(World Geography) Glacial Processes and Landforms - Landforms of Highland Glaciations & Glaciated Lowlands
Landforms of Highland Glaciations
By plucking the glacier freezes the joints and beds of the underlying rocks, tears out individual blocks and drags them away. By abrasion, the glacier scratches, scrap, polishes and scours the valley floor with the debris frozen in to it.
1. Corrie, cirque or cwm: The down slope movement of a glacier from its snow-covered valley-head, and the intensive shattering of the upland slopes, tend to produce a depression where the fern or never accumulates. The process of plucking operates on the back-wall, steepening it and the movement of the ice abrades the floor, deepening the depression into a steep, horse-shoe-shaped basin called a cirque.
2. Aretes and Pyramidal peaks: When two corries cut back on opposite sides of a mountain, knife edged where three or more cirques cut back together, their ultimate recession will form angular horn or pyramidal.
3. Bergschrund: At the head of a glaciers, where it begins to leave the snowfield or a corrie, a deep vertical crack opens up called a bergschrund.
4. Hanging Valley: The main vallety is eroded much more rapidly than the tributary valleys as it contains a much larger glacier. After the ice has melted a tributary valley therefore ‘hangs’ above the main valley so that its stream plunges down as waterfall
5. Moraines :Moraines are made up of the pieces of rock that are shattered by the frost action, imbedded in the glaciers and brought down the valley. Those that fall on the side of the glaciers, mainly screes , form lateral moraines. When two glaciers converge, their inside lateral moraines unite two form a medal moraine. The rock fragments which are dragged along beneath the frozen ice are dropped when the glacier melts and spread across the floor of the valley as ground moraine. The glacier eventually melts on reaching the foot of valley, and the pile transported materials left behind at the snow is the terminal moraine or end moraine.
Landforms of Glaciated Lowlands
1. Rôche moutonnée: This is a resistant residual rocks. Its upstream side is smoothened by abrasion and its downstream side is roughened by plucking and is much steeper.
2. Crag and Tail: The crag is the mass of hard rock with a precipitous slope on the upstream side, which protects the softer leeward slope from being completely worn down by the on coming ice
3. Erratics: These are boulders of varying sizes that were transported by ice. They came with the advancing glaciers or ice sheets but when the ice melted, they were left ‘stranded’ in the regions of deposition. They are called erratic. Because they are composed of materials entirely different from those of its region in which they are found.
4. Eskers: These are long, narrow, sinous, ridges composed of sand and gravel which mark the former sited of sub glacial melt water streams.
5. Outwash Plains: These are made up of fluvio glacial deposits washed out from the terminal moraines by the streams and channels of the stagnant ice mass. Small rounded hillocks of sand and gravel may cover part of the plain. Where the deposition takes the form of alternating ridges and depressions, the later may contain kettle lakes and give rise characteristics ‘knob and kettle’ topography.