glacial landforms Flashcards
what are corries and how are they formed
- armchair hollow shape, steep back wall,
over depend basin, - starts with nivation of a small hollow, snow collects, and accumulates, hollow enlarges, glacier enlarge, rotational movement causes plucking of the back wall, debris falls into crevasse and erodes back wall causing it to deepen, thinner ice can’t erode so lip is created, over time fills up with water
what are arêtes and how are they formed
narrow steep sided ridge, between two corries, knife edge, steeping of slopes and the retreat of corries back to back,(striding edge), 200-300m high
what is a pyramidal peak and how are they formed
three or more corries develop a hill or mountain, back walls retreat, remaining mass steepen to form a pyramidal peak, weathering sharpens, 1200m high (matterhorn swiss alps)
what are through and how r they formed
parabolic due to weathering and mass movement, of upper part of valley sides as glacier retreats, resultant scree slopes accumulate at the base of the valley sides lessen the slope angle, compressing flow = over-deepened to form rock basins and rock steps, weather rocks eroded more rapidly to form basins
what are roche mountanées and how are they formed
ice passed over there’s PMP on up valley side, are then smooth end and streamlined by abrasion and has striations, down valley side pressure is reduced and meltwater re-freezes, plucking and steepening, indicate direction ice moved through, vary in size 1-5m high 5-20m long (condition area)
what are ellipsoidal basins and how are they formed
major erosion all landforms created by ice sheets, (lauren tide ice sheet) covered 13million km, thickness of 3000m, produced series of ellipsoidal basins (hudson bay), leads to isotonic lowering
what are drumlins and how do they form
mound of glacial debris, streamlined into an elangated hill, prominent landforms, km length, 100m high, pear shaped, aligned with direction of ice flow, high wider stows faces ice flow, lee side tempered, occur in large groups (north yorkshire), caused by reshaping of previously deposited material during a re-advance
what are erratics and how are they formed
individual price of rocks, small pebble - bolder, composed of different geology from area in which they have been deposited, caused by plucking and added to supra-glacial debris by weathering and rock fall, area of one rock type then transported and deposited in are of different rock, (norber yorkshire dales)
what is till sheets and how are they formed
formed when a large mass of unstratified drift is deposited at end of advance period, smooths underlaying surface, significant landforms, variable in composition depending on the nature of rocks over which ice has moved, high clay content = lead to relatively hard deposit (minnesota, USA)
what is terminal moraine and how is it formed
ridge of till extending across trough, steeper on up-valley side, crescent shaped, further down valley in centre, maximum advance of ice, deposited at glacier snout, credit shape due to position of snout, no friction as no sides in middle (franz josef 430m high)
what is lateral moraine and how is it formed
ridge of till along edge of a glacial valley, material accumulates on top of the glacier due to weathering on valley sides, as glacier retreats material sinks through ice to ground, (athabasca)
what is recessional moraine and how is it formed
series of ridges, transversely across glacial trough, parallel to each other and terminal moraine, further up valley, form during still stand in retreat, 100m high
what is push moraine and how is it formed
formed by glaciers, retreat then advance, proof climate becoming cooler, material deposited shoved into pile due to advance, characteristic differences in orientation of rock, pushed upwards form original horizontal position
