Physical Geology Slides-Ground Water
Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay
Water For Human Use
||California doesn't have a water shortage; it has a
people overage. The rainfall in this environment
is perfectly sufficient to support the savanna ecosystem
seen here. It's just not sufficient to support ecosystems
like Los Angeles and San Francisco. The reservoir here is
part of California's water supply system, severely
depleted by a succession of dry years.
||Los Angeles recognized early in the 1900's that water
was what limited its growth, so the city purchased the
water rights in most of the Owens Valley, east of the
Sierra Nevada. This shows the aqueduct that carries water
from the valley to Los Angeles.
||Los Angeles water usage lowered the water level in
Mono Lake by over 40 feet before a court order forced the
city to limit withdrawals.
||This aqueduct in the San Bernardino Mountains is part
of the water system supplying southern California.
||In the 1920's and 1930's, San Francisco dammed the
Hetch Hetchy Valley, the next major canyon north of
Yosemite Valley. This is a distant view of the dam. It's
surprisingly inconspicuous, but that's the point of a dam
- impound the most water using the least materials.
||California conservationists considered the damming of
the valley a bitter blow, but it's hard to look at the
lake and see an environmental catastrophe. There is no
fishing, swimming or boating on the lake (the boat
belongs to the water authority).
||These circles in Nebraska are due to a revolutionary
development in farming called center-pivot irrigation.
Center-pivot irrigation has made it possible to farm land
that otherwise could not be farmed, but has also
dramatically increased the pressure on aquifers.
||A center pivot rig. Each set of wheels is
independently driven. Linkages between wheels turn the
motors on and off and keep the overall rig straight. In
Wisconsin a center-pivot rig means the difference between
a poor crop and a good one. In the High Plains it means
the difference between farming and not farming.
||Some places have more water than they need. New
Orleans is kept low and dry by a massive pumping
operation. This boom is returning water to the
||New Orleans is famous for its above-ground cemeteries,
partly a matter of European fashion but also due to the
high water table that can cause coffins to float upward.
This is not exactly what they had in mind by "the
South will rise again!"
||This is your intestinal tract. This is your
intestinal tract with cholera. Any questions? A scene
from Bosnia, illustrating why clean water is such a
problem even now for so much of the world's population.
Women in some Third World countries spend a third of
their time just gathering water.
||This gypsum block at Knossos in Crete has been
severely etched by solution, probably in only the century
or so since the site was excavated.
||A karst landscape in Turkey. Below the valley, a
limestone layer is dotted by hundreds of sinkholes. The
limestone has been eroded away above the valley.
||In areas with a lot of water, karst looks like this.
There are innumerable flooded sinkholes. This example is
in Argentina but large areas of Florida look similar.
||The word "karst" comes from Serbo-Croatian,
and the archetypical karst landscapes are in the former
Yugoslavia. In this valley in Bosnia, several sinkholes
have merged to create a larger depression called a solution
||Karst in Wisconsin tends to be subtle. The glaciers
buried or carried off much of it, and dolomite is not as
soluble as limestone. This small sinkhole at High Cliff
State Park has been largely obliterated by road
reconstruction. The surrounding dolomite sags smoothly
into the sinkhole.
||In September, 1992, seven inches of rain fell in a
day in western Wisconsin, and the weight of water caused
a small cave beneath this stream to collapse. The
students are standing in the now-dry stream bed.
||The water in the stream is now flowing underground.
The cave is probably not big enough for a person to crawl
||Rockhounds find this phenomenon fascinating.
||Looking down the former stream bed. The water
gradually re-enters the stream by seepage a couple of
Karst in China
||Most people, if they ever gave the matter any thought
at all, tend to assume traditional Chinese art like this
is artistic license. In fact, this is a realistic
depiction of the landscape of part of southern China.
||This is about as perfect a realization of Chinese art
in real life as anyone could imagine.
||Guilin has become one of China's top tourist
attractions because of its spectacular tower karst
landscape. Tower karst forms in tropical regions when
thick limestone dissolves rapidly, and occurs throughout
southeast Asia. More than one night mission in Vietnam
ended by flying into a karst tower. A submerged tower
karst on the coast of Thailand was the setting for scenes
in the James Bond films Man with the Golden Gun
and Tomorrow Never Dies. Less spectacular examples
occur in Cuba and Puerto Rico.
||This aerial view shows that the pinnacles actually
surround large solution valleys. The pinnacles are
columns left behind when sinkholes expand and merge. The
pinnacles are riddled with caves and are geologically
very ephemeral features.
||Geothermal phenomena like Mammoth Hot Springs in
Yellowstone National Park typically get their heat from a
shallow magma chamber. The terraces form when dissolved
minerals (mostly silica) form a rim around a shallow
puddle. As the puddle rises, so does the rim. Eventually,
the puddle overflows and the flowing mineralized water
rounds off the rim of the terrace with new mineral
||Films often portray Old Faithful going off with a
roar. In reality it sounds a lot more like a giant fire
hose. Geysers are very transient phenomena. They plug up
with mineral deposition or blow themselves apart with
violent eruptions. Old Faithful probably didn't exist a
few thousand years ago and probably won't exist in a few
thousand years more.
||Looking into the Grand Canyon of the Yellowstone, it
becomes obvious that the present geothermal phenomena in
Yellowstone are the tiniest fraction of what has occurred
there. The entire plateau has simmered in boiling water,
and the vivid colors of the canyon are all due to
hydrothermal alteration of the rocks.
||20 million years ago, the San Juan Mountains of
southwestern Colorado were another Yellowstone, a
volcanic plateau parboiled in geothermal waters. The
orange stain on the mountainside is a zone of
hydrothermal alteration and mineralization. The San Juan
Mountains were once a rich mining district. 20 million
years from now, Yellowstone may look like this.
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Created 13 July 1998, Last Update 12 January 2001
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