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Question : If cratering rate on Earth is same as our Moon, why are their so few craters preserved?

Question : If cratering rate on Earth is same as our Moon, why are their so few craters preserved? Answer : Erosion. Estimating natural erosion rates. Accumulation of sediment versus time in alluvial fans.

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Question : If cratering rate on Earth is same as our Moon, why are their so few craters preserved?

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  1. Question: If cratering rate on Earth is same as our Moon, why are their so few craters preserved? Answer: Erosion

  2. 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.

  3. mm/y = m/Ka = Km/Ma Erosion Rate for Cascades ~ 0.05 – .25 Km/Ma

  4. Erosion Rate for Central France: 55 m/MA

  5. 1 t/ha/y => 30 m/Ma

  6. 1 mm/a = 1km/Ma

  7. 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

  8. Question If erosion can flatten mountain topography in only a few million years, why are there mountains at all?

  9. 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

  10. L = cA½ Channel length and drainage area

  11. Streamflow and drainage area… or River basins in Kentucky, USA, from Solyom and Tucker, 2004 Q = 0.0171*A0.9932 R2 = 0.9977

  12. Channel Width: Data from the Clearwater River, Washington State, from Tomkin et al., 2003. Q = 0.1335 * A0.9 W=4.2*A0.42

  13. W = b(AP)½ Should actually be discharge = Area x precipitation

  14. Precip Distance Spatially Variable Precipitation, Ellis, Densmore & Anderson, 1999

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