Lecutres Part 3

Lecutres Part 3 - Weathering and removal of material A...

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Weathering and removal of material
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A purpose of Earth surface process studies is to show how process form • Express express process rates in terms of topographic factors (e.g. slope, distance from divide) • Assume continuity (e.g. mass balance) To do this:
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A generalized hillslope y=0 y=y 0 y=elevation IN OUT change in land surface elev. addition of weathered rock
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Lots of weathered rock (soil)
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If a hillslope is transport limited….
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…hillslope development depends on the transporting capacity of relevant processes,
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…weathering rate is reduced to equilibrium value by an increase in soil thickness….
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….leading to a well developed soil cover.
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What do this and the next 3 have in common?
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thin or no soil cover.
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Wherever the removal is weathering limited…
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…hillslope development depends on variations in weathering rate…
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…and transport rate is reduced to the rate at which fresh rock weathers
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…leading to thin or no soil cover.
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Denudation may produce lots of unconsolidated material (stuff, regolith, soil, overburden etc….)
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And it is transported downslope at different rates….
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A generalized hillslope y=0 y=y 0 y=elevation IN OUT change in land surface elev. addition of weathered rock
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Transport Rate > Weathering Rate WEATHERING LIMITED Thin Soil Threshold slope angles Parallel retreat (slope angle preserved)
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Transport rate < Weathering rate TRANSPORT LIMITED Well-developed soil cover Concavo-convex slopes (slope angle not preserved)
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RECALL: Bedrock weathering depends mainly on water circulation through it.
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Soil thickness affects weathering rates by affecting residence time of water. • Very thin soils have negligible storage and very rapid runoff. • Thick soils store a lot of water and attenuate its delivery to the bedrock interface • Intermediate depth soils therefore will have maximum bedrock weathering rates.
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Soil Depth Effects on Bedrock Weathering Rates Soil d epth (L) Rate of bedrock W eathering (L/T)
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Bedrock Weathering Rates: Effects of Increased Soil Depth Soil d epth (L) Rate of bedrock W eathering (L/T)
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Bedrock Weathering Rates: Effects of Decreased Soil Depth Soil d epth (L) Rate of bedrock W eathering (L/T)
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This note was uploaded on 06/03/2011 for the course GEOL 315 taught by Professor Torres during the Spring '11 term at South Carolina.

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Lecutres Part 3 - Weathering and removal of material A...

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