Rivers Flashcards
What are the 4 types of erosion?
Attrition, abrasion, soluion, hydraulic action
What is attrition?
Rocks bash together and get smaller and smoother
What is abrasion
Rocks thrown at cliff base break apart or are dragged along the river bed
What is solution (erosion)?
Chemical reaction that dissolves rocks
What is hydraulic action?
Water enters cracks in river bank, air compresses and causes crack to expand- sheer force of water
What are 4 types of transportation?
Solution
Suspension
Saltation
Traction
What is solution (transportation)?
Minerals dissolved in water are carried along
What is suspension?
Sediment carried along in flow of water
What is saltation?
Pebbles bounce along the river bed
What is traction?
Boulders roll along bed by force of water
What is the definition and the two types of weathering?
The breakdown of rocks in situ
Mechanical and biological
What is mechanical weathering?
Breakdown of rocks without changing its chemical composition
What is biological weathering?
Breakdown of rock by plants and animals
What is deposition?
When river loses energy it drops sediment. Heaviest material deposited first.
What are 3 landforms resulting from erosion?
Interlocking spurs
Waterfalls
Gorges
How are interlocking spurs formed?
Most erosion is vertical in upper course.
Creates steep v-shaped valley
Not powerful enough to laterally erode
Wind around hillsides
How are waterfalls formed?
River flows over area of hard rock changes into soft rock
Soft erodes via hydraulic action and abrasion quicker
Creates step in river
Hard rock creates undercut and plunge pool
Unsupported and collapses
How are gorges formed?
More water full undercutting leads to collapses
Waterfall retreats
Leaves steep sided gorge
How are oxbow lakes formed?
Flow stronger on outside of river
Where flow is slower, sediment is deposited
Meander gets bigger and cuts through neck of meander
River takes shorter course
Sediment builds up and cuts off loop from river
What are 3 landforms resulting from deposition?
Levees
Floodplains
Estuaries
How are floodplains formed?
Erosion removes interlocking spurs
Flat area either side of river
Height of floodplain increases as material deposits either side
How are levees formed?
Flooding occurs due to increase in water volume
When river floods, sediment spreads across floodplain
Most material deposited on sides of bank, and smaller bits further away
Sediment builds and increases height of river bank
Chanel can carry more water
However, levees are fragile and made from loose silt
What are human risk factors and physical risk factors of floods?
Urbanisation and river capacity
Precipitation and geology
How is urbanisation a flood risk factor?
More impermeable surfaces
Decreases time taken for water to flow into river
Flash flooding
How is capacity of river a flood risk factor?
Filled with rubbish
Channel size decreases
River carries less water- more likely to flood
How is precipitation a flood risk factor?
If there’s a storm, amount of water in river increases
Increases risk of flash flooding downstream
How is geology a flood risk factor?
Impermeable rocks
Rainwater cant run into soil and underground storage
Runs straight into river
Increases risk of flash flooding
