© boardworks ltd 2003 1 of 25 volcanoes. © boardworks ltd 2003 2 of 25 most slides contain notes...

© Boardworks Ltd 20031 of 25

Volcanoes


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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?


Around which plate do we find most volcanoes?

Where are volcanoes found?


•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


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.

Destructive Plate Boundary

Why do they happen?


Destructive plate boundary


Constructive 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 at this type of boundary. 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


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.


Volcano Shapes

Why are these volcanoes different shapes?


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?


Mt St Helenslocated on the ‘Ring

of Fire’

Mt St Helen’s eruption (May 1980)

Internet Linkshttp://volcano.und.nodak.edu/vwdocs/msh/msh.html


Mt St Helens – causes of the eruption

Juan de Fuca plate North American Plate

Which is the oceanic plate?


Mt St Helens – the eruption


N

0 10km

Mt St Helens – consequences of the eruption


Mt St Helens

BEFORE

AFTER


Hot mudflows raise the temperature of the rivers and lakes to 30ºC

Two million birds, animals and fish are killed.

60 people die from the eruption.

Up to 70mm of ash falls across Washington and East Montana… 7000 school students have an early summer vacation due to problems on the roads

Mudflows block and divert rivers. The US army takes 18 months to dig out the debris from the River Toutle.

Communications routes threatened – railway and road bridges destroyed, Portland harbour blocked

Gophers, through their tunnelling, mix the soil with the ash. This increases the fertility of the soil.

An increase in tourism

Deer mice, chipmunk, vole, gophers, salamander survive the blast. Their population steadily increases due to the absence of predators.

A decrease in tourism

What damage did the eruption cause?

Separate the above into the short term and long term impacts of the eruption.

The post office and Lone Fir Motel shut down in Cougar.

Damage to crops=$175million


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?

Deer mice, chipmunk, vole, gophers, salamander survive the blast. Their population steadily increases due to the absence of predators.


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

Tourists are attracted to areas of volcanic activity.

Geothermal energy (heat from the earth) can be produced in many volcanic areas.

Can you think of any other reasons?

Why do people live in volcanic areas?


Nevada del Ruiz is located in the Andes. The volcano had been giving signs of increased activity for some time and on the 13th 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 60km/hour towards the town of Armero and engulfed the town with mud up to 5m 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.

Nevada del Ruiz is located in the Andes. The volcano had been giving signs of increased activity for some time and on the 13th 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 60km/hour towards the town of Armero and engulfed the town with mud up to 5m 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.

The eruption started at 9.08pm. If the mudflows reached Armeno at 11.30pm, 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’?

23,000 dead5,000 injured 5,000 homes destroyed

Nevada del Ruiz, Colombia (November 1985)


Virtual field visitshttp://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!

© boardworks ltd 2003 1 of 25 volcanoes. © boardworks ltd 2003 2 of 25 most slides contain notes...

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