Geography

Topic 4 - Physical geography

Igneous rocks

Igneous rocks

made from lavas and deep magmas. They were once molten, cooled and crystallised. Most igneous rocks are resistant to erosion. E.g granite

Sedimentary rocks

Formed when layers of sediment are compacted together until they become solid rock. Two main types: limestone and chalk, clays and shales

Metamorphic rocks

Igneous or sedimentary rocks changed by heat or pressure e.g shale becomes slate, limestone becomes marble

Granite formation

Magma slowly cools deep underground

Granite key characteristics

• hard

• resistant

• jointed

• impermeable

Granite environments

Forms uk high mountain environments including the Grampian mountains and dartmoor, landscapes badly drained -boggy

Slate formation

Formed from shale when heated and compressed

Shale key characteristics

• very hard

• very resistant

• impermeable

• foliated(very thinly layered)

Shale environments

Usually in upland environments including the Cambrian mountains

Carboniferous limestone and chalk formation

Shells, fish skeletons and dead coral collect on the ocean form and are compressed. Calcium carbonate crystallise around the fragments cementing them together

Carboniferous limestone key characteristics

• resistant

• heavily jointed

• permeable

• non porous

Carboniferous limestone environments

Forms upland environments such as the Yorkshire dales in the Pennines

Chalk key characteristics

• medium resistant

• porous

• permeable

Chalk environments

Often forms escarpments in lowland regions such as the South Downs

Clay formation

Deposition of muds by river or at sea

Clay key characteristics

• weak

• impermeable

• not jointed

• slightly porous (fine pores)

Clay environments

Forms lowland environments such as the Cheshire plain

Jointing

Cracks in rocks, usually caused by cooling when rock are formed or unloading when weight is taken off them as material above is eroded

Permeability

How easily water can move through a rock

Porosity

How easily a rock can absorb water into it via its pores

Why do the hardest rocks form the UK's upland environments whereas the softest rocks form the UK's lowland environments?

Harder rocks are weathered and eroded more slowly so remain standing as mountains whereas softer rocks are weathered and eroded more quickly creating lowland plains

Tees-Exe line

An imaginary line spreading the UK's uplands and UK's lowland

Past tectonic processes

• Plate movements created faults (cracks in the Earth's crust). These have been eroded over millions of years to create large valleys e.g Great Glen, Scottish highlands

• millions of years ago, volcanic activity caused the formation of hard igneous rocks which now form the UKs highest mountains

Glacial erosion in development of landscapes

During the ice age, valley glaciers in the high mountains caused erosion creating features such as u-shaped valleys, corries, arêtes, pyramidal peaks e.g Grampian mountains, Cumbrian mountains

Glacial deposition in development of landscapes

Ice sheets transported vast amounts of loose eroded sediment known as glacial till and deposited it during their expansion and contraction, creating lowland plains

Weathering

The breakdown and decay of rocks by natural processes in situ

Physical weathering

(Freeze thaw) Rainwater enters cracks in rocks and then freezes if temperatures drop below 0 degrees. Water expands as it turns into ice and then exerts pressure on the rocks, causing it to break into smaller pieces

Chemical weathering

All rain is slightly acidic. If the air is polluted, it can become more acidic. When rain falls on rocks, the acid in it can react with weak minerals, causing them to dissolve and the rock to decay

Biological weathering

The roots of plants, especially trees, can grow into cracks in a rock and split the rock apart

Slope processes (mass movement)

The downslope movement of material due to gravity, the extent of the mass movement will depend on how steep the slope is, the speed at which the rock and sediment move and how much water is present

Soil creep

Individual particles of soil move slowly down a slope due to gravity and collect at the bottom of valley sides. The river may then erode this material

Slumping

This happens when the bottom of a valley side is eroded by the river. The slope becomes steeper and the material above slides downwards, rotating as it does so. Movement is often triggered by periods of heavy rain

How do weathering processes cause slope processes?

Freeze thaw loosens rocks, creating rockfalls. This material forms scree at the base of slopes

How do weathering processes cause river processes?

Biological weathering on river banks breaks down rocks so they are more easily eroded by the river

How do slope processes cause river processes?

Processes such as landslides on valley sides provide sediment for river to transport and erode with

How do climatological processes cause weathering processes?

High rainfall increase chemical weathering (rainwater reacts with rocks) e.g limestone

How do climatological processes cause river processes?

High rainfall will result in greater river flow so more erosion and transport

How do climatological processes cause slope processes?

High rainfall will increase rate of landslides/ slumping on slopes

Features of the Lake District

Location: Cumbria
Upland or lowland? Upland
Key characteristics: mountainous area dominated by glacial landscape features such as carries, arêtes and glacial troughs.

Geology, tectonic and glacial processes: During last ice age, almost all of the Lake District was covered in ice except from the highest peaks. Ice eroded the mountains creating glacial landscape features.

Weathering and slope processes: Freeze thaw is common creating angular rock fragments. Slope processes are rapid particularly rocks which contribute to scree. Landslides relatively common due to high rainfall which adds weight to loose sediment.

Post-glacial river processes: Since the last ice age, the rivers have been flowing through the u shaped valleys of the Lake District.

Human processes: Hill farming dominates as climate/ environment is too harsh for arable (steep slopes, poor soils, high rainfall, low temps) therefore sheep are a better option. Tourism has also affected enviro through dev of hotels and footpath erosion scars on popular mountains.

Features of the Yorkshire Dales

Location: North Yorkshire
Upland or lowland? Upland
Key characteristics: karst (limestone) landscape

Weathering and slope processes: Carboniferous limestone is chemically weathered. Joints are opened by weathering created grykes and the blocks of limestone left upstanding are called clints.

Post-glacial river processes: Rivers enter the limestone through swallow holes and open up joins to form caves.

Human processes: main sheep farming as enviro is too harsh for arable. Quarrying is common as limestone is used as a building material and in the manufacturing of glass and concrete

Features of the The Weald

Features of the The Weald
Location: Kent and Sussex
Upland or lowland? Lowland
Key characteristics: lowland area consisting of undulating hills, escarpments and vales.

Geology, tectonic and glacial processes: the softer rocks such as Gault clay were eroded to form vales. Harder rocks left to form hills.

Weathering and slope processes: Chalk is calcium carbonate so it's affected by chemical weathering of acidic rainwater. Biological weathering also breaks down chalk through trees and shrub roots. Limited freeze thaw due to relatively warm climate of south of uk.

Post-glacial river processes: unusual to find rivers in chalk areas as chalk is porous except when it's saturated after wet weather. Common to find rivers in vales as clay is impermeable

Human processes: water percolates through chalk until meets the impermeable clay where it emerges at the surface of the base of the escarpment (called the spring line.) Historically, settlements developed along this line due to availability of water. Dominated by both arable and sheep farming. Thin soils and steep slopes of the chalk suit sheep farming and thick soils and flat land of the clay suit arable.

Watershed

The area of highland forming the edge of a drainage basin

Tributary

A small river joins a larger river

Source

The starting point of a river

Mouth

The point where a river leaves its drainage basin

Confluence

A point where to rivers meet

Channel

Where the river flows

Drainage basin

The area of land drained by a river and its tributaries

How does a valley profile change with distance downstream?

Becomes wider. Near the source, the steep river gradient means the river eroded vertically (vertical erosion) forming a v shaped valley. Near the mouth, the low river gradient means the river erodes sideways (lateral erosion) making the valley floor wider

How does the gradient change with distance downstream?

It decreases. Near the source, the landscape is more mountainous/ hilly so the river gradient is high. The river flattens it as it reaches the gently sloping lowlands so the gradient is low.

How does channel width with change with distance downstream?

It increases. There is is a greater volume of water with distance from the source as tributaries join the main channel resulting in an increased channel width

How does channel depth change with distance downstream?

It increases. There is is a greater volume of water with distance from the source as tributaries join the main channel resulting in an increased channel depth

How does the velocity change with distance downstream?

It increases. Generally there will be less friction in a wider, deeper channel because less of the water is close to/ in contact with the river bed and banks.

How does the discharge change with distance downstream?

It increases, it is a function of cross section area (width x depth) and velocity. Measured in cubic metres per second, cumecs

Hoe does sediment size change with distance downstream?

It becomes smaller. As material travels downstream, it collides with other particles, causing pieces to be 'knocked off.' This is known as attrition

How does sediment shape change with distance downstream?

It becomes rounder. As material travels downstream, it collides with other particles, causing pieces to be 'knocked off.' This is known as attrition

Erosion

The action of water wearing away and removing sediment from the river's bed and banks

The extent of erosion depends on...

The rock type, river gradient and the volume of river sediment

Hydraulic action (erosion)

The sheer force of water hitting the river bed and banks and wearing them away

Abrasion (erosion)

Sediment carried by the river rubbing against the river bed and banks and wearing them away

Solution(erosion)

River water is slightly acidic so can dissolve some rocks and minerals. Limestone and chalk are most affected.

Attrition(erosion)

Sediment carried in the river collides, causing the edges to be worn. Continued collision causes sediment to become more rounded and smaller with distance down stream

Traction (transportation)

The largest sediment (boulders, large pebbles) are rolled along the river bed by the water's current

Saltation (transportation)

Medium sized sediment (small pebbles, large grains of sand) 'bounce' along the river bed

Suspension (transportation)

Small sediment (fine clay or silt) is carried along 'suspended' in the water

Solution (transportation)

Some rock minerals are dissolved in water and are transported in solute form

Deposition

When a river no longer has enough energy to transport its load, deposition occurs

Upper course characteristics

• Furthest upstream

• Steep gradient

• vertical erosion is dominant

• landforms include v shaped valley, interlocking spurs and waterfalls

Middle course characteristics

• lateral erosion, transportation and deposition

• landforms include floodplains and meanders

Lower course characteristics

• furthest downstream

• low gradient

• deposition is dominant

• landforms include floodplains, meanders, oxbow lakes, levees, estuaries and deltas

Hydrograph

Shows how a river responds to a rainfall event

Rising limb

Shows the river discharge after rainfall

Lag time

The difference between the time of the peak rainfall and the time of peak discharge

Falling limb

Shows discharge falling as less water reaches the channel

Precipitation

Water falling to earth from the atmosphere, as rain, sleet, hail, snow

Condensation

Water turning from vapour to liquid - results in cloud formation

Evaporation

Water turning from liquid to gas (vapour)

Interception

The catching of precipitation by vegetation before it reaches the ground

Throughflow

Water moving downhill through the soil towards a river

Riverflow

The volume of water moving down a river channel

Transpiration

Water returned to the atmosphere from plants and trees

Groundwater flow

Water that is deep under the ground and moves towards the river

Infiltration

When water is absorbed into the upper layer of the soil

Percolation

When water moves deeper down in the ground

Factors that affect the shape of a hydrograph

• rainfall

• rock type

• drainage basin size

• soil

• relief

• vegetation

• land use

• deforestation

• urbanisation

These physical factors result in a greater or faster...

These physical factors result in a greater or faster surface runoff. The hyrdrograph has a steeper rising limb, shorter lag time and higher peak discharge

These factors result in less or slower...

These factors result in less or slower surface runoff. They hydrographic has a gentler rising limb, a longer lag time and lower peak discharge

How does intense rainfall result in faster surface runoff?

Rainfall all enters the basin at the same 'time' - unlikely to infiltrate quickly enough so surface run off and rapid transfer to the river

How does prolonged, steady rainfall result in slower surface runoff?

Water has time to infiltrate and is more likely to be stored, resulting in a slower transfer to river

How do impermeable rocks result in a faster surface runoff?

They cannot absorb water so less percolation, less groundwater store and flow so water transferred to river quickly

How do permeable rocks result in a slower surface runoff?

They absorb water so more percolation, more groundwater store and water is transferred slowly to the river via groundwater flow

How does a small drainage basin result in a greater surface runoff?

Rainfall reaches river channel quickly as it has less distance to travel resulting in a shorter lag time

How does a large drainage basin result in slower surface runoff?

Rainfall reaches the river channel more slowly as it has greater distance to travel resulting in a longer lag time

How do thin soils result in faster surface runoff?

This reduces the size of soil store and so infiltration capacity is reached quickly resulting in more surface ruff and rapid transfer of water to river

How do thick soils result in slower surface runoff?

There is more soil storage so surface runoff is less likely resulting in slower transfer of water to river via through flow

How do steep slopes result in faster surface runoff?

There is a shorter lag time because water flows quickly by surface runoff therefore the water reaches the river more quickly

How do gentle slopes result in slower surface runoff?

There is a longer lag time because water is more likely to infiltrate and will travel more slowly to the river via through flow and groundwater flow

How does lack of vegetation result in faster surface runoff?

There is less interception and less vegetation store so water is transferred more rapidly to the river

How does more vegetation result in a slower surface runoff?

There is more interception and vegetation store so water is slow in reaching the ground surface (or may be lost trough transpiration) and therefore is transferred to the river more slowly

How does recent rainfall cause faster surface runoff?

If recent high rainfall has already caused saturated ground the infiltration is reduced so any new rainfall causes rapid surface runoff