Volcanoes 1 of 25 Boardworks Ltd 2003 Teachers

Volcanoes 1 of 25 © Boardworks Ltd 2003

Teacher’s notes and Flash files 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’ (Power. Point 97) or ‘Normal View’ (Power. Point 2000/2002). Notes Page View Normal View This icon indicates that a Flash file has been embedded into the Power. Point slide. These files are not editable. 2 of 25 © Boardworks Ltd 2003

What is a volcano? A volcano is an opening or vent in the earth’s surface through which molten material erupts and solidifies as lava. Volcanic vent 3 of 25 © Boardworks Ltd 2003

Where are volcanoes found? Around which plate do we find most volcanoes? 4 of 25 © Boardworks Ltd 2003

Label this cross section of a volcano • Volcanic bombs, ash, lava, gases • Magma chamber • Parasitic cone • Crater • Main vent 5 of 25 © Boardworks Ltd 2003

Cross section of a volcano Crater Volcanic bombs, ash and gases Parasitic cone Main vent Magma chamber 6 of 25 © Boardworks Ltd 2003

Why do they happen? A destructive plate boundary is found where a continental plate meets an oceanic plate. Destructive Plate Boundary 7 of 25 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. © Boardworks Ltd 2003

Destructive plate boundary 8 of 25 © Boardworks Ltd 2003

Why do they happen? At a constructive plate boundary, two plates move apart. Constructive Plate Boundary 9 of 25 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. © Boardworks Ltd 2003

Constructive plate boundary 10 of 25 © Boardworks Ltd 2003

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. 11 of 25 © Boardworks Ltd 2003

Volcano Shapes Why are these volcanoes different shapes? 12 of 25 © Boardworks Ltd 2003

Do 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! 13 of 25 © Boardworks Ltd 2003

The Hawaiian islands are a chain of volcanoes in the Pacific Ocean. Look at their location on the map below. Why is this an unusual place for them to be located? 14 of 25 © Boardworks Ltd 2003

Hot spot volcanoes In the animation above, why are the volcanoes to the left of the ‘hot spot’ extinct? 15 of 25 © Boardworks Ltd 2003

Mt St Helen’s eruption (May 1980) Mt St Helens located on the ‘Ring of Fire’ Internet Links http: //volcano. und. nodak. edu/vwdocs/msh. html 16 of 25 © Boardworks Ltd 2003

Mt St Helens – causes of the eruption Juan de Fuca plate North American Plate Which is the oceanic plate? 17 of 25 © Boardworks Ltd 2003

Mt St Helens – the eruption 18 of 25 © Boardworks Ltd 2003

Mt St Helens – consequences of the eruption N 0 19 of 25 10

Mt St Helens AFTER BEFORE 20 of 25 © Boardworks Ltd 2003

What damage did the eruption cause? Up to 70 mm of ash falls across Washington and East Montana… 7000 school students have an early summer vacation due to problems on the roads An increase Mudflows block and divert rivers. The US army takes in tourism 18 months to dig out the debris from the River Toutle. Two million birds, animals and fish are killed. A decrease in tourism Communications routes threatened – railway and road bridges destroyed, Portland harbour blocked Hot mudflows raise the temperature of the rivers and lakes to 30ºC Deer mice, chipmunk, vole, gophers, salamander survive the blast. Their population steadily increases due to the absence of predators. 60 people die from the eruption. Gophers, through their tunnelling, mix the soil with the ash. This increases the fertility of the soil. Damage to crops=$175 million The post office and Lone Fir Motel shut down in Cougar. Separate the above into the short term and long term impacts of the eruption. 21 of 25 © Boardworks Ltd 2003

Deer mice, chipmunk, vole, gophers, salamander survive the blast. Their population steadily increases due to the absence of predators. Why do you think animals such as the vole and gopher survived the blast? What benefits might the volcanic activity have brought to Mt St Helens? 22 of 25 © Boardworks Ltd 2003

Why do people live in volcanic areas? This lava is weathered (broken down) to form a fertile soil, Can you think of any other reasons? Tourists are attracted to areas of volcanic activity. 23 of 25 Geothermal energy (heat from the earth) can be produced in many volcanic areas. © Boardworks Ltd 2003

Nevada del Ruiz, Colombia (November 1985) 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 60 km/hour towards the town of Armero and engulfed the town with mud up to 5 m 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. 23, 000 dead 5, 000 injured 5, 000 homes destroyed The eruption started at 9. 08 pm. If the mudflows reached Armeno at 11. 30 pm, 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’? 24 of 25 © Boardworks Ltd 2003

Internet links! Volcano World - a fun and informative web site http: //volcano. und. nodak. edu/ Virtual field visits http: //educeth. ethz. ch/stromboli/ The Michigan Technological University Volcanoes Page http: //www. geo. mtu. edu/volcanoes/ Global Volcanism Program http: //www. volcano. si. edu/gvp/ Fallout: Eye on the Volcano http: //www. nationalgeographic. com/features/98/volcanoes/ Savage earth http: //www. pbs. org/wnet/savageearth/ 25 of 25 © Boardworks Ltd 2003