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Q3: Tectonic Landscapes 15 marks Location and characteristics of tectonic activity The distribution of earthquakes and volcanoes in the world • Volcanoes and earthquakes usually occur in narrow lines along the plate boundaries. • An exception to this are volcanoes that occur at hotspots. • Areas of particular note include; The Pacific Ring of Fire, the Mid-Atlantic Ridge, SE Europe, SE Asia Reasons why earthquakes and volcanoes both occur where they do • The Earth’s crust is divided into plates. • Oceanic crust found under seas & oceans is thin but dense (heavy) • Continental crust found on land is thicker but less dense Reasons why earthquakes and volcanoes both occur where they do • • • • The plates move 5-10cm every year as they are floating on the mantle. This movement is caused by convection currents in the mantle. The convection currents can cause the plates to collide or move apart. The pressure or gaps created at the boundaries of the plates can result in either earthquakes or volcanoes Reasons why earthquakes and volcanoes both occur where they do The movement of the land mass on the crust is known as Continental Drift. • Most volcanoes are found at plate boundaries, however, a hotspot is another place where volcanoes can occur • Hotspots are fixed points in the mantle which generate heat – they usually occur under oceans • Intense heat causes a build-up of pressure and magma erupts through the crust • If magma rises above the ocean surface it will form a volcano • Hotspots usually create chains of volcanic islands as the plate moves over the hotspot. Hawaii and the Galapagos Islands were formed in this way. The characteristic features of plate boundaries Conservative Plates can move in 3 directions Convergent plate boundary continental and oceanic crust • • • • • • • • • Plates move together Heavier oceanic crust is subducted Friction during subduction causes earthquakes The oceanic plate melts as it sinks, turning into magma Magma builds up in the magma chamber Pressure increases Pressure forces magma upwards through weak points in the continental crust Magma erupts to surface Repeated eruptions build a volcano, e.g. Mount St Helen’s, USA Convergent plate boundary oceanic and oceanic crust • • • • • • • • Plates move together The heavier of the two oceanic crusts is subducted Friction during subduction causes earthquakes The oceanic plate melts as it sinks, turning into magma Magma builds up in the magma chamber Pressure increases and forces magma upwards through weak points in the crust Magma erupts to surface Repeated eruptions build a volcano in the ocean – these are called volcanic island arcs e.g. Japan Convergent plate boundary continental and continental crust • • • • Plates move together Plates fold and fault crust upwards to form fold mountains, e.g. The Himalayas Earthquakes can also happen as rock is folded and faulted There are no volcanoes as the crust is NOT subducted and melted. Divergent plate boundary oceanic and oceanic crust • • • • Plates move apart Magma rises to fill the gap Repeated eruptions of lava will build ocean floor ridges (Mid-Atlantic Ridge) If enough lava builds to reach sea level, this will form volcanic islands (Iceland) Conservative plate boundary • • • • • Plates move past each other The plates are jagged and get stuck As they try to move pressure builds up Eventually the pressure snaps and the plates jerk forward This releases shockwaves, which travel through the Earth’s crust, e.g. San Andreas Fault, California The methods used to measure earthquake magnitude The Richter Scale • • • • Measures the strength and magnitude of an earthquake Seismographs measure the vibrations The vibrations are printed out on a seismogram The seismogram is translated to give a score on the Richter Scale ranging from 1-9 Scientific Easier comparison Objective Remote measurement Requires scientific equipment Can be misleading The methods used to measure earthquake magnitude The Mercalli Scale • Measures the intensity and amount of destruction of an earthquake • Measures on a scale from 1-12 • Uses information from eyewitnesses No expensive equipment needed Gives a useful indication on the effects Is a subjective score (based on opinion) The person measuring has to be on site of the earthquake The characteristics of the focus and epicentre of an earthquake • The focus is the point below the surface where the pressure snaps and the shockwaves are released from. This where the earthquake begins. • The epicentre is the point directly above the focus on the surface of the Earth. The shockwaves are felt strongest at the epicentre. • The most damage and destruction will occur at the populated area nearest to the epicentre. Management of the effects of tectonic activity The reasons why people continue to live in areas of volcanic activity Fertile soil for crops Ash makes the soil fertile, for example coffee grown on slopes of volcanoes in Columbia. Perception People think that scientists who monitor the volcano can give enough warning for an evacuation if an eruption happens. Friends & Family People who have lived in a volcanic area for years and/or have many friends & family nearby will not want to move. Poverty may also prevent people from leaving the area. Geothermal energy Properties in Reykjavik, Iceland benefit from cheap electricity produced by geothermal power. Tourism The areas around volcanoes are scenic & many people want to visit features like craters, geysers & hot springs, e.g. Iceland. Many people have jobs in the tourism industry. The reasons why people continue to live in areas of earthquakes Jobs Earthquake areas are usually rich in minerals. Many people have jobs in the mining industry here. Environment Many earthquake areas have been developed for the wealthy. People want to live there for the fantastic environment, e.g. Malibu in California Perception People think that earthquake proof buildings will keep them safe in the event of a tremor, e.g. Japan Tourism Many earthquake prone areas have amazing scenery and people have jobs in the tourism industry, e.g. San Francisco & New Zealand Prediction and prevention of the effects of earthquakes Prediction Prediction is not possible, but seismometers can measure movement. An increase in tremors can suggest a large earthquake is increasingly likely, so people can begin to prepare. Building Design Education & Planning Earthquake-proof buildings Schools & businesses in have automatic shutters on Japan practice windows to stop glass earthquake drills such as shattering onto streets, ducking under tables. In interlocking frameworks, the USA the government counter-weights and rubber shock absorbers. San Francisco has info packs about how airport has columns standing to prepare an earthquake emergency survival kit. on 1.5m ball bearings. Prediction and prevention of the effects of volcanic eruptions Monitoring Tiltmeters and GPS can be used to detect changes in the shape of the volcano and crater as the magma rises. Gases can be monitored as CO2 and Sulphur Dioxide increase just before an eruption. Defence Lava flows can be cooled with water to make them move more slowly and stop. Diversion channels can be built to guide lava flows away from villages. In Iceland in 1973 lava was directed out to sea and away from a town. Education People who live close to volcanoes are taught to look out for signs the volcano is going to erupt. Locals who live on Sicily know how to look for changes in the consistency of the lava. Cause and effects of a named earthquake: Turkey 1999 Causes: Destructive plate boundary; Eurasian, African & Arabian plates caused the north Anatolian fault to move 3m. The epicentre was at the town of Izmit, which lies on top of soft rock; clay & sand. Effects on People: 18,000 dead, 300,000 homeless, motorway destroyed - hard for emergency services to access the scene, people suffered emotional trauma, $10 billion rebuild costs. Effects on Environment: A fire at the Tupras oil refinery meant 700,000 tones of oil was burnt causing air pollution, Pekim sewage works damaged causing rivers to be polluted, Yaolva chlorine factory leak, land raised out of the sea at the coast near the Sea of Marmara. Cause and effects of a named volcanic eruption: Montserrat 1997 Causes: Destructive plate boundary; North American plate is subducting below the Caribbean plate. Chances Peak erupted ash, which covered the southern half of the island. There was also several pyroclastic flows of hot rock and ash. Effects on People: 19 dead, 150 homes destroyed, Farm Village and Trant Village totally buried under ash, Bramble Airport was closed, roads were covered with ash and rocks, 8,000 people had to leave the island and never returned – emotional trauma. Effects on Environment: Ash and rock covered 4km2 of the island, pyroclastic flows caused the River Belham to flood, pyroclastic flows removed all the vegetation in the south of the island including the ridges surrounding Farrell’s Yard.