Volcanoes are classified as active, dormant, or extinct. If they have erupted during the last 50 years, they are clearly classified as active. On what bases are dormant or extinct volcanoes classified, and how can geologists be sure an extinct or dormant volcano may not suddenly become active?
Answer to relevant QuestionsMt. Somma (ancestral Mt. Vesuvius), which towered above the Roman seaside resort cities of Pompeii and Herculaneum, hadn’t erupted for 800 years, when in A.D. 79, it erupted. What happened to the two cities?Figure 3.14 is a sketch of lava flows in the Columbia Plateau region of northwestern United States. What do the flows indicate about the viscosity and composition of the lava?If volcanoes are dangerous, as illustrated when Mt. St. Helens erupted in May 1980, why are some volcanic regions such as Sumatra in the East Indies so densely populated?How might the big rounded granite “boulders” in Fig. 4.3 have formed? (Clue: They have been formed at this site and have not been carried here by ice, water, or humans.)When a biotite granite weathers in a temperate climate, what products remain to form the soil?
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