Rivers Flashcards
What are the 4 processes of erosion?
- abrasion
- hydraulic action
- attrition
- solution
What are the 2 processes of transportation?
- saltation
- traction
What is abrasion?
-small boulders scratch and scrape their way down the bank, wearing the bank and bed
What is hydraulic action?
- water is forced into cracks by the fast flowing river
- repeated causes weakened rocks, banks
What is attrition?
-stones transported down the river collide with each other and the banks and causes the stones to be small and round
What is solution?
-dissolving of rocks e.g chalk and limestone
What is saltation?
-small pebbles and stones bounce along the river bed
What is traction?
-large boulders and rocks are rolled along the river bed=bedload
Describe the upper course of a river
- wet and boggy valley
- narrow and shallow river
- steep v-shaped valley
- more vertical some lateral
- waterfalls
- small streams
Describe the middle course of the River Tees
- there are gorges as the waterfall moves upstream
- river meanders-changing shape
- the town Yarm=in a meander (18km from sea)
- less rainfall
- 95%of land is farmland
- river is at it’s most powerful + broadens out
Describe the lower course of a river
- flat and floodplain
- no power for erosion
- small bedload and fine silt
- large cities and factories built on the marshy land
Describe the middle course of a river.
- large sized bedload, smoother rocks
- lateral erosion=wide river
- area of warmer temps and less rain
- towns built
- arable and pastoral farming
Describe the upper course of the river Tees.
- the source starts where Cumbria borders county Durham and is a big soggy mass
- cuts a v-shaped valley and carries lots of sediment
- at 5km, the angular rocks are mainly smooth
- high force waterfall, made of rhinestone
- the flow rate = 20km per second
Describe the lower course of the river Tees.
- carries a small amount of material
- next to a factory, used for ships to off load goods
- 15 degrees at the end
- man made
- Stockton on Tees= the main town
How do waterfalls occur?
-when a band of hard rock overlies softer rock
What does splash back cause?
- hydraulic action which weakens the rock behind the fall of water.
- the undercutting leads to an overhang
What develops at the bottom of the waterfall?
-An indentation which turns into a plunge pool
What happens when the overhang breaks off?
-rocks swirl in the plunge pool creating abrasion
What is created as the undercutting continues?
- the waterfall retreats upstream creating a gorge
- the gorge retreats and grows longer
What is an interlocking spur?
-projections of high land entering the valley from alternate sides
How are interlocking spurs made?
- the winding path of the river is due to obstacles being in the way
- the river takes the easiest route over the land resulting in projections of high land
Why do rivers meander and how are meanders created?
- due to obstacles in the way
- fastest flowing on outside bend which cause lateral erosion making the river wider
- outer bends are eroded by abrasion and hydraulic action
What is the fastest flowing part of a river called and why is it the fastest?
- the thalweg
- there is less friction because it is the deepest part
How are ox-bow lakes created?
- the meanders become very narrow and at times of high discharge, the river takes the shortest route and does not meander
- the deposition of alluvium seals off the meander forming a straight river channel
- The cut off meander is called an ox-bow lake
What is the name for a dried up meander?
-meander scar
How are levees made?
- at times of high discharge, the river will overflow it’s banks
- the increase in friction =drop in river’s velocity, resulting in the river’s load being deposited (coarsest and sediment deposited first)
- as this process repeats, the deposition builds up creating natural levees