Specification
Fluvial processes involved in river valley and river channel formation: erosion (vertical and lateral), weathering and mass movement, transportation and deposition and factors affecting these processes (climate, slope, geology, altitude, aspect).
Remember that these processes, along with river transportation all act together to create river landscapes and landforms. Erosion takes place in the river itself, weathering loosens material beside the river, mass movement moves this loose material downhill and into the river and then the water in the river transports it away. Eventually it will be deposited downstream at the mouth of the river (forming a delta?) or at the inside of a meander (forming a point bar) or anywhere else where the river slows down and has reduced energy.
1. Erosion
Water erodes the land in four ways. These are:
- Hydraulic action - this is the sheer force of the water crashing against the banks and bed of the river. It is most effective when there are cracks in which air can be compressed by the force of the water, forcing the material apart.
- Abrasion/Corrasion - this is where material which is being carried by the river (sand, pebbles) collide with the banks and bed. They increase the power of the water and some say they act a bit like the particles of sand in sandpaper.
- Corrosion - this is where slightly acidic river water dissolves the rocks in the bank and bed of the river. It is particularly effective in areas of chalk or limestone as the calcium carbonate in those rocks is dissolved.
- Attrition - this is slightly different from the others as it affects the size and shape of the material being carried by the river rather than the river channel. It happens when rocks/pebbles carried by the river collide with each other. This knocks off the rough edges and makes material smaller and smoother downstream.
2. Weathering
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Weathering is the wearing away of the land "in situ" in other words not involving movement. There are three main kinds shown below:
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1) Physical or mechanical weathering - this is where changes in the moisture levels or temperatures. There are many different kinds. Two are shown below.
1) Physical or mechanical weathering - this is where changes in the moisture levels or temperatures. There are many different kinds. Two are shown below.
Freeze-thaw weathering
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2) Biological weathering - this is when the actions of biological organisms break up the soil/rock. This might be due to the roots of trees or other plants or burrowing mammals or even insects.
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3) Chemical weathering - this is where weak acids in rainfall dissolve rocks and other surfaces.
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3. Mass movement
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Mass movement is all about the movement of material downhill due to the force of gravity. It includes:
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