Geoscience Reference
In-Depth Information
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.
5
A variety of large-scale denudation chronologies and associated large-scale schemes for slope evolution
have been proposed over the years. These reflected slope evolution in particular climate regimes and crude
estimated rates of denudation. Modern research focuses on more detailed slope models and a materials
science approach. Denudation rates, calculated from sediment yields and laboratory experiments, show
that surface lowering rates are ultimately attuned to tectonic cycles and rates of plate motion.
FURTHER READING
Duff, P. M. D. (ed.) (1993) Holmes's 'Principles of Physical Geology', fourth edition, London: Chapman & Hall. This volume
of nearly 800 pages is a major reference text for any student of the physical environment. Although it ranges over the
entire geological environment, a large portion deals generally and then specifically with the processes which denude
and sculpture Earth's surface. Well written and concise, the text is supported by copious illustrations.
Fookes, P. G., Lee, E. M. and Milligan, G. (2005) Geomorphology for Engineers, Dunbeath, Scotland: Whittles. An enormous,
comprehensively illustrated textbook, at the forefront of the applied field, which bridges the academic and engineering
fields of geomorphology in a manner entirely readable and suitable for both students and practioners.
Huggett, R. J. (2003) Fundamentals of Geomorphology, London: Routledge. A good, straightforward and clearly written
geomorphology textbook, with a sound geological and tectonic introduction and clear illustrations.
Selby, M. J. (1993) Hillslope Materials and Processes, Oxford and New York: Oxford University Press. This remains
an outstanding text which commences with a review of rock and soil properties and strength. It proceeds via
weathering to geomorphic processes, focusing on slopes, slope failure and mass wasting before concluding with hill
slope models and denudation rates. The topic is exceptionally well illustrated, with case studies, line drawings and
photographs.
