Geography Reference
In-Depth Information
6
Landslides
Michael Crozier
research effort aimed at reconstructing past
climates and climatic change in Europe, based on
landslide evidence preserved in the landscape
(Crozier 1997).
The third reason landslides are often studied by
geographers is that landslides can present a serious
natural hazard (Varnes 1984; Crozier 1996). A full
appreciation of hazard requires knowledge not
only of the physical process but also of the nature
of the threatened society. In a sense, hazards are an
aspect of human ecology. They involve
interrelationships between physical, social and
economic systems; as such, they constitute a field
of study in which geographers are able to make a
valuable contribution.
This chapter focuses on the principles of
landslide hazard and risk assessment. It briefly
introduces the physical process and then goes on
to discuss different approaches to landslide hazard
assessment.
INTRODUCTION
Landslides are of interest to geographers for three
main reasons. First, by eroding, transporting and
depositing soil and rock, they represent one of the
important geomorphic processes involved in
shaping the surface of the Earth. In unstable areas,
they may displace up to 2000 m3/km2/year
(Crozier 1989), severely depleting the soil resource
and threatening the sustainability of primary
production (Sidle et al . 1985). Although they are
particularly common in tectonically active
mountainous areas, and along river banks and
coasts, they may also occur in other areas that have
weak material or a susceptible geological structure.
The second reason for geographical interest is
that landslides are sensitive indicators of
environmental change. As a geomorphic process, a
landslide represents a short-term adjustment to
disturbance of the natural system. As they take
place, they rapidly convert unstable slopes to a
more stable condition, allowing other slow-acting
processes to assume the role of denudation. In
terms of landform evolution, this means that most
slopes are stable for most of the time. Thus when
landslides occur they are generally responding to
some significant change within the natural system.
Initiating factors may include tectonic activity,
climate change, and natural or human-induced
disturbance to the vegetation cover, slope
hydrology or slope form. Knowledge of both past
and present landslide activity can therefore provide
useful information on environmental change.
Indeed, there has been a major international
THE PHYSICAL PROCESS
In dealing with landslides, it is important to use
a classification that distinguishes between
characteristics that are relevant to the intended
end-use of the study. The classification should
use clearly defined and internationally
understood terms. The working party on the
World Landslide Inventory (1990) has made an
attempt to standardise terminology and defines
a landslide simply as: 'the movement of a mass
of rock, earth, or debris down a slope.' A more
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