Slope Processes and the Susceptibility of Lithologies to Erosion

Weathering, atmospheric deposition, and the fixation of atmospheric gases are the ultimate sources of the material transported by rivers. These 

The erosion process on slopes can be envisioned as a continuum between the weathering-limited and transport-limited extremes (Carson and Kirkby, 1972 Stallard, 1985). Erosion is classified as transport-limited when the rate of supply of material by weathering exceeds the capacity of transport processes to remove the material. Erosion is weathering-limited when the capacity of the transport process exceeds the rate at which material is generated by weathering. These two styles of erosion represent an interesting parallel to controls of weathering reaction rates on mineral surfaces, discussed earlier, wherein a similar continuum was defined between surface reaction control and transport (diffusion) control (Stallard, 1988). 

In contrast, under transport-limited conditions, weathering rates are ultimately limited by the formation of soils that are sufficiently thick or impermeable to restrict free access by water to unweathered material. Erosion rates are low, and soils and solid weathering products are cation-deficient. In regions where transport-limited erosion predominates, soils are thick and slopes are slight and convexo-concave (Fig. 6-2b). With time, these 

Slight slopes that are Steep slopes that are 

Erosion rates independent Erosion rates depend on 

In contrast, under transport-limited conditions, weathering rates are ultimately limited by the formation of soils that are sufficiently thick or impermeable to restrict free access by water to unweathered material. Erosion rates 

Slight slopes that are convexo-concave Steep slopes that are straight and at a threshold angle 

Weathering limited potential transport processes greater than weathering supply. Transport limited supply by weathering greater than the capacity of transport processes to remove material (until weathering is slowed by feedback). 

For a given set of conditions (lithology, climate, slope, etc.), there is presumably an optimum soil thickness that maximizes the rate of bedrock weathering (Fig. 9-3) (Carson and Kirkby, 1972 Stallard, 1985). For less than optimum soil thicknesses, there is insufficient pore volume in the soil to accept all the water supplied by precipitation and downhill flow. Excess water runs off and does not interact with the subsurface soil and bedrock. In contrast, water infiltrates and circulates slowly through thick soils (especially where forested If profile thicknesses greatly 

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