Water Cycle

Water moves in a steady cycle. It never disappears but it changes from solid to liquid to gas.

When the sun heats up water it becomes a gas and evaporates . As it rises it cools down and clouds form. Clouds have many very small droplets of water in them. When they get too heavy they fall down to the ground as rain or snow.

Although some of this precipitation rises directly into the atmosphere again, most of it gets into the ground and remains in aquifers . Snow and ice remain on glaciers and ice caps until it gets warmer. Then it starts melting and the liquid follows into lakes and rivers.

Water has shaped the surface of the earth for many years. It causes erosion , makes mountains smoother , rivers carve themselves into valleys and makes them wider . Ocean waves form coastlines .

Water cycle
Image: USGS - http://ga.water.usgs.gov/edu/watercycleprint.html