Laboratory Manual for Introductory Geology 4e

FIGURE 5.12 Distribution of volcanoes in
North America.
Stratovolcanoes (FIG. 5.11d) include some of the most famous
volcanoes on the Earth—Vesuvius, Mt. Etna, Denali, Mt. Rainier,
Mt. St. Helens, Mt. Fuji, to name only a few. This type of volcano
has by far the most violent eruptions and poses the greatest danger
to humans. Stratovolcanoes are made of large amounts of
both lava and pyroclastic material. They have the steepest slopes
of all volcanoes because the pyroclastic material is so hot when it
accumulates that the particles are welded together, so the pile is
not flattened by the pull of gravity. Stratovolcanoes are most commonly
found in subduction zones, and their explosive eruptions
are caused by large amounts of steam produced by flux melting
associated with the subducting slab.
5.6.2 Living with Volcanoes
Hundreds of millions of people literally live on volcanoes, including
citizens of some of the world’s most populous nations; more than
half a billion people live on volcanoes in Indonesia (the fourth most populated country),
Japan (the tenth), and the Philippines (the thirteenth) alone. Millions more in
the Andean nations, Italy, Africa, and, yes, the United States (FIG. 5.12) also live on or
close to active volcanoes. All must cope with the potential impact of volcanic eruptions.
EXERCISE 5.14
Volcanic Hazard Risk Assessment in North America
Name:
Course:
Using Figure 5.12 as a reference, answer the following questions:
Section:
Date:
(a) What parts of North America have the greatest risk of problems associated with local volcanic eruptions? Why are
volcanoes located there rather than in other regions?
(b) What volcanic hazards do Alaskans have to worry about that Hawaiians don’t? Explain
(c) What parts of North America need not be concerned about local volcanic eruptions? Why not?
The power of a major stratovolcano eruption is, in the true meaning of the word,
awesome. The 1883 eruption of Krakatau in Indonesia was heard 3,000 miles away
(more than the distance between Los Angeles and New York!), created 100-foot tsunamis,
and killed more than 35,000 people. The 1912 eruption of Novarupta in Alaska is
described by the U.S. Geological Survey as the loudest sound of the twentieth century,
dwarfing all the nuclear bomb tests. It should come as no surprise that a stratovolcano
eruption in or near a major population center would be a huge natural disaster.
134 CHAPTER 5 USING IGNEOUS ROCKS TO INTERPRET EARTH HISTORY