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Guide
to Reading 
In this chapter the author explains that there are
many possible manifestations of volcanic activity, and numerous variables
to consider when trying to understand what has occurred or predict
what will occur at some specific location. The nature of volcanic
activity depends on the chemistry of the situation (chemical compositions,
temperatures, and pressures) and the environment in which it's occurring
(submarine or subaerial/not underwater).
There's lots of vocabulary to learn and many classification
schemes to use. Keep reminding yourself that scientists establish
classification schemes to organize data, discern patterns, and thus
reach an understanding of why things happen as they do. Look for
these patterns; make logical associations of such things as lava
types, cone types, and styles of eruption. But be aware that volcanoes
are the result of the interplay among so many factors they're not
always perfectly predictable. They've been known to fool even the
smartest volcanologists.
The chapter begins with discussion of the three types
of volcanic products: lavas, pyroclastic debris, and gases. It continues
with the vocabulary of volcanic structures: "magma chambers," "chimneys,"
"fissures," "craters," and "calderas." With these basic terms to
build on, the author discusses the three basic types of cones (shield,
cinder, and composite or stratovolcanoes), the differences between
summit eruptions and flank eruptions, and eruptive styles (effusive
and explosive).
Any history buff will feel right at home in this
chapter because woven throughout it are accounts of historic volcanic
eruptions that have affected human society, often in devastating
fashion. Pay particular attention to the geographic locations of
these eruptions; they're determined by plate tectonics. The phenomena
of hot spots, mid-ocean ridges, convergent margins, and continental
rifts reappear, this time with emphasis on their association with
volcanic activity.
The chapter continues with societal issues:
- What specifically are the dangers? (lava; ash, pumice, and lapilli
falls; pyroclastic flows; blast; landslides; lahars; earthquakes;
tsunamis; gas)
- Can humans protect themselves and their property? (prediction
and control)
- How is climate affected?
This chapter will probably convince you that volcanoes
are natural hazards that pose significant threats to humans and their
property. The next chapter continues the theme of “humans beware!”
It’s about earthquakes.
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Key Terms
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