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Volcanoes

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?

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?

Volcanic bombs, ash, lava, gases

Magma chamber

Parasitic cone

Crater

Main vent

Label this cross section of a volcano

CraterVolcanic bombs, ash and gases

Main vent

Parasitic cone

Magma chamber

Cross section of a volcano

Volcanic emissions

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?

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.

Why do they happen?

Destructive 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. However, since the magma can escape easily at the surface, the volcano does not erupt with much force.

Why do they happen?

Constructive plate boundary

Why do volcanoes have different shapes?

Volcano shapes

Volcanic activity at plate margins

Around which plate do we find most volcanoes?

Where are volcanoes found?

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?

Hawaii

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

Hot spot volcanoes

Mt St Helens is located on the ‘Ring of Fire’.

Internet Links

http://volcano.und.nodak.edu/vwdocs/msh/msh.html

Mt St Helens eruption (May 1980)

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.

Mt St Helens – causes of the eruption

Mt St Helens – the eruption

0 10km

Mt St Helens – consequences of the eruption

BEFORE

AFTERMt St Helens – consequences of the eruption

What damage did the eruption cause?

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?

How did their survival benefit the area?

Mt St Helens – consequences of the eruption

Predicting eruptions

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.

The problem of prediction

Tourists are attracted to areas of volcanic activity.

Geothermal energy can be produced in many volcanic areas.

Can you think of any other reasons?

This lava is weathered (broken down) to form a fertile soil.

Why do people live in volcanic areas?

Virtual field visits

http://educeth.ethz.ch/stromboli/

The Michigan Technological University Volcanoes Pagehttp://www.geo.mtu.edu/volcanoes/

Global Volcanism Programhttp://www.volcano.si.edu/gvp/

Fallout: Eye on the Volcanohttp://www.nationalgeographic.com/features/98/volcanoes/

Savage earthhttp://www.pbs.org/wnet/savageearth/

Volcano World - a fun and informative web sitehttp://volcano.und.nodak.edu/

Internet links

Volcanoes › ... › 05 › Volcanoes-13asi89.pdfVolcanologists (people who study volcanoes) are...

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