Geology Reference
In-Depth Information
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bizarre-shaped deposits found in them. Although a great
many different types of cave deposits exist, most form in
essentially the same manner and are collectively known as
dripstone
. As water seeps into a cave, some of the dissolved
carbon dioxide in the water escapes, and a small amount
of calcite is precipitated. In this manner, the various drip-
stone deposits are formed (Figure 13.11c).
Stalactites
are icicle-shaped structures hanging from
cave ceilings that form as a result of precipitation from
dripping water (
What Would You Do
Your well periodically goes dry and never produces the
amount of water you would like or need. Is your well too shal-
low, is it drilled into Earth materials with low permeability, or
are nearby irrigation pumps causing your problems? What can
you do to resolve these problems?
Figure 13.12). With each drop of wa-
ter, a thin layer of calcite is deposited over
the previous layer, forming a cone-shaped
projection that grows down from the ceil-
ing. The water that drips from a cave's ceiling
also precipitates a small amount of calcite when
it hits the fl oor. As additional calcite is depos-
ited, an upward-growing projection called
a
stalagmite
forms (Figure 13.12). If a sta-
lactite and stalagmite meet, they form a
col-
umn
. Groundwater seeping from a crack in a
cave's ceiling may form a vertical sheet of rock
called a
drip curtain
, and water fl owing across
a cave's floor may produce
travertine terraces
(Figure 13.11c).
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Figure 13.10
Karst Landscape in Kunming, China, and Bowling Green,
Kentucky
GROUND WATER SYSTEM
AND ITS EFFECTS
Groundwater is a valuable natural resource that is
rapidly being exploited with seemingly little regard
to the effects of overuse and misuse. Currently,
approximately 20% of all water used
in the United States is groundwater.
This percentage is rapidly increas-
ing, and unless this resource is used
more wisely, sufficient amounts of
clean ground water will not be avail-
able in the future. Modifi cations of
the groundwater system may have
many consequences, including (1)
lowering of the water table, caus-
ing wells to dry up; (2) saltwater
incursion; (3) subsidence; and (4)
contamination.
a
The Stone Forest, 125 km southeast of Kunming, China, is a high-relief karst
landscape formed by the dissolution of carbonate rocks.
Withdrawing groundwater at a
significantly greater rate than
it is replaced by either natu-
ral or artificial recharge can
have serious effects. For ex-
ample, the High Plains aquifer
is one of the most important
aquifers in the United States. It
b
Solution valleys, sinkholes, and sinkhole lakes dominate the subdued karst topography east of
Bowling Green, Kentucky.
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