Sunday, September 30, 2007
Hills are elevations of the earth's surface that have distinct summits, but are lower in elevation than mountains. Hills may be formed by a buildup of rock debris or sand deposited by glaciers and wind. Hills may be created by faults. Faults are a slight crack in the earth which can cause earthquakes. Hills are formed when these faults go slightly upward. The most famous hills in the world are the Loess hills. The Black Hills are also famous. You can find hills in low mountain valleys, valleys, plains, and even in your own backyard.
Hills are also formed by deep erosion of areas that were raised by disturbances in the earth's crust. Erosion forms hills by carrying away all of the soil on a mountain, causing a hill to be left behind. Humans also make hills by digging soil up and dumping it in a giant pile. Volcanoes are also another way that hills are formed. Volcanoes form hills when they erupt. During the eruption, volcanic ash is spewed through the air; after the eruption, the lava or molten rock hardens and builds up a thick layer of lava rock. The ash falls on the hardened lava causing a layer of ash to form on the hill. When rain falls, this layer of ash mixes with the rainwater to form black colored water. This black water will freeze causing the lava rock to crack and crumble and eventually erode to form a hill.
Posted by Princessa at 9/30/2007 08:52:00 PM