River Landforms (Erosional) 

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  • River Landforms (Erosional)
    • V-Shaped Valleys
      • 1) Generally found in the upper course of the river.
      • 2) At this stage the river has lots of potential energy but little kinetic energy
      • 3) The river cannot erode laterally (sideways) although it can erode vertically.
      • Formation  1)The river erodes downwards because it has potential energy and therefore there is lots of vertical erosion
      • 2)The erosion forms a gorge. The valley sides get weathered away and become weakened
      • 3) Rocks from the weathered sides fall into the river where they are taken away
      • 4) Over time the erosion wears down the sides to create the "V" shape
    • Interlocking Spurs
      • 1)An interlocking spur is a natural feature in a rivers course. They appear in the upper course
      • 2)They look like small hills interlocking like a zip
      • Formation  1)When there is a small stream in an upland area it begins to erode the land downwards due to vertical erosion
      • 2)A small "V" shaped valley is formed. This causes very little lateral erosion. With only vertical erosion taking place steep valleys begin to form
      • 3) Because of the hill obstacles the river tries to weave its way round. As  more erosion  takes place small hills begin to form. The edges of these hills are the interlocking spurs
    • Rapids
      • A fast-flowing and turbulent part of the course of a river.
      • 1) When a river crosses a band of hard rock different erosion occurs
      • 2)The hard rock erodes less quickly than softer rock below. This steepens the river gradient and increases the velocity of the water
      • 3)  The rapids will be formed where the water rushes over the hard rock producing white water as it speeds down the steepened section
      • 4) The danger of a rapid is measured in grades, 1 being calmest and 6 being most aggressive
    • Waterfall
      • 1) A waterfall is usually a geological formation resulting from a river, flowing over an erosion-resistant rock formation that forms a sudden break in elevation or 'nickpoint'
      • 1) Typically a river flows over a large step in the rocks. Over time the edges of this step will gradually break away and the waterfall will retreat upstream
      • 2) Often, the rock just below the top rock will be a softer type causing undercutting due to splash-back  This makes a rock shelter or plunge pool
      • 3) Eventually the more resistant top rock will collapse to add blocks of rock to the base. This retreat upstream will often leave a gorge
    • Pot Holes (Kettle Holes)
      • Bowl shaped feature, circular depressions
      • 1) Mainly formed by corrasion/abrasion (material carrie by the river hitting banks and beds)
      • 2) Pebbles which are trapped in holes are swirled around in turbulent eddies
      • 3)Often formed in flood conditions
    • Meanders
      • 1) Riffles are shallow areas of water caused by the deposition of material during times of low energy
      • 2) During times of high flow water will flow inefficiently and the flow of least frictional drag  round the sides. They tend to occur on the entry and exit of a river.
      • 3) Pools are deeper parts of rivers where active erosion is occuring
      • 4) Often rivers will demonstrate a pool riffle sequence. This causes water in the river to move to the edges of the river causing more erosion on one bank of the river
      • 5) The meander will start to form as water flowing round the outside of the bend has to travel faster causing more erosion. Deposition will occur on the inside causing a point bar.
      • 6) The river cliffs and slip off slopes are extended as helicoidal flow takes material from the outside bend to the inside bend
      • A winding curve or bending of a river
    • Ox Bow Lakes
      • 1) Crescent shaped lake positioned next to a river
      • 2) Unless very recently formed there will be a hollow as opposed to a lake
      • Formation   1) As a meander becomes more sinuous the neck of the meander becomes narrower
      • 2) In time of flood the neck can be completely eroded causing the meander to be cut off by the new   straight  channel


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