Environmental Engineering Reference
In-Depth Information
Figure 13.16
A hypothetical nine-unit land surface model.
Source: After Dalrymple et al. (1968).
KEY POINTS
1
Denudation is the total effect of all processes which wear away Earth materials and
thereby lower the land surface. It normally commences with rock weathering on
exposure to the atmosphere and biosphere. Weathering products are subsequently
transferred downslope under gravity by a range of dynamic forces mobilized by water,
wind and ice in a variety of geomorphic environments.
2
Denudation exploits rock susceptibility in Earth's surface environment, which is alien
to that in which most rocks form. The strength of rock, acquired during formation and
diagenesis, depends on cohesive ionic bonds, interparticulate friction and its own
mass. If material resistance is exceeded by static and dynamic gravitational forces,
mobilized by tectonic and geomorphic processes, Earth material fails in a manner
reflecting its own properties and the nature of the forces applied.
3
Weathering reduces rock mass strength by the generation of internal stresses or the
alteration of geochemical properties. Physical or mechanical processes are initiated by
positive internal pressures through heating, hydration or the growth of salt or ice
crystals, or elastic strain release caused by the removal of the confining pressures of
adjacent rock. Chemical weathering processes operate through hydrothermal
alteration, since they involve solution, carbonation, hydration, hydrolysis and
oxidation, and are generally most effective in warm, moist conditions.
4
Mass wasting occurs when residual rock or earth material strength after weathering is
insufficient to withstand the downslope component of gravity. Slope material
properties, including water and air in voids and slope angle, determine the rate and
mode of mass wasting, for which several classifications exist. However, properties
often change in transit and most mass wasting proceeds as compound translation
failure.
