Processes in a River
Hydraulic Action: This is the pressure of the water being pushed against the banks and the bed of the river. It also includes the compression of air: as the water gets into the cracks in the rock, it compresses the air; this puts even more pressure on the cracks and pieces of rock may break off.
Corrasion: Particles (the load) carried by the river are thrown against the river banks with considerable force.
Corrosion (Soulution) - This is a chemical reaction between certain rock types and the river water.
Attrition- This is a slightly different process that involves the wearing away of the rocks which are in the river. In the upper course of the river rocks continually roll around and knock into each other.They chip away at each other untill smooth pebbels or sand are formed.
Deposition: This is the laying down of the load of the river.
There are three main types of weathering know as physical,biological and chemical.
Physical weathering: Freeze-thaw action
- The first thing that happens is there is a little crack in a rock and water gets trapped inside.Then when it gets cold around -5C the water freezes. The pressure on the rock created by 9% increase in volume as the water freezes therefore the crack increased in size
- A seed falls into a crack,then it rains so the seed starts to grow,roots force their way into cracks and as the roots grow they break up the rock.
- Another way is by humans/animals burrowing or digging can also break up rock.
-Rain water contains natural acids. So the carbonates in limestone are dissolved by weak acids therefore the cracks expand.
Mass movement is when material moves down a slope,pulled by gravity. There are two types of mass movement.
- Slowest downhill movement.
- Gravity pulls water in the soil downhill.
- Soil particles move with the water.
- Heavy rainfall causes faster downhill movement.
- The slope appears to have ripples.
- The ripple are known as terracettes.
- This is most common on river banks.
- A large area of land moves down the slope
- This common on clay river banks
- During dry weather the clay contracts and cracks
- When it rains the water runs into the cracks and is absorbed
- The rock becomes saturated
- This weakens the rock and,due to the pull of gravity.
- It slips down the slope on the slip plane