2.Various landscapes of the earth`s surface.

Mountain building. As you have read, earthquakes and volcanic eruptions can change the earth’s surface in a matter of seconds. However, the process of mountain building can take millions of years. Depending on how the mountains are formed, geographers classify them as fault block or folded mountains. Under pressure, the earth’s crust may fold and the mountain ranges are formed. The Andes of South America, the Alps of Europe and the Himalayas of Asia are examples of folded mountains.

Sometimes sections of the earth’s crust break up into blocks and mountains develop. One block, with its layers of rock, moves up or sinks down. In the eastern part of Africa faulting has been responsible for the formation of great depressions called rift valleys. Faulting helped give the Sierra Nevada Range in California its block shape.

Surface forces create distinctire landforms. As plate movements reshape the earth’s continents and ocean floor, certain external processes are at work, changing surface features. These processes are weathering and erosion. They work much more slowly than earthquakes and volcanoes. In fact, like the process of mountain building, they often go unnoticed for generations. Over time, however, they can produce results as dramatic as the Grand Canyon, carved out by erosion — and it is more than l.5 km deep.

Physical weathering breaks rocks down into smaller and smaller pieces. Chemical weathering alters the composition of rocks. When the minerals that make up limestone, for instance, dissolve in water it is called chemical weathering. Both types of weathering often occur simultaneously. Even granite, one of the hardest rocks, slowly decomposes. The chemicals present in acid rain speed the process of weathering even more.

Erosion moves weathered products from one place and deposits them in another. The major agents of erosion include running water, waves, moving ice, and wind. Running water, found almost everywhere, probably, does more to change the earth’s surface than any other agent of erosion.

Waves cause erosion and other changes along the shores of the ocean and large lakes. Along rocky coasts waves cut into the land causing parts of cliffs to drop into the water. In other spots waves wash up eroded materials to form sand beaches.

Large masses of moving ice, known as glaciers, erode the land in the colder regions of the world. As the glaciers move through mountain passes, they create distinctive U-shaped mountain valleys by eroding soil and rocks from the valley floor and walls.

Wind is a powerful agent of erosion, especially in regions that receive little rainfall. Winds carry sand, volcanic ash, and even gravel. High winds carrying such windblown materials cut even the hardest rocks into many different and often fantastic shapes.

Because of all these forces and processes, the surface of Earth has a tremendous variety of landforms or shapes of the earth’s surface. Plain, plateau, hill, mountain, canyon, valley, island, ridge, and fjord are a few of the names given to these landforms. Landforms help to characterize the natural landscape of each place which is the combination of a place’s physical features. Other aspects of the physical environment include climate, vegetation, and soils. Landforms have an important impact on human activity. Most landforms have both advantages and disadvantages for human use and settlement.