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Dynamic Earth Study Guide 2

Dynamic Earth Study Guide 2 - What is a volcano-a place on...

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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 -can be a hold in the ground, or a crack in the earth’s 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.
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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. --molten magma hitting the ground flow away as lava flows, whereas cooled magma produces cinders (spatter) near the vents.
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Dynamic Earth Study Guide 2 - What is a volcano-a place on...

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