The Action of
Groundwater
Earth Science
Grade 8
Groundwater
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The water that soaks into the ground and
collects in pores is called groundwater.
Rocks have varying amounts of pore space.
If they allow water into them, they are called
permeable.
If they do not allow water into them then they
are called impermeable.
Groundwater
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Groundwater will continue to go lower into the
ground (by the force of gravity), until it reaches
a layer of impermeable rock.
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This acts like a dam, and the water does not
move any further.
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The water fills in all of the pore space of the
permeable rocks.
Groundwater
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A layer of rock that allows the water into it, and also allows
the water to flow through it is called an aquifer.
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A layer that is completely filled with water is called the
zone of saturation.
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The very top of this zone is called the water table. This
location varies from place to place.
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The area above this zone is called the zone of aeration. It
is filled with air, except after a rain when the water moves
through it on its way to the saturated layer.
Groundwater
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If you were going to dig a well for your house,
you would have to dig deep enough to reach the
zone of saturation. Otherwise you would not
always have water.
If too many people dig wells in similar locations,
there is a chance the well would run dry-which
means that there is no more water available.
(Zone of aeration)
Groundwater Diagram
(Lake)
(Zone of saturation)
Groundwater
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Most of the time you need a pump to get the
water to the surface (from the zone of
saturation).
A special case called an artesian well -there is no
need for a pump. The water moves up by itself.
Aquifer and Artesian well
Groundwater
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Sometimes the land dips low enough to reach
the water table level. Water that flows to the
surface here are called springs.
They are what feeds many of our rivers and
lakes. If the land around those springs is heated
(near a volcano or magma), they heat the water
it becomes a hot spring.
Springs and Hot springs
Groundwater
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A special type of Hot spring is one that erupts
periodically. This is called a geyser.
The most famous of this type of hot spring is
Old Faithful in Yelllowstone National Park. It
shoots out nearly 12,000 gallons of water every
60-90 minutes.
Geysers
Old Faithful, Yellowstone
Groundwater
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As groundwater travels it will eat away at some
of the softer rocks in the ground. Sometimes it
can eat away so much of an area that it will
create a cave.
Inside this area it is very cool and very wet. The
walls constantly have moisture on them.
Caves
Groundwater
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The water contains dissolved materials, which
build up and form new mounds of rock
When they build up from the ground, they are
called stalagmites.
When they hang from the ceiling, they are called
stalactites.
Sometimes the two shall meet, which we call a
column.
Stalactites, stalagmites, columns
Groundwater
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If the cave becomes large enough or it is close
enough to the surface, the land above it may
become unstable.
If the cave collapses, it will create a sinkhole.
Sinkholes
Sinkholes
Sinkholes
How do pot holes form?
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video
Neshaminy Falls
Picture by Bill Heasley