3Structure of the earth Earth is made up of four distinct layers Crust (oceanic/ Continental)MantleOuter coreInner core
4Structure of the earth Crust is broken up piece called tectonic plates 7 large plates and 12 small platesThese plates move because of Convection Currents in the magmaWhere two plates meet is a plate marginVideo -
6Constructive Plate Margins Two oceanic plates move away from each other shield volcanoes form creating mid ocean ridges e.g. mid Atlantic ridge.When two continental plate move apart a rift valleys are formed. Shield volcanoes found here e.g. Iceland
9Destructive Plate Margins Oceanic and continental CrustWhere it involves oceanic and continental crust, the oceanic crust is always subducted below the continental because it is denser.The subduction of the oceanic crust creates a deep sea trench and earthquakes are formed at the subduction zone.Fold mountains are created on the continental crust .The subducted oceanic crust melts in the mantle rising up into the fold mountain to create composite volcanoesE.g. Mount St Helens
14Types of VolcanoesShield Volcanoes found on constructive plate margins. Lava is hot and runny. Not as explosive. Not very high. Very wide baseComposite volcanoes found on destructive plate margins. Thick stick lava. Erupt explosively. Very tall cone shaped.Video -
16Do all volcanoes erupt? Active volcano – liable to erupt e.g. Mt Etna. Dormant (sleeping) volcano – a volcano which has not erupted for many years. For example, Mt Pinatubo erupted in 1991 after 500 years of dormancy.Extinct volcano – a volcano which has not erupted for many thousands or millions of years e.g. Edinburgh.However, it is often very difficult to tell whether a volcano will erupt again…El Chichon, Mexico erupted in 1982 after being dormant for approximately 1200 years!
20Earthquakes – CausesEarthquakes are cause by shock waves travelling through the earth crustThe source of the earthquake is called the focus, the epicentre is the point immediately above it on the surfaceSize of an earthquake can be measured by a seismometer along the Richter scaleTsunamis are a secondary hazard of an earthquake
23How can we measure earthquakes? The Richter ScaleThis measures the magnitude of a tremor (how powerful it is) using an instrument called a seismograph.On the Richter Scale, magnitude is expressed in whole numbers and decimal fractions. Although the Richter Scale has no upper limit, the largest earthquake ever recorded was in 1960 in Chile. It measured 9.5 on the Richter Scale.Largest earthquakes list -While all care is taken to ensure web links contain useful information, Boardworks does not take responsibility for the content or accuracy of external web sites.
24Earthquakes - FactorsStrength of the earthquake (magnitude) – more shaking means more damage will be causedDistance from epicentre – closer to the epicentre the more damage will be caused.Depth of the focus – the shallower an earthquake the more damage will causedNumber of people living in an area (population density)- the epicentre is close to a city then more people will be affected.Type of rock – softer rocks are likely to shake more and fro longer causing more damageTime of day – if more people are in building more people are likely to die.The extent of preparation – some countries are well prepared for earthquakes and therefore have little impact (see later on how to prepare for an earthquake
25Why do people live there? 500 million people live in active zonesDramatic scenery created attracts tourists, bringing income to an area e.g. Mount Vesuvius, ItalyLava and ash provide nutrients to the soil, making the land near volcanoes very fertile and good for agriculture. E.g. Mount Etna, ItalyOpportunities to generate electricity using the heat from the earth (geothermal energy) E.g. IcelandVolcanic rock is a good building stoneMany people cannot afford to Move (LEDCs) E.g. Mount Pinatubo, PhilippinesTectonic hazards are rare and often to affect an area in a persons lifetime E.g. Montserrat volcano had not erupted for 300yrs until recentlyPrediction and earthquake resistant building are improving. E.g. Kobe Japan has many earthquake proof buildingsDON’T FORGET YOU NEED TO GIVE EXAMPLES
26Predicting and preparing - Earthquakes Laser beams used to detect plate movementsSeismometer used to pick up vibrationsRadon gas – escape from the cracks in the crust before an earthquake – this can be monitoredPreparingEducating people via TV or in schools what to doEarthquake drills to prepareEarthquake proof buildings, designed to absorb the energy of an earthquake and withstand movement
27How can we limit earthquake damage? predictplanprotectwater levels can rise in wells and lakes because of cracks in the rocka tiltmeter can check any movement within the rocksPredictforeshocks before the main quake can be detected by a seismometeranimals can act strangely before the earthquake
28How can we limit earthquake damage? Plan and protect
29Building in earthquake zones This is San Francisco in the USA.San Francisco is near the San Andreas Fault and therefore the city experiences earthquakes.This skyscraper has been built to be ‘earthquake-proof’.Its wide base lowers the centre of gravity of the building and makes it more stable.
30Predicting and preparing - Volcanoes Remote sensing – satellites monitor temperature and gas emissionsSeismometers – measures earthquakes activity that occurs before an eruptionTiltmeters – monitor changes in the shape of a volcano as it fills with magmaGas emissions – indicate an increased riskUltra sound – to detect movements of magmaPreparingExclusion zones created around volcanoesAuthorities must be ready to evacuateEmergency supplies of basic provisions must be gatheredGood communication systems in place
32The problem of prediction Volcanologists (people who study volcanoes) are skilled at predicting the likelihood of an eruption.However, it's very difficult to pinpoint exactly when an eruption will happen. Often, moving magma doesn't result in an eruption, but instead cools below the surface.Monitoring potential eruptions is expensive. With many volcanoes erupting only every few hundred years, it's not possible to monitor every site.