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The changing landforms down a river's long profile

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Introduction

The changing landforms down a river's long profile As the water in a river moves from its source to its mouth it causes three main processes to occur. These are erosion, transportation and deposition and they shape the landforms down a rivers path. Erosion: This is a group of natural processes by which material is worn away from the river's basin. These include: * Dissolution - the acidity of the water dissolves the rock. * Corrasion - material scrapes along the river bed. * Attrition - rock bash together and break up. * Hydraulic action - Water compresses air into small holes in the rock which causes cracks. Once material is eroded away to become part of the rivers bedload, these processes will work continually to reduce their size. When weathering and erosion are combined to eat away at the earth's surface it is called denudation. Transportation: This is the process whereby the material is moved in the river. The river carries material in three ways: * Suspended load - where small particles are suspended in the water. * Dissolved load - where small particles are dissolved into the water. * Bedload - larger chunks of material are moved along the river bed by saltation and traction. ...read more.

Middle

This causes it to revert to vertical erosion again making it loose the floodplain and meanders to follow a narrow gorge through the rock. The mouth: Once past the gorge the river widens out again with a large floodplain and meanders in a broad valley. The lake it flows into starts to slow the velocity of the river causing deposition and so it has a delta at its mouth. The different landforms: * Interlocking spurs (fig.2) - near the source of the river where there is high relief a steep valley is formed which has to take the easies route between hills that juts out. This forms interlocking spurs. * Waterfalls (fig.3) - are caused by changes in the rock that a river flows over. If a river flows over a hard rock followed by a soft one the soft rock will wear away faster leaving the hard rock sticking out. Over time the water falling from the band of hard rock cuts a plunge pool in the soft rock. This undercuts the hard rock which eventually collapses back and this process can happen over and over again causing the water fall to move back over time. * Rapids (fig.4) - Upstream where rivers discharge is low the water is forced to flow over shallow rock and bedload. ...read more.

Conclusion

Over time it will fill with silt and disappear. * Flood plain (fig.8) - When a river passes bankfall it will spill over onto its flood plain, an area of flat land surrounding the channel which is covered when there is a flood. A flood plain can be made wider by the lateral erosion of meanders and they are often built up by rich sediment that is deposited every time the river floods. The clearly definable edge of a flood plain is called the bluff line. * Levees (fig.8) - The rivers load in a flood is usually deposited near to the river bank. This makes the sides build up higher with every flood until the rivers water level can actually be higher than the rest of the floodplain while the levees at the sides of the river hold all the water in. Artificial levees are built by man to help prevent flooding. * Delta (fig.9) - Formed at the mouth of the river when it reaches a lake or a sea that doesn't have very strong currants to take the sediment away. As the river is slowed by its impact with the standing water it drops almost its entire load. This over time will build up and extend the river out from the land on its own delta. ...read more.

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