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© Boardworks Ltd of 25 Volcanoes
© Boardworks Ltd of 25 Most slides contain notes to accompany the presentation. This icon indicates that the notes contain particularly detailed instructions or extension activities. To access these notes go to ‘Notes Page View’ (PowerPoint 97) or ‘Normal View’ (PowerPoint 2000/2002). Normal ViewNotes Page View This icon indicates that a Flash file has been embedded into the PowerPoint slide. These files are not editable. Teacher’s notes and Flash files
© Boardworks Ltd of 25 A volcano is an opening or vent in the earth’s surface through which molten material erupts and solidifies as lava. Volcanic vent What is a volcano?
© Boardworks Ltd of 25 Around which plate do we find most volcanoes? Where are volcanoes found?
© Boardworks Ltd of 25 Volcanic bombs, ash, lava, gases Magma chamber Parasitic cone Crater Main vent Label this cross section of a volcano
© Boardworks Ltd of 25 Crater Volcanic bombs, ash and gases Main vent Parasitic cone Magma chamber Cross section of a volcano
© Boardworks Ltd of 25 A destructive plate boundary is found where a continental plate meets an oceanic plate. The oceanic plate descends under the continental plate because it is denser. As the plate descends it starts to melt due to the friction caused by the movement between the plates. This melted plate is now hot, liquid rock (magma). The magma rises through the gaps in the continental plate. If it reaches the surface, the liquid rock forms a volcano. Destructive Plate Boundary Why do they happen?
© Boardworks Ltd of 25 Destructive plate boundary
© Boardworks Ltd of 25 Constructive Plate Boundary At a constructive plate boundary, two plates move apart. As the two plates move apart, magma rises up to fill the gap. This causes volcanoes at this type of boundary. However, since the magma can escape easily at the surface, the volcano does not erupt with much force. Why do they happen?
© Boardworks Ltd of 25 Constructive plate boundary
© Boardworks Ltd of 25 At destructive plate boundaries the lava is viscous (thick like treacle) and it cannot flow very far from the volcano’s vent. This makes the volcano steep sided. At constructive plate boundaries the lava is runny and it can flow far away from the volcano’s vent. This makes the volcano gentle sided.
© Boardworks Ltd of 25 Volcano Shapes Why are these volcanoes different shapes?
© Boardworks Ltd of 25 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! Do all volcanoes erupt?
© Boardworks Ltd of 25 Mt St Helens located on the ‘Ring of Fire’ Mt St Helen’s eruption (May 1980) Internet Links
© Boardworks Ltd of 25 Mt St Helens – causes of the eruption Juan de Fuca plate North American Plate Which is the oceanic plate?
© Boardworks Ltd of 25 Mt St Helens – the eruption
© Boardworks Ltd of 25 N 0 10km Mt St Helens – consequences of the eruption
© Boardworks Ltd of 25 Mt St Helens BEFORE AFTER
© Boardworks Ltd of 25 Hot mudflows raise the temperature of the rivers and lakes to 30ºC Two million birds, animals and fish are killed. 60 people die from the eruption. Up to 70mm of ash falls across Washington and East Montana… 7000 school students have an early summer vacation due to problems on the roads Mudflows block and divert rivers. The US army takes 18 months to dig out the debris from the River Toutle. Communications routes threatened – railway and road bridges destroyed, Portland harbour blocked Gophers, through their tunnelling, mix the soil with the ash. This increases the fertility of the soil. An increase in tourism Deer mice, chipmunk, vole, gophers, salamander survive the blast. Their population steadily increases due to the absence of predators. A decrease in tourism What damage did the eruption cause? Separate the above into the short term and long term impacts of the eruption. The post office and Lone Fir Motel shut down in Cougar. Damage to crops=$175million
© Boardworks Ltd of 25 What benefits might the volcanic activity have brought to Mt St Helens? Why do you think animals such as the vole and gopher survived the blast? Deer mice, chipmunk, vole, gophers, salamander survive the blast. Their population steadily increases due to the absence of predators.
© Boardworks Ltd of 25 This lava is weathered (broken down) to form a fertile soil, Tourists are attracted to areas of volcanic activity. Geothermal energy (heat from the earth) can be produced in many volcanic areas. Can you think of any other reasons? Why do people live in volcanic areas?
© Boardworks Ltd of 25 Nevada del Ruiz is located in the Andes. The volcano had been giving signs of increased activity for some time and on the 13 th November the volcano erupted, producing a cloud of steam, ash and rocks. The heat melted snow on the volcano and the water produced combined with ash, creating a mudflow. This mudflow rushed down the valley at 60km/hour towards the town of Armero and engulfed the town with mud up to 5m deep. It was just before midnight and most people were in bed. By the time the rescue team reached Armero, the next day, the mudflows had set hard. The eruption started at 9.08pm. If the mudflows reached Armeno at 11.30pm, how far is Armero from Nevada del Ruiz? What could have been the volcano’s ‘signs of increased activity’? Why wasn’t Armero evacuated when the volcano had shown these ‘signs of increased activity’? 23,000 dead 5,000 injured 5,000 homes destroyed Nevada del Ruiz, Colombia (November 1985)
© Boardworks Ltd of 25 Virtual field visits The Michigan Technological University Volcanoes Page Global Volcanism Program Fallout: Eye on the Volcano Savage earth Volcano World - a fun and informative web site Internet links!
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