.
-Description - A pointed mountain peak with three or more cirques.
-Formation - The erosional processes within nearby cirques mean they erode backwards towards each other, creating a sharp, pointed mountain summit. Plucking is important.
Landforms of glacial erosion - Glacial trough:
-Scale - Macro.
-Location example - Lauterbrunnen valley, Switzerland.
-Description - A U-shaped valley with steep sides and a wide, flat floor. It also has a misfit river.
-Formation - A V-shaped river valley is widened and deepened as a result of powerful plucking and abrasion by a valley glacier, which goes through the landscape rather than around it.
Landforms of glacial erosion - Truncated spur:
-Scale - Macro.
-Location example - Three Sisters, Glencoe, Scotland.
-Description - A steep rocky valley side where spurs of a river valley used to interlock before glaciation.
-Formation - Valley glaciers are less flexible than rivers and remove the ends of interlocking spurs by plucking and abrasion as they move down the river valley.
Landforms of glacial erosion - Hanging valley:
-Scale - Macro.
-Location example - Mitre Peak, Milford Sound, New Zealand.
-Description - A small tributary V-shaped or small U-shaped valley high above the main glacial trough floor, often with a waterfall as the river flows over the edge.
-Formation - Powerful thick glacial ice in the main glacial trough eroded vertically downwards more rapidly than thinner ice or rivers in tributary valleys. The floors of the tributary valleys are left high above the main valley floor.
Landforms of glacial erosion - Ribbon lake:
-Scale - Macro.
-Location example - Scarfed Pike, England.
-Description - A long and narrow lake along the floor of a glacial trough.
-Formation - Areas of increased plucking and abrasion by the valley glacier deepen part of the valley floor, as a result either the confluence of glaciers or weaker rocks. Sometimes the lake forms behind a terminal moraine after glaciation.
Landforms of glacial erosion - Roche Mountonnée:
-Scale - Meso.
-Location example - Stellmningletscher, Bernese Alps, Switzerland.
-Description - Asymmetrical, bare rock outcrop with a smooth stoss (up-valley side) and a steep jagged lee (down-valley side).
-Formation - As ice crosses a resistant rock outcrop, the increased pressure causes melting and basal sliding and the up-valley side is smoothed by abrasion. On the leeward side pressure is reduced, refreezing occurs and plucking takes place, causing a steep, jagged slope.
Landforms of glacial erosion - Knock and Lochan:
-Scale - Meso.
-Location example - East Shetland, Scotland.
-Description - A lowland area with alternating small rock hills (knock) and hollows, often containing small lakes (lochan).
-Formation - Scoring at the base of a glacier excavates areas of weaker rock, forming hollows that fill with meltwater and precipitation following ice retreat.
Landforms of glacial erosion - Crag and tail:
-Scale - Meso.
-Location example - Salisbury Crags, Edinburgh, Scotland.
-Description - A very large mass of hard rock forms a steep stops with a gently sloping tail of deposited material.
-Formation - A large mass of hard rock is resistant to ice scouring and creates steep stoss. Reduced glacier velocity on the ;ee protects softer rock and allows deposition, but the sheltering effect diminishes with distance, creating a sloping tail.
Landforms of glacial erosion - Striations/chattermarks:
-Scale - Micro.
-Location example - Kilve, Somerset, England.
-Description - Grooves on exposed rocks.
-Formation - Abrasion by debris embedded in the base of the glacier as it passes over bare rock. The can indicate the direction of ice movement.
How do Roche Moutonnées demonstrate abrasion and plucking?
Roche moutonnées are bare outcrop of rock on the valley floor that were sculpted by moving ice. They demonstrate two processes of glacial erosion - abrasion and plucking:
-Upstream side (stoss): increased pressure due to the resistance of the outcrop to moving ice caused localised pressure melting. This led to basal slip and abrasion as the glacier slid over the outcrop. The abraded upstream side shows polishing and striations.
-Downstream side (lee): Reduced pressure meltwater to freeze - forming a bond between rocky outcrop and overlying glacier. As the glacier moved forward, it plucked away loose rock, leaving a jagged surface.
Explain how underlying geology plays a part in the formation of crag and tail landforms:
The underlying geology plays a part in the formation of crag and tail landforms. A crag and tail is formed when a very large resistant object, or crag, obstructs the flow of a glacier (e.g. the basalt volcanic plug on which Edinburgh Castle sits). The ice is forced around the obstruction, eroding weaker rock. However, material immediately in the lee of the obstruction is protected by the crag, which leads to the formation of a gently sloping tail of deposited material.
Erosional process: Scouring:
-Ice sheet scouring occurs when ice sheets and glaciers expand out beyond contained mountain valleys and erode large areas of lower relief land.
-This is typical of warm-based ice (temperate glaciers) which are moving relatively slowly and eroding the bedrock beneath (subglacial).
-The landforms are largely dependent on the bedrock (hard/soft) leading to different rates in erosion.
Exam style question:
Explain the formation of two ice contact depositional features (4 marks):
-Terminal/end moraine - moraine is carried forward by the glacier, which is then deposited at the point of maximum advance when it retreats. When ice melts it deposits this material as unsorted angular morainic material along the with of the valley.
-Recessional moraine - moraine is carried forward and deposited by a glacier as it retreats. When the ice retreat stops, more moraine is deposited leaving clear ridges running across the valley behind the terminal moraine. The glacier will then retreat again, leaving a series of recessional moraines. Material is deposited as unsorted angular morainic material across the valley.
