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Explosive Eruptions

Felsic magmas erupt explosively and cause widespread damage, including many fatalities.

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Vancouver! This is it!

Vancouver! This is it!

Credit: Harry Glicken
Source: http://en.wikipedia.org/wiki/File:MSH80_david_johnston_at_camp_05-17-80_med.jpg
License: CC BY-NC 3.0

Those are the last words spoken by David A. Johnston. Johnston was killed as he observed Mount St. Helens on May 18, 1980. He worked as a volcanologist, taking measurements very close to active volcanoes in order to better predict eruptions.

Amazing But True!

  • There were more than 10,000 local earthquakes before the May 18 eruption. However, the earthquakes increased in frequency then reached a plateau. Many people thought the danger of an eruption had passed.
  • There was only one seismometer near the volcano so it was unclear where the quakes were coming from.
  • Monitoring has improved since 1980 with GPS and satellites, among other tools.
  • What was learned at St. Helens is now used to predict eruptions on other volcanoes; e.g. Mount Pinatubo in 1991.

Show What You Know

With the links below, learn more about predicting the 1980 Mount St. Helens eruption. Then answer the following questions.

  1. Why was David A. Johnston where he was then Mount St. Helens erupted?
  2. Why is eruption prediction better now than it was in 1980?
  3. Will another eruption on the scale of the 1980 eruption occur on St. Helens within the next few decades?
  4. Why were so many people killed by the 1980 eruption? Why were they in the dangerous region?

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    Image Attributions

    1. [1]^ Credit: Harry Glicken; Source: http://en.wikipedia.org/wiki/File:MSH80_david_johnston_at_camp_05-17-80_med.jpg; License: CC BY-NC 3.0

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