Weathering erosion rate

Soil is a key component of the rock cycle because weathering and soil formation processes transform rock into more readily erodible material. Rates of soil formation may even limit the overall erosion rate of a landscape. Erosion processes are also a key linkage in the rock cycle... 

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... 

In regions where the erosion regime is weathering limited, susceptibility of the bedrock to chemical and physical weathering controls erosion rates. This susceptibility relates directly to the chemical and physical properties of the rock. Susceptibility also depends on local climate. Moreover, weathering rates are affected by the... 

Based on predicted weathering and erosion rates of the region, we estimate the profile to be several million years old. Because the soil has developed in situ, the topmost grains have reacted with water for the greatest extent of time. With depth, the total "lifetime" of the particles as soil decreases. This implies that the topmost quartz surfaces should be "reactively mature" (all fines removed, deep grown-together etch pits) and the bottom-most quartz surfaces should be "reactively young" (plentiful fines, fresh surfaces). ... 

Weight loss (percent) after weathering period Erosion rate at 2,400 h (/im/h)... 

Latewood also erodes away through weathering. Its erosion rate for most softwood species is slow (Table IV). Eventually, however, the face veneer of unprotected plywood will erode away, regardless of the grain pattern or wood species. 

Although global transport balance modelling thus provides some perspective on the rate at which CO2 could have been removed from the atmosphere in early Earth history, the resolution of the method is inherently poor and it can provide only broad outlines. The large uncertainties and the problems encountered highlight the need to find independent constraints on weathering and erosion rates in Archaean time to understand the early evolution of the Earth s atmosphere, climate and life. 

This erosion or weathering is not to be confused with decay. Decay is caused by fungi and can lead to rapid deterioration throughout the volume of the wood. Weathering, on the other hand, is a surface deterioration and, although the initial color changes can be seen within days or even hours, the surface erosion proceeds very slowly. The erosion rate for solid wood in temperate zones is in the order of 1/8 to 1/2 inch per century and depends mainly on amount of UV exposure and the wood species (1, 2). Other degrading factors include moisture, mechanical abrasion, temperature, and pollution (3). 

Feist (20) and Williams ( ) have used xenon arc accelerated weathering to determine the efficacy of surface treatments of wood. The degradation of the surface is manifest as erosion and can be measured microscopically (2). In recent work at the Forest Products Laboratory (22), these techniques were used to determine the effect of acid treatment on the erosion rate of western redcedar (Thuja plicata Bonn ex D. Don). 

Five replicate specimens of western redcedar and their longitudinally end-matched controls were artificially weathered (xenon arc Weather-Ometer, approximately 24-h light and 4-h deionized water spray daily). The Weather-Ometer was shut down for about 1 h Monday through Friday in order to soak the specimens in dilute acid for 15 min. Six types of acid soaks were used nitric and sulfuric acids at pHs of 3.0, 3.5, and 4.0. I found similar results with both acids. Compared with the unsoaked controls, the 3.0 pH acid caused a 10% increase in erosion rate. At a pH of 3.5 the effect was a 4% increase due to the acid, and no effect was found at a pH of 4.0. 

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... 

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