Page 341 - Laboratory Manual in Physical Geology

BIG IDEAS PRE-LAB VIDEO

Groundwater is subsurface water, beneath the landscape
rather than on its surface. Most bodies of groundwater
form when rainwater seeps into the ground under
the influence of gravity and fills up (saturates) spaces
in cracks and between grains. Some groundwater is
unconfined and must be pumped from the ground to be
used. Confined groundwater is under pressure and will
flow on its own if a well is drilled to its location. Karst
topography and rapid movement of water can occur
when groundwater dissolves caves in soluble rocks,
and land subsidence can occur when humans withdraw
groundwater faster than it can be replenished.

FOCUS YOUR INQUIRY

THINK
About It | How does groundwater behave underground?
ACTIVITY 12.1 Groundwater Inquiry (p. 312 )

|
THINK What is karst topography and how does water
About It flow beneath it?
ACTIVITY 12.2 Karst Processes and Topography (p. 312 )
ACTIVITY 12.3 Floridan Limestone Aquifer (p. 314 )

|
THINK What can happen if groundwater is withdrawn
About It faster than it is replenished?
L A B O R A T O R Y12 Withdrawal (p. 317 )
ACTIVITY 12.4 Land Subsidence from Groundwater

Introduction
Water that seeps into the ground is pulled downward
by the force of gravity through spaces in the soil and
bedrock (rock that is exposed at the land surface or
Groundwater underlies the soil). At first, the water fills just some spaces
and air remains in the other spaces. This underground
Processes, zone with water- and air-filled spaces is called the zone of

aeration ( FIGURE 12.1 ; also called the unsaturated zone or

vadose zone ). Eventually, the water reaches a zone below
Resources, and the zone of aeration, where all spaces are completely
saturated with water. This water-logged zone is called
Risks the zone of saturation, and its upper surface is the water
table ( FIGURE 12.1 ). Water in the saturated zone is called

groundwater , which can also be withdrawn from the
ground through a well (a hole dug or drilled into the
C O NTRIBUTING A UTH O RS

Garry D. McKenzie • Ohio State University ground). Most wells are lined with casing , a heavy metal
Richard N. Strom • University of South Florida, Tampa or plastic pipe. The casing is perforated in sections where
James R. Wilson • Weber State University water is expected to supply the well. Other sections of
the casing are left impervious to prevent unwanted rock
particles or fluids from entering the well.
Stalactites hang from the ceiling of Luray Caverns, Virginia. Some
merge with stalagmites forming on the cave floor.
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