Geoscience Reference
In-Depth Information
Figure 1.4 Location of stream-gaging stations in the United States.
The dense concentration of stations in the eastern half
of the country reflects the fact that many more streams occur in the eastern United States than in the interior western states. The
map is color-coded to illustrate the amount of water in any given stream on October 29, 2012, relative to its average flow on that
day calculated over time. For example, red dots reflect very low water levels, whereas dark blue/purple dots mean that stream low
was relatively high on that day. Black dots represent localities on streams that have very high flow and may be close to flooding.
The concentration of black dots along the central Atlantic coast reflects prodigious rains dropped by Hurricane Sandy on this day.
do not occur in isolation from one another. Instead, they are
interconnected in often complicated ways that may at first ap-
pear chaotic. Despite this apparent complexity, natural systems
are, in fact, self-organizing entities that internally adjust toward
an equilibrium condition. These adjustments can be readily ex-
plained by understanding how dynamic feedbacks, oscillations,
and delays in reaction time influence outcomes.
To see an example of how environmental variables relate
to one another and can be viewed holistically within a natural
system, imagine you want to explain the spatial distribution of
rivers in the United States. One way to see the geographical
concentration of rivers in the country is with a map showing
the location of gaging stations, which are places where the U.S.
Geological Survey continuously monitors the flow of water in
the streams (Figure 1.4). Observe that the eastern part of the
country contains many more gaging stations than the interior
west in places such as Nevada and Utah. This pattern reflects
the fact that far more streams are found in the eastern part of the
United States than in the interior west.
The question a geographer would ask about this pattern is:
Why
do more rivers occur in the eastern United States than in the
western part of the country? This question would naturally lead
you to holistically examine streams as natural systems that re-
flect the input of water from some kind of source to the output of
water actually flowing in rivers and creeks. Understanding these
relationships, in turn, helps explain the geographical patterns
observed in Figure 1.4. The simple reason for the geographical
distribution of streams in the United States is that far more pre-
cipitation falls in the eastern part of the United States than in the
western states. You will later study why this geographical vari-
ability occurs, but for now it is sufficient to say it exists because
the atmosphere over the eastern United States typically contains
more water than in the interior parts of the western states. Thus,
more water flows from the atmosphere to the ground as precipita-
tion in the eastern United States than in the western states. Some
of this water flows directly across the Earth's surface as input
into streams. A great deal of it slowly absorbs into the ground
where it is steadily released into streams. As a result of these in-
terconnected processes, the eastern United States contains more
streams than the western part of the country.
The Earth's Four Spheres
As you can imagine, a huge number of component/process
combinations exist for geographical study in a holistic way. In
physical geography, these various combinations can be grouped
into the four “spheres” on Earth (Figure 1.5):
1.
Atmosphere
—The atmosphere is the gaseous shell that
surrounds Earth. This sphere is composed of many criti-
cal components essential to life, such as oxygen, carbon,
water, and nitrogen, that flow around Earth.
2.
Lithosphere
—The lithosphere is the solid part of Earth,
including soil and minerals. A good example of a natural
Atmosphere
The gaseous shell that surrounds Earth.
