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Erosion Notes

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Glacial Erosion Glacial Erosional Forms

1. Small-scale forms:
- Striae - abrasion by asperities - flow direction including multiple glaciation directions + small scale variations (Veillette 1986 - Ontario/Quebec border; Sharp et. al. amount of erosion in Snowdon N. Wales)
- Rats tails also showing direction (differential abrasion in lee of resistant rock knobs)
- Chattermarks/gouges/fractures - quarrying by overpassing clast
- P-Forms inc. Transverse (Sichelwanne, transverse trough), Longitudinal (inc cavetto, furrow), non-directional (potholes). Allen 1971 fluvial parallels & origin but Boulton 1974 - glacial/fluvial/intermediate & separation of debris rich/poor ice around bed obstructions. Gray 1992 - 2 stage fluvial erosion then glacial abrasion in Isle of Mull

2. Intermediate-scale forms
- Roches mountonnées - abraded up-ice/stoss faces, quarried down-ice faces - 1100s of ms - large asymmetric hills (flyggbergs), superimposed Roches Moutonnees. Concentrated abrasion stoss of existing hills/bumps, cavitation on lee, helped by presence of water cavities - thin, temperate valley glaciers + near melting margins of ice sheets. Lindstrom 1988 'Alternative weathering hypothesis' - further alteration.
- Whalebacks/rock drumlins without quarried lee faces so where cavity formation suppressed under thick ice (Evans 1996).
- Crag & tails showing direction (large rats tails) - Edinburgh Castle/Royal Mile (Sissons 1967).
- Nye channels 10m1km/Tunnel valleys up to 100km. Time-transgressive so careful interpretation. Generally parallel flowlines. Anastomising/arborescent reflecting efficient/inefficient or unstable drainage. Large tunnel valleys Boulton
& Hindmarsh 1987 lateral sediment creep around tunnels; Mooers 1988 seasonal meltwater from surface during deglac; Brennand et. al. 2006 Ontario - catastrophic floods (O'Cofaigh 1996 = Review). NY Finger Lakes near Ontario, Polish Ribbon Lakes & Northern Germany.

3. Large forms
- Rock basins - overdeepnings suggesting meltwater (Hooke 1991 Positive feedback, Störglaciaren)
- Troughs & fjords - modelled by Harbor 1992.
- Cirques: flat-floored/overdeepened basin connected to steep backwall by concave slope. Frost action higher up. Dynamic interplay between past & present interpretation Crag & tails = big rats tails Essay Plan: How can erosional landscapes, which, by definition, are landscapes from which material has been removed, be used to infer the dynamics of past glacial activity?
Erosional potential depends on topographic, substratum characteristics but also those to do with glacier itself, including size, orientation, thermal regime, velocity, hydrology &
evolution over time. Thus (while paradoxically) removed material  insight on glacial characteristics, especially in conjunction with sedimentology/statigraphy.

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