erosion

• When does erosion occur most rapidly?

  When a river is in flood, as this is when it has the most energy.
• Describe the process of hydraulic action.

  The force of the river compresses air trapped in cracks in the banks. The increased pressure weakens and gradually wears away the banks.
• Describe the process of abrasion.

  Rocks carried by the river rub and scrape along the river bed and banks, wearing them down.
• Describe the process of attrition.

  Rocks carried by the river collide with each other and break into smaller pieces.
• Describe the process of solution.

  Where water is slightly acidic, it dissolves certain types of rock on the river bed and banks (e.g. limestone) and carries them as the water flows.
• When does lateral erosion occur & where is it most common?

  Lateral erosion occurs when riverbanks are eroded, making the river channel wider. This is most common in the middle and lower courses.
• When does vertical erosion occur & where is it most common?

  Vertical erosion occurs when the river bed is eroded, making the channel deeper. This is most common in the upper course.
• Give example of erosional landforms.

  Interlocking spurs, waterfalls and gorges.
• Describe the process of the formation of interlocking spurs.

  • In the upper course of a river, water and the material it carries cut into the river bed, creating a steep-sided V-shaped valley.

  • The river is not powerful enough to erode laterally through areas of hard rock, so it winds and bends around them.

  • The winding path of the river creates a winding valley of interlocking spurs.
• Where do waterfalls occur and why?

  Waterfalls occur where there are rocks of varying hardness and density. Softer, less dense rock is eroded away faster than the overlying hard rock.
• How does erosion after a waterfall has formed lead to a gorge forming?

  As erosion continues, the waterfall retreats upstream, leaving a steep-sided valley downstream. This is known as a gorge.