Geography GCSE Edexcel A - Physical Processes

Weathering, rivers, glaciers

Types of weathering

Types of weathering

Chemical, mechanical, biological

Chemical weathering

When minerals in rocks go through chemical reactions e.g. Iron oxidising softens the rock

Mechanical weathering

When weather and environmental changes affect the rock e.g. Water filled cracks/density change from day to night/pressure from freezing water

Biological weathering

When organisms affect the density and size of cracks in rocks e.g. Weeds growing in cracks/animals burrowing

Shear strength

The strength of the forces holding slope material together

Shear stress

The pressure exerted on slope material via gravity

Shear stress > shear strength

Slope material moves downward

Factors increasing shear stress

Rainfall, human activity, increase in organisms

Factors decreasing shear strength

Rainfall, human activity, earthquake, weathering

Drainage basin

The area around a river that is drained by the main channel and its tributaries.

Source

The starting point of a stream or river, this is often a spring, glacier or upland lake.

Mouth

The point a river leaves its drainage basin and enters the sea

Tributary

A smaller stream/river that joins a larger stream within the drainage basin.

Confluence

The point where a stream/river joins a larger stream/river

Watershed

The boundary of a drainage basin, usually a point of high ground, such as hills or ridges.

Main river channel

The largest river channel that only flows into the sea.

River erosional processes

Hydraulic action, attrition, abrasion, solution

Hydraulic action

The pressure of water compressing air into river bank cracks, potentially fracturing the rocks

Attrition

Rocks carried by a river grinding against each other, breaking down into smooth pebble and sand

Abrasion

Materials grinding against the river bank and bed, resulting in a sandpaper effect

Solution (erosion)

Rocks, especially limestone and chalk being dissolved in slightly acidic river water

River transportation processes

Traction, saltation, suspension, solution

Traction

Large sediment e.g. pebbles being rolled along the river bed

Saltation

Small sediment e.g. shingle/large pieces of sand being bounced along the river bed

Suspension

Small sand and clay particles carried in the river flow. Causes muddy-coloured water, especially after rainfall

Solution (transportation)

Minerals dissolved in the water are carried in the flow.

Characteristics of the middle course of river

Uneven flow of water, meanders and formations of river cliffs and point bars

Meander

A large bend in a river

River cliff

Formed from erosion and found on the outer bend of meanders, where there is more hydraulic action and abrasion from a faster flow of water. The bank sediment is undercut and a steep undercliff is formed

Point bar

Formed from deposition and found on the inner bend of meanders, where there is less energy from a slower flow of water. Sediment eroding from the outer bend is deposited there, forming a sloping landform.

Oxbow lake

A meander that has been cut off from the river though erosion and deposition, then turned into a crescent-shaped lake

Floodplain

An area of flat land around a river, built up by deposition

Sorting

Deposition of materials in order of heaviest. Happens after a flood, when the river's cross-sectional area increases, and makes up levees

Levee

A raised bank of a river, formed from multiple deposition processes after floods

Inputs into a river

direct precipitation into the channel, surface runoff, throughflow (water entering via soil), groundwater flow (water infiltrating through the bedrock)

Outputs into a river

Channel flow into the sea, evaporation

Flow

The rate at which water can be moved through the system

Dam

Large concrete wall built across a river to hold back water

Channelisation

The artificial deepening and straightening of a river

Flood plain zoning

Allocating different areas of land to different uses according to their flood risk

Washland

Area on the floodplain that is left for flooding. Usually for farming and recreation

Weathering

The breaking down of sediment

Erosion

The breakdown and removal of sediment by physical processes

Transportation

The movement of sediment across the landscape

Deposition

The laying down of sediment across the landscape

Compaction

The crushing of sediment due to weights of deposits above it

Cementation

The sticking together of rock particles due to compaction

Uplift

The movement of rock towards the surface due to the pressure of rocks forming underneath it

Sedimentary rock

Rock composed of rounded grains pushed together. Usually have distinct layers and contain fossils. Come in a variety of colours

Examples of sedimentary rocks

Sandstone, chalk

Igneous rock

Rock formed from molten rock and made of randomly arranged crystals. Very erosion-resistant and contains no fossils. Can be intrusive or extrusive

Examples of igneous rocks

Basalt, granite

Metamorphic rock

Formed from other types of rocks exposed to great heat or pressure and made of crystals arranged in layers. Can contain fossils squeezed out of shape

Examples of metamorphic rocks

Shale, marble