Landform Formation Flashcards
How are floodplains formed?
When a river floods the capacity and competence falls so deposition occurs
It is a combination of lateral erosion and deposition processes
Increased wetted perimeter and reduction in hydraulic radius so velocity is reduced
How are levees formed?
When a river bursts its banks silt is deposited because the water slows, the heaviest particles are deposited first then the lighter ones
How does Braiding form?
They are caused by fluctuations in discharge levels.
At higher velocities it has a high amount of sediment and slows in sections causing deposition (eyots), the stream splits into many channels
How do Deltas form?
They form when a river reaches a body of standing water ( where fresh and salt water mix, flocculation) where it deposits sediments, these overtime build it into layers.
Top set bed- heaviest material
Foreset bed - ,medium material
Bottom set - finest material
How do Oxbow lakes form?
Form when the neck of a meander is overtime being laterally eroded.
The neck is cut through and joins the river. Deposition occurs on the inside bend which eventually seals off the meander bend which is then left as an abandoned oxbow lake.
How do potholes form?
They form when pebbles get trapped in depressions in the rock.
The pebbles are rotated by the moving water and drill ( form of abrasion) the depression over time which makes it deeper.
This causes more pebbles to become trapped.
How do rapids form?
They are caused by localised increase in gradient or where the river flows over alternating bands of hard rock and soft rock, the soft rock is eroded quicker
How do waterfalls and gorges form?
Waterfalls- where a layer of hard rock is on top of a layer of softer rock which is then undercut by hydraulic action as a plunge pool is formed at the bottom of the waterfall.
This gets bigger and causes the hard rock to overhang, it eventually collapses.
This process continues and the waterfall retreats upstream (gorge)
How are meanders formed?
Occur when the faster flowing water on the outside bend of a river laterally erodes the bank and undercuts it.
This causes the river to curve.
Deposition occurs on the inside bend which forms a slip off slope
Where in a rivers course do oxbow lakes occur.
Why?
Lower course but can be middle
Most lateral erosion and deposition
Where in s rivers course do floodplains occur?
Why?
Lower course
This is where lateral erosion and deposition happen
Where in a rivers course are levees found?
Why?
Lower course
Flooding happens here and deposition
Where in a rivers course does braiding occur?
Why?
Anywhere but commonly upper course.
The discharge is variable
Where in a rivers course do deltas occur?
Why?
Lower course
As this is where the mouth of the river is and where the river begins to slow down
Where in a rivers course do potholes occur?
Why?
Upper course/early middle.
More potential for down cutting, this is where the river bed is more likely to be rocky
