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Geography Rivers - Rejuvenation


Geography Rivers - Rejuvenation
George Hudson
Mind Map by George Hudson, updated more than 1 year ago
George Hudson
Created by George Hudson over 6 years ago

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Geography Rivers - Rejuvenation
  1. Where does rejuvenation occur?
    1. Rejuvenation occurs when their is either a fall in sea level relative to the level of the land or a rise of the land relative to the sea. This enable a river to renew its capacity to erode as its potential energy is increase. The river adjusts to its new base love, at first in its lower reaches and then progressively inland. In doing so, a number of landforms may be created: knick points, waterfalls and rapids, river terraces and incised meanders
    2. Knick points
      1. A knick point is a sudden break or irregularity in the gradient along the long profile of a river. Some knick points are sharply defined, for example waterfalls, where as other are barely noticeable. Although a number of factors can cause such features to occur, they are most commonly attributed to a rejuvenation. When a river is rejuvenated, adjustment to the new base level starts at the sea and gradually works its way up the course of the river. The river gain renewed cutting power (in the forms of vertical erosion), which encourages it to adjust its long profile. In this sense the knick point is where the old long profile join the new long profile. The knick point recedes upstream at a rate which is dependent on the resistance of the rocks, and may linger at a relatively hard outcrop. It can be difficult to determine whether a waterfall occurs due to variability in a rock type or to rejuvenation. Headward erosion upstream may mean that a waterfall cuts back through the vally towards
        1. Knick point: Usually marked by rapids, this represents rejuvenation and is a sudden break in the long profile of the river
        2. River terraces
          1. A river terrace is a remnant of a former floodplain, which has ben left at a higher level after rejuvenation of the river. Where a river renews its downcutting, its stinks its new channel into the former floodplain, leaving the old floodplain above the level of the present river. The terraces are cut back as the new valley is widened by lateral erosion. If renewed rejuvenation takes place, the process is repeated and anew pair of terraces is formed beneath the original ones. The River Thames has created terraces in its lower course by several stages of rejuvenation. Terraces provide useful shelter from floods in a lower-course river valley, and natural rhouteways for roads and railways. The built-up areas of Oxford and London are mainly located along the terraces of the River Thames.
            1. River terrace: A narrow, flat piece of ground that runs parallel to the river on either side, above the level of the floodplain. The are usually created following a fall in base level.
            2. Incised meanders
              1. If a rejuvenated river occupies a valley with well-developed meanders, renewed energy results in them becoming incised or depended. Incised streams and rivers have cut deeply into the landscape in many parts of the British Isles. The nature of the landforms created is largely a result of the rate at which vertical erosion has taken place. When incision is slow and lateral erosion is occurring, an ingrown meander may be produced. The valley becomes asymmetrical, with steep cliffs on the outer bends and more gentle slip-off slopes on the inner bends. With rapid incision, where downcutting or vertical erosion dominates, the valley is more symmetrical, with steep sides and a gorge-like appearance. These are described as entrenched meander
                1. Incised meander: This is caused by rejuvenation. it is a meander that has cut deeply into the floodplain, creating steep cliff-like banks
                2. What is rejuvenation?
                  1. An increase in the energy of a river caused by either a fall in its base level or an uplift of the land
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