Geology Reference
In-Depth Information
II. Introduction to Geologic
Hazards
INTRODUCTION
"Civilization exists by geological consent, subject to
change without notice."
automobiles, nuclear power plant emergencies, and
terrorism activities). And there has not been room to
include some of the very slow or chronic geologic
processes, such as wind and water erosion of soil,
permafrost degradation and desertification. We realize
that all these hazards are important and intercon-
nected. This is most obvious when considering the
impact that global climate change (GCC) has on
processes in the Earth system. The current warming
of the globe is a geologic and geophysical hazard
that impacts surficial geologic processes and the
biosphere. GCC also has a technological component
because of the human systems that are changing the
chemistry of the atmosphere. Global warming is the
ultimate geologic hazard that impacts everything from
local land-use planning to global long-range plan-
ning; we include it in the final exercise of the manual.
And as we look at planning we realize that many of
the natural hazards are not completely natural. They
occur because human activity modifies a component
of the Earth system (e.g., triggers landslides by
overuse of water on slopes) or selects hazardous
sites for building because of poor land-use planning
and enforcement (Wijkman and Timberlake, 1984).
The changing impact of human activity on the Earth
system is driven by changes in human population
and per capita consumption.
—W ill D urant
Humans and our societies are ultimately dependent
upon geology. Our food is grown from soils that are
the weathering product of rocks, our bodies need
water that moves in the hydrologic cycle, and we
build using either trees grown on soils, metals and
other resources mined from the earth, or plastics that
come from oil and other geological products. Global
energy resources are primarily oil, natural gas, coal or
nuclear; these are all geological. In brief, what we eat,
what we wear, where we live, how we work, and how
we move about are all ultimately dependent upon
geology.
One aspect of living with geology, however, is
that there are hazardous geologic events such as
earthquakes, volcanoes, or floods that can become
human disasters if we choose not to live wisely and
be aware of them. A geologic hazard is a geologic
condition, process or potential event that poses a
threat to the human colony (safety, health, structures,
functions of society and the economy). A natural haz-
ard (of which geologic hazard is one category) may
be defined as a natural geologic or biologic process
or condition that has the potential to harm humans or
their structures. Section II provides an introduction to
the nature, occurrence and mitigation of most of the
important geologic hazards.
It is not possible to include all hazards in the
exercises selected for this topic. Biological hazards
(e.g., plagues and disease, pests, and overpopulation
by humans) and most weather-related geophysical
hazards (e.g., tornadoes, lightning, extreme heat and
cold, winter storms, and wildland fires) are omitted.
Also omitted are magnetic storms, asteroid impacts,
and most technological hazards (e.g., air pollution,
Geography and geologic hazards globally
and in the USA
No one is entirely without risk from geologic hazards.
They are everywhere but do exhibit geographic varia-
tions. On a global scale earthquakes and volcanoes show
definite patterns of occurrence (Figures II. 1 A and B). At
the national scale, geographic variation of natural haz-
ards is. well illustrated by expansive soils, those that
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