Geography-Hydrosphere-River features

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Author:
Smyth159
ID:
77590
Filename:
Geography-Hydrosphere-River features
Updated:
2011-04-05 14:29:48
Tags:
Geography Hydrosphere River features
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Geography-Hydrosphere-River features
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  1. Explain the formation of a waterfall
    • A waterfall is formed when harder rock is on top of soft rock
    • Softer rock is eroded quicker than the hard rock by the force of the running water
    • This is called differential erosion
    • Eventually the softer rock is eroded away and the hard rock is left overhanging
    • Eventualy the hard rock collapses as there is nothing supporting it
    • This rock gets swirled around by the river and erodes a plunge pool
    • This process is repeated over a long period of time causing the waterfall to gradually retreat upstream leaving a steep sided gorge
  2. Explain the formation of a meander
    • Alternating series of irregularities develop on the river bed- This starts off the meander
    • This causes the river to develop a winding or sinuous course
    • Slower areas are found in deeper parts of the river filled with fine sediments and are called pools.
    • Faster areas are found in shallower parts of the river around larger stones and are called riffles.
    • Faster flow on outerbend results in erosion and formation of river cliff- more energy
    • Slower flow on inside bend results in deposition and formation of slip off slopes- less energy
    • Helicolidal flow further assists meander formation and transports sediment from river cliff to the slip off slope on the inside of the next bend
  3. Explain the formation of an Oxbow lake
    • lateral erosion on outside of bends of pronounced meanders
    • Narrow neck of meander gradually becomes narrower due to erosion on outer bends
    • Neck is cut through by river during floods and river forms new straighter channel
    • Cutt-off is sealed by deposition
    • Ox-bow lake begins to silt and evaporate. Over time it will completely dry up
  4. Explain the formation of a levee
    • When a river floods and it's water spills over onto the flood plain, friction increases, velocity decreases and the river begins to deposit it's load
    • The coarsest material (sand and gravel) is deposited at the channel edge and form natural ridges or levees, which increase in height each time the river floods
    • The finest alluvium is carried further
    • The gradual accumulation of alluvial bed-load causes river-level to rise slowly
  5. Explain the formation of a river terrace
    • River terraces are examples or rejuvenated landforms
    • The terraces are portions of a former floodplain, formed before rejuvenation, and they flank either side of the present floodplain
    • Rejuvenation occurs when:
    • Base level(sea level is lowered)
    • Erosional processes are initiated again and the river regrades its bed to the new case level

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