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"Landslide incidence" is a measure of
how frequently landslides occur in any given area.
This map shows areas of high landslide incidence in
deep red. In these areas, over 15% of the earth's
surface is either an active landslide or an historic
landslide. Areas of high landslide incidence usually
have at least two of the following three risk factors:
1) steep slopes, 2) slide prone soils, or, 3) high
precipitation. As you can see, the mountainous and
high precipitation areas of the west coast have many
areas of high incidence as do many parts of the Rocky
Mountain area. Areas shown in orange have a moderate
landslide incidence.
This map also shows "landslide susceptibility"
(the probable degree of response of near-surface rocks
and soils to natural or artificial excavation, loading
of slopes, or unusually high precipitation The pink
and brown colors used on the map have high landslide
susceptibility. In these areas, at least 15% of earth's
surface has all of the risk factors associated with
an elevated landslide hazard but landslide incidence
is not high.
The map is a portion of the Landslide Overview
Map of the Conterminious United States (USGS Special
Paper 1183). This paper and others can be accessed
via the web at the USGS
Geologic Hazards website.
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