Volcanoes

Volcanoes

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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?

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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

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Label this cross section of a volcano

Volcanic bombs, ash, lava, gases Magma chamber Parasitic cone

Crater Main vent

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Cross section of a volcano Crater

Volcanic bombs, ash and gases Parasitic cone

Main vent

Magma chamber

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Cross section of a volcano

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Volcanic emissions

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Volcanic emissions

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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!

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Learning objectives


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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.

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Destructive plate boundary

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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.

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Constructive plate boundary

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Volcano shapes Why do volcanoes have different shapes?

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Volcano shapes

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Volcanic activity at plate margins

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Learning objectives


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Where are volcanoes found?

Around which plate do we find most volcanoes? 19 of 35


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?

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Hot spot volcanoes

In the animation above, why are the volcanoes to the left of the ‘hot spot’ extinct? 21 of 35


Learning objectives


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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


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


Mt St Helens – the eruption

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Mt St Helens – consequences of the eruption

N 0

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10km


Mt St Helens – consequences of the eruption AFTER BEFORE

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What damage did the eruption cause?

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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? 29 of 35


Learning objectives


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Predicting eruptions

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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.

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Learning objectives


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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.

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Geothermal energy can be produced in many volcanic areas.


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/

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Volcanoes

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