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| Sunday, 31 October 2004 |
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Junior Observer |  |
| News Business Features Editorial
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Eroding of the soil What do you understand by the term erosion? It is the wearing away and removal of soil and rocks due to rain, winds, ice, animals and humans. Many mountain ranges have formed and disappeared over millions of years of geological time. These mountains would have been created due to continental drifting, faulting and other earth movements. Their disappearance could be attributed to weathering and erosion. Weathering Weathering is the process of the break-down of rocks as a result of changes in temperature, rain and frost. The high temperature during the day makes the rocks heat up and expand, while the low temperature during the night cools and contracts them. These constant expansions and contractions create cracks in the rocks, leaving small pieces flaking off.
Rain water collects in rock crevices and when it freezes, it expands with great force, splitting off pieces in a procedure known as frost-wedging. Weathering first wears away land in higher altitudes. The broken-down fragments are carried down by rain, ice and wind and deposited in lower regions like plains, lakes and rivers where they are known as sediment. Rocks are weathered by trees too. Soil is collected in the cracks in rocks and plants may grow in this soil. The growing roots push against the rock, making it weak and after some time, the rock could break into pieces. Rain water and gases in the air can also react with the minerals in rocks, forcing them into pieces. Weathering takes place more quickly in a wet climate than a dry one. Large pieces of rocks and massive quantities of soil are carried away by river water specially if the river is fast-flowing or in floods. Another powerful agent of erosion are waves crashing onto cliffs, sometimes hurling pebbles and boulders at the rock face.
The round and smooth pebbles one sees in a stream are initially parts of larger rocks with rough edges. While they were being carried away by the water, they rubbed against sand and other rocks, which smoothed their edges. Erosion is also caused by the sea along the coastal belt. The wind blowing loose grains of soil and sand also causes erosion. The wind can also blow sand into piles called dunes in deserts and along the shores of lakes and oceans. The wind can blow a sand dune right across the land. Soil erosion is caused by human activities as well. Trees, with their roots digging firmly into the ground, keep the soil tightly in place. Cutting them down on a large scale removes this grip and cover, making the soil loose in the process and it is easily washed or blown away. Animals also responsible Some animals like cattle, goats and sheep are also responsible for erosion as they could eat too much grass in the pastures, leaving the soil bare, and making it easier for the rain, ice and wind to carry it away. Erosion removes the rich and fertile top soil, making the land unsuitable for agriculture. ###### Grand Canyon The Grand Canyon in Arizona, USA is the best example of erosion in the world. It is a large gorge (narrow, steep-sided valley) which runs across the dry, rocky region for 350 kilometres. It was formed over the past six million years as the land was pushed up by more than 1,200 metres by the earth movements. The land had been eaten away by the fast-flowing Colorado River. This resulted in the steep-sided canyon, 16 kilometres wide on average and 1,600 metres deep in places. The river is specially fast in spring when the melting snows increase the quantity of water in the river. The water takes with it boulders and rocks which chip away at the river bed and banks. The lowest layers of rocks in the canyon are said to be over 1700 million years old. Great Sphinx The Great Sphinx in Egypt has also been weathered by people as well as by nature. It was carved over four thousand years ago from a rock. Those days, it was plastered and painted in bright colours. However, this plaster and much of the rock have worn away now. Erosion caused by the wind is a reason for these changes. The nose of the Sphinx had also been used for target practice by soldiers in the 1700s under the orders of the then ruler. ###### Reducing erosion So, how do you reduce soil erosion? One way is to replant new trees through a process called reforestation. Strip cropping or planting strips of small plants between strips of larger plants is a method employed by farmers as a solution. The smaller plants can absorb and hold water better than the large ones, preventing the water from running down the fields causing erosion. Contour ploughing or ploughing in rows that go around a hill instead of straight up and down the hill also reduces erosion. These two methods can stop three fourths of the erosion in farmlands. Large trees are also grown as a barrier to control erosion caused by the wind. |
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