Geology Reference
In-Depth Information
cause damage to structures by expanding and con-
tracting with available moisture. This soil problem is
related to the mineral materials and chemistry of the
soils. Soils also exhibit regional trace element differ-
ences that can contribute to excesses and deficiencies
in plants and animals, thus creating a potential health
hazard. Other hazards, such as floods, can occur
almost anywhere that people live or work. It is impor-
tant, therefore, that each citizen be aware of geologic
events that exist where they live, and be prepared to
cope with these events, should they occur and become
hazards.
In this Introduction to Geologic Hazards, we
include two sets of questions. The first set is related to
the general nature and types of hazards, their occur-
rence on a global scale, and the key concepts of haz-
ards. The second set of questions explores disasters in
the USA: types, locations, and relationships between
population, population density and number of disas-
ters (Presidential Disaster Declarations).
Geologic events are natural. The events become hazards
and disasters when people chose to live unwisely in
areas that can be impacted. For instance, much flood
damage and many coastal problems can be avoided by
not living on floodplains (or "in the river" as some
geologists suggest) or living directly on the changing
coast.
People can avoid or reduce the risks that the hazards
present. Understanding why geologic events happen
in the way they do, when they are likely to happen,
where they are likely to happen and the impacts
they can have on humans is a major goal of these
exercises.
Geologic events may not be predictable. Geologists
distinguish "predictions" (3 pm Friday) from "forecasts"
(there is a 20% chance sometime in the next 30 years).
Some events, such as some landslides are more likely to
occur in wet seasons (i.e., they have rainfall as a
precursor) and therefore general statements about the
times of their occurrence, or a forecast, may be made.
Other events, such as earthquakes, have proven to be
very difficult to predict. People need to be prepared,
therefore, to cope with events that may occur
unexpectedly.
Key concepts about geologic hazards
When working the exercises in Section II, it will be
helpful to keep the following concepts in mind.
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