River landcapes and processes

• Weathering


  The breakdown of rocks
• Biological weathering


  When the roots of plants grow inside the rocks, causing it to crack and break apart. Can also happen when animals burrow inside the rock.
• Chemical Weathering


  This happens because rainwater can be slightly acidic. The weakly acidic rainwater causes the breakdown of particular rocks over time.
• Mechanical Weathering(freeze-thaw)


  This is caused by drops in temperatures, especially during the evenings in winter. Rocks break down because the water expands and contracts as the water freezes and melts,putting pressure on the rock.
• Mass movement


  The large-scale movement of material downhill
• Sliding


  This happens on steep slopes.Heavy rainfall saturates rocks,which become heavy and fall downwards.
• Slumping


  This happens when loose material is saturated by rainwater.The slope collapses because of gravitational energy,in a circular motion.
• Erosion


  The wearing away of rock using movement
• Attrition


  Where pieces of bed load (material carried by a river or seawater)are hit against one another.This causes them to break apart and become smaller and more rounded.
• Hydraulic Action


  Where the force of the water hits against the river or sea bed and banks and causes the rock to break off
• Abrasion


  Where pieces of rock are picked up by the river or sea water and hit against the bed or the banks.This wears them away.
• Solution


  Where soluble rocks are dissolved by the water in the river or the sea (limestone and chalk in particular).They are carried along the river or sea
• Transportation


  The movement of material by solution,suspension,saltation and traction
• Solution(transportation)


  Where rocks that are soluble are dissolved by water.They are transported within water
• Suspension


  Where silt and sand particles are held in water (but not dissolved).The silt and sand particles are then transported along with the water.
• Saltation


  Where small sand and gravel particles bounce along the river bed or sea bed.They will travel in the direction of the flow of water
• Traction


  Where large rocks or large particles are dragged along the river bed or sea bed by the current
• Deposition


  When the sediment that a river is transporting is dropped this usually happens in the middle and lower courses of the river
• Reasons why rivers lose velocity and drop material are

  -The rivers mouth is reached

  -Increased amount of sediment in the channel

  -Reduced volume of water in the channel

  -Water becomes shallower
• Waterfalls 


  When a river flows over hard rock that overlays a soft rock,a waterfall can form.Gorges are formed when waterfalls retreat over time.
• Stage 1 of waterfalls forming

  The less resistant rock begins to erode because of abrasion and hydraulic action.A step or notch forms in softer rock,creating a river rapid
• Stage 2

  Over time,the softer rock gets more eroded.This leaves the hard rock sticking out above the soft rock.The height of the drop increases as the water pounds the less resistant rock at the base.Eventually,a waterfall forms
• undercutting


  When the less resistant rock starts to be eroded underneath the hard rock
• Stage 3

  1)Undercutting takes place.

  2)The overhanging harder rock collapses as there is nothing underneath to support it.

  3)The harder rock crumbles into the base and the abrasion between the hard rock and soft rock base creates a plunge pool.

  4)Hydraulic action keeps undercutting behind the waterfall

  5)If the process repeats over a long time,a gorge may form