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7/29/2019 Groundwater and Karst Topography Ch 92
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Groundwater and Karst
TopographyChapter 9, Section 2
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The Hydrologic Cycle (WATER CYCLE)
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Evaporation
Condensation
Precipitation
Runoff
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Soil is made up of many small rock andmineral fragments.
Holes, cracks, and crevices exist in therock underlying the soil.
Water that soaks into the ground and
collects in these pores and empty spacesbecome part ofgroundwater.
Groundwater
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Water is recharged to the ground-water
system by percolation of water from
precipitation and then flows to the stream
through the ground-water system.
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14 % of all freshwater on Earth exists as
groundwater, 30 times more water than is
contained in all of Earths lakes and rivers.
Water that soaks into the ground becomes
a part of the groundwatersystem.
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A groundwatersystem is similar to a river
system.
Instead of having channels that connectdifferent parts of a drainage basin, the
groundwater system has connecting
pores.
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Soil and rock are permeable if the pore
spaces are connected and watercan pass
through them easily.
If a rock or sediment has few pore spaces,
or they are not well connected, then theflow of groundwater is blocked.
These materials are impermeable, which
means that watercannot pass through them.
Granite and clay are impermeable;
sandstone is permeable.
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Permeabi l i ty
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Groundwater keeps going deeper into the
Earths crust until it reaches a layer of
impermeable rock.
At this point, the water stops moving
down.
Water begins filling up the pores in the
rocks above. The layer ofpermeablerock that lets water move freely is an
aquifer.
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The zone of aeration is the first layer of
soil that is permeable. Water and air pass
through this layer easily.
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The area where all of the rocks are filled
with wateris called the zone ofsaturation.
The upper surface of this zone is called
the water table.
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GROUNDWATER FEATURES
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Groundwater Zones
Zone of
Saturation
Zone of
Aeration Precipitation
Body of water
Earths Surface Water Table
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Many people get their water from
groundwaterthrough wells that have been
drilled into the zone ofsaturation.
The supply of groundwater is limited.
During a drought the water table drops,which is why you should conserve water.
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People get the majority of their water from
wells. A good well extends deep into the
zone ofsaturation, where groundwaterflows into the well and a pump brings it to
the surface.
If too much water is pumped out, then
wells can go dry.
The land level can sink from the weightof the sediments above the now-empty
pore spaces.
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What does a normal household
well look like?
Water flows into a
well and then a pump
brings the water to
the surface. Wells can go dry if too
many are located in
one area, or if a
drought takes place.
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ARTESIAN WELL
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Water pumped from the ground-water system causes
the water table to lower and alters the direction of
ground-water movement. Some water that flowed to the
stream no longer does so and some water may bedrawn in from the stream into the ground-water system,
thereby reducing the amount of streamflow.
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CONES OF DEPRESSION
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Shallow wells go dry due to
excessive pumping
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In some places, the water table is so
close to Earths surface that water
flows out and forms a spring.
Springs are found on hillsides orother places where the watertable
meets a sloping surface.
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SPRING FORMATION
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HOT SPRINGS
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Hot Spring
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A geyseris a hot spring that erupts
periodically, shooting waterand steam into
the air.
Groundwater is heated to high
temperatures from magma under the
Earths surface. As the water heats, it
expands, forcing water out of the ground
along with steam, as the remaining
water boils.Old Faithful in Yellowstone National Park
is a famous geyser.
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GEYSERS: OLD FAITHFUL
http://www.yellowstone.net/russfinley/tour/video/oldfaith2.rm
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Picture of a geyser in action!
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Geyser
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Groundwater mixes with carbon dioxide to
form carbonic acid.
Limestone is a rock that is easily dissolved
by carbonic acid.
As the acidic groundwater moves through
pores in limestone, the rock dissolves,
enlarging cracks until an underground
opening called a cave is formed.
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Groundwater not only dissolves limestoneto make caves, but it also can makedeposits on the insides of caves.
Water dripping from the cave wallscontains calcium ions dissolved from the
limestone. If the waterevaporates whilehanging from the ceiling, the calciumcarbonate is left behind and builds up to
form a stalactite.
Where water drops fall to the floor, astalagmite forms.
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Cave
Development
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CAVE ENTRANCE
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Disappearing Stream
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Disappearing Stream
NATURAL CHIMNEYS
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NATURAL CHIMNEYS
NATURAL BRIDGE
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NATURAL BRIDGE
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If underground rock is dissolved near the
surface a sinkhole may form.
A sinkhole is a depression on the surface
of the ground that forms when the roof of
a cave collapses, or when rock near thesurface dissolves.
These are common in areas that have lotsoflimestone and enough rain water to
keep the groundwater system supplied
with water.
Sinkhole
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Sinkhole
SINKHOLE
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SINKHOLE
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Karst topography is common in the
Valley and Ridge Province of Virginia,
where limestone is abundant.
KARST TOPOGRAPHY FEATURES
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KARST TOPOGRAPHY FEATURES
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H I t G d t
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Human Impact on Groundwater
Groundwater accounts for 20% of all waterused in the U.S.
Unwise use of this valuable resource can
damage or deplete groundwater reservoirs
Some of the problems related to groundwater
use include:
overpumping-lowering the water table
subsidence
contamination
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Pollutants
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Pollutants
Contaminants introduced at the land surface may
infiltrate to the water table and flow towards a point
of discharge, either the well or the stream.
A SOURCE OF GROUNDWATER
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A SOURCE OF GROUNDWATER
CONTAMINATION: SEPTIC TANKS
Contamination results in a decline
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Contamination results in a decline
in water quality.
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ANOTHER SOURCE OF POLLUTION:
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STORAGE TANKS
YET ANOTHER SOURCE OF POLLUTION:
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LANDFILLS
Groundwater Moves Usually
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Groundwater Moves Usually
Slowly
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