LANDFORMS

Landforms are natural features of the landscape, natural physical features of the earth’s surface

Main examples are:

A valley is a hollow or surface depression of the earth bounded by hills or mountains, a natural trough in the earth’s surface, that slopes down to a stream, lake or the ocean, formed by water and/or ice erosion. Rivers and streams flowing through valleys drain interior land regions to the ocean. At the bottom of many valleys is fertile soil, which makes excellent farmland. Most valleys on dry land are formed by running water of streams and rivers .The bottom of a valley is called its floor. A valley’s sides are called valley walls or valley slopes. A valley wall is the side slope of a stream or glacial valley. Rain, frost, wind and the atmosphere are loosening materials which fall into the stream and are carried away.

A plateau is a large highland area of fairly level land separated from surrounding land by steep slopes. Some plateaus, like the plateau of Tibet, lie between mountain ranges. Others are higher than surrounding land. Plateaus are widespread, and together with enclosed basins they cover about 45 percent of the Earth’s land surface. Plateaus, like all elevated regions, are subject to erosion, which removes great amounts of the upland surface. Low plateaus are often farming regions, while high plateaus are usually suitable for livestock grazing. Many of the world’s high plateaus are deserts.

Over long periods of time, mountains are created by tremendous forces in the earth with a steep top usually shaped up to a peak or ridge. Mountains are formed by volcanism, erosion, and disturbances or uplift in the earth’s crust. Most geologists believe that the majority of mountains are formed by geological forces heat and pressure producing changes under the earth’s crust and movements in the earth’s crust. The Himalayas were raised by the compression that accompanied collision of the Indian plate with the Eurasian plate. Volcanism causes mountains to form. Examples of mountains formed by periodically dangerous volcanic action are Mount Ranier and Mount Saint Helens in the United States.

Plains are broad, nearly level stretches of land that have no great changes in elevation. Plains are generally lower than the land around them.Plains are usually well populated because the soil and terrain are good for farming, and roads and railways are easily built between rural towns and cities. A coastal plain is a stretch of lowland along a seacoast which slopes toward the sea. Coastal plains generally have a few poor harbors, but the mouth of rivers seacoast have produced some fine harbors. A flood plain is the floor of a river valley beyond the riverbed. A flood plain is formed of mud, sand, and silt.. Coastal plains generally rise from sea level until they meet higher landforms such as mountains or plateaus. Inland plains may be found at high altitudes.

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 rocks 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. 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. The ash falls on the hardened lava causing a layer of ash to form on the hill.

Ice sheets and glaciers form the largest component of perennial ice on this planet. Over 75% of the world’s fresh water is presently locked up in these frozen reservoirs. A glacier is a huge mass of ice that flows slowly over land. They form in the cold polar – regions and in high mountains. The low temperatures in these places enable large amounts of snow to build up and turn inti ice. Glaciers are formed when more snow falls during the winter than melts and evaporates in summer. The extra snow gradually builds up in layers. Its increasing weight causes the snow crystals under the surface to become compact, grainlike pellets. These crystals combine to form glacial ice. The ice eventually becomes so thick that it begins to move under the pressure of its own great weight.