Base level is the lowest point to which erosion by running water can occur.
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Changes in base level result from:
Climatic change and Tectonic change.
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What is climatic change?
Glaciations and changes in rainfall.
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What is tectonic change?
Where land is uplifted after plate movement or volcanic activity. Changes can be positive sea level rises in relation to the land, or negative sea level fall in relation to the land.
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What is Rejuvenation?
If land emerges from the sea following a negative change in base level, the potential energy of a river for erosion is revived and a re-grading of the river can occur.
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What is one of the causes of rejuvenation?
Rejuvenation causes the river to increase its downcutting activity. Rejuvenation is caused by tectonic activity causing dynamic rejuvenation, an increase in the volume of water in the drainage system, changes in base level either sea level falls.
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What is the other causes of rejuvenation?
Land rises due to eustatic fall in sea level (global fall in the level of the sea) or an isostatic change in the level of the land (local uplift of land).
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What are knick points?
Knick points are breaks in gradient along the profile of a river usually marked by rapids or waterfalls.
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What are river terraces?
River terraces are simply where vertical erosion occurs in a floodplain that was previously being formed by the normal conditions of deposition and lateral erosion.
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How are the caused?
The river cuts downwards and abandons the old flood plain as a river terrace - ideal for building settlements upon!
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What happens over time?
Over time once the profile is regraded, the river may recommence eroding laterally and depositing sediment, resulting a secondary flood plain formation.
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What does it result in?
Where this occurs and the river is meandering, the river can maintain its meandering form but its energy is focussed upon vertical erosion. This can result in spectacular incised meanders.
Destruction of communications and buildings. Loss of life and property. Drainage problems. Spread of disease. Destruction of crops. Impacts on economy.
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