CHAPTER 6.3 WATER BENEATH THE SURFACE
• Fact: The ground you walk on is
not solid!
• Fact: There are countless tiny
pore spaces between grains of soil.
• Fact: The spaces fill with water.
• Fact: The water in the spaces
collects and moves.
Distribution and Movement of Water Underground
When rain falls…
…some of the water runs off,
…some of the water evaporates,
…and the rest soaks into the ground.
How much water soaks into the ground
depends on…
…steepness of slopes,
…natures of surface materials,
…intensity of the rainfall
…type and amount of vegetation.
Distribution of Water
A lot of the water in soil seeps down until it reaches the
ZONE OF SATURATION.
Zone of Saturation = area where water fills all open
spaces in sediment and rock (GROUNDWATER)
GROUNDWATER
Water Table = upper limit of the zone of saturation
Zone of Aeration = area where soil is not saturated
with water.
(Underground) Movement of Water
Subsurface Material:
• Porosity = the percentage of total volume of rock
or sediment consisting of pore spaces.
Can still block the
movement of water
underground.
• Permeability = ability to release a fluid
• Groundwater moves by twisting and turning
through pores that are connected.
Groundwater moves more
slowly when pore spaces are
smaller.
Goes through too fast!
Goes through too slow!
Goes through just right.
Aquafer = permeable
rock that allows the
movement of
underground water.
AQUAFER
Aquatard =
impermeable layers
that prevent the
movement of
underground water.
SPRINGS
Spring = forms wherever groundwater intersects the
ground surface.
Hot Springs = 6oC to 9oC warmer than the air temperature
around where the spring occurs.
Geysers = intermittent hot spring or fountain in which a
column of water shoots up with great force
Flash: Hot Springs of Baniff
Geysers = intermittent hot spring or fountain in which a
column of water shoots up with great force
1. Pg 173 Fig 16:
Groundwater
enters
underground
caverns and
fractures in hot
igneous rock
and is heated to
almost boiling.
2. The hot water
expands and some
is forced out at the
surface.
This reduces the
pressure and
temperature of the
remaining water.
3. The water flashes
to steam which
forces the water
out and produces
the geyser.
4. The now empty
chamber begins
to fill again and
the cycle starts
over.
Flash: Geysers 3:52
WELLS
Well = hole bored into the zone of saturation.
Artesian Well = any formation in which groundwater rises
on its own to the surface.
Environmental Problems with Groundwater
Renewable or Nonrenewable?
• 65% of groundwater is
used for crop irrigation
• High plains have a
severe groundwater
depletion.
• When groundwater is
removed faster than it
can be replenished
ground may sink as
water is removed. (See
pg 175 Figure 18)
India
Groundwater Contamination
Common sources of
contamination:
• sewage from leaking
septic tank
• farm waste
• inadequate/broken
sewers
Pg 176 Figure 19
Extremely permeable
aquifers allow water to flow
to fast for it to be cleansed
properly.
Caverns
Cavern = naturally formed underground chamber.
Rainwater dissolves CO2 in the
air creating carbonic acid.
Carbonic acid reacts with
calcite in limestone forming
calcium bicarbonate.
Rock is slowly eroded as the
water moves through cavities
and a cavern is formed.
Caverns form in the Zone of Saturation,
But Dripstone forms after the cavern is above the water table.
• Streams cut their valleys deeper and deeper.
• As the elevation of the stream drops so does the water table.
• This leaves the cavern high and dry.
Linville Caverns
Marion, NC
Travertine = calcium carbonate limestone that makes dripstone.
Dripstone = deposits of calcium carbonate limestone made
from the continuous dripping of calcium carbonate deposits.
• Stalactite = icicle-like
stone hanging from the
ceiling of a cavern.
• Stalagmite = conelike stone coming up
from the floor of the
cavern made from the
drips off stalactites.
Flash: Caverns
Karst
topography =
landscape
shaped by the
dissolving power
of groundwater.
Guatamala City
Venezuela
Sinkhole = depression produced in a region where
groundwater has removed soluble rock.
In Soviet Russia, the ground moves you.
Berezniki’s sinkhole began in 1986 and just
grows worse with each passing year.
The vast Qattara west of Cairo, Egypt is the
largest natural sinkhole in the world,
measuring 80km long by 120km wide.