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Let the Cycle Begin

The movement of water from one reservoir source to another is mainly powered by the sun's energy. The water cycle illustration below is courtesy of the USGS.

To understand the water cycle, there must be an understanding of the processes that move the water in its different phases. The energy from the sun heats the liquid water, causing it to turn into a gas in a process called evaporation. The oceans contribute most of the water for evaporation, but other large bodies of water such as the Great Salt Lake can also be major contributors.  This is called the "lake effect." The heated moist air rises and provides for a major process called convection, which is a principle component of moving air in weather. Transpiration is a process by which plants release water vapor. Some rain forests emit enough water vapor to create daily rains.
As the water vapor rises, it cools and condenses to form very small drops that make up clouds (often this creates the cloud "cap" seen at the tops of mountains in Utah). Wind moves the vapor and clouds to new locations. When the drops combine and/or grow large enough to fall, they form precipitation in the forms of rain and snow.

Gravity pulls the water down rivers in runoff or pulls the water underground in groundwater toward the oceans. Groundwater often flows very slowly; sometimes taking many thousands of years to return to the surface. This can be due to gravity pull or a hydrothermal force (convection due to Earth's heat).

Visit Pioneer Library and search for the e-Media video "Earth Science Collection: the water cycle" - start with the section labeled "Sun."


  1. Where does the energy come from to move water from one place to another in the water cycle?
  2. Describe the movement of energy into or out of water during each of the following processes: evaporating, condensing, freezing and melting.
  3. Are clouds made of gas water? Explain.
  4. Why do some clouds produce precipitation and others do not?
  5. Which part of the water cycle is the beginning? Explain.
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Teachers should view the Teacher Site Map to relate Sci-ber text and the USOE Earth Systems Science core.


Updated October 24, 2008 by: Glen Westbroek

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