Landslides - Extreme Events: A Physical Reconstruction and Risk Assessment - page 183

Landslide impacts
Landslide events in the USA cost $1.5 billion annually in direct eco-
nomic losses (Murck et al ., 1996). Twenty five to fifty lives are also lost each year
to this geological process. While these losses in human lives appear great, they
are considerably fewer in number than those occurring in less developed coun-
tries. This is, in the latter case, due to high-population densities, inappropriate
zoning laws, a lack of scientific information regarding landslide events and the
likelihood of such events occurring at any given site, and poor preparatory mea-
sures in case of such events. Although it has been pointed out that slope failure
cannot always be predicted, planning schemes can be adapted to a specific site if
economic prerequisites and scientific knowledge is available. Some of the largest
losses of human lives due to landslide events are listed in Table 7. 2 .
Generally the cost of slope movements can be grouped into three categories.
These are personal costs such as death and injury, economic loss by individuals
or the general public and environmental damage. Environmental damage fol-
lowing a landslide event is usually short lived unless the event had a great range
and extent, or the area in which it occurred is extremely unstable. The main
impact on a slope following a landslide is loss of in situ biologic and pedologic
material. Although these changes have traditionally been seen as a degradation
of the habitat that prevent climax conditions from developing, it is likely that
such slope movement events may play an important role in the maintenance of
species diversity and rejuvenation. This can be compared to the effects of fire
on many natural habitats. Larger slides have the potential to cause more severe
and long-term impacts as the entire environment can be deformed and lose
its biota. Slides can also derange natural stream patterns in an area as drainage
pathways are altered, sometimes resulting in the development of poorly drained
depressions and ponds. In more severe cases, as described in Chapter 6,land-
slides can cause the development of large lakes causing the submergence of
previously terrestrial areas. Riparian vegetation and fish habitats may also be
affected downstream from landslide events (Crozier, 1986).
palaeolandslides
Landslide events are often preserved for several thousands of years or
more in a given landscape. This is because landslides involve the displacement
of sometimes considerable volumes of rock, soil and sediment, and because
these materials weather or break down relatively slowly. Records of past land-
slides, therefore, are often present in the stratigraphic record. They can also be
recorded by other means, especially where they have impacted upon vegetation