1. Gradual, Incremental Hillslope Transport:
Creep
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2. Not Creep
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3. Schedule Conversion of Rock to Regolith on Hillslopes
Soil Transport by Creep on Hillslopes
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4. Two Fundamental Distinctions Between Hillslopes
Transport Limited Hillslopes Weathering Limited Hillslopes
Strength Limited Hillslopes
supply >> capacity
soil mantled landscape
capacity >> supply
bare, rocky landscape
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(premise from Carlson and Krikby, 1972)

5. Creep
Classic textbook images
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6. Hillslope erosion: Diffusive Processes
Gabilon Mesa, California
With and without vegetation, Images from Taylor Perron, MIT
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7. Soil Production From bedrock to regolith As uplifted to surface:
Mechanical alteration
Chemical alteration
Regolith:
Mobile regolith
Detached, motion
Vertical and lateral movement
Saprolite
Intact rock structure
Can be dug into
Weathered rock
Not mobilized
Weakly fractured/weathered
“Reactive
Zone”
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(Anderson and Anderson, 2010)

8. Strength and Mobility of Material
From bedrock to regolith
Strain measurement shows the expansion of soil
0 = no change
3 = 300% vol. increase
Fracture Production
Deepest are steep (tectonic)
Unweathered
Near-surface are horizontal
Increasingly oxidized
Highly weathered
Exfoliation
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9. Contrasting regolith profiles
Fractured but unweathered rock
Thin saprolite
Thin colluvial soil
Colorado Granodiorite
High Slope
Highly weathered rock
2m mobile regolith
5m saprolite
S. India Gniess.
Low Slope
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10. Breaking rock: Fracture formation
Thermal Stress: expansion/contraction
Strains are small (typically <0.1%)
But non uniform stress does most the work:
Thermal expansion coefficient different for each mineral
Non-uniform heating
Produces:
1. granular disintegration,
2. spallation
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(McFadden et al., 2005)

11. Exfoliation
As rocks approach the surface, constraining stresses are no longer isotropic and stressed rocks delaminate parallel to surface. NOT GLACIAL.
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Little Shut-eye Pass, Sierra Nevada, California, J. David Rogers

12. Frost Cracking Frozen water expands 11% …but not important!
Why? Not a sealed, closed system.
Water migrates toward the freezing front and freezes in existing cracks.
Thin film, unfrozen transport toward crack tips
Freezing opens tip, generating tension in fluid
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(Walder and Hallet, 1985)

13. Frost Cracking
Experiment to test this:
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14. What are the soil temperature conditions through the year?
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(Anderson et al., 2012)

15. Frost Cracking Depth dependent, not maximum at surface
(Anderson, 1998)
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16. Model Comparison: Two mean temperatures
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(Anderson et al., 2012)

17. Model Comparison: Two mean temperatures
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(Anderson et al., 2012)

18. Frost Cracking
Hales and Roering, 2005
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19. Mineral Stress (Expansion and Contraction)
Salt and Expansive Clays
Sandstone vs. Mudstone Slaking, New Zealand
Salt pits
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20. Seepage and Salt Weathering carves canyon alcoves
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(Lamb et al., 2006)

21. Biotic processes Roots: crack expansion, transmission of wind stress
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Danjon et al., 2008

22. Chemical Weathering (not covered)
Humic acid production by decomposition of organic matter
Mineral conversion (feldspar to clay)
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23. Chemical Weathering
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(Mudd et al., 2013)

24. Chemical Weathering
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(Mudd et al., 2013)

25. Chemical Weathering
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(Mudd et al., 2013)

26. Chemical Weathering
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(Mudd et al., 2013)

27. Chemical Weathering
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(Mudd et al., 2013)