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This PowerPoint file contains information about the water cycle. The first slide shows a picture that
includes all processes in the water cycle. Subsequent slides discuss each process individually. The last slide provides information on the distribution of
water on the earth.
The water cycle is the continuous movement of water on, above, and below the surface of the Earth
United States Geological Survey (http://ga.water.usgs.gov/edu/watercycle.html)
Evaporation is the process by which water changes from a liquid to a gas. The rate of evaporation
depends on how dry the air is and the temperature difference between air and water.
Water Evaporating
from hot springs
United States Geological Survey (http://ga.water.usgs.gov/edu/watercycle.html)
Transpiration is the process by which water evaporates from plants
United States Geological Survey (http://ga.water.usgs.gov/edu/watercycle.html)
Evaporation and transpiration are often combined into a single
term called evapotranspiration.
Condensation is the process by which water vapor in the air is changed into liquid water. As air rises it
cools. Cold air holds less water than warm air. Thus, as the air cools, clouds form.
United States Geological Survey (http://ga.water.usgs.gov/edu/watercycle.html)
Some clouds form during the day as the air temperature and
evaporation increase. Other clouds are associated with weather systems, such as a
warm or cold front, in which warm air is forced
over colder air.
Precipitation is water released from clouds in the form of rain, freezing rain, sleet, snow, or hail. It
happens when clouds can no longer hold water. The water then falls to the earth because of gravity.
A thunderstorm in the western United
States. Thunderstorms form
when air is forced upward at a very fast
rate and therefore cools very quickly.
United States Geological Survey (http://ga.water.usgs.gov/edu/watercycle.html)
Infiltration is the process by which water
soaks into the ground.
Infiltration is faster on dry soils and in sandy soils
compared to wet and clay
soils.
SAND
CLAY
Water
Water infiltrates much faster and
deeper into a sand compared
to a clay. This is because the pore
spaces in the sand are much larger than in
the clay and can therefore
transport more water.
Surface runoff is precipitation or melted snow that runs off over the landscape. Runoff occurs when the rate of precipitation or snowmelt is greater than the
rate of infiltration.
Oregon State University Extension Service (http://extension.oregonstate.edu/streaming/transcripts/after_the_rain/sect3.php)
Runoff water flows to sewers in some urban areas (then usually to
surface water), to retention basins in
other urban areas (then usually soaks into the
ground), and to rivers, lakes, and wetlands in
nonurban areas.
Water that infiltrates the soil can either be taken up by plants, evaporate, be stored in the soil, or become
ground water.
United States Geological Survey (http://ga.water.usgs.gov/edu/watercycle.html)
Ground water is water stored in the saturated part of soil or
rock
Soil holds water but is usually not
saturated with water.
Ground water moves from high to low elevations due to gravity. It eventually flows to a spring, lake,
river, wetland, or well.
United States Geological Survey (http://ga.water.usgs.gov/edu/watercycle.html)
In this illustration,
ground water flows to a
stream and a well
Water in lakes, streams, and wetlands may come from precipitation, surface runoff, and ground water
discharge.
Water in lakes, streams, and wetlands can evaporate, flow to a lake, stream, or the ocean, or infiltrate into the ground.
Water in oceans comes from precipitation, runoff, ground water discharge, and streams
Water in the ocean may stay there fore a long time, but some of it evaporates
United States Geological Survey (http://ga.water.usgs.gov/edu/watercycle.html)
Water in ice and snow, including glaciers and icecaps, comes from precipitation
Water in glaciers and icecaps is stored for a long time. Some evaporates and glaciers slowly flow toward oceans and lakes.
United States Geological Survey (http://ga.water.usgs.gov/edu/watercycle.html)
97% of the earth’s water is in the oceans. Of the remainder, 69% is in glaciers and icecaps, 30% in
ground water, and 1% in lakes, rivers, and wetlands. Very little water is stored in the atmosphere.
United States Geological Survey (http://ga.water.usgs.gov/edu/watercycle.html)