River landscapes Flashcards
What are the four processes of erosiomn?
Hydraulic action
Abrasion
Attrition
Solution
What is hydraulic action?
The force of the river water colliding with rocks breaks rock particles away from the river channel
What is abrasion?
Eroded rocks picked up by the river crash into each other and break into smaller fragments
What is solution?
River water dissolves some types of rock
What are the four methods of transportation?
Traction
Saltation
Suspension
Solution
What is traction?
Large particles like boulders are pushed along the river bed by the force of the water
What is saltation?
Pebble-sized particles are bounced along the river bed by the force of the water
What is suspension?
Small particles like slit and clay are carried along by the water
What is solution?
Soluble materials like limestone dissolve in the water and are carried along
What is deposition?
It is when a river drops eroded material
Why do rivers slow down and deposit material?
- They lose velocity and energy
- The volume of the water falls
- The amount of eroded material increases
- The water is shallower
- The river reaches its mouth
How do waterfalls form?
When a river flows over an area of hard rock followed by an area of soft rock, the soft rock is eroded by hydraulic action and abrasion
This creates a step in the river which is eroded even more once more water flows over it
A steep drop is eventually formed
How do gorges form?
After a waterfall is made, the hard rock is eventually undercut by erosion. It becomes unsupported and collapses
The collapsed rocks are swirled around at the foot of the waterfall where they rode the softer rock by abrasion. This creates a deep plunge pool
Over time, more undercutting causes more collapses. The waterfall retreats, leaving a steep-sided gorge
How do meanders form?
A relatively straight river begins to bend.
The current is faster on the outside of the bend because the river channel is deeper (less friction)
More erosion takes place on the outside of the bend, forming river cliffs
The current is slower on the inside of the bend because the river channel is shallower
More eroded material is deposited on the inside of the bend, forming slip off slopes
It could eventually become an oxbow lake
How do ox-bow lakes form?
When a meander becomes larger over time, erosion can cause the outside bends to get closer
This is until there’s only a small bit of land left between the bends. This is called the neck
The river breaks through this land (usually during a flood) and the river flows along the shortest course
Deposition eventually cuts off the meander forming an oxbow lake. An example would be the River Calder
What are flood plains?
They are flat areas of land that flood
What are levees?
They are natural embankments along the edges of a river channel
How are levees formed?
During a flood, eroded material is deposited over the whole flood plain
The heaviest material is deposited closest to the river channel because it gets dropped first when the river slows down
Over time, the deposited material builds up, creating levees along the edges of the channel
What are estuaries?
They are tidal areas where the river meets the sea
What are some characteristics of a meander?
On the outside of the meander, there would be a river cliff. It is deeper here due to faster flowing water, causing erosion
On the inside of the meander, there would be a slip off slope which would have shallower, slower flowing water
Explain how river meanders may change over time?
The river starts off relatively straight.
Due to erosion, deposition and helicoidal flow, the river begins to bend
Over time, the river deepens on the outer end and shallower on the inner bend, causing the meander to bend even more.
Afterwards, an oxbow lake may begin to form
What were the natural causes of the flash flooding of Boscastle, Cornwall?
Heavy rainfall caused the river to burst its banks
Ground was already saturated from previous wet weather
The rock type is hard sandstone with limited permeability
Steep valley sides increased surface run-off
What were the human causes of the flash flooding of Boscastle, Cornwall?
Deforestation higher up in the river valley meant water was not intercepted
Building on the floodplain meant less infiltration (car parks-tarmac)
Both of these increase surface run off
What were some of the primary effects of the Boscastle floods?
No deaths but property damage was high
Telephone, water, electricity and gas supplies were all interrupted
6 properties collapsed entirely due to the force and speed of the floodwaters
What were some of the secondary effects of the Boscastle floods?
Many residents suffered stress and anxiety in the year that followed
Many businesses suffered-loss of stock
What were some of the immediate responses to the Boscastle floods?
Emergency services are on the scene to helps with the rescue operation
Helicopter winches lifted stranded home-owners off the roofs of their houses and trees
What were some of the long term responses to the Boscastle floods?
Large clean up operation
A £4.5 million scheme to improve flood defences
