L2 Waterfalls

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L2 Waterfalls

  1. 1. River landforms 1 Distinctive landforms result from different processes as rivers flow downstream. NT page 104
  2. 2. Learning objectives <ul><li>To describe and explain landforms resulting from erosion – waterfalls and gorges </li></ul>
  3. 7. Eventually as the waterfall retreats upstream, a gorge is formed downstream
  4. 8. <ul><li>2004 Question 4 (7 marks) </li></ul><ul><li>With the aid of a diagram(s) explain the formation of a waterfall </li></ul><ul><li>Waterfalls are formed where the river meets a band of softer , less resistant rock after flowing over a relatively hard, resistant rock. Initially a series of rapids may form </li></ul><ul><li>The softer rock is worn away more quickly by the processes of hydraulic action (the sheer force of the water eroding the soft rock) and abrasion (the swirling action of the river and its load which also erode the softer rock). The harder band of rock is undercut . In time the overlying harder rock ( overhang ) will become unsupported and will collapse . </li></ul><ul><li>At the foot of the waterfall is a deep plunge pool formed through abrasion . The water and rock debris from the overhang will help to deepen the plunge pool. The back wall is further eroded through the process of hydraulic action . </li></ul><ul><li>The whole process is repeated many times and will cause the waterfall to retreat upstream forming a gorge </li></ul>
  5. 9. 20 PLUNGE POOL 19 INFILTRATION 18 THROUGHFLOW 17 CONDENSATION 16 HYDRAULIC ACTION 15 SUSPENSION 14 PERCOLATION 13 GORGE 12 ABRASION 11 CORROSION 10 INTERLOCKING SPUR 9 SOLUTION 8 TRANSPIRATION 7 WATER TABLE 6 SALTATION 5 EVAPORATION 4 ATTRITION 3 TRACTION 2 SURFACE RUN OFF 1 PRECIPITATION

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