Introduction - VOLCANOES What is a volcano? A place on the...

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1 VOLCANOES What is a volcano? ± A place on the earth’s surface (or any other planet) where molten rock and gases are erupted. ± A hill or mountain built up by the eruption of molten rock. There are, however, many kinds of volcanoes. A volcano does not have to be a beautiful snow- capped conical peak. It can be a hole in the ground, or a crack in the earth’s surface This is what we tend to think of when we think of volcanoes – beautiful, snow-capped, conical peaks. In this case Mount St. Helens prior to its 1980 eruption.
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2 Holes in the Ground! Zuni Maar, New Mexico Vitti, an explosion crater that erupted in Iceland in 1720 AD. Maars and explosion craters are produced when hot magma (usually basalt) reacts violently with shallow water, or water- soaked ground. These types of eruptions are known as phreatomagmatic Cracks in the ground (fissure eruptions) Lava and steam erupting from cracks at Krafla, Iceland in 1981 Lava flows from cracks in the Snake River Plain, Idaho.
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4 Some Volcano Facts The total number of recognizable volcanoes is about 10,000 ACTIVE – volcanoes known to have erupted during historical times. Total Number = 529 DORMANT – volcanoes that have not erupted during historical times, but will probably erupt again. Total Number = 1,340 EXTINCT – volcanoes that are unlikely to erupt again. more volcano facts…… ± About 500 volcanoes are currently active. ± Typically there are about 5 – 10 volcanoes erupting every month (about 50/year). ± About 262,000 people have been killed by volcanoes since 1600A.D. (this averages out at one person per year per volcano!).
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5 Repose Period This is the time interval between successive eruptions. It can range from minutes to thousands of years! In general the longer the repose period the more explosive and dangerous the next eruption. The Major Killers 1783 Laki, Iceland 9,340 (mostly starvation) 1815 Tambora, Indonesia 92,000 (80,000 starvation) 1883 Krakatao, Indonesia 36,000 (mostly tsunami) 1902 Mt. Pelee, Martinique 29,000 (ash flows) 1985 Nevada del Ruiz Colombia 22,000 (mud flows) Deaths Cause Year Volcano
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A Simple Guide to Volcanic Rocks Lava Pyroclastics MAGMA molten rock and dissolved gases Ash Volcanic Bombs Ignimbrites Produced by melting in the crust or mantle Gases = water, sulfur and fluorine gases High gas content, explosive eruptions
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This note was uploaded on 02/22/2012 for the course GEA 3000 taught by Professor Staff during the Fall '09 term at UMass (Amherst).

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Introduction - VOLCANOES What is a volcano? A place on the...

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