Laboratory Manual for Introductory Geology 4e

EXERCISE 5.15
Stratovolcano Disaster Case Histories (continued )
Name:
Course:
Section:
Date:
Using the figure from the previous page of the timeline and nature of significant eruptions at Mt. St. Helens as a reference,
answer the following questions:
(d) What is the average number of years that the volcano has remained dormant between eruptions during this
period?
(e) Does the active/dormant cycle appear to be regular or erratic?
(f) Suggest a geologic explanation for this pattern.
(g) Based on the average dormant interval following significant eruptions, predict when the next significant eruption is
likely to occur.
(h) What factors make such predictions difficult and sometimes inaccurate? How do the 2004 eruption and 2017
earthquake swarms affect your prediction?
?
What Do You Think Every time Old Faithful spews steam
into the air in Yellowstone National Park, it reminds us that there is hot
magma beneath the park capable of producing an eruption. This deceptively
peaceful volcanic activity is not the first to occur in the Yellowstone area. About
640,000 years ago, one of the most violent eruptions ever detected (VEI 5 8,
the maximum) blasted ash over much of the central and southwestern United
States, blanketing the area shown in Figure 5.14 and dwarfing the areas affected
by ash from other major eruptions.
Comparison of the Yellowstone eruption with the effects of Mt. St. Helens
gives us an idea of the difference between VEI 5 and VEI 8 eruptions. We cannot
predict when or if a VEI 8 eruption will happen at Yellowstone again, but if
it did, what would be its effect on the areas directly impacted by the ash? Which cities and states
would suffer the most? Consider effects on the local economy, health, food supplies, and transportation
networks. And although not all of the United States would be directly affected by the
ash fall or explosion, what do you think the effects would be on the rest of the country? Answer
on a separate sheet of paper.
5.6 VOLCANOES AND VOLCANIC HAZARDS
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