4b.1 - Erosion Processes & Landforms Flashcards
How do rivers erode?
Hydraulic Action
Attrition
Abrasion
Corrosion
How do rivers transport sediment?
Traction (rolling)
Saltation (bouncing)
Suspension
Solution (Dissolved)
How do rivers find the path of least resistance in upland areas?
They flow around the hardest part of the mountain - interlocking spurs
Which way do rivers erode in the upper course?
Vertically / downwards
creating v-shaped valleys
Where is river flow the fastest?
On the outside of bends
Where do you get meanders?
Lower/Middle course
High enough velocity
Less resistant geology
How does a meander become an ox-bow lake
The river erodes the outside of the bend fastest
It cuts through the neck of the meander
The new river channel by passes the meander - which dries up, leaving an ox-bow lake
Rivers erode laterally to create
A wide, flat, valley floodplain
How do meanders get more meander?
Lateral erosion on the outside of the bend
Outer bank undercuts and ‘expands’
Inner bank - deposition of material
What is a river cliff
Outside of a meander bend
High velocity of water undercuts the bank
What is a point-bar?
Deposited material on the inside of a bend in the river
Where do you get a waterfall?
Where hard rock meets sofer less resistant rock
How does the waterfall get bigger?
The river undercuts the less resistant rock, leaving the harder rock hanging
What is a plunge pool
When a waterfall undercuts hard resistant rock, which collapses and debris swirls around
How does a gorge form
The waterfall retreats upstream leaving narrow valley sides behind it
How are meanders formed?
Abrasion takes place closer to the outside of the bend (the fastest-flowing part of the channel)
the slowest-flowing water is on inside of bend so deposition
occurs there.
Why does river velocity increase downstream?
The channel becomes wider and deeper which reduces the amount of friction.
The channel becomes a more efficient shape (smoother) which means that there is less friction (1).
Tributaries join the main channel which means that there is more water in the river
Explain one way the weather and climate can affect river erosion
Global climate change/global warming/rising temperatures,
which increases the amount of evaporation and therefore
reduces erosion
Seasonal variations in rainfall/temperature, which increases discharge during winter months/reduces erosion during summer months
Periods of intense/sustained rainfall will increase erosion
Periods of drought/low rainfall will decrease erosion
How do erosional processes lead to waterfalls being formed?
In areas where hard and soft rock overlay, the river is able to erode the softer rock more rapidly creating a waterfall and its associated features: plunge pools and gorges. The soft rock is eroded through a combination of corrasion and hydraulic action.
How do erosional processes create V-shaped valley?
Vertical erosion (mainly corrasion) in the upland river can dig deep valleys into the landscape. The exposed sides of these valleys are changed by weathering and mass movement creating a interlocking spurs and a distinctive V-shape valley.
How do floodplains form?
‘Migrating’ meanders make the valley floor flat.
When floods occur the floodplain becomes inundated •As the flood waters run out of energy they deposit their silty load leading to the formation of alluvium soil.
