Question: If cratering rate on Earth is same as our Moon, why are their so few craters preserved?...
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![Page 1: Question: If cratering rate on Earth is same as our Moon, why are their so few craters preserved? Answer: Erosion.](https://reader036.fdocuments.us/reader036/viewer/2022062320/56649d4d5503460f94a2cea8/html5/thumbnails/1.jpg)
Question: If cratering rate on Earth is same as our Moon, why are their so few craters preserved?
Answer: Erosion
![Page 2: Question: If cratering rate on Earth is same as our Moon, why are their so few craters preserved? Answer: Erosion.](https://reader036.fdocuments.us/reader036/viewer/2022062320/56649d4d5503460f94a2cea8/html5/thumbnails/2.jpg)
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Estimating natural erosion rates
• Accumulation of sediment versus time in alluvial fans.
• Ratio of cosmogenic isotopic creation rate/unit area to concentration/unit volume of sediments.
• Closure age of exposed minerals at surface plus increase of temperature with depth.
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Erosion Rate for Cascades ~ 0.05 – .25 Km/Ma
mm/y = m/Ka = Km/Ma
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Erosion Rate for Central France: 55 m/MA
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1 t/ha/y => 30 m/Ma
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1 mm/a = 1km/Ma
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Summary of Erosion rates
• Himalaya: 2-3 m/Ky = 2-3 km/Ma
• Eastern edge of Bolivian Altiplano: 3 km/Ma
• Cascades: 300 m/Ma
• Massif Central (France): 50 m/Ma
• Atacama Desert (Chile/Peru): 0.5 m/Ma
• Central Australia: 0.5 m/Ma
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Question
If erosion can flatten mountain topography in only a few million years, why are there
mountains at all?
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Question: If erosion can flatten mountain topography in only a few million years, why are there mountains at all?
Answer: Uplift is continuous
Implication: Earth is a dynamic planet
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L = cA½
Channel length and drainage area
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Streamflow and drainage area…
QPA c
River basins in Kentucky, USA, from Solyom and Tucker, 2004
Q = 0.0171*A0.9932
R2 = 0.9977
Q = Fluvial Discharge P = Effective Precipitation Rate = Rainfall - lossesc = positive constant 1
Q Piaii
or
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Channel Width:
W Qb
W Channel Width
Q = Fluvial Discharge PA c
b = positive constant ~ 0.5
Data from the Clearwater River, Washington State, from Tomkin et al., 2003.
Q = 0.1335 * A0.9
W=4.2*A0.42
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W = b(AP)½Should actually be discharge = Area x precipitation
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Spatially Variable Precipitation, Ellis, Densmore & Anderson, 1999
Pre
cip
Distance
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