Weathering, erosion, transportation and deposition
A river uses all of these processes in shaping the land around us. There are three types of weathering that occur in shaping the land:
- Physical Weathering
- Freeze thaw weathering – Water gets into a crack in a rock and freezes. Water expands when it freezes so widens the crack over time.
- Onion skin weathering – A rock is repeatedly heated and cooled. Heating causes the outer layer of the rock to expand and cooling causes it to contract. Continual expansion and contraction causes the outer layers of the rock to peel off like an onion.
- Biological Weathering
- Due to the action of plants and animals. Plants in terms of roots and seeds widening cracks and animals by burrowing.
- Chemical Weathering
- Caused by the action of water. Acids in water can react with certain types of rock breaking them down.
Erosion also wears away the land and provides material to be transported by the river before being deposited elsewhere.
Landforms created on the coast are either formed by erosional processes or by deposition. The distinctive landforms produced are:
- Erosional Landforms
- Headlands and Bays
- Cliffs and Wave cut platforms
- Caves, arches, stacks and stumps
- Depositional Landforms
- Spits and Bars
Coasts are also effected by transport of material along the coastline. The sea is able to transport material in two ways; up and down the beach and along the beach by longshore drift. Waves moving up and down the beach can move eroded material up in swash and down in backwash. Movement along the beach also involves swash and backwash; waves break at an angle so swash moves up the beach at this angle. The backwash returns at right angles to the sea and the result is beach material moving along the coastline in a zig zag pattern.
Landforms along a river change from its source to its mouth because of differences in the velocity, width, depth and gradient. A river can be seen as being in three main sections; the upper, middle and lower courses.
- Upper Course
- Steep gradient, small width and shallow depth
- V shaped valley
- Interlocking spurs
- Middle Course
- Gradient shallows, width and depth increases
- Lower Course
- Wide river, shallow gradient and depth increased
- Ox Bow Lake