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)

Although there are many excellent websites that deal with the Water Cycle, the United States Geological Survey has

by far the most comprehensive information on the Water Cycle

http://ga.water.usgs.gov/edu/watercycle.html