erosional/depositional landforms Flashcards
define ‘erosion’:
wearing away and removal of material by a moving force (e.g. a river)
define ‘deposition’:
when material being transported by the river is dropped due to a loss in energy
what factors lead to deposition?
- shallow water
- when the river reaches the end of its journey, at the river’s mouth
- when the volume of water decreases (when it becomes more shallow)
what is a meander?
- a bend in the river
- found in the middle and lower course
- created by lateral erosion and deposition
what is the ‘thalweg’:
the point where the water flows fastest. in meanders, the thalweg is always on the outside of the bend.
- so, in a river, the thalweg will swing from side to side, eroding the outside bend.
describe deposition and erosion in a river, eventually resulting in a meander:
- erosion (e.g. abrasion, hydraulic action) occurs on the outside of the bend, as that’s where water flows fastest. this creates a river cliff.
- deposition occurs on the inside of the bend, as that’s where water flows slowest. this creates a slip-off slope.
- this continues over time, and the meander becomes more sinuous (bendy). it migrates through lateral erosion.
describe the formation of an ox-bow lake:
when deposition and erosion continue to occur, the neck of the meander becomes gradually narrower. when the river floods, it can cut through the meander neck, forming a new, straighter channel. deposition cuts off the old meander loop, and an ox-bow lake is formed.
what can occur to an oxbow lake over time?
they can become marshes, and vegetation will grow.
what are floodplains?
the relatively flat areas of land that form the valley floor each side of a river channel, which are sometimes flooded.
what are levees?
the embankments of sediment running along the banks of a river.
- a raised, steep bank along the river channel, and then gradually slopes towards the floodplain.
what are estuaries?
tidal mouth of a river where it meets the sea; wide banks of deposited mud are exposed at low tide.
how are levees formed?
- form in lower course of the river
- at times of heavy rain, river discharge increases. rivers burst their banks. water carries fine particles through solution, and drop them on the valley floor.
- the water has lost energy, so it deposits heavy particles first, down to light particles last - forming a levee.
how are floodplains formed?
after many floods, layers of alluvium build up on the valley floor, creating a floodplain over time.
how do estuaries form?
- estuaries are found at the river mouth
- water is tidal (rises and falls)
- during a rising tide, the sea moves up the river, slowing the river water
- the river loses energy, sediment is deposited
- at low tide, these deposits are seen in the form of mudflats. and overtime, they can develop into salt marshes
