Rivers Flashcards
Explain the 4 erosional processes
Corrasion - the wearing away of the river bed and banks by the rivers load.
Attrition - the wearing down of the load as rocks hit the river bed and each other, breaking into smaller, rounder pieces.
Solution - the water in the river dissolves minerals from the rocks and washes them away.
Hydraulic action - the wearing away of the river bed and banks by the sheer force of the water getting into small cracks and forcing buts of rock to fall of.
Explain the 4 methods of transportation
Traction - when stones are dragged or rolled along the river bed by the force of the water.
Saltation - when small stones bounce of each other and are carried by the water.
Solution - when the river dissolves minerals from the rocks that are carried in the water.
Suspension - small particles are lifted in the water and carried long distances.
State the steps involved in the formation of a v-shape valley
Stage 1 - 4 erosional processes
Stage 2 - transportation
Stage 3 - formation of a v-shape valley
Explain the formation of a v- shape valley
A river flows downhill quickly and erodes the landscape vertically.
The river cuts a deep gash into the landscape using hydraulic action and corrasion.
As the river eroded downwards the sides of the valley are exposed to freeze thaw weathering. This process loosens the rocks and they fall into the river which helps to produce steep valley sides.
The rocks that have fallen into the river assist in the process of corrasion which leads to further erosion.
State the states involved in the formation of a waterfall
Stage 1 - 4 erosional processes
Stage 2 - transportation
Stage 3 - formation of a waterfall
Explain the formation of a waterfall
The river flows over bands of soft rock and hard rock.
Softer, less resistant rock is quickly eroded by the processes of hydraulic action and corrasion.
The river undercuts the harder rock leaving an overhang of hard rock.
The river erodes the softer rock below the waterfall and this forms a plunge pool
State the stage involved in the formation of a meander
Stage 1 - 4 erosional processes
Stage 2 - transportation
Stage 3 - formation of a meander
Explain the formation of a meander
In the middle stages of a river the gradient is less steep. The width of the river begins to increase and bends or meanders begin to form through the process of hydraulic action and corrasion.
The bends begin to form as the river finds the course of least resistance.
Pools form in the slower and deeper parts of the river, whereas riffles form in the shallower, faster parts of the river.
The rate of flow is much slower on the inside bend and this is where the river deposits material.
On the outside bend the river is at its fastest and the river erodes the bank.
Helicoidal flow moves materials across the river channel. This leads to river cliffs and beaches developing.
State the 4 stages involved in the formation of an ox bow lake
Stage 1 - 4 erosional processes
Stage 2 - transportation
Stage 3 - formation of a meander
Stage 4 - formation of an ox bow lake
Explain the formation of an ox bow lake
As the size of the meander increases,eventually the river may cut a new channel at the narrowest point of the bend.
The feature that is left cut off from the river is called an ox bow lake.
State the 3 stages involved in the formation of floodplains and levees
Stage 1 - 4 erosional processes
Stage 2 - transportation
Stage 3 - formation of flood plains and levees
Explain the formation of floodplains and levees
The river flows on a flat floodplain in the lower course.
The water if flowing slowly and deposits silt on the river bed.
When the river floods, a lot of silt is deposited on the river banks.
Regular flooding continues this build up of salt at the sides of the river.
The build up levees usually protect the land from further flooding.
