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Volcanoes These icons indicate that teacher’s notes or useful web addresses are available in the Notes Page. This icon indicates the slide contains activities created in Flash. These activities are not editable. For more detailed instructions, see the Getting Started presentation. 1 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? 2 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 3 of 35 © Boardworks Ltd 2005 Label this cross section of a volcano Volcanic bombs, ash, lava, gases Magma chamber Parasitic cone Crater Main vent 4 of 35 © Boardworks Ltd 2005 Cross section of a volcano Crater Volcanic bombs, ash and gases Parasitic cone Main vent Magma chamber 5 of 35 © Boardworks Ltd 2005 Cross section of a volcano 6 of 35 © Boardworks Ltd 2005 Volcanic emissions 7 of 35 © Boardworks Ltd 2005 Volcanic emissions 8 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! 9 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? 10 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. 11 of 35 © Boardworks Ltd 2005 Destructive plate boundary 12 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. 13 of 35 © Boardworks Ltd 2005 Constructive plate boundary 14 of 35 © Boardworks Ltd 2005 Volcano shapes Why do volcanoes have different shapes? 15 of 35 © Boardworks Ltd 2005 Volcano shapes 16 of 35 © Boardworks Ltd 2005 Volcanic activity at plate margins 17 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? 18 of 35 © Boardworks Ltd 2005 Where are volcanoes found? Around which plate do we find most volcanoes? 19 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? 20 of 35 © Boardworks Ltd 2005 Hot spot volcanoes In the animation above, why are the volcanoes to the left of the ‘hot spot’ extinct? 21 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? 22 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 23 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. 24 of 35 © Boardworks Ltd 2005 Mt St Helens – the eruption 25 of 35 © Boardworks Ltd 2005 26 of 35 © Boardworks Ltd 2005 27 of 35 © Boardworks Ltd 2005 28 of 35 © Boardworks Ltd 2005 Mount St. Helens woke up on March 20, 1980, with a Richter magnitude 5.1 earthquake. Steam venting started on March 27. By the end of April, the north side of the mountain started to bulge. With little warning, a Richter magnitude 5.1 earthquake triggered a massive collapse of the north face of the mountain on May 18. This was the largest known debris avalanche in recorded history. The magma inside of St. Helens burst forth into a large-scale pyroclastic flow which flattened vegetation and buildings in an area of over 230 square miles (600 km²). This eruption was a 5 on the Volcanic Explosivity Index scale. For more than nine hours, a vigorous plume of ash erupted, eventually reaching 12 to 15 miles (20 to 25 km) above sea level. The plume moved eastward at an average speed of 60 miles per hour (95 km/h), with ash reaching Idaho by noon. The collapse of the northern flank of St. Helens mixed with ice, snow, and water to create lahars (volcanic mudflows). The lahars flowed many miles down the Toutle and Cowlitz Rivers, destroying bridges and lumber camps. A total of 3.9 million cubic yards (3.0 million cubic meters) of material was transported by the lahars. By around 5:30 PM on May 18 the vertical ash column declined in stature but less severe outbursts continued through the night and the following several days. In all, St. Helens released an amount of energy equivalent to 27,000 Hiroshima-sized atomic bombs and ejected more than a cubic kilometre of material. The removal of the north side of the mountain reduced St. Helens' height by about 1300 feet (400 m) and left a 1 to 2 mile (1.6 to 3.2 km) wide and 0.5 mile (800 m) deep crater with its north end open in a huge breach. Fifty-seven people were killed along with 1500 elk, 5000 deer, and an estimated 11 million fish. In addition, 200 homes, 47 bridges, and 185 miles (300 km) of highway were destroyed. 29 of 35 © Boardworks Ltd 2005 VEI Description Plume Height Volume Classification How often Example 0 non-explosive < 100 m 1000s m3 Hawaiian daily Kilauea 1 gentle 100-1000 m 10,000s m3 Haw/Strombolian daily Stromboli 2 explosive 1-5 km 1,000,000s m3 Strom/Vulcanian weekly Galeras, 1992 3 severe 3-15 km 10,000,000s m3 Vulcanian yearly Ruiz, 1985 4 cataclysmic 10-25 km 100,000,000s m3 Vulc/Plinian 10's of years Galunggung, 1982 5 paroxysmal >25 km 1 km3 Plinian 100's of years St. Helens, 1981 6 colossal >25 km 10s km3 Plin/Ultra-Plinian 100's of years Krakatau, 1883 7 super-colossal >25 km 100s km3 Ultra-Plinian 1000's of years Tambora, 1815 8 mega-colossal >25 km 1,000s km3 Ultra-Plinian 10,000's of years Yellowstone, 2 Ma 30 of 35 © Boardworks Ltd 2005 Mt St Helens – consequences of the eruption N 0 31 of 35 10km © Boardworks Ltd 2005 Mt St Helens – consequences of the eruption AFTER BEFORE 32 of 35 © Boardworks Ltd 2005 What damage did the eruption cause? 33 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? 34 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? 35 of 35 © Boardworks Ltd 2005 Predicting eruptions 36 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. 37 of 35 © Boardworks Ltd 2005 Precautions during an eruption 38 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? 39 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. 40 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/ 41 of 35 © Boardworks Ltd 2005