Geography Y10 revision

Chemical weathering

caused by rainfall which creates a chemical reaction when hitting rocks

Freeze-thaw weathering

when water enters cracks in the rock and freezes, prizing open the rock over time, as water expands by 8% when frozen

Erosion

the process by which soil and rock are removed from the earth’s surface by wind, water, ice or biological activity

Weathering

the breaking down of rocks in situ (without moving)

Biological weathering

the breakdown of rocks by living organisms

Mechanical weathering

the physical breakdown of rocks into smaller pieces through extreme temperatures

Vertical erosion

when erosional energy is focused downwards (vertically) due to gravity

Lateral erosion

when erosion acts in a sideways motion

Transportation

when a river carries material downstream

Traction

large, heavy pebbles are rolled along the river bed, mainly near the source as the load is larger

Saltation

pebbles are bounced along the surface, mainly near the source

Suspension

lighter sediment is suspended within the water, mainly near the mouth

Solution

the transport of dissolved chemicals along the river

Deposition

when a river loses energy and drops its load

Formation of waterfalls

1. The river meets a band of more resistant rock, typically in the middle course

2. Erosion of the soft rock leads to an undercutting of the hard rock and creating a plunge pool

3. As the soft rock is eroded quicker, an overhang is created which causes the hanging hard rock to collapse and fall into the plunge pool

4. The waterfall is forced to retreat upstream over time as this process continues, leaving a steep valley or gorge

Formation of levees

1. During floods, water is slowed at the banks so silt is deposited on the side

2. In-between floods, the slow moving river deposits silt on the riverbed

3. The levees continue to build up as more floods take place and create a new river level

4. Material continues to build up on the riverbed, causing the river to go back to its original volume or possibly even less

Land use by humans

• Agriculture - around 85% of South Downs National Park is farmed, due to chalk grassland being ideal for grazing sheep, clay for grazing cows, and lower slopes for arable farming

• Forestry

• Many forests have been felled or replaced with faster-growing, non-native trees to improve the demanding timber industry

• Some regions have become more vegetated de to afforestation by humans

• UK charities such as Woodland Trust protect and increase forests

• Settlements

• Building materials recently haven’t reflected traditional design

• Downs suitable for spring line settlements built on south slopes, leading to 12,000 residents (most populated UK NP)

• Mostly rural area but some major towns and cities surrounding SDNP, like Brighton and Southampton

Metamorphic rocks

• Pre-existing rock whose shape or form has been changed by heat and/or pressure

• They contain regularly aligned crystals and can b shiny and hard, and sometimes flake into layers

• Contact metamorphism is when nearby igneous intrusions change characteristics in the rock

• Regional metamorphism occurs during an orogenic event (mountain building).When large continental plates collide, they create hue compressional forces that change the rock’s characteristics

• examples include slate and marble

Igneous rocks

• Rock that began as magma in the interior of the Earth.

• Formed when magma/lava cools and solidifies

• 2 types of igneous rock - extrusive and intrusive

• Extrusive formed when magma erupts and lava cools quickly on the ground. They typically have small crystals.

• Intrusive formed when magma is deep underground and intrudes into other rocks without reaching the surface, after which it cools slowly. They typically have larger crystals.

• Igneous rocks are impermeable.

• examples include granite and basalt

Sedimentary rocks

• Rocks that began as sediment, usually on the seabed.

• When eroded fragments of rocks and organisms settled to form a sediment. Over millions of years, layers built up and are buried on top of one another and compressed by their own weight which squeezes out the water.

• They have a layered appearance called strata. May contain fossil remains of animals and plants that were trapped as the rock was formed and they can can be used to date the rock. They are usually permeable.

• examples include chalk, sandstone and limestone

Batholiths and Tors

• A batholith is an enormous mass of intrusive igneous rock made of once molten material that has solidified below the Earth’s surface. They are only exposed after lots of erosion of overlying mountain. Dartmoor batholith is made of granite.

• A tor is a rock outcrop formed by weathering, and a result of magma at very high temperatures and deep underground being cooled very slowly a long time ago, causing crystal formation. It then solidified and got exposed when the soft rock above was eroded away.

• An example of a famous tor is Haytor in Dartmoor - it is ~300 million years old.

• Joints are create by shrinkage in the cooling granite and weakened by weathering widening them

Types of ice

• Glacier: A finger of ice usually extending downhill from an ice cap and occupying a valley. Can also form in lower latitude areas when there is high altitude. When accumulation>ablation, glacier grows and extends. When ablation>accumulation, glacier shrinks and retreats

• Ice sheet: A large body of ice >50,000km in extent

• Ice cap: A smaller dome-shaped body of ice, <50,000km in extent, and usually found in mountainous areas.

Corrie formation

• Snow collects in a depression on the mountainside.

• Over time, more snow builds up and the extra weight compresses the snow, turning it into névé and then ice.

• The hollow gets deepened and widened through abrasion and plucking. the glacier moves in a rotation due to the pressure and therefore deepens the hollow and creates a distinct armchair shape. The corrie lip also forms here as there is less erosion on this part as it is focused on the back wall

• Erosion is the greatest at the back wall, near the bottom, and at the base of the hollow as the ice is thickest there.

• The ice moves due to rotational slip causing loose rock fragments from erosion to embed in the ice and cause abrasion on the surface of the hollow.

• Water seeps down the bergschrund crevasse, leading to freezing and freeze-thaw weathering on the back wall. The freeze-thaw of rocky outcrops create rocky fragments called scree.

• At the front of the corrie, the ice is thinner so a raised lip is formed as there is less erosion here.

• After glaciation when all the ice is melted, a tarn(also known as corrie lake) forms in the hollow due to meltwater.

Arete

An arete forms when two glaciers erode towards each other on opposite sides of the mountain, which carves out corries with steep back walls. As the glaciers continue eroding the corrie, the rock in between becomes narrower, steeper and sharper, forming a sharp ridge exaggerated by freeze-thaw.

Pyramidal peak

Forms when 3+ corries form on different sides of the same mountain, which have steep walls. As the glaciers erode towards the centre, the peak becomes pointed and further sharpened by freeze-thaw.

Erratic

stones and rocks of a foreign type to the area they have been deposited in and they were deposited during an ice age. Typically found in the U-shaped valley (glacial trough) in the ablation zone

U-shaped valley/glacial trough

• Up to 500m wide and can be kms long

• Was a v-shaped valley in pre-glacial times

• During glaciation, glaciers form in the valley and use abrasion and plucking to deepen and widen the valley

• The front end bulldozes soil and plucks rock from interlocking spurs to truncate them and create truncated spurs

Misfit stream

A small stream of water that occupies the glacial floor, a landscape created by the glacier, not the river

Hanging valley

When a smaller tributary glacier meet, the tributary erodes less deep than the main glacier as it had less mass and moraine, so the tributary glacier is left hanging high above the main valley and when rivers return, they often form waterfalls

Roche moutonnée

• An outcrop of resistant bedrock with a gentle abraded slope on what would’ve been the upstream side of the ice (stoss slope) and a steep rougher slope on the downstream slope (lee slope)

• Generally between 10-15m long but can be much larger

• Striations found on the stoss side- parallel grooves indicating direction of ice flow

• Smooth upstream slope caused by abrasion as the ice advances over the rock

• Rough lee side due to plucking where ice has attached to the rock and pulled fragments away

• Plucking occurred because as the ice has moved up the stoss slope, reduction in pressure which allowed liquid water to re-freeze and attach to underlying rocks

Drumlin

• A piece of more resistant rock is found on the valley floor in the ablation zone

• As the the glacier meet the moraine, it doesnt have enough energy to erode resistant moraine which leads to deposition of till

• As glacier moves over the resistant moraine, it begins to smooth the material as it moves down the lee slope

• Drumlins are blunt at one end, where resistant moraine is found, and tapered at the other

• Tapered end points in direction of ice flow

• Up to 50m tall, 800m long

Crag and Tail

• A rock hill (crag) with a tapering ridge on its lee side (tail)

• Range in size from several metres to kms in length

• Tail points in direction of ice flow

• Edinburgh castle is an example

• Formed by erosion and deposition

• When glacier meets more resistant bedrock, ice is forced to flow over and around

• Plucking and abrasion on upstream side steepen the slope and make it jagged, forming crag

• At the crag, velocity and pressure of ice decreases

• If there’s a hollow in the softer rock behind the crag, deposition occurs and decreases with distance from the crag creating the tail

Types of moraine

• Lateral: found at sides of glacier, formed from frost-shattered rock that falls onto glacier

• Ground: material carried in the base of the glacier, as it moves, it melts and leaves a trail of till, forming an uneven hummocky floor

• Terminal: found at the furthest extent of glacial advance

• Recessional: found at the glacier snout

• Medial: found in the centre and is from the meeting of 2 lateral moraines where 2 glaciers join

Factors affecting temperature worldwide: Latitude and angle of incidence

• Angle of incidence is the angle at which suns rays strike earths surface

• At equator, angle is ~90° so heat is concentrated and covers smaller area, so temperatures are high

• At higher latitudes, angle is larger so heat covers larger area and is less concentrated, leading to colder temperatures

• Further from equator=higher angle of incidence=colder

Winter darkness

• Earth revolves on a tilt

• During winter poles are tilted away so these areas don’t get sunlight

• Poles have nearly 5 months of summer light and 5 of winter darkness which makes them very cold

Altitude

• For every 1km upwards, air temp decreases by 6.4°C due to factors such as air pressure and water vapour

• When warm air rises it expands which requires energy drawn from heat from air air around it

• As it expands with increasing altitude, rising air becomes cooler

• Higher areas are much colder than lower areas

Albedo effect

• Defined as ability of a surface to reflect sunlight

• Light coloured surfaces (high albedo) reflect more sunlight than dark coloured surfaces (low albedo)

• ice or snow-covered areas have high albedo like the Arctic

• At the poles up to 90% of sunlight is reflected which keeps the area very cold

Continental effect

• Oceans take longer to heat up and cool down than land masses, leading to milder temperatures in coastal areas

• Inland areas have warmer summers and colder winters

Prevailing winds, aspect and ocean currents

• Temperature of prevailing winds depend on where they originate from, winds blowing over seas tend to be warmer in winter and cooler in summer

• Hillsides alter angle of incidence for the ground - south facing slopes are warmer than north facing

• Ocean currents regulate heat around the world, warm currents go towards the poles and cold currents go towards the equator

Relief rainfall

• Wet air rises over an ocean over a mountain

• The higher air cools and condenses causing cloud formation and precipitation

• Air goes back down the mountain and warms

• Evaporation means no or little clouds, meaning this area is dry

Frontal rainfall

• Mostly occurs in mid-latitude regions where warm tropical air meets cold polar air

• Jet stream from W=>E, when warm air meets cold air, the arm, less dense air is lifted over the dense cold air

• As a result, rain is produced from warm air condensing

Convectional rainfall

• Produced by buoyant air rising in clouds as a result of warm air rising due to evaporation from sunlight, called low pressure air

• As air gets higher, water vapour condenses as it is colder, forming cumulonimbus storm clouds

3 cell model

• Equator - low pressure, Hadley cell

• wet and cloudy, windy as wind gets sucked from high to low pressure areas, warm due to latitude

• Wet sue to low pressure air rising and cooling, so water vapour condenses and forms clouds and causes rain

• 30°N/S - Ferrell+Hadley cells

• Dry, extreme temperatures, very hot or cold

• High pressure air sinks causing water vapour to evaporate which means clouds cannot form, causing dry weather

• 60°N/S - Ferrell+Polar cells

• Wet and cloudy, windy as wind gets sucked from high to low pressure areas, milder weather due to latitude

• 90°N/S - Polar cell

• Dry, cold due to latitude

• High pressure air sinks causing water vapour to evaporate as temperature increases causing dry weather

Factors affecting UK climate: Latitude and relation to cells

• Between 50-60°N of equator

• Near boundary of Ferrell and Polar cells

• Warm air from S and cool air from N meet leading o depressions and unsettled weather

• Distance from equator affects climate as it receives less solar radiation than areas near equator, temperate climate with very rare extreme weather events

• Frontal rainfall is common

Ocean currents for UK

• Warm ocean current called North Atlantic drift brings warm water from Gulf of Mexico to N driven by prevailing winds

• Warm water makes UK climate milder than expected for latitude

Prevailing wind for UK

• Prevailing wind is SW

• Travelled over large expanses of warm ocean so air is warm and wet

• PW reaches western areas of UK first and releases moisture as rain there

• Therefore east is relatively dry

Regional variations in UK climate

• NW - Cool summers eg. 10°C, mild winters eg. 5-6°C, heaviest rainfall eg. 2800-4700mm average/year

• NE - Cool summers eg. 12-13°C, cold winters eg. -1-0°C, dry eg. 800-1300mm average/year

• SW - Warm summers eg. 14-16°C, mild winters eg. 5-6°C, heavy rainfall eg. 1700-2800mm/year

• SE - Warmer summer eg. 16°C+, colder winters eg. 3-5°C, driest eg. 400-800mm rainfall/year

Tropical storms

• Formed 5-30°N/S of equator due to Coriolis effect being negligible on equator or too weak near it

• Warm ocean, 27+°C as this is where the storm gets energy from

• Depth of water must be ~60-70m

• Occurs when warm air rises to create an are of intense low pressure

• As warm, moist air rises, powerful winds spiral around calm eye and warm air condenses into heavy rainfall and thunderstorms

• When it goes over land a large amount of water is thrown onto the land called storm surge

• Due to lack of energy source through deep warm water

• Storm collapses and dissipates

• Wind speeds must be >74mph to be hurricane/cyclone/typhoon

Chemical weathering

caused by rainfall which creates a chemical reaction when hitting rocks

Freeze-thaw weathering

when water enters cracks in the rock and freezes, prizing open the rock over time, as water expands by 8% when frozen

Erosion

the process by which soil and rock are removed from the earth’s surface by wind, water, ice or biological activity

Weathering

the breaking down of rocks in situ (without moving)

Biological weathering

the breakdown of rocks by living organisms

Mechanical weathering

the physical breakdown of rocks into smaller pieces through extreme temperatures

Vertical erosion

when erosional energy is focused downwards (vertically) due to gravity

Lateral erosion

when erosion acts in a sideways motion

Transportation

when a river carries material downstream

Traction

large, heavy pebbles are rolled along the river bed, mainly near the source as the load is larger

Saltation

pebbles are bounced along the surface, mainly near the source

Suspension

lighter sediment is suspended within the water, mainly near the mouth

Solution

the transport of dissolved chemicals along the river

Deposition

when a river loses energy and drops its load

Formation of waterfalls

1. The river meets a band of more resistant rock, typically in the middle course

2. Erosion of the soft rock leads to an undercutting of the hard rock an creating a plunge pool

3. As the soft rock is eroded quicker, an overhang is created which causes the hanging hard rock to collapse and fall into the plunge pool

4. The waterfall is forced to retreat upstream over time as this process continues, leaving a steep valley or gorge

Formation of levees

1. During floods, water is slowed at the banks so silt is deposited on the side

2. In-between floods, the slow moving river deposits silt on the riverbed

3. The levees continue to build up as more floods take place and create a new river level

4. Material continues to build up on the riverbed, causing the river to go back to its original volume or possible even less