Springs
The Water Cycle
What
is a spring?
A spring is a water resource formed when the side of a
hill, a valley bottom or other excavation intersects a flowing body of
groundwater at or below the local water table, below which the subsurface
material is saturated with water.
A spring is the result of an aquifer being filled to the
point that the water overflows onto the land surface.
They range in size from intermittent seeps, which flow
only after much rain, to huge pools flowing hundreds of millions of gallons
daily.
Springs are not limited to the Earth's surface, though.
Recently, scientists have discovered hot springs at depths of up to 2.5
kilometers in the oceans, generally along mid-ocean rifts (spreading ridges).
The hot water (over 300 degrees Celsius) coming from
these springs is also rich in minerals and sulfur, which results in a unique
ecosystem where unusual and exotic sea life seems to thrive.
How
are springs formed?
Springs may be formed in any sort of rock. Small ones are
found in many places.
In Missouri, the largest springs are formed in limestone
and dolomite in the karst topography of the Ozarks. Both dolomite and limestone
fracture relatively easily.
When weak carbonic acid (formed by rainwater percolating
through organic matter in the soil) enters these fractures it dissolves bedrock.
When it reaches a horizontal crack or a layer of
non-dissolving rock such as sandstone or shale, it begins to cut sideways.
As the process continues, the water hollows out more
rock, eventually admitting an airspace, at which point the spring stream can be
considered a cave. This process often takes tens to hundreds of thousands of
years to complete.
Water
flow from springs
The amount of water that flows from springs depends on
many factors, including the size of the caverns within the rocks, the water
pressure in the aquifer, the size of the spring basin, and the amount of
rainfall.
Human activities also can influence the volume of water
that discharges from a spring-groundwater withdrawals in an area can cause
water levels in the aquifer system to drop and ultimately decreasing the flow
from the spring.
Most people probably think of a spring as being like a
pool of water—and normally that is the case.
But, as this picture of the wall of the Grand Canyon in
Arizona, USA shows, springs can occur when geologic, hydrologic, or human
forces cut into the underground layers of soil and rock where water is in
movement.
Spring
water is not always clear
Water from springs usually is remarkably clear. Water
from some springs, however, may be "tea-colored."
This picture shows a natural spring in southwestern
Colorado. Its red iron coloring and metals enrichment are caused by groundwater
coming in contact with naturally occurring minerals present as a result of
ancient volcanic activity in the area.
In Florida, many surface waters contain natural tannic
acids from organic material in subsurface rocks, and the color from these
streams can appear in springs.
If surface water enters the aquifer near a spring, the
water can move quickly through the aquifer and discharge at the spring vent.
This
water is cold and clear—is it fit to drink?
The quality of the water in the local groundwater system
will generally determine the quality of spring water.
The quality of water discharged by springs can vary
greatly because of factors such as the quality of the water that recharges the
aquifer and the type of rocks with which the groundwater is in contact.
The rate of flow and the length of the flowpath through
the aquifer affects the amount of time the water is in contact with the rock,
and thus, the amount of minerals that the water can dissolve.
So, should you feel confident about whipping out your
canteen and filling it with cool and refreshing spring water? No, you should be
cautious.
The temperature of an Ozark spring comes from its passing
through rock at a mean annual temperature of 56 degrees Fahrenheit.
The water is crudely filtered in the rock, and the time
spent underground allows debris and mud to fall out of suspension. If
underground long enough, lack of sunlight causes most algae and water plants to
die.
However, microbes, viruses, and bacteria do not die just
from being underground, nor are any agricultural or industrial pollutants
removed.
By the way, no, this man is not getting a drink from this
tempting spring. He is a USGS hydrologist sampling the near-boiling water from
a spring in Wyoming.
Thermal
springs
Thermal springs are ordinary
springs except that the water is warm and, in some places, hot, such as in the
bubbling mud springs in Yellowstone National Park, Wyoming.
Many thermal springs occur
in regions of recent volcanic activity and are fed by water heated by contact
with hot rocks far below the surface.
Even where there has been no
recent volcanic action, rocks become warmer with increasing depth. In such
areas water may migrate slowly to considerable depth, warming as it descends
through rocks deep in the Earth.
If it then reaches a large
crevice that offers a path of less resistance, it may rise more quickly than it
descended.
So, should you feel confident about whipping out your
canteen and filling it with cool and refreshing spring water? No, you should be
cautious.
The temperature of an Ozark spring comes from its passing
through rock at a mean annual temperature of 56 degrees Fahrenheit.
The water is crudely filtered in the rock, and the time
spent underground allows debris and mud to fall out of suspension. If
underground long enough, lack of sunlight causes most algae and water plants to
die.
Water that does not have
time to cool before it emerges forms a thermal spring.
The famous Warm Springs
of Georgia and Hot Springs of Arkansas are of this type.
And, yes, warm springs can
even coexist with icebergs, as these happy Greenlanders can tell you .
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https://water.usgs.gov/edu/watercyclesprings.html
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