RIVER LANDSCAPES

River Landscapes OCR

What are the 3 types of weathering?

Mechanical, chemical, biological

What is mechanical weathering?

The breakdown of rock into smaller pieces by physical means

What is biological weathering?

Rocks and river banks are broken down by living organisms, such as plants and and aniamls

What is chemical weathering?

The process that breaks down rock through chemical changes

What is transportation?

The movement of material along the coast by waves, or along a river bed by the river

What is solution (transportation)?

Soluble materials dissolve in the water and are carried along

What is saltation?

Small pebbles and stones are bounced along the river bed in a series of short jumps

What is traction?

The movement of larger sedimentrolling on the bottom of a sea or river

What is erosion?

The wearing away of material by a moving force

What is abrasion?

When sediment is thrown against a surface by water and rubs the material to smooth the landform

What is solution (erosion)?

Where rocks are dissolved in water

What is hydraulic action?

where water forces its way into cracks, which creates weaknesses in rocks, splitting them apart

What is attrition?

Where pebbles hit each other or landforms, making rocks break and get smaller and rounder

What is abrasion?

When sediment is thrown against a surface by water and rubs the material to smooth the landform

What is deposition?

the laying down of eroded materials that have been transported

What is mass movement?

Sudden movement of material down a slope due to the pull of gravity

What is sliding?

Where a section of land falls down a slope and dislodges other material on its way down.

What is slumping?

Where material at the bottom of a slope moves outward

How is a V-shaped valley formed?

When it is nearer its source, a river is shallow and there is a lot of friction between the water and the river bed. This erodes the rocks beneath it, leading to a steeper gradient which in turn makes the water in the river descend quickly. This gives it the energy to erode the river bed further, producing a V shaped valley

How is a gorge formed?

The gradual retreat of waterfalls upstream. The overhang of hard rock falls in the water and the new plunge pool causes the waterfall to erode even more

How is a floodplain formed?

As the river floods and flows outwards from the river channel, the flow has less energy so it deposits the fine sediment (alluvium) being carried within it onto the surrounding area

How is a levee formed?

As the water in a floodplain retreats after a flood, the water drops the heavier material first. This means more sediment is dropped close to the river channel. After the river has flooded several times, this can build up to forfm levees

How is a waterfall formed?

• waterfalls form where a river flows over an area of hard rock followed by and area of soft rock

• the softer rock is eroded, by hydraulic action and abrasion, more than the hard rock => creating a 'step' in the river

• as water flows over the step, it erodes more and more of the softer rock

• a steep drop is eventually created; a waterfall

How is a meander formed?

As the river makes its way to the middle course, it gains more water and therefore more energy. Lateral erosion starts to widen the river. When the river flows over flatter land it can develop large bends called meanders.

How are oxbow lakes formed?

Due to erosion on the outside of a bend and deposition on the inside, the shape of a meander will change over a period of time. Erosion narrows the neck of the land within the meander and as the process continues, the meander necks move closer together. When there is a very highdischarge (usually during a flood), the river cuts across the neck, taking a new, straighter and shorter route. Deposition will occur to cut off the original meander, leaving a horseshoe-shaped oxbow lake.