Chapter 7: The Wrath of Vulcan: Volcanic Eruptions
Study Plan
During a volcanic eruption, molten rock rises from inside the Earth and flows out as lava, or blasts into the air as ash.
Credit: Doukas, USGS
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 gas content) 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 categories as lava types, cone types, and styles of eruption. But be aware that because 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, conduits, fissures, craters, calderas, and resurgent domes. 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, explosive, and phreatomagmatic.)
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 are the positive effects of volcanic activity?
- 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?
- How long have humans been affected? (The record goes way back in both the popular and religious literature.)
The author ends with some really far out material, literally. He addresses the question, "Is Earth the only planet blessed (or cursed) with volcanism?" Read on to learn the answer.
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