Geology Reference
In-Depth Information
see new pressures on world soil resources and may potentially
contribute new solutions to perennial soil problems.
cleaning up chemical dump sites and fuel spills around gas
stations, but they may also prepare environmental impact
statements that are required for government-fi nanced projects
such as building highways and dams, or oil and gas drilling
near national parks and monuments. It is also important to
note that geologists are increasingly working with scientists in
other disciplines, because the problems confronting human-
ity reach across the artifi cial divisions between the sciences.
In several of the preceding chapters, we have discussed envi-
ronmental problems such as soil degradation (Chapter 6), fl ood
control (Chapter 12), groundwater contamination (Chapter 13),
and global warming (Chapter 14). In this section, we address
some other equally important environmental issues, such as acid
rain, ozone depletion, and radon gas.
Any geologic phenomenon that endangers property and
people is a
geologic hazard.
Earthquakes, volcanic erup-
tions, landslides, and river fl oods and coastal fl ooding dur-
ing hurricanes immediately come to mind, because they are
spectacular geologic hazards that commonly cause property
damage, injuries, and fatalities. However, some of the more
subtle hazards, such as soil creep and expansive soils, cause
more property damage, but rarely rate headlines in newspa-
pers or on news reports. Radon gas is also a geologic haz-
ard that is usually mentioned only in passing in the popular
press (see the section on “Geology and the Environment”).
Geologic hazards account for thousands of injuries and
fatalities each year, as well as billions of dollars in property
damages. You may read in the more sensational press that
geologic hazardous events, especially earthquakes, have
been increasing. The incidence of these events has not in-
creased, but there has been an increase in the amount of
property damages and the number of injuries and fatalities
because more and more people live in disaster-prone areas.
Population density and poor construction practices are
obvious contributors to disasters such as fl ooding and earth-
quakes in developing countries. The recent (August 2007)
flooding from monsoon rains in India and Bangladesh is
a good example. As we noted in Chapter 1 and reiterated
in this chapter, most scientists agree that the single greatest
environmental problem is overpopulation.
Of course, we cannot eliminate geologic hazards, but
we can better understand these phenomena, enact prudent
zoning and land-use regulations, and at the very least, de-
crease the amount of human suffering and monetary costs
associated with disasters. Unfortunately, geologic informa-
tion that is readily available is often ignored. A case in point
is the Turnagain Heights subdivision in Anchorage, Alaska,
that was heavily damaged when the soil beneath it lique-
fi ed during the 1964 earthquake (see Figure 11.18). Not only
were reports on soil stability ignored or overlooked before
homes were built there, but since 1964 new homes have been
built on part of the same site! La Conchita, California, lies
at the base of steep, unstable slopes that collapsed in 1995
and again in 2005, killing 10 people in the latter event (see
Figure 11.6). There are many examples of building subdivi-
sions on known landslide masses in the Los Angeles area, and
development in some coastal areas continues where erosion
will surely destroy homes and other structures.
One result of industrialization is atmospheric pollution, which
causes smog, possible disruption of the ozone layer, global
warming, and acid rain. Acidity, a measure of hydrogen ion
concentration, is measured on the pH scale (
Figure 24.3a).
A pH value of 7 is neutral, whereas acidic conditions corre-
spond to values less than 7, and values greater than 7 denote
alkaline, or basic, conditions. Normal rain has a pH value of
about 5.6, making it slightly acidic but
acid rain
has a pH of
less than 5.0. Some areas experience acid snow and even acid
fog with a pH as low as 1.7.
Several natural processes, including soil bacteria meta-
bolism and volcanism, release gases into the atmosphere that
contribute to acid rain. Human activities also produce added
atmosphere stress, especially burning fossil fuels that release
carbon dioxide and nitrogen oxide from internal combustion
engines. Both of these gases add to acid rain, but the greatest
culprit is sulfur dioxide released mostly by burning coal that
contains sulfur that oxidizes to form sulfur dioxide (SO
2
).
As sulfur dioxide rises into the atmosphere, it reacts with
oxygen and water droplets to form sulfuric acid (H
2
SO
4
), the
main component of acid rain.
Robert Angus Smith fi rst recognized acid rain in Eng-
land in 1872, but not until 1961 did it become an environ-
mental concern when scientists realized that acid rain is
corrosive and irritating, kills vegetation, and has a detrimen-
tal effect on surface waters. Since then, the effects of acid rain
are apparent in Europe (especially in Eastern Europe) and
the eastern part of North America, where the problem has
been getting worse for the last three decades (Figure 24.3b).
The areas affected by acid rain invariably lie downwind
from plants that emit sulfur gases, but the effects of acid rain
in these areas may be modifi ed by local conditions. For in-
stance, if the area is underlain by limestone or alkaline soils,
acid rain tends to be neutralized; however, granite has little
or no modifying effect. Small lakes lose their ability to neu-
tralize acid rain and become more and more acidic until
some types of organisms disappear, and in some cases, all
life-forms eventually die.
Acid rain also causes increased chemical weathering
of limestone and marble and, to a lesser degree, sandstone.
The effects are especially evident on buildings, monuments,
◗
Geologists who specialize in
environmental geology
are in-
volved in understanding the relationship between humans
and their geologic environment. Put another way, environ-
mental geologists are concerned with studying and resolv-
ing the problems that human occupation has caused in the
environment. Some environmental geologists are engaged in
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