Thinking about volcanoes

The eruption of Mt St Helen’s USA, 1980.

A Named example.

Make a table in your books…

Causes of the eruption Effects of the eruption

Cause is the reason something happens (Pressure makes the volcano erupt).

Effect is the result of what happens (The lava covers the soil and kills the crops).

• http://www.youtube.com/watch?v=FnDT_6V4qVw 30min

• http://www.youtube.com/watch?v=-H_HZVY1tT4&feature=related 9min

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

Mt St Helens eruption (May 1980)

Mount St .Helens before the eruption

Mount St. Helens is located in Washington State, in the Cascade mountains of the United States of America

Mt St Helens is located on a destructive plate boundary where a continental plate (North American) meets an oceanic plate (Juan de Fuca)

Mt St Helens – causes of the eruption

Juan de Fuca plate North American plate

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?

Causes of eruption – write down on your map

Before the eruption

The eruption

Mt St Helens – the eruption

March 20th 1980- after a quiet period of 123 years Mount St Helens spouted ash and steam

April the 27th 1980, a bulge has developed on the side of Mount St Helens.

During the eruption-

May the 18th 1980

Mt St Helens before and after the eruption

The effects of the eruption

Spirit Lake turned brown with dust ash and lava.

A crater caused by one of the explosive lava balls

The area around the volcano looks like the moon, stripped of all life!

BEFORE

AFTERMt St Helens – consequences of the eruption

N

0 10km

Mt St Helens – consequences of the eruption

http://www.youtube.com/watch?v=zp5MO77bFA4 Mt St Helen’s song!

Extended Writing

• Imagine that you are a volcanologist. (A volcanologist is someone who studies volcanoes.)

• As a volcanologist you have to produce a report for the volcano society regarding what happened to cause the eruption, what happened afterwards and what it was like during the eruption

• You may want to include relevant diagrams/pictures.

Homework

Causes of the eruption Effects of the eruption

Short term effects of the eruption Long term effects of the eruption

Short term effect is something that has changed but only changes for a little while and might change back to normal. Long term effect is something that has changed and will remain changed for a long period of time or forever.

Extend the table already in your books. Using the following slide, separate the effects of the eruption of Mt. St Helens into short term and long term.

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?

In your table from the video, 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