Regents Earth Science - Chapter 9
Water Moving Underground
I. Fresh Water & Water Budgets
A. The Earth has about 1.3 billion km3 of water!
B. Distribution of Earth’s water:
- 97% is in the oceans as salt water
- 2% is frozen fresh water at the Earth’s poles
- 1% is useable fresh water (98% of that is underground)
C. All of the water at the Earth’s surface makes up the hydrosphere.
D. The water is constantly in motion in the hydrosphere. This
movement can be traced by the water cycle.
(Understand the diagram on pg. 150)
1. Important definitions to know:
a. Condensation - water releases energy as it goes from a
gas to a liquid.
b. Evaporation - water absorbs energy as it goes from a
liquid to a gas.
c. Transpiration - water vapor released from the leaves
of plants.
d. Precipitation - water falling to Earth from the
atmosphere.
e. Runoff - water that flows across Earth’s surface.
E. We can describe the income and use of water in a given region. We
use a water budget to do this.
1. Important water budget terms to know:
a. Recharge - moisture soaks into the soil and refills the
aquifer.
b. Surplus - When rainfall is greater than the need for
moisture and the ground water supply is
filled.
c. Usage - Time when water need is greater than rainfall.
d. Deficit - Time when need is greater than rainfall and
ground water storage is empty.
F. Note the Water budget graphs on pages 151 & 152… you have to be
able to read these!
1. Tips on reading water budget graphs:
- Graphs with a large peak in the middle of the graph
indicate areas with a lot of moisture deficit.
ex. : Phoenix, AZ; Las Vegas, NV
- Areas with abundant rainfall and little usage have a
lot of surplus. These areas peak at the ends of the
graph.
II. Water in the Ground
A. Rocks have the ability to hold water. It is measured with porosity,
or, the percentage of a material’s volume that is pore space that
can hold water.
1. Factors controlling porosity -
a. particle shape - rounded particles have more space
between them, thus more porosity. Angular
fragments do not.
b. sorting - well sorted materials (uniform sizes) have
more porosity. Mixed up materials have small rocks
that fill in the pore spaces between larger particles.
c. amount of cement - more cement in a sedimentary
rock (i.e. sandstones) equates to less porosity.
B. If water can pass through a rock, it is said to be permeable to
water. (sand & gravel) Rocks that do not are impermeable. (clays)
C. Forming a water table:
1. rainfall that soaks into the ground flows between particles
until it reaches a zone of saturation, where water fills all of
the spaces between rock particles.
2. The depth of this zone is called the water table.
3. Above the zone of saturation lies an area where the
particles of rock/soil have air between them. This is the
zone of aeration. (aeration = air)
4. The capillary fringe borders these 2 zones. It is an area
where water “wicks” up into the zone of aeration like water
in a paper towel does.
D. Water tables are at the surface at rivers, streams, lakes, swamps,
etc.
E. Water tables generally follow the topography of the land.
F. A hole drilled into the zone of aeration is called a well. If the
water from this zone flows onto the surface on its own, it is called
a spring.
G. If an aquifer forms between 2 impermeable layers of material, the
water in he aquifer will flow downhill as an artesian formation. If
it is tapped by a well, it is called an artesian well that flows
constantly.
III. Groundwater Characteristics
A. Groundwater is usually cool …. between 5 and 15 degrees Celsius.
B. Magma activity can heat groundwater to form hot springs,
geysers, or fumaroles.
Hot spring - usually originate deep in the crust. Water flows
out hot.
Geyser - boiling hot spring with a partially obstructed tube.
Pressure builds up and periodically explodes a plume of
hot water & steam.
Fumarole - hole in surface from which steam & hot gases escape
C. Mineral springs form when groundwater dissolves minerals as it
passes through the ground.