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Todd Ehlers - University of Michigan Peter Reiners, Gerard Roe, Sara Mitchell, David Montgomery

Todd Ehlers - University of Michigan Peter Reiners, Gerard Roe, Sara Mitchell, David Montgomery. Climate, Tectonics, and Topographic Evolution of the Washington Cascades: Insights from Coupled Process Models and Thermochronometry. [ George Collot, 1796 ]. Washington Cascades, U.S.A.

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Todd Ehlers - University of Michigan Peter Reiners, Gerard Roe, Sara Mitchell, David Montgomery

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  1. Todd Ehlers - University of Michigan Peter Reiners, Gerard Roe, Sara Mitchell, David Montgomery Climate, Tectonics, and Topographic Evolution of the Washington Cascades:Insights from Coupled Process Models and Thermochronometry [ George Collot, 1796 ]

  2. Washington Cascades, U.S.A.

  3. Hypothesis Tested: • Long term erosion rates across the Cascades are best explained by young, transient, topography and a strong orographic effect. • Observations and conceptual models tested • Methods: Coupled atmospheric-surface processes model • Comparison of model predictions and data

  4. Observations: Erosion Rates Across Topography Max Elevation Apparent Erosion Rate (mm/yr) Elevation (m) Mean Elevation Min Elevation Distance East (km)

  5. Conceptual Models Tested

  6. Conceptual Models Tested

  7. Conceptual Models Tested

  8. MethodsCoupled Numerical Models

  9. Atmospheric Model: Similar to approach of Alpert [1986] and Roe et al. [2002]

  10. Atmospheric Model PerformanceCentral Washington Cascades

  11. Surface Process Model: Based on the CASCADE algorithm of Braun and Sambridge (1997)

  12. Uniform Precipitation

  13. Physically Based Atmospheric Model

  14. Topographic Evolution and Precipitation Rate

  15. Animation: Topographic Evolution and Precipitation Rate

  16. Topographic Evolution and Erosion Rate

  17. Animation: Topographic Evolution and Erosion Rate

  18. Erosion Rate and Topography:u = 0.4 mm/yr

  19. Washington Cascades, U.S.A.

  20. Conclusions: • Influence of climate on topographic evolution in orogens: • Strong orographic effect results in asymmetric topography. • Pulse of high erosion rates propagates across the range. • Young AHe ages predicted on windward side of range. • Comparison with Data – Model A.5! • AHe ages are generally consistent with uniform uplift and transient topography over last 10 Ma. • Model discrepancies with data are due to neglection of isostasy which would introduce a component of non-uniform uplift.

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