Geosphere Lecture 6

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Early theories explained landforms in the context of
the great flood or ‘deluge’
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Uniformitarianism
the present is the key to the past’
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Hutton
introduced Uniformitarianism & Gradualism. He explained the features of the Earth’s crust by means of natural processes over geologic time -> “Father of Modern Geology”
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Catastrophism
Many landforms are a product of extreme events
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Lyell
Principles of Geology , popularising James Hutton’s theory about Uniformitarianism & Gradualism (friend of Charles Darwin)
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The total amount of sediment eroded from a hillslope, or the total amount transported by a river during a year is a
measure of geomorphic ‘work’
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Landslide Sediment Flux =
Magnitude x Frequency
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1:1 linear relation between
frequency and areaa
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SMALL AND LARGE LANDSLIDES HAVE
EQUAL CONTRIBUTIONS to total sediment flux
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Stream power =
the rate of energy dissipation against the bed and banks of a river or stream per unit downstream length
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Linear relationship between Q and S is
0.012
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Stream Power big rivers on flat terrain >>
small rivers on steep terrains
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Missoula floods:
the cataclysmic floods that swept periodically across eastern Washington and down the Colombia River Gorge at the end of the last ice age.
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Glacial lake outburst floods were the result of periodic sudden
ruptures of the ice dam on the Clark Fork River that created Glacial Lake Missoula. After each ice dam rupture, the waters of the lake would rush down.
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At least twenty-five massive floods, the largest discharging
10 cubic kilometres
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Dry Falls Washington
plunge pools left behind when Glacial Lake Missoula's debris-clogged waters rushed over the rocky precipice known today as Dry Falls. (length 3.5 miles and a height of 121m)
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Giant current ripples ( between 1 and 15 m) high and are regularly spaced, relatively uniform hills.
Need Huge amounts of water
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The Scablands are littered with large boulders called
glacial erratic's that rafted on glaciers and were deposited by the glacial outburst flooding. The lithology of erratics usually does not match the rock type that surrounds it, as they are often carried very far from their origins.
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Competence of the river can be calculated based on
dimensions river channel and sediment characteristics
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Velocity can be estimated based on
roughness and diameter of largest particles
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Shear stress =
Critical shear stress of largest particles, some constants rho, g, k -> giving us h.S = 0.1D
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N. Kasei -> one of the longest continuous outflow channels on
Mars.
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Earthquake- and storm-triggered landslides in actively deforming orogens increase
the supply of sediment to rivers.
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The decadal pattern of sediment yield from seismically active areas such as Taiwan is controlled by
large earthquakes
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Key channel responses:
Initial aggradation Subsequent incision and widening Bed armouring
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All fine sediments washed out so sediment size increases of sediment still present
critical shear stress increases
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Shear stress decrease because
slope declines due to erosion
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Upper fan surface forms when slope supply >
river transport capacity
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Fan entrenchment occurs when slope supply
< river transport capacity
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Other cards in this set

Card 2

Front

Uniformitarianism

Back

the present is the key to the past’

Card 3

Front

Hutton

Back

Preview of the front of card 3

Card 4

Front

Catastrophism

Back

Preview of the front of card 4

Card 5

Front

Lyell

Back

Preview of the front of card 5
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