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| cone shaped hill or mountain formed at a vent from which molten rock erupts |
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| when magma reaches the surface |
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| controls when a rock becomes magma and depends on pressure and the availability of water |
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| large masses of molten magma that rise through Earth's crust |
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| low viscosity (fluid), black, magnesium, iron, calcium rich. 1100 to 1200 degrees. mostly lava flows |
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| high viscosity, pale color, potassium and silica rich, 800 to 900 degrees, more water, mostly ash |
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| medium viscosity, dark colors, lava flows, ash, broken fragments |
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| dissolved gas a volcano contains |
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| crack in floor of the valley |
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| formed in water, basalt cylindres |
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| cone shaped piles of basalt cinders tens or hundreds or meters high |
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| depression created as ash blasts out |
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| lava rich in steam and gases, ropy form |
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| less steam and gases, clinkery surface |
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| fragments of solidified magma |
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| a flow of pyroclastic material, collapse on volcano flank and spills downslope |
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| volcanic explosivity index |
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| quantifies eruption size, volume, violence |
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| violent steam driven explosions driven by water in the ground |
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| steam dominates and magma is not erupted |
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| steam bubbles in the magma blow it into cinders and bomb size blocks that fall around the vent and tumble down the steep slopes to form a cindercone |
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| ash falls may dominate, pyroclastic and lateral blast may follow |
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| ash columns that collaspe to form incandescent pyroclastic flows |
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| silica rich ash falls accompany incinerating pyroclastic flows |
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| magma collapses to form one |
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| depression or crater forms where the vent is excavated by the violent eruption |
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| gently sloping pile of thin flows, basalt |
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| large, steep sided cone over a subduction zone, also called composite volcanoes |
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| rhyolitic volcanoes characterized by their small to moderate size, high magma viscosity, steep flanks and low to moderate volatile content |
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| rhyolite volcanoes characterized by high viscosity, high volatile content, gently sloping flanks and ash content |
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| magma that continues to rise beneath the filled caldera |
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| hot volcanic ash and steam that pours downslope because it is to dense to rise |
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| high speed ash rich shock wave |
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| composed of bits of pumice less than 2 millimeters across, light enough to drift some distance on the wind |
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| eruptions generate their own weather |
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| caused when ash combines with water to pour down the flanks at high speed and with a consistency similar to wet concrete |
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| gasses come out of solution |
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| interpreting deposits from prehistoric eruptions and reconstructing a record using age dates on plant material |
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| low frequency rolling ground movement that precedes many eruptions |
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| measure summit elevations and slope steepness associated with eruptions |
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