Landforms Causes By Erosion And Deposition+ Flooding Flashcards
Why do interlocking spurs form
If there are areas of hard rock which are harder to erode, the river will bend around it
How do waterfalls form
-The river flows over bands of less resistant (softer) and resistant (harder) rocks.
-The less resistant rock is more quickly worn away due to differential
erosion
-The river undercuts the harder rock leaving an overhang which becomes unsupported and collapses into the
plunge pool
below.
-After the overhang falls, some of the rocks are swirled around by the river and this helps to form a deep plunge pool below the waterfall.
-The plunge pool is also deepened during times of high discharge when hydraulic action is most powerful.
-The waterfall is moved upstream, the process continues and a steep-sided gorge is cut back into the hillside.
How do gorges form
The waterfall retreats upstream and
a steep-sided valley is left where the waterfall once was. This is called a
gorge
Meanders
As the river erodes laterally, to the right side then the left side, it forms large bends, and then horseshoe-like loops called meanders.
-The formation of meanders is due to both deposition and erosion and meanders gradually migrate downstream.
-The force of the water erodes and undercuts the river bank on the outside of the bend where water flow has most energy due to decreased friction. This will form a river cliff.
-On the inside of the bend, where the river flow is slower, material is deposited, as there is more friction. This will form a slip-off slope.
-Over time the horseshoe becomes tighter, until the ends become very close together
How do oxbow lakes form
-Over time, continual erosion and deposition narrows the neck of the meander.
-Often during a flood the river will cut through the neck of the meander.
-The river continues on its straighter path and the meander is abandoned.
-The fastest current will now be flowing in the centre of the river channel and
deposition is more likely to occur beside the banks.
-New deposition seals off the ends and the cut-off becomes an ox bow lake that will eventually dry up, except during periods of very heavy rainfall.
How do levees form
Levees are formed by the repeated
flooding
of the river. When the river floods, during periods of high energy, the water and the load it is carrying will leave the channel.
-Due to the drop in energy caused by friction, the biggest, most coarse material will be dumped close to the river banks. With repeated flooding, this will continue to build up the levee over time
How do floodplains form
A floodplain is the area around a river that is covered in times of flood. This is a large, flat area of land that is formed by erosion and deposition.
Why are floodplains good for farming
It is a very fertile area due to the rich alluvium deposited by floodwaters.
What is an estuary
An estuary is where the river meets the sea. The river here is tidal and when the sea retreats the volume of the water in the estuary is reduced. When there is less water, the river deposits silt to form mudflats which are an important habitat for wildlife.
What processes occur in the upper course of a river
Interlocking spurs
What processes occur in the middle course of a river
Meander and oxbow lake
What processes occur in the lower course of a river
Levees, floodplain and estuary
What is floodplain zoning
The land near a river that often floods is not built on the defences like farming land but areas that rarely get flooded are used for houses and industry
What is flood relief channeling
The building of new artificial channels which are used when a river is close to maximum discharge and therefore reduces flood risk
What is Channel straightening
Straightening the river to remove meanders in order to reduce flood risk
