Geologic erosion

It should be mentioned that, in addition to deposition of material on a forming soil, erosion is also occurring. Even under the best protection, soil is always undergoing what is called geologic erosion. Because of this, soil development will always reach a quasi equilibrium between deposition, development, and erosion leading to a soil where the horizons change very little over time. 

Wellman, H.W. and Wilson, A.T. (1965) Salt weathering, a neglected geological erosive agent in coastal and arid environments, Nature 205, 1097... 

Qualitative method by the diagram of soil depth / slope angle etc, by rating system (topography, geology, erosion, water spring, soil creep, etc.)... 

Let us now consider a chemical reaction whose initial and final states are different. Then the potential energy surface will not be symmetrical. This geological analogy will be helpful Suppose the valleys are formed by erosion. Then the valley that has eroded faster (or for a longer time) will be both deeper and longer than the less eroded valley, with the necessary consequence that the saddle between the two valleys is shifted toward the shallower valley. Figure 5-4 shows such a surface on which the reactant valley is longer and deeper than the product valley clearly the transition state is located closer to the final state than to the initial state as a result of this disparity in stabilities. 

Physiographic development of the surface of the earth refers to the landforms and shapes of the landscape. These surface features are subject to continuous change from constructive (e.g., uplift, volcanic activity, and deposition of sediments) and destructive (e.g., erosion) processes. Landform modifications are continuous and sequential. These modifications establish a predictable continuity that can be helpful in determining certain aspects of relative geologic ages. 

In developing and applying the erosional-depositional system, careful consideration was given to the environmental factors which influence the potential for erosion, transport and deposition climate, topography, geology and soils, as well as human activity. 

Brown, W.M. Hines, W.G. Rickert, D.A. Beach, G.L. A Synoptic Approach for Analyzing Erosion or a Guide to Land Use Planning. Geological Survey Circular 715-L. US6S, Reston, VA, 1979 1-45. 

Fig. 9-3 Conceptual model to describe the interaction between chemical weathering of bedrock and down-slope transport of solid erosion products. It is assumed that chemical weathering is required to generate loose solid erosion products of the bedrock. Solid curve portrays a hypothetical relationship between soil thickness and rate of chemical weathering of bedrock. Dotted lines correspond to different potential transport capacities. Low potential transport capacity is expected on a flat terrain, whereas high transport is expected on steep terrain. For moderate capacity, C and F are equilibrium points. (Modified with permission from R. F. Stallard, River chemistry, geology, geomorphology, and soils in the Amazon and Orinoco basins. In J. I. Drever, ed. (1985), "The Chemistry of Weathering," D. Reidel Publishing Co., Dordrecht, The Netherlands.)...

Sugden, D. E. (1976). A case against deep erosion of shields by ice sheets. Geology 4,580-582. 

Carbon is released from the lithosphere by erosion and resides in the oceans ca. 10 years before being deposited again in some form of oceanic sediment. It remains in the lithosphere on the average 10 years before again being released by erosion (Broecker, 1973). The amount of carbon in the ocean-atmosphere-biosphere system is maintained in a steady state by geologic processes the role of biological processes is, however, of profound importance... 

Among the oldest rocks on Earth are those on Isua, an island off the coast of Greenland they are 3.8 Gyr old, formed some 0.7 Gyr after accretion of the Earth. The rocks mark the beginning of the Archean period of geological time. The Isua rocks suggest that there was an extensive hydrosphere at this time, with erosion, transportation and deposition of minerals from water solution. The oldest lunar rocks, however, record an earlier high-temperature event - the Earth-Moon capture event. 

The geology not only provides the chemical source for trace-element mobility but it also provides the physical framework for water-flow paths. The structural properties of the rocks, the porosity, permeable fractures, provide for water-mineral reaction and element mobility. The geomorphology contributes to water-table levels, aquifer permeability, surface-water travel times, and time periods for erosion and sediment transport. Examples of... 

---