1. Thinking about volcanoes

2. The eruption of Mt St Helen’s
USA, 1980.
A Named example.

3. 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).

4. • http://www.youtube.com/watch?v=FnDT_6V4q
30min
• http://www.youtube.com/watch?v=-H_HZVY1tT
9min

5. Mt St Helens eruption (May 1980)
Mt St Helens is located on the ‘Ring of Fire’.

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

7. 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

8. 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
Causes of eruption – write down on your map

9. Before the
eruption

12. The eruption

17. Mt St Helens – the eruption

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

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

20. During the eruption-
May the 18th 1980

21. Mt St
Helens
before and
after the
eruption

22. The effects of
the eruption
Spirit
Lake
turned
brown with
dust ash
and lava.

23. A crater
caused by
one of the
explosive lava
balls
The area around
the volcano looks
like the moon,
stripped of all
life!

24. Mt St Helens – consequences of the eruption
AFTER
BEFORE

25. Mt St Helens – consequences of the eruption
N
0 10km

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

27. 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.

28. Homework
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.
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.

29. What damage did the eruption cause?
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
An increase Mudflows block and divert rivers. The US army takes
in tourism 18 months to dig out the debris from the River Toutle.
Two million birds, animals Communications routes threatened – railway and
and fish are killed. road bridges destroyed, Portland harbour blocked
A decrease in Hot mudflows raise the temperature of 60 people die from
tourism the rivers and lakes to 30ºC the eruption.
Gophers, through their tunnelling, mix the soil
Deer mice, chipmunk, vole, with the ash. This increases the fertility of the
gophers, salamander survive soil. Damage to crops=$175million
the blast. Their population
steadily increases due to the The post office and Lone Fir Motel shut
absence of predators. down in Cougar.
In your table from the video, separate the above into the
short term and long term impacts of the eruption.