4. What are the processes that help develop landscapes?
There are 5 main processes by which the landscape is changed
  • Erosion
  • Transportation
  • Deposition
  • Weathering
  • Mass movements

Erosion is the wearing down o
f the land by water, ice or wind. It achieves this in four different ways:

· Abrasion or corrasion – pebbles that are being carried by the river wear away the bed (bottom) and the banks (sides) of the river.
· Hydraulic action – the sheer forces of the water (especially when the discharge is high) dislodges material from the bed and the banks
· Solution or corrosion – some rocks can be dissolved if the water flowing over them contains small amounts of acid (which could have come from acid rain).
· Attrition – When rocks are being transported, they knock against each other and smooth off the rough edges, turning them into pebbles. Over time attrition will create gravel, sand and silt.
Transportation is the way in which rivers carry material from one place to another
  • Traction is when the larger boulders are rolled along the river bed
  • Saltation is when the smaller pebbles are bounced along the river bed, often leaping over each other
  • Suspension is the way that the river will carry small particles in the water, most often after heavy rain when the river will appear very muddy
  • Solution is the way the river carries the dissolved material that has been added to the river by corrosion
Deposition is the laying down of material that has been transports from elsewhere. Material is deposited as soon as the river has too little enery to carry it further. So the largest material will be dropped first while smaller lighter particles are still carried further. As the river slows, as the ground over which the river is travelling is more level, then small grains will be dropped and fine silt will continue to be carried.
Weathering is the name given to the break up and disintegration of rocks on the earth’s surface in situ (where they are) without any movement taking place.

There are 2 types of weathering
  1. Mechanical or physical weathering which is further divided into
  • Freeze-thaw which happens when water gets into cracks in the rock, freezes and expands, so making the crack bigger. Repetitions of this process cause pieces to break off. This often gives rise to at the base of steep mountain slopes.
  • In hot deserts where there is a large diurnal (daily) range of temperature, the outer surfaces of rock expand by day and then contract at night. This is called exfoliation. This leads to cracks appearing and thin layers pealing off the outer surface. You can tell when a rock has been exfoliated because it looks egg-shaped.
  • Trees, shrubs, mosses, lichens and burrowing animals can also lead to the disintegration of rocks (biological weathering). Roots enlarge cracks causing the rock to split and break off.
2. Chemical weathering involves chemicals, usually dissolved in water, that remove part of the rock, e.g. limestone caves are formed this way. Tors of granite uplands are also caused by this
Mass movement. Once material has been weathered it may start to move down hill. This will happen continuously under gravity, so the steeper the slope the faster the movement. The slow movement is called soil creep. While faster movements, especially when mixed with water are called mudslides or if more rocky than that are called landslides. These latter sometimes occur during earth movements like earthquakes.
More about mass movement here

What do you need to remember?

  • Know the meaning of all the terms on BOLD