Geology Reference
In-Depth Information
distinctive shapes of active volcanoes are typical fea-
tures that easily can be identified on topographic maps.
This manual introduces you to many of the tools
and techniques that geologists use to gather data and
answer questions. Doing well on these exercises will
help you become a more aware, and safer, citizen.
become more aware of the importance of and potential
impacts from current geologic issues.
Geologists must often accept that answers to
questions may be uncertain. As a field-based science,
geologists are often limited by nature in the ability to
observe complex processes directly. We can not, for
instance, cut through an active volcano and observe
directly how magma is working at depth. Nor can
geologists, despite fervent wishes, travel through time
to see the past directly. Limits of nature, however,
mean that geologists must be very careful about obser-
vations that can be made, so the maximum amount of
knowledge can be gained.
Many apparently permanent geological features
are actually moving slowly, often in interconnected
cycles. Continents move on large plates; rocks are cre-
ated and erode. These processes form new rocks and
illustrate the continual tug of war between constructive
and destructive Earth processes. The hydrologic cycle
links circulation of waters in the atmosphere, on land,
underground and in the ocean. It has been said that one
can never cross the same river twice, which means that
it is not possible to regather all the same water mole-
cules moving in exactly the same way. Through geol-
ogy, however, humans are able to view the processes of
the river, and to understand, for instance, that floods
are a normal part of a river's cycle, and that a river is a
normal part of the hydrologic cycle.
OVERVIEW OF EXERCISES 1-3
The three exercises in this section provide basic con-
cepts, tools, and techniques of the geosciences. For
some this material will be a review, for others an intro-
duction, and for all a handy reference while answering
questions in this manual.
In
Exercise 1,
we explore minerals; common
igneous, sedimentary, and metamorphic rocks; regolith
(the engineer's soil); and geologic time and geologic
processes in the Earth system. Understanding minerals
is important for our use of geologic resources and build-
ing on sediments and rocks. Sedimentary rock, because
of its widespread extent, is most likely to be the bedrock
encountered in environmental investigations. But more
important is a related component of the rock cycle, the
surficial sediment or regolith that overlies the rocks.
With geologic time, we focus on the last few hundred
thousand years and present a geologic time chart that
emphasizes this. At the same time we realize that
understanding paleoenvironments and changes over
deeper time is important. In this exercise we ask you to
explore the Earth system, the connections that exist
between the processes (Figure
1.3),
and the rates of
these processes. In seeking to understand and address
environmental problems, an Earth systems science
approach which looks at frequency, rates, connectivity
and controls on events is essential.
In
Exercise 2
we gain increased familiarity with
maps and images that provide the spatial framework
for understanding environmental problems. A review
of topographic maps is followed by interpretation of
geologic maps and an introduction to other useful
images including aerial photographs and satellite and
LIDAR images. Fortunately for the environmental geol-
ogist, as our impact on the planet has increased expo-
nentially, the technology to observe the nature, extent,
and rates of change has grown in a similar fashion.
Scientific measurements and notation, useful cal-
culations and conversions, display of data on graphs
and tables, and simple statistics are in
Exercise 3.
Addi-
tional useful information for problem-solving exer-
cises in this manual is in the Appendices.
OBSERVATIONS AND DESCRIPTIONS
A key skill in geology is careful observation and
description of geologic products and processes. Fea-
tures of rocks can be interpreted to reveal a great deal
about their history. Deposits at the surface of the Earth
will be different if they form from a river, from a land-
slide, or from a volcanic eruption.
Where direct observation is not possible, geolo-
gists use other methods to gather data. In environmen-
tal geology, these methods may include seismographs,
in order to measure earthquakes and interpret subsur-
face structures of the Earth. Another method is satellite
imagery. Satellite images are able to show us parts of the
world that we can not see in other ways. Airp les fly-
ing over sites take photographs or gather radt. images.
Maps are a very powerful tool in geologic studies.
Patterns made by contours on U.S. Geological Survey
topographic maps are very useful in interpreting
zones with geologic hazards. Hummocky topography
of landslides, rivers meandering on floodplains and
Bibliography
Baker, V. R., 1996, The geological approach to understanding
the environment:
GSA Today,
v. 6, no. 3, p. 41-43.
Bretz, J H., 1940,
Earth sciences:
New York, Wiley and Sons,
260 p.
Frodeman, R, 1995, Geological reasoning: Geology as an
interpretive and historical science:
Geological Society of
America Bulletin,
v. 107, p. 960-968.
Thorleifson, H., 2003, Why we do geology:
Geology,
v. 32, no. 4,
p. 1 and 4.
