Robert Mckeegan Jonathon Knox James Hennessy References: •Essential As Geography (Stanley Thrones) •Geography in Focus •Encarta Premium •Google Images (France) •http://www.nps.gov/ (United State National Park) Potholes Waterfalls Interlocking Spurs River Valleys Rapids Potholes Term: A Circular depression on a river bed carved out of solid rock How: The Drilling Action as pebbles are caught in currents and Whisked around in a small cracks or Hollow. Over time the potholes increases in size due to lateral and horizontal erosion on the bed of the pothole and the bank. This is a form of Corrasion. Where: Commonly found near Waterfalls and Rapids, This is because the Hydraulic Action is a significant process due to the rivers increased discharge. Waterfall Term: Sudden step in a River long Profile How: The sheer force of Hydraulic Action results in a band of less resistant soft rock being eroded or undercut, as neighbouring hard rock cannot be eroded as quickly its forms a steep step. As the Hard Rock is not eroded as quickly, and the soft rock recedes upstream, this results in a layer of hard rock overhanging the plunge pool. As the Waterfall recedes upstream causing steep-sided gorge to be formed. Waterfalls Case Study: High Force At High Force, the River Tees falls in a single sheet some 20m into the swirling pool below. Two types of rock can be seen at the fall; the lower has horizontal layers and forms part of the carboniferous limestone. The upper has dark colored rocks has vertical joints within it making it denser than the underlying limestone. In fact it’s an outcrop of igneous dolerite. The Tees also boasts Caldron Snout which is a series of cascades with a total drop of 60m. Image: High Force, River Tees An Example of a Plunge Pool Example of Steep Sided Gorge Rapids When rocks of varying resistances cut across a valley a series of smaller steps may form rapids. Rapids are associated with very disturbed turbulent water Example of rapids are: Yukon Rapids, Yukon Territory (Northern Canada) V-Shaped Valleys V-shaped valleys have steep valley walls with narrow valley floors. In cross section it has a "V" shape. They are created by fast flowing rivers with steep gradients. As rivers flow downhill quickly, they remove more sediment from the bottom of the stream channel than from the sides. This process is called down cutting. It can be compared to a knife cutting through a cake. The resulting landform is a narrow canyon with a fast flowing river and little bank, or floodplain, on the river sides. An example of such a valley is found in Grand Canyon National Park and Black Canyon of the Gunnison National Park.