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Rivers - Coggle Diagram
Rivers
Waterfalls and Gorges
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2 -- Over time more soft rock is eroded, leaving a hard rock ledge over the soft rock. The height of the gap increases as the river erodes the less resistant rock at the base. A waterfall forms.
A plunge pool is also formed at the base, where erosion has created a pool where the water lands
3 -- The less resistant rock underneath the hard rock is eroded, this is called under cutting.
4 -- The overhanging rock collapses, because there is nothing underneath it to support it.
As the last stage repeats the waterfall keeps retreating creating a steep sided valley made of hard rock
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Errosion
Abrasion
This is where pieces of rock are picked up by the river, they then jit the river bed or bank, wearing them away
Attrition
This is where pieces of the bed load (material carried by the river) collide with each other, this causes them to brake into smaller more rounded pieces.
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Hydraulic action
This is where the forces of the water hitting the river bed and bank, causing the rocks to break off.
Transportation
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Suspention
This is where silt (sand, clay or other material) and sand particles are held in water, but do not dissolve. The particles are then transported along with the river.
Saltation
This is where small sand and gravel particles bonce along the sea bed and travel in the direction of the river flow.
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Interlocking spurs
Formed in the upper course. Rivers in the upper course don't have the energy to erode the hard rock so instead go round the hard rock, leaving spurs of hard rock where they could not erode.
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Meanders and Oxbow lakes
Meanders
1 -- When a river bends, the current is fastest at the outside of the bend, this high energy water erodes the side of the rive creating a river cliff.
2 -- The current is weakest where the water is shallowest, opposite the river cliff. More energy is deposited here creating slip-off slopes.
3 -- This creates bends in the river, as the river cliffs and slip-off slopes are formed.
Oxbow
1 -- As erosion continues, the river's bends get nearer to each other and create a swan neck meander (a small piece of land between meanders)
2 -- During a flood high energy water will breach the meander neck, this makes the river flow in a straighter, faster course. Over time deposits will fill in the meanders bends and the meander will be cut off from the river, forming an oxbow lake.
Deposition
This is where the river losses energy and so needs to drop sediment (staring with the largest), this occurs in the middle and lower courses