Environmental Engineering Reference
In-Depth Information
SLOPE LANDFORMS AND SLOPE DEVELOPMENT
Slope landforms are either residual scars from which material has moved, or debris
deposits downslope. These components relate to each other and constitute features of a
slope landsystem of recognizable, recurring elements (Figure 13.15). Both are transient,
since scars represent local oversteepening beyond an unsustainable shear stress ( F s = < 1)
and deposits are probably connected with the fluvial landsystem. As with mass
movements, slope landform and development models abound, and one of the most
enduring and widely used is the hypothetical nine-unit land surface model (Figure 13.16).
By no means all elements are found on every slope but it is instantly recognizable, for
example, in the alpine landsystem described in Chapter 25.
CONCLUSION
It seems scarcely appropriate to review rock destruction so soon after its formation. Yet
destruction commences as soon as rock is elevated above sea level, or brought within
range of percolating water and air by the removal of overlying rocks. In essence, a new
set of environmental conditions have replaced those in which the rock formed, and its
susceptibility is roughly proportional to the degree of change. Weathering may be seen as
a means to an end, 'softening up' and further reducing the strength of Earth materials and
so facilitating subsequent mass wasting and erosion. Appreciation of the components and
origins of rock-mass strength is a prerequisite to understanding how the environment
mobilizes hydrothermal alteration, mechanical processes and gravity to overcome rock
strength. Denudation, weathering and mass wasting produce unstable and transient
surface materials but thereby also access to soil parent materials, nutrients and economic
mineral deposits vital to the biosphere and human societies.
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