Using paper patterns, students are able to construct a model that depicts Karst topography, including typical features such as caves, limestone bedrock, sink holes, and springs. The accompanying Teachers Guide provides extensive background information about the dissolutional processes that form caves. Information is also provided about unique animals found in caves and the importance of understanding ... Full description.

The European Space Agency's Mars Express Satellite has recorded images in three different bands of the southern polar cap of Mars, which show both frozen carbon dioxide and water ice. The images are presented with a brief caption and links to other Mars Express imagery and status reports. Full description.

This site uses a picture of a covered swimming pool as an example of a watershed and describes real-world watersheds and their processes, including precipitation, infiltration, evaporation, transpiration, and storage. Links to an interactive rainfall calculator and to related websites are included. Full description.

This site describes how snow and ice runoff become surface water and emphasizes how runoff from snowmelt is a major component of the global movement of water. A hydrograph from the U.S. Geological Survey shows a four-year time series of streamflow and illustrates how runoff from snowmelt affects the daily mean values, particularly at certain times of the year. Full description.

Students in this lesson will be introduced to the concept of tides and tidal forces. By viewing a related applet which visualizes the relationship between the Earth, moon and tides, students will gain an understanding of why the Earth experiences tides. In the process they are asked to observe and explain how the relative positions of Earth, the moon, and the sun are responsible for the moon phases, ... Full description.

This website presents the story of Comet LINEAR, which broke apart in 2000, revealing what many scientists thought all along - water in Earth's oceans could have come from outer space. The article discusses findings from the breakup of Comet LINEAR and the possibility of water in its composition. Full description.

This article discusses the necessity of locating water ice as astronauts explore the solar system, for oxygen and fuel as well as for drinking. Topics include the possible occurrence of ice at the lunar poles and in comets, and some of the National Aeronautics and Space Administration (NASA) missions to locate it. Full description.

This site provides a discussion of the downward movement, or infiltration, of water from the surface into soil or porous rock. Graphics illustrate the processes affecting infiltration, including precipitation, soil characteristics and saturation, land cover, slope, and evapotranspiration. Links to additional sources of information are also provided. Full description.

This site presents clues to suggest that liquid water once flowed on Mars - raising hopes that life could have arisen there - but the evidence remains inconclusive and sometimes contradictory. Full description.

The materials presented here highlight the fact that Earth's supply of water is finite and is constantly recycled. We depend on water for drinking, washing, recreation, agriculture and industry. It controls the world's weather and sustains the natural systems above and below the earth's surface. Users can examine an illustration that shows the role played by groundwater in the hydrologic cycle and ... Full description.