The crust is similar tothe shell of acracked egg, and is madeup of largeplates of rock.Underneath, themantle is made up ofmolten rock.The plates move slowlydue toconvection currents.
PlateNamesAfrican PlateIndo Australian PlateNorth AmericanSouth AmericanEurasianPacificNazcaAntarctic
• A destructive plate margin is where twoplates are moving towards each other.• The point where the two plates meet is calledthe subduction zone.• One plate is forced beneath another into themantle.• This can lead to the formation of featureslike oceanic trenches and volcanic foldmountains.•http://www.absorblearning.com/media/item.action?quick=12shttp://www.classzone.com/books/earth_science/terc/content/visualizations/es0804/es0804page01.cfm?chapter_no=visualization
At a constructive plate boundary, twoplates move apart. As the two platesmove apart, magma rises up to fill thegap. This causes volcanoes at this typeof boundary. However, since the magmacan escape easily at the surface thevolcano does not erupt with muchforce. Earthquakes are also found atconstructive boundaries.An example of a constructive boundaryis the Mid-Atlantic Ridge.Sometimes plates pull apart beneath thesea. Magma wells up and cools to formnew crust. This leads to a ridge beingdeveloped such in the Atlantic oceanwhere the Mid-Atlantic ridge is found.Earthquakes can also take place.
Constructive plate boundariescan also be found on land. ThePlates can pull apart to leave arift valley with steep sides.This has happened in Icelandalong the Mid-Atlantic ridge toform the Thingvellir rift valley
These are low, broadvolcanoes and are producedby runny lava that flowsover a large area.These volcanoes can bevery large and ash canbuild up around their ventsto leave a cinder cone.
These are steep sided,made by layers of ashand lava, high summit(top) and explosivevolcanoes
PrimaryHazardsSecondaryHazardsThese happen because of a change inthe environment following anearthquake or eruptionThese happen as a direct result of theearthquake or volcanic eruption
• Lava flows are usually slow but can destroybuildings, roads and trees.
• Pyroclastic flows – A landslide of hotash, rocks and gases from a violenteruption.
• Lahars or mudflows are produced when ashor mud mixes with rainwater. These can havevery serious consequences.
• Ash – Powdered rock fragments that arethrown from a volcano during an explosivereaction
Mt St HelensConsequences of the EruptionNO 10km
Hot mudflows raise the temperatureof the rivers and lakes to 30ºC.Two million birds, animals and fish are killed.60 people die fromthe eruption.Mudflows block and divert rivers. The US army takes18 months to dig out the debris from the River Toutle.Communications routes threatened – railway androad bridges destroyed, Portland harbour blockedGophers, through theirtunnelling, mix the soil withthe ash. This increasesthe fertility of the soil.Anincrease intourismDeer mice,chipmunk, vole,gophers, salamandersurvive the blast.Their populationsteadily increasesdue to the absenceof predators.A decrease intourismWhat benefits might the volcanic activity have brought to Mt St Helens?Damage to crops=$175millionThe post officeand Lone Fir Motelshut down inCougar.Up to 70mm of ash falls across Washington andEast Montana…7000 students have an earlySummer vacation due to problems on the roads
This lava is weathered(broken down) to form afertile soilTourists are attracted toareas of volcanic activityGeothermal energy(heat from the earth)can be produced inmany volcanic areasCan you think of any other reasons?Why do people live in volcanic areas?
• Buildings, roads and pipelines can break dueto the intense ground shaking.
• Strong aftershocks can cause more damageand restrict rescue efforts.
• Marshy soil can lose its strength and becomevery soft ( like wet concrete) when violentlyshaken. This causes the foundations ofbuildings to collapse.
• A tidal wave that is created when anearthquake occurs.
• In built up area this is major threat straight after anearthquake. Broken gas pipes can ignite and firescan be quickly spread.
• Soil, rock and mud can move quickly downhill,blocking road and rail links.
• The Richter Scale is the best known scale for measuring themagnitude of earthquakes. It is logarithmic. A recording of 7,for example, indicates a disturbance with ground motion 10times as large as a recording of 6.• A Seismograph which is used to measure the size of anearthquake. The needle moves as the ground shakes and theink moves across the page to record the size = bigger shake –bigger line!!
Sometimes snakes and animals behave oddly beforevolcanic eruptions. There have been observations of thisin places like Asia.The ground often changes shape. For example, at Monserratthe lava dome swelled in size in the weeks leading up to 28thJuly 2008 ( use tilt meters)This is a sure sign that volcanic activity going to happen. Asthe magma moves up the volcano pressure is put upon thevolcano, causing cracks and small earthquakes to occur. Maylead to rockfallsIf there is a steady increase of sulphur dioxide, this showsthere is likely to be an eruption. This shows magma is risingto the surface.
1) Development of Observatories, eg Montserrat VolcanoObservatory (MVO), collect data on a particular volcano2) Monitoring Stations placed around volcano, powered by solarpanels3) Seismographs measure even the smallest tremor in the earth’ssurface, which trigger warnings for towns and cities4) Global Positioning Systems (GPS) satellites are used to recordeven the slightest change in the shape of the volcano5) Tilt meters are used to measure larger changes in the surfaceof the ground6) Radar and Aerial Photographs can be used to record changesin shape7) Remote sensing satellites can be used to detect changes inheat / temperature of rock surfaces indicating magma rising tothe surface.
Responses to the EarthquakeThe Chinese government respondedquickly and provided 50,000 troops to helpthe relief effort.In the first few days rescuers had to siftthrough rubble with their hands.Large heavy earth-moving equipment hadto be brought in from over seas.Expertise from Japan was needed.Temporary camps were set up.http://news.bbc.co.uk/1/hi/world/7397838.stmAll Short Term
Many residents and rescuers first usedtheir bare hands to clear the debris fromcollapsed buildings.Local emergency services were quickly onthe scene. The army helped to rescuevictims.In LAquila, 95km (60 miles) north-east ofRome, over 3000 buildings in the medievalcity were damaged.A university dormitory, churches and abell tower are believed to be among thebuildings that had collapsed.Local medical facilities were used and afield hospital were set up. http://news.bbc.co.uk/1/hi/world/europe/7984867.All Short Term
http://news.bbc.co.uk/1/hi/world/7397838.stmSpraying lava with water to cool itand solidify it.Earth barriers have been used tochannel the direction of lava flow.Dropping concrete blocks viahelicopter to divert the flow.Aerial bombing lava tubes withdynamite to widen them andreduce the flow.All Short Term
Now Think Long Term !!This is section is about theThree Ps – Plan, Predict and Prepare1) Planning - a) using strict planning laws to control whereareas of new development so that less buildings are indangerous areas, b) design and create buildings to with standthe effects of earthquakes and minimise damage, c)|Emergency services with specialist teams trained to react toan event;2) Predict – use technology to predict when hazard mayoccur ( see slide above) but think Early Warning Systems,Tsunami ocean buoys use to monitor size of waves andpredict when wave hits land;3) Prepare people to react to the effects of an earthquake /volcano – education in schools (earthquake drills) and TV /Radio on what to do – think Tsunami warnings in Japan;