GCSE Geography AQA - Restless Earth

Continental Crust:

•  30 - 50km thick
• Over 1500 mil years old
• Mainly granite, silicon, O2, aluminium
• Can't sink, can't be destroyed, 2.6 density

Oceanic Crust:

• 6 - 10km thick
• Less than 200 mil years old
• Mainly bascut, silicon, magnesium, O2
• Can sink, can be destroyed, 3.0 density

Inner core < outer core < mantle < oceanic crust < continental crust

• Constructive plate margins - 2 plates move away from each other, magma rises to surface to form volcanic islands, volcanoes & earthquakes

• Collision zones - 2 cont. plates move towards each other, neither can be destroyed so form fold mountains, no volcanoes but some earthquakes

• Destructive plate margins/subduction zones - 2 plates move towards each other, heavier oceanic crust sinks below cont. crust, causes deep sea trenches, volcanoes & earthquakes

• Conservative plate margins - 2 plates move sideways next to each other, same direction or different directions, violent earthquakes

Fold mountains:

• many places e.g. Alps, Himalayas, Carcasas
• Rivers carry sediment into sea between 2 plates, sediments build on sea bed
• Geosycline  filled with sediment, compression as plates move towards each other
• Continued compression from 2 plates, sediments folded into fold mountains

Ocean trenches:

• found in subduction zones, edge of Pacific ocean e.g. Peru-Chile trench
• Oceanic plate sinks below cont. crust, causes a trench

Volcanoes found in long narrow belts e.g. 'Pacific Ring of Fire' & mid Atlantic ocean, south Europe & centre of Pacific ocean

Shield volcanoes:

• Constructive plate margins
• Lava - runny, basic, hot
• Cone - wide base, gentle slopes made of lava
• e.g. Mauna Loa, Hawaii; Hekla & Heimaey, Iceland

Composite volcanoes:

• Destructive plate margins
• Lava - acidic, sets quickly
• Cone - tall, narrow base, steep sides made of layers of lava & ash
• Pyroclastic flows, secondary cones
• e.g. Mt St Helens, USA; Pinatubo, Philippines

• Caused by sudden release of pressure due to movement along faults

• Most occur along plate margins, strongest at destructive, constructive & conservative

• Plates suddenly lurch, point where pressure is released called the focus

• At destructive plate margins focus is deep & sinking of subducting plate & its subsequent melting can trigger strong earthquakes

• Longitudinal & transverse waves, surface of focus called the epicentre

• Constructive - Mid-Atlantic Ridge, Iceland

• Destructive/subduction - Nazca & South American plate boundaries, Andes mountains (fold mountains), Peru-Chile Trench (8km deep, 45,00km long from Panama to Tierra del Fuego) 

• Collision - Indo-Australian & Eurasian plate boundaries, Himalayas

• Conservative - Pacific plate (faster) & North American plate (slower), San Andreas Fault

• Why is human activity hard? - relief high & steep, accessibility hard; narrow mountain valleys, making roads/railways hard; soil is stony, thin & infertile; colder, windier & wetter as you go up

Human activity:

• Forests - timber from coniferous forests main building material & winter fuel, pulp & paper
• Farming - on south-facing slopes are warmer, transhumance - seasonal movement of animals, summer cattle on higher alp, fodder grows on valley floor, winter cattle to valley floor, feed on fodder; new techology - cable cars carry milk to valley floor, turn milk into butter & cheese
• HEP - Hydro-electric Power, power generated from fast-moving rivers due to steep slopes, precipitation & melting glaciers; cheap, renewable, used by sawmills etc, supplies with electricity
• Tourism - skiing, snowboarding, e.g. St Montz Chomonix; glacial lakes, scenery e.g. Interlaken
• Safety - building tunnels & shelters along roads from avalanches, expensive, needs technology

• 9th June 1991, not erupted since 1380; largest eruption of 20C, near city of Manila, destructive plate margin; Philippines plate (oceanic) & Eurasian plate (cont.)
• Primary effects - 200,000 homes destroyed, local hospital, schools & factories, contaminated water, unusable roads & bridges, ash ruined harvest of 1991, 6 died as direct result of eruption
• Secondary effects - planting in 1992 impossible, over 1 mil animals died, farmers forced to city, disease like malara & diarrhoea, 1991 & 1993 monsoon rains - flooding & lahars, lowered world temps & blocked sun, 700 died from disease/lahars
• Immediate responses - many didn't believe it would happen, fled with panic to refugee camps, emergency aid from Japan - food, medicine, blankets, April - June 1991 early warning signs, evacuation of 58,000, 15,000 at Clark Air Base
• Long term responses - Nov 1991 US abandoned CAB, Aeta tribe returned to slopes, Japan granted materials for rehabilitation, people from Angeles stayed in refugee camps due to lahars, 10 years later CAB now a thriving tourist resort, 1993 Clark Development Corporation for Aeta, 7 industries

Predicting:

• Magma moving causes small earthquakes, measure using seismomenters, recorded 2 months before eruption
• Ground temps increased - heat seeking cameras
• Bulging lava dome - tiltmeasures by CAB
• Gurgling magma, gas & steam
• GPS - detect movement

Preparing: 

• Forecast eruption, predict how powerful it will be
• Evacuate those in danger area, provide transport, accommodation & food
• Train more emergency service teams
• 2nd April, first evacuation of 2,000 people
• Organise emergency supplies & water

Supervolcano characteristics:

• erupts at least 1000km3 of material
• formed by boiling reservoir of magma, grows to enormouse size & colossal pressure
• when it erupts & collapses, it causes a huge depession called a caldera

Facts: north-west Wyoming, USA; 55km by 65km; recurrence interval of 600,000 years; geysers, mud pits & hot springs; ground risen by 70cm in some places

Local effects - devastating for 100 mile radius; pyroclastic flows for 50-100 miles at 500 mph; ash rise 80,000 feet, then 20-30 feet would fall; 400,000 people at risk; inhaling ash is dangerous; animals & crops die; day turns to night

National effects - north-west USA devastated; ash particles stay in air for years, crops fail for 6 years, biggest supplier of grain so big consequences

International effects - severe air traffic disruption; global temps & climates effected; ash particles in air for 6 years

Location - epicentre on Awaji Island in Osaka Bay off coast of Kobe, south Japan

Magnitude & duration - Philippine plate under Eurasian plate along Nokima fault, 7.2 Richter scale, 20 seconds

Date & time - Jan 17th 1995, 5:46 am

Primary effects - 200,000 buildings destroyed; bullet train bridges collapsed; 120/150 quays destroyed; 1km of Hanshin Expressway collapsed; almost every house flattened

Secondary effects - electricity, water, gas supplies cut off; fires; massive traffic jams help up emergency crews; 230,000 homeless; Panasonic & Mitsubshi temporarily closed; 5,500 dead & 40,000 injured

Immediate responses - Hanshin Expressway still closed; hospitals struggled to cate for everyone

Long term responses - all services working by July; fire areas by Aug; total damage £56 bn, Sept 1996 H. Expressway open again, buildings further apart, flexible steel frames, rubber blocks 

Location - Sichuan country, central China, epicentre in Wenchuan

Magnitude & duration - Indian Plate & Eurasian plate along Longmenshan fault; 7.9 Richter scale, 120 seconds

Date & time - May 12th 2008 at 2:28 pm

Primary effects - 8,700 dead initially, 374,000 injured; 5-10 mil homeless; 5 million buildings collapsed, Juyuan school in Dujiangyuan 900 pupils killed; communications stopped

Secondary effects - 69,000 dead, 18,000 missing; landslides blocked roads & rivers; fear of flooding; £75 bn damage

Immediate responses - 20 helicopters bring relief & rescue; army troops parachuted & hiked to worst areas; clean water, food supplies & tents

Long term responses - teams from Japan, Russia & South Korea helped; donation of £100 mil from Red Cross, went to running camps

Location - epicentre in Sumatra

Magnitude - 9.1 Richter scale, 10m vertical displacement of seabed along 750 mile fault line

Date - 26 Dec 2004

Effects - highest wave 25m; 220,000 died, 650,000 injured; 2 mil homeless; tourist resorts damaged, affected local economy, many foriegn nationals died

Responses - rescue services & emergency teams swamped by scale of disaster; wounds turned gangerous; fresh water, water purification tablets, food, sheeting & tents from whole world; £75 million from UK, build 20,000 new homes; Indian Ocean Tsunami Warning System set up in June 2006