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Unformatted text preview: What is a volcano?-a place on the earths surface (or any other planet) where molten rock and gases are erupted-a hill or mountain built up by the eruption of molten rock-can be a hold in the ground, or a crack in the earths surface Stratovolcano cones are built up of layers (strata) of lava and volcanic ash.-Ex. Mount Hood, Mount Shasta Cinder Cones These volcanoes are often referred to as monogenetic volcanoes. This is because, unlike stratavolcanoes, they usually erupt once.-Ex. Halekala volcano, Ojo de Agua, Mexico, Surtsey Volcano Shield Volcanoes unlike stratavolcanoes that are composed of viscous lavas and ash, shield volcanoes are made of fluid basalt lavas flows that flow much further, thus giving them their shield-like shape.-OLYMPUS MONS, a giant shield volcano on Mars that is believed to be the largest volcano in the solar system (entire island of Hawaii would fit in its caldera) **explosion craters are produced when hot magma (usually basalt) reacts violently with shallow water, or water-soaked ground **Crater Lake, Oregon used to be a large stratovolcano that blew itself to bits 6,845 years ago Fissure eruptions lava erupting from cracks can produce huge thick piles of lava Where do volcanoes occur? PLATE MARGINS Spreading Margins-Mid-Ocean Ridges (ex. Iceland)-Rifting Continents (ex. East Africa Rift) Converting Margins-Island Arcs (ex. Aleutians, Japan)-Continental margins (ex. Cascades, Andes) PLATE INTERIORS Oceanic Plates (ex. Hawaii, Reunion) Continental Plates (ex. Yellowstone) Active Volcanoes volcanoes known to have erupted during historical times Total Number = 529 Dormant Volcanoes volcanoes that have not erupted during historical times, but will probably erupt again Total Number = 1,340 Extinct Volcanoes volcanoes that are unlikely to erupt again **Typically there are about 5-10 volcanoes erupting every month (about 50/year) **About 262,000 people have been killed by volcanoes since 1600 AD (average to about one person per year per volcano) Repose Period 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 eruption. A Simple Guide to Volcanic Rocks Types of Eruptions-eruption types are based on the eruption characteristics of a well-known volcano. There are five such types:-Hawaiian-Surtseyan-Strombolian-Vulcanian-Plinian (Krakatoan) The most useful classification of eruption types is based on :-how big the eruption is-how explosive or violent it is Examples of Hawaiian Eruptions: Kilauea, 1971-fire-fountaining (or curtains of fire)--molten magma is ejected from cracks to produce fire fountains that jet the lava 30- 50 feet into the air....
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This note was uploaded on 05/08/2008 for the course ANTHRO 102 taught by Professor Johnson during the Spring '08 term at UMass (Amherst).
- Spring '08