Geoscience Reference
In-Depth Information
Chapter 6 examines flash flood and regional flooding
events that are usually severe enough to invoke states
of emergency. In addition, regional flooding accounts
for the largest death toll registered for any type of
hazard. This chapter begins by introducing the climatic
processes responsible for flash flooding. This is
followed by examples of flash flooding events in the
United States and Australia. Regional flooding is dis-
cussed in detail for the Mississippi River in the United
States, the Hwang Ho River in China, and Australia
where floods are a general feature of the country.
Drought-induced bushfires or forest fires are then
treated as a separate entity in Chapter 7. The conditions
favoring intense bushfires and the causes of such disas-
ters are described. Major natural fire disasters, including
in the United States and Australia, are then presented.
Two of the main issues discussed in this chapter are the
continuing debate over
prescribed burning
as a strategy
to mitigate the threat of fires (especially in urban areas),
and the regularity with which fire history repeats itself.
Both the causes of fires and the responses to them
appear to have changed little between the ends of the
nineteenth and twentieth centuries.
These climatic chapters are followed by Chapter 8's
discussion of aquatic hazards - encompassing a variety
of marine and lacustrine phenomena. Most of these
hazards affect few people, but they have long-term
consequences, especially if global warming becomes
significant over the next 50 years. Because of their
spatial extent and long period of operation, most of
the phenomena in this chapter can be ranked as
middle-order hazards. Waves are described first with
the theory for their generation. The worldwide occur-
rence of large waves is discussed, based upon ship and
satellite observations. This is followed by a brief
description of sea-ice phenomena in the ocean and at
shore. One of the greatest concerns today is the
impending rise in sea level, supposedly occurring
because of melting of icecaps or
thermal expansion
of
oceans within the context of global warming. World-
wide sea level data are presented to show that sea
levels may not be rising globally as generally believed,
but may be influenced in behavior by regional climatic
change. Finally, the chapter discusses the various
environmental mechanisms of sandy beach erosion
(or accretion) caused mainly by changes in sea level,
rainfall, or storminess. This evaluation utilizes an
extensive data set of shoreline position and environ-
mental variables collected for Stanwell Park Beach,
Australia. Much of the discussion in this chapter draws
upon the author's own research expertise.
Geological hazards - forming the second part of this
topic - are covered under the following chapter
headings: causes and prediction of earthquakes and
volcanoes; earthquakes and tsunami; volcanoes; and
land instability. Chapter 9 presents the worldwide distri-
bution of earthquakes and volcanoes and a presentation
of the scales for measuring earthquake magnitude. This
is followed by an examination of causes of earthquakes
and volcanoes under the headings of plate boundaries,
hot spots, regional faulting, and the presence of reser-
voirs or dams. Next, the presence of clustering in the
occurrence of earthquakes and volcanoes is examined,
followed by a discussion of the long-term prediction of
volcanic and seismic activity. The chapter concludes
with a presentation of the geophysical, geochemical, and
geomagnetic techniques for forecasting volcanic
and seismic activity over the short term.
Two chapters that are concerned separately with
earthquakes and volcanoes then follow this introductory
chapter. Both hazards, because of their suddenness and
high-energy release, have the potential to afflict human
beings physically, economically, and socially. Both rank
as the most severe geological hazards. Chapter 10 first
describes types of seismic waves and the global seismic
risk. Earthquake disasters and the seismic risk for
Alaska, California and Japan are then described. The
associated phenomenon of
liquefaction
or
thixotropy
,
and its importance in earthquake damage, is sub-
sequently presented. One of the major phenomena
generated by earthquakes is tsunami. This phenomenon
is described in detail, together with a presentation
of major, worldwide tsunami disasters. The prediction of
tsunami in the Pacific region is then discussed. Chapter
11, on volcanoes, emphasizes types of volcanoes and
associated hazardous phenomena such as lava flows,
tephra clouds, pyroclastic flows and base surges, gases
and acid rains, lahars (mud flows), and glacier bursts.
The major disasters of Santorini (~1470 BC), Vesuvius
(79 AD), Krakatau (1883), Mt Pelée (1902), and Mt St
Helens (1980) are then described in detail.
The section on geological hazards concludes, in
Chapter 12, with a comprehensive treatment of land
instability. This chapter opens with a description of
basic soil mechanics including the concepts of stress
and strain, friction and cohesion, shear strength of
soils, pore-water pressure, and rigid, elastic, and plastic
solids. Land instability is then classified and described
