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+ In this section you will learn about the interior of the Earth. Journey to the centre Continental crust (thick) No one has ever seen the inside of the Earth. The deepest we have managed to get is 3.5 km 35km in the Witwatersrand gold mine in South Africa. Miners would have to drill another 6365 km to reach the centre of the Earth. What we know about the Earth's interior comes from direct and indirect evidence. We can get direct evidence from the Earth 's surface. Indirect Asthenosphere 75-250km Lower mantle evidence, like earthquakes and material from space, also helps us to understand the Earth. Examining the crust The diagram on the right shows the structure of the Earth. The crust is the surface of the Earth. lt is a rock layer forming the upper part of t he lithosphere. The lithosphere is split into tectonic plates. These plates move very A. Geologists (scientists who study the Earth and its structure) think the Earth has a layered structure, like an onion. slowly, at 2-5 cm per year, on a layer called the asthenosphere. + The lithosphere is the uppermost layer of the Earth. lt is cool and britt le. lt includes the very top of t he mantle and, above this, the crust. There are two types of crust: • Continental crust forms the land. This is made mostly of granite, which is a low density igneous rock. Continental crust is on average 30-50 km thick. • Under the oceans is oceanic crust. This is much thinner, usually 6-8 km thick. lt is also denser and made of an igneous rock called basalt. A. Geologists collect samples of the crust and compare the two types: polished granite from continental crust (left} and basalt from oceanic crust (right). Restless Earth The asthenosphere and mantle The movement of the tectonic plates is evidence that there is a 'lubricating ' layer underneath the lithosphere. This is the asthenosphere. You might think that this layer would be a liquid. But if it was a liquid, the heavy tectonic plates would sink into it. Geologists think the asthenosphere is partly molten rock and partly solid rock. it may be like very thick, dense, hot porridge! The asthenosphere is in the top layer of the mantle. The mantle is the largest of the Earth's layers by volume, and is mostly solid rock. We know this because sometimes you can see the top of the mantle attached to an overturned piece of crust. Earthquake waves tell us about the physical state of the Earth. They speed up, change direction or stop when they meet a new layer in the Earth. Some waves travel .A. The Japanese have built a 57 000-tonne international scientific drilling ship, the Chikyu, which will drill 7 km through the oceanic crust to reach easily through the crust, mantle and inner core, but not the mantle - further than anyone has ever gone before. through the outer core. This suggests that the outer core has a different physical state and may be liquid, not solid. Clues from space At a depth of 2900 km , we can't sample the Earth's core. Geologists Lithosphere - .--· Composition Layer 2.7 Solid Granite Air temp- 900 Oceanic crust 3.3 Solid Basalt Air temp- 900 Asthenosphere 3.4-4.4 Partially molten think that it is metal - mostly nickel Continental crust and iron. Evidence for this comes from meteorites, which are fragments of rock and metal that fall to Earth from Mantle space. Most come from the asteroid belt between Mars and Jupiter. ;-.-.--...=.....:....., Lower mantle Core_ _...1 Outer core ~,;,.;;.;.;;. Solid 900-1600 Peridotite 1600-4000 Iron and nickel Meteorites come in several types: • Stony meteorites, with a similar composition to -basalt. • Stony-iron meteorites, containing a lot of the mineral olivine. • Iron meteorites, which are solid lumps of iron and nickel. These meteorites may be fragments of the lithosphere, mantle and core of a shattered planet. Iron meteorites may show that the Earth 's core is made up of iron and nickel. your questions 1 Draw a cross-section of the Earth. You need a large circle divided into layers. Label the layers with details of density, temperature and physical state. 2 What are the main differences between the lithosphere and asthenosphere? 3 Exam-style question Describe the differences between the oceanic and continental crust. (4 marks) + In this section you will learn how the Earth's core drives the process of plate tectonics. 0"' yo~Af' pfe4."'ef + In a few billion years the core and mantle will stop convecting, because the radioactive heat will run out. This will shut down our magnetic field, and life on Earth will be destroyed by radiation from space. Hot rocks Inside t he Earth it is hot. We know this because of: • molten lava spew ing from active volcanoes • hot springs and geysers . Heat from inside the Earth is called geot hermal (' Earth-heat'). The heat is produced by the The inner core is so deep and is under such huge pressure that it stays solid. The outer core is liquid radioactive decay of elements such as uranium because it is under lower pressure. As heat rises a nd thorium in the core and m antle. This ra ises from the core, it creates convection currents in the core 's tempe rature to over 5 000 oc. + Some elements are naturally unstable and radioactive. Atoms of these elements release particles from their nuclei and give off heat. This is called rad ioactive decay. Convection cell in the mantle the liquid outer core and mantle (see below). These vast mantle convection currents are strong enough to move the tectonic plates on the Earth's surface. The convection currents move about as fast as your fingernails grow. Radioactivity in the core and mantle is the engine of plate tectonics. Crust Constructive plate margin, _ _ _ ~d~~,, where two plates are pulled apart -+--Yr- -----\+Vi&\\-- Convection in t he liquid outer core Destructive plate _ _ _J!,_. margin, where two t plates are pushed \ together Plumes of heat rise in the mantle; the mantle is less dense Plumes ill' Sometimes The parts of convection you can see the magnetosphere. 0"' yo&Af' pf&il'\e-f cells where heat moves towards the surface are called plumes. These are concentrated zones + Did you know that the Earth's magnetic field sometimes 'flips', so north becomes south and south becomes north? of heat. In a plume, the mantle is less dense. Plumes bring magma (molten rock) to the surface. If magma breaks through the crust, it erupts as lava in a volcano. The northern lights (aurora borealis) form when radiation from space hits the magnetosphere and lights up the sky. • Some plumes rise like long sheets of heat. These form constructive plate boundaries at the surface. • Other plumes are like columns of heat. These form hot spots. Hot spots can be in the middle of a tectonic plate, li ke Hawaii and Yellowstone in the USA. Magnetic field The Earth is surrounded by a huge invisible magnetic field called the magnetosphere. This is a force field. lt protects the Earth from harmful radiation from space and the sun (see right). The Earth's magnetic field is made by the outer core. As liquid iron in the outer core flows, it works like an electrical dynamo. This produces the magnetic field . , your questions 1 Why is the centre of the Earth at over 5000 °C? 2 Look at the diagram of the Earth's convection currents. What happens to the crust at the top of one of the convection currents in the mantle? 3 Find out why Mars is a 'dead' planet with no plate tectonics. You might like to visit this website: http:// mars.jpl.nasa.gov/classroom/students.html 4 Each set of words below has an odd one out. For each: a say which is the odd one out b explain your choice. • inner core, outer core, mantle, crust • convection, northern lights, plume, cell, current • lava, uranium, magma, geyser 5 Exam-style question Describe the different layers of earth's interior. (4 marks) + In this section you will find out how the Earth's tectonic plates have moved in the past, and about plate boundaries. Pangea, the supercontinent Scientists know that the continents were once all joined together. They formed a supercontinent called Pangea. The diagram on the right shows the position of the continents 250 million years ago. Identical rocks and fossils dating from this time have been found in West Africa and eastern South America. This tells AFRICA us that Africa and South America were once joined. Pangea started to split apart about 200 million years ago. Since then, plate tectonics has moved the continents to the positions they are in today. Moving plates Today, the Earth's lithosphere is split into 15 large tectonic plates and over 20 small ones. These are like the patches that make up a football. The plates move very slowly on the asthenosphere. Where two plates meet, there is a plate boundary. There are three types of plate boundary, as shown on the map opposite: • Constructive plate boundaries formed when two plates move apart. • Destructive plate boundaries - formed when two plates collide. • Conservative plate boundaries formed when two plates slide past each other. Plate boundaries are where the 'action' is. Most earthquakes and volcanoes are found on plate boundaries. Oh yo~A1" pf~"'ef + Every year, the distance between the UK and the USA grows by about 2 cm. This is because the mid· Atlantic constructive plate boundary creates new oceanic crust. Restless Earth Pacific Direction of plate movement Antarctic """"""- Constructive boundary """'-- Destructive boundary - - Conservative boundary Crust: old and new 0"' yo ~.A.,.... pfeiJ'\ef Most continental crust is 3-4 billion years old. The oldest oceanic crust is only 180 million years old. Why the age difference? New oceanic crust forms constantly at constructive plate boundaries: • Convection currents bring magma up from the mantle. • The magma is injected between the separating plates. • As the magma cools, it forms new .oceanic crust. • The plates continue to move apart, allowing more magma to be injected. Old oceanic crust is destroyed by subduction at destructive plate boundaries- it is 'recycled ' by the Earth. Continental crust was formed billions of years ago, and has not formed since. it is less dense than oceanic crust, so can't be subducted and destroyed. + Subduction describes oceanic crust sinking into the mantle at a destructive plate boundary. As the crust subducts, it melts back into the mantle. + Look at the map of plates and plate boundaries above. The circle of plate boundaries around the Pacific Ocean is called the 'Pacific r ing of fire, because it has many active volcanoes. your questions 1 Compare the map of Pangea with a modern world map from an atlas. Describe how India has moved since the time of Pangea. 2 Look at the map of tectonic plates. a Which plate is the UK on? b Name a country which is split by two plates. c Name two plates that are moving apart. d Name two plates that are colliding. 3 Exam-style question Explain why earth's tectonic plates move. (6 marks) + In this section you will learn which hazards happen at different plate boundaries. Conservative Tectonic hazards Earthquakes and volcanoes (tectonic hazards) occur at plate Constructive boundaries. Different plate boundaries produce different tectonic hazards. Destructive Conservative boundaries As plates slide past each other, friction between them causes earthquakes. These are rare but very destructive, because they are shallow (close to the No volcanoes. Iceland, on the mid-Atlantic ridge. The Eurasian and North American oceanic plates Ipulling apart. • Small earthquakes up to 5.0-6.0 on the Richter scale. Andes mountains in Peru and Chile. Nazca oceanic plate is subducted under the South Amencan continental plate. • Very destructive, up to magnitude 9.5. • Tsunami can form. ____ .___ Volcanoes San Andreas fault • Destructive in California, USA earthquakes up to magnitude 8.5. North American and Pacific plates sliding • Small earth past each other. tremors almost daily. Himalayas. Formed as the Indian and Eurasian continental plates push into each ...... other. Collision zone Earthquakes Example Plate boundary • Not very explosive or dangerous. • Occur in fissures (cracks in the crust). • Erupt basalt lava at 1200 °C. lr •Very explosive, destructive volcanoes. • Steep sided, cone shaped. • Erupt andestte lava at 900-1 000 oc. • Destructive earthquakes, up to magnitude 9.0. • Landslides are triggered. Volcanoes are very rare. surface). The San Andreas Collision zones fault is shown below. San Francisco Key e major earthquake location and date 0 200 km + USA ""o~ Los Angeles "0,: Pacific Ocean N + Collision zones are a type of destructive boundary. They form mountain ranges like the Himalayas (see right). Two continental plates of low-density granite collide, pushing up mountains. Earthquakes happen on faults (huge cracks in the crust) in collision zones. Mountain range ~ Asthenosphere .A. A conservative p late boundary .A. A collision zone boundary Constructive boundaries Destructive boundaries As plates move apart, magma rises up through As the plates push together (see the diagram the gap, as the diagram below shows. The magma below), oceanic plate is subducted. As it sinks, is basalt and is very hot and runny. lt forms lava it melts and makes magma called andesite (after flows and shallow sided volcanoes. the Andes). Sea water is dragged down with the oceanic plate. This makes the magma less dense Earthquakes are caused so it rises through the continental crust. The water Oh yo~r pf&ihef by friction as the plates tear apart. erupts as steam making volcanoes very explosive. + These earthquakes are small. They don 't cause much damage. Every year there are about 100 000 earthquakes strong enough to be felt. The largest earthquake recorded was a magnitude 9.5 in Chile in 1960. Sinking oceanic plate can stick to the continental plate. Pressure builds up against the friction . When the plates finally snap apart, a lot of energy is released as an earthquake. These earthquakes can + Tectonic hazards are natural events that affect people and property. be devastating, especially if they are shallow. Constructive plate boundary Destructive plate boundary ~--Lava erupts forming volcanoes Plates spread apart Convection currents from mantle bring magma towards the surface Magma is forced up between the plates. When this cools new oceanic plate forms I Dense oceanic plate is subducted under the less dense continental plate The oceanic plate melts --..:....;,.A Earthquakes back into the mantle your questions 1 Which type of plate boundary is most dangerous for humans to live on? 2 Match the words below into pairs: constructive fault collision zone fissures landslides explosive destructive conservative Write a brief explanation of your pairs. 3 Look at the diagram of the San Andreas fault. The two plates can 'lock', stopping them from sliding. Why do you think this is? 4 Exam-style question Compare the physical features and tectonic hazards of constructive and destructive plate boundaries. (6 marks} + In this section you will examine the impact of volcanoes on developed countries. Destructive power The most devastating volcanoes are the most Ash and gas column explosive ones. The Volcanic Explosivity Index (VEl) measures destructive power on a scale from 1 to 8. Mount St Helens, which erupted in May 1980, measured 4. Modern humans have never experienced an eruption measuring 8. Ash fall builds up on roofs, causing buildings to collapse , . Volcanoes produce many hazards. Some are Lava bombs can kill people close to the crater from the primary effects of the volcano, whereas others are secondary. Some benefit the Pyrocla~st~ic:_f~lo~w"!:::.=====::::: Pyroclastic flows are deadly clouds of hot ash and gas that sweep along at 200 km/h _j areas affected, whereas others cause problems. Sakurajima, Japan Lahar (volcanic mudslide) occurs when rain or snow Japan is on a destructive plate boundary where the Pacific plate is subducted beneath the Eurasian plate, causing active volcanoes. One, Sakurajima (below) , has erupted since the .A. Volcanic hazards 1950s, sometimes 200 times a year. Ash and lava have buried buildings and destructive plate boundary --....... plate movement KYUSHU ISLAND 7000 people live at the base of the volcano. Hot springs and lava flows are a popular tourist attraction; the area is a national park. The 1914 lava flow joined the island to the mainland. < ~ Restless Earth Lava lake farmland, poisonous gases have caused alerts in local towns and brought acid rain, killing plants. Volcanic eruptions can be predicted - scientists can say Layers of ash from pyroclastic flows Side vent when a volcano will erupt. They can then warn people to take shelter or evacuate. The diagram below shows how Sakurajima is monitored and also the evacuation procedure there. ~ Lava pi pe Japan is a developed country. lt can afford to spend money on monitoring, protection and evacuation . When Magma chamber Sakurajima does erupt, it will probably not cause many deaths. Homes, crops and industries will be destroyed, but most people have insurance and the Government ~ Stratovolcano (or composite cone volcano) will help to repair the damage. In developed countries, tectonic hazards damage property (economic costs) but cause less harm to people (social costs). Aircraft are used to measure the amount of gas the volcano gives off _,..; seismometers. These r earthquakes which as magma rises so scientists can predict an eruption Tiltmeters detect when the volcano swells up as it fills with magma Concrete lahar channels divert dangerous '""'-__,_ m udflows Boreholes measure water temperature as magma heats it up ~ ~ Hot springs / are monitored Concrete shelters protect against volcanic bombs and ash Evacuation clearly sign posted; regular evacuation drills your questions 1 Copy and complete the following table to show the effects of Sakurajima: Benefits Problems Primary effects Secondary effects 2 Make a table like the one on the right: IProtection .6. Two men take cover in a lava bomb shelter during an eruption of Sakurajima (in the background). + Primary effects- caused instantly by the eruption. These are directly linked to the volcano e.g. lava, acid rain, gases and earthquakes. + Secondary effects - in the hours, days, and weeks after the eruption. These are often caused by the volcano e.g. disease, food and water shortages. IPrediction Use it to list methods used to protect people from Sakurajima, and how scientists predict an eruption. 3 Exam-style question Using examples, explain how volcanic eruptions can be predicted. (4 marks) + In this section you will learn how volcanoes can have devastating consequences for people in the developing world. At risk In the developing world , people are at greater risk from tectonic hazards than those in developed countries: • They often live in risky locations, because there is nowhere else to live. • They can't afford safe, well-built houses, so buildings often collapse. • They don't have insurance. • Their governments don't have the money and • resources to provide aid. Communications are poor, so warning and evacuation may not happen. Most volcanic eruptions with high death tolls are & Lava destroyed 40% of Goma, covered half the airport and destroyed 45 schools. Water and electricity supplies were also cut off by the lava. in the developing world. Mount Nyiragongo In January 2002, a fast flowing river of basalt lava, 1OOOkm wide, poured out of Mount Nyiragongo and into the city of Goma (see photo). 100 people died, mostly from poisonous gas and getting trapped in lava. A number of social impacts also resulted: • 12 500 homes were destroyed by lava flows and earthquakes - and as the eruption was predicted, 400 000 people were evacuated. Many people had to move to overcrowded refugee camps. • Disruption to the mains water supplies caused concern for the spread of diseases. Many economic impacts also resulted: • Poisonous gases caused acid rain which affected farmland and cattle - many farmers lost income. 1 Magma rising from the mantle 2 Convection currents pull the two plates apart 3 The valley has formed as some of the crust has sunk downwards Mt Sakurajima, Japan • Due to poverty, most people could not afford to rebuild their homes. Within days, people began returning to Goma. Over 120 000 were homeless. This was a crisis and people needed help quickly. With little clean water, food and shelter, diseases like cholera could spread. The United Nations and Oxfam began a relief effort to help. • The United Nations sent in 260 tonnes of food in the first week. Families got 26 kg of rations. • In the UK, a TV appeal asked people to give money to help. • Governments around the world gave $35 million to get aid to the refugees. • Emergency measles vaccinations were carried out by the World Health Organisation. In a developing country, the main problem is poverty. Most people fled from the lava with nothing. lt was months before many could start building new homes. By June 2002, however, some roads had been cleared of lava and the water supply repaired . Future threats Mount Nyiragongo was active again in 2005. lt could erupt at any time. There is also volcanic activity under Lake Kivu. Gases like carbon dioxide and sulfur djoxide rise through the Earth into the lake. They get trapped in mud on the lake bottom. An earthquake could shake these gases free. In 1986 this happened to volcanic Lake Nyos in Cameroon, also in Africa. 1700 people suffocated from breathing in too much carbon dioxide. Mt Nyiragongo, DRC Volcano type Steep-sided stratovolcano (or composite cone) over 1000 meters high Stratovolcano over 3400 metres, high but not as steep as Mt Sakurajima Magma type Andesite. High gas conten t, high viscosity. Basalt. Low gas content, very low viscosity. Explosivity VE14-5 VE11 Hazards Lava flows , volcanic bombs, pyroclast ic flows, ash fall. Erupts aim ost continually, but with major eruptions once every 200-300 years. Lava flows and gas emissions. Contains a lava lake within its crater, which can drain causing huge, fast moving lava flows. + Social impacts are the impacts upon people. + Economic impacts are the impacts upon the wealth of an area. + Refugees are people who are forced to move due to nat ural hazards or war. + Aid is help. lt can be short-term such as food given in emergency, or long-term such as training in health care. + A relief effort is like aid. lt is help given by organisations or count ries to help those facing an emergency. your questions 1 Explain in your own words what we mean by aid and relief effort. 2 a Draw an identical table to that for Question 1 on page 17, and complete it to show the effects of Mount Nyiragongo. b Which volcano seems to have the greatest effects Nyiragongo or Sakurajima? Explain your answer. 3 How successful was the relief effort in helping people affected by Mount Nyiragongo's eruption? 4 Why do you think people still live around Mount Nyiragongo and Lake Kivu? 5 Exam-style question Using a named example, explain the economic and social impacts of a volcanic eruption. (6 marks) + In this section you will learn how earthquakes are measured and about their awesome power. Why is the ground shaking? Earthquakes can't be predicted. They start without warning and can be catastrophic. An earthquake is a sudden release of energy. it's a bit like bending a pencil until it suddenly snaps. Underground, tectonic plates try to push past each other The shaking is worse on the surface if the focus is shallow Earthquake waves travel out in all directions Huge devastation en Q) .::s:. ell .r::: en Lots of devastation and deaths "'0 c :::> e Ol .r::: Damage begins, but deaths are rare (.) :.c ~ 0 +-' +-' c Q) earth's surface above the focus +-' X w The earthquake starts at the focus - building up pressure. The pressure is suddenly released IKey along faults (cracks in the crust), sending out a huge pulse of energy. This travels out in all directions as earthquake waves A magnitude 6.0 earthquake is 10 times more powerful than a magnitude 5.0. how much the ground shakes - is its magnitude. A seismometer measures this using the Richter scale (see right) or Moment magnitude scale. Port-au-Prince, Haiti On 12 January 201 0, a magnitude 7.0 earthquake struck Haiti. This was very similar in size to the 1995, magnitude 7.2 Kobe earthquake in Japan. However, the earthquakes had very different causes and effects. & The shallower the focus, the more destructive the earthquake tends to be. The epicentre experiences the most shaking. Port-au-Prince, Haiti 2010 Kobe, Japan 1995 • The power of an earthquake - I Magnitude & The Richter scale is a logarithmic scale. (see the diagram on the far right). Magnitude \ Plate movement • • Magnitude - 7.2 (soft ground also made the shaking worse) Focus - 16km deep on a fault Epicentre - 20km from Kobe (population 1.5 million) • • • Magnitude - 7.0 Focus - 13km deep on a conservative plate boundary Epicentre - 25km from Port-au-Prince (population 2.5 million) Primary effects: • 5000 people died and 26 000 were injured. The population density is very high and people were still in bed when it struck at 5:46am. • Bridges and roads collapsed, train lines were damaged - disrupting transport and communication links. • £1 00 billion of damage was caused to roads, houses, factories and infrastructure (gas, electric, water and sewage pipes). Pr imary effect s: • 316 000 people died and a further 300 000 were injured. • Many houses were poorly built and collapsed instantly. 1 million people were made homeless. • The port, communication links and major roads were damaged beyond repair. Rubble from collapsed buildings blocked road and rail links. Secondary effects: • Many fires broke out throughout the city, triggered by broken gas pipes, resulting in further deaths. • Businesses were affected for many weeks due to disruption caused by rebuilding. • Homelessness, disrupted schooling, unemployment and increased stress problems lasted for many months as the authorities struggled to cope with the scale of the damage caused. Secondary effects: • The water supply system was destroyed - a cholera disease outbreak killed ove 8000 people. • The port was destroyed - making it hard to get aid to the area. • Haiti 's important clothing factories were damaged. These provided over 60% of Haiti's exports. 1 in 5 jobs were lost. • 1 year after the earthquake, 1 million people remained displaced - many still living in refugee camps. Restless Earth Long-term planning Tsunami Earthquakes beneath the sea bed can generate The secret of survival is long-term planning. tsunami (see below). Tsunami are waves that travel Japan is a developed country, so it can afford at up to 900 km/ h, with wavelengths of over t o do this. There is a 70 % probability (chance) 200 km. In the open ocean wave height is less than of a magnitude 7.2 earthquake hitting Toyko in 1m, but as the waves approach the coast they the next 30 years. lt could kill 7000 and injure slow down, bunch up and wave height increases 160 000. There is no way of predicting when up to 30m. When tsunami hit, they cause a very it might happen. powerful flood, pushing several kilometres inland • Every year Japan has earthquake drills. destroying homes, bridges and infrastructure. • Emergency services practise rescuing people. Warning systems in the ocean can detect tsunami • People keep emergency kits at home and set off sirens and alarms but this is only useful containing water, food , a torch and radio. ..__+---:,~+- "-<--~!----""~;:+- 1'--r-r-~ if the epicentre is some distance from the coast. None of the countries affected by the 2004 Asian A damper in the roof acts like a pendulum, red ucing building sway Cross bracing stops floors collapsing Shock absorbers bui lt into cross braces tsunami received any warning because there was no warning system in the Indian Ocean. Tsunami w aves . - spread out in---all directions Tsunami waves slow d own and w avelength drops, but wave height increases dramatically Wat er forced upward ~ . . . . .- seabed jolts upward \ \ \fFault \ \ \ , Earthquake focus A strong steel frame which is also flexible, stops cracking ryou-rquestions · Strong double glazed windows stop broken glass showering down Very deep --:-"-- foundations, to prevent collapse .A Many buildings in Japan are earthquake proof like this one. They can withstand a major earthquake. Gas supplies automatically shut off, reducing the risk of fire. t·r~..~,-~ ~ • \ Sea bed becomes s hallower c loser to coast : 1 Earthquake damage is reduced as you move away from the epicentre. Why is this? 2 a Draw a large version of the Richter scale diagram b Use a website, like Wikipedia, to find a list of earthquakes since 2000. Mark their magnitudes and death tolls on your diagram. c Is there a link between magnitude and death toll? 3 Using the diagram above, list and number the stages in the formation of a tsunami. 4 a Classify earthquake impacts in Japan into social and economic. b Which are greater? Explain your answer. 5 Exam-style question Using named examples, compare the social and economic impacts of two earthquakes. (6 marks) + In this section you will find out about the impacts of earthquakes on developing countries, and how people respond to them. Death and destruction Earthquakes in the developing world often have very high death tolls compared to volcanoes. Destructive earthquakes happen regularly, as the table shows. Location Sendai, Japan I Kashmir, Pakistan Aceh, Indonesia -'·"llf' 201 1 15 800 2005 1186 000 2004 280 000 Bam, Iran Magnitude Key facts 9.0 The tsunami (secondary effect) caused the most of the deaths. The economic costs were over $200 billion.--...;;::::::::::..:..o;;;;;;;;;O andslides (secondary l One third of the deaths were due to Ibuilt colla sed schools. 7.6 effect). Many children died in poorly 9.3 Most of the deaths were caused by a tsunami (secondary effect) that hit 14 countries around the Indian Ocean. 6.6 Many people were trapped when their poorly built, mud brick homes collapsed in the densely populated city. Earthquake in Sichuan Sichuan is a province in central Many of the areas hit were poor and rural. ASIA D China. On 12 May 2008 it was hit by a magnitude 8.0 earthquake. There Key Q was no warning. The social impacts were devastating: • 70 000 people died • 375 000 people injured INDIAN OCEAN Epicentre N ' - Collision zone o 500 km t~ ' - Direction of plate movem ent ( Beijing• Mountainous region • 5 million homeless The economic impacts were large too. Over 1 million people lost their job because their workplace was destroyed. The rebuilding costs Shanghai~ ""' eChengdu Wenchuan- .f Linqiong• \ Sichuan were estimated at $75 billion. Many landslides occurred (a secondary province effect), some of which dammed rivers creating dangerous 'quake lakes' which can burst, causing flooding. There were up to 200 large aftershocks. On 27 May a magnitude 6.0 aftershock caused 420 000 buildings to collapse. the Himalayas. Earthquakes are common in this collision zone. Restless Earth + Aftershocks often occur as the fault 'settles' into its new position. They can injure or kill rescuers. In the developing world, aftershocks often destroy buildings that were weakened by the first earthquake. Local responses Heavy rain, landslides and aftershocks made the rescue effort difficult: • The Prime Minister, Wen Jiabao, flew to the area very soon after the earthquake. • 50 000 soldiers were sent to help dig for survivors. • Helicopters were used to reach the most isolated areas. • Chinese people donated $1.5 billion in aid. International responses China quickly asked the rest of the world to help: • Some countries sent money. The UK gave $2 million. • Finland sent 8000 six-person tents, and Indonesia sent 8 tonnes of medicines. Cross-braced wood • Rescue teams flew in from Russia, Hong Kong, South Korea and Singapore. Building for the future? The Sichuan earthquake caused over 700 schools to collapse. China has strict building rules, so schools should have withstood the shaking. Even in a poorer developing country, buildings can be made cheaply to withstand earthquakes. The diagram on the right shows how. Concrete ring ties the walls to the foundations Simple steel rod foundations Walls made of mud and straw packed between wooden slats your questions 1 Explain why the Sichuan earthquake happened. Remember to include plate names and boundary types in your answer. 2 a Make a list of all the effects of the Sichuan earthquake. b Use two colours to circle social effects (effects on 3 Look back on the effects of the two volcanoes and two earthquakes you have studied. a Compare impacts each had on people and property. b Explain the differences. 4 Exam-style question Explain why earthquakes people) and economic effects (effects to do with happen on destructive plate margins. You may draw a money). diagram to help with your answer. (4 marks)