waterfall

• waterfalls are an example of erosion
• waterfalls

  where water falls down a vertical drop in the channel, usually from a considerable height
• where are waterfalls s found?

  in the upper course, eg break its neck waterfall on a tributary of the river severn
• characteristics of a waterfall:

  • hard rock with soft rock underneath
  • overhang leaving a cap of rock
  • bare rock
  • white water at the base into a plunge pool
  • erosion at the base through hydraulic action and abrasion
• stage 1

  the softer, less resistant rock is eroded quicker than the harder, more resistant cap of rock above
• stage 2

  it is eroded through hydraulic action - the force of the water hitting the softer rock as it falls into the pool (termed splashback) and through rock particles hitting the base of the rock and wearing it away through the process of abrasion
• stage 3

  the erosion of the softer rock causes undercutting of the harder rock
• stage 4

  the harder rock can no longer support its own weight and collapses, adding large blocks of rock to the base of the waterfall
• stage 5

  the force of the water moves the rock around creating a deep plunge pool, this motion then causes the rocks to break up through the process of hydraulic action and attrition
• stage 6

  over a long period of time, this process is repeated several times, causing the waterfall to retreat upstream. this creates a gorge (sometimes known as the gorge of recession)
• 1= a plunge pool forms

  2 the overhang collapses

  3 rocks erode the base

  4 the waterfall retreats to form a gorge

  A) 2

  B) 3

  C) 4

  D) 1