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A volcano is an opening (Vent) in the ground where magma forces its way to the surface. Magma which reaches the Earth’s surface is called lava. 1 of 35 © Boardworks Ltd 2005 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 2 of 35 © Boardworks Ltd 2005 Label this cross section of a volcano Volcanic bombs, ash, lava, gases Magma chamber Parasitic cone Crater Main vent 3 of 35 © Boardworks Ltd 2005 Cross section of a volcano Crater Volcanic bombs, ash and gases Parasitic cone Main vent Magma chamber 4 of 35 © Boardworks Ltd 2005 Cross section of a volcano 5 of 35 © Boardworks Ltd 2005 Volcanic emissions 6 of 35 © Boardworks Ltd 2005 Volcanic emissions 7 of 35 © Boardworks Ltd 2005 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! 8 of 35 © Boardworks Ltd 2005 How they form. 9 of 35 © Boardworks Ltd 2005 Volcano builds up 10 of 35 © Boardworks Ltd 2005 Volcano formed 11 of 35 © Boardworks Ltd 2005 A conduit feeds magma to the surface. 12 of 35 © Boardworks Ltd 2005 Why do they happen? 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. 13 of 35 © Boardworks Ltd 2005 Destructive plate boundary 14 of 35 © Boardworks Ltd 2005 Why do they happen? 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. However, since the magma can escape easily at the surface, the volcano does not erupt with much force. 15 of 35 © Boardworks Ltd 2005 Constructive plate boundary 16 of 35 © Boardworks Ltd 2005 Volcano shapes Why do volcanoes have different shapes? 17 of 35 © Boardworks Ltd 2005 Volcano shapes 18 of 35 © Boardworks Ltd 2005 Volcanic activity at plate margins 19 of 35 © Boardworks Ltd 2005 Where are volcanoes found? Around which plate do we find most volcanoes? 20 of 35 © Boardworks Ltd 2005 Hawaii 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? 21 of 35 © Boardworks Ltd 2005 Hot spot volcanoes In the animation above, why are the volcanoes to the left of the ‘hot spot’ extinct? 22 of 35 © Boardworks Ltd 2005 Learning objectives What is a volcano? Why do volcanoes occur? Where are volcanoes found? What happened in the 1980 Mount St Helens eruption? Can volcanic eruptions be predicted? Why do people live in volcanic areas? 23 of 35 © Boardworks Ltd 2005 Mt St Helens eruption (May 1980) Mt St Helens is located on the ‘Ring of Fire’. Internet Links http://volcano.und.nodak.edu/vwdocs/msh/msh.html 24 of 35 © Boardworks Ltd 2005 25 of 35 © Boardworks Ltd 2005 • • • • • • • • Volcanoes and Earthquakes of note: Christchurch Earthquake, New Zealand Mount Saint Helens, Washington, USA Mount Pinatubo, Philippines Mt. Fuji, Japan Paricutin Volcano, Mexico Santiago Earthquake, Chile Sendai Earthquake, Japan 26 of 35 © Boardworks Ltd 2005 Mt St Helens – causes of the eruption Mt St Helens is located on a destructive plate boundary where a continental plate (North American) meets an oceanic plate (Juan de Fuca). Juan de Fuca plate North American plate Which plate is denser? Describe what happens when the oceanic plate descends under the continental plate. 27 of 35 © Boardworks Ltd 2005 Mt St Helens – the eruption 28 of 35 © Boardworks Ltd 2005 Mt St Helens – consequences of the eruption N 0 29 of 35 10km © Boardworks Ltd 2005 Mt St Helens – consequences of the eruption AFTER BEFORE 30 of 35 © Boardworks Ltd 2005 What damage did the eruption cause? 31 of 35 © Boardworks Ltd 2005 Mt St Helens – consequences of the eruption Why do you think animals such as the vole and gopher survived the blast? How did their survival benefit the area? What benefits might the volcanic activity have brought to Mt St Helens? 32 of 35 © Boardworks Ltd 2005 Learning objectives What is a volcano? Why do volcanoes occur? Where are volcanoes found? What happened in the 1980 Mount St Helens eruption? Can volcanic eruptions be predicted? Why do people live in volcanic areas? 33 of 35 © Boardworks Ltd 2005 Predicting eruptions 34 of 35 © Boardworks Ltd 2005 The 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. 35 of 35 © Boardworks Ltd 2005 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. 36 of 35 Geothermal energy can be produced in many volcanic areas. © Boardworks Ltd 2005 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/ 37 of 35 © Boardworks Ltd 2005