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| General term refers to all the phenomena associated with the origin and movement of molten rock. |
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| When magma is extruded onto the Earth's surface (extrusive). |
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| Shallow intrusive activity. |
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| Broad, gentle slopes; non-explosive; high temperature (basaltic) lavas; made of many lava layers; hotspots & divergent boundaries. |
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| Composite or Stratovolcano |
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| Large steep sided; alternating lava layers & pyroclastic (esp. ash & cinders) layers; pyroclastic layers; convergent boundries. |
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| Small (usually < 2,000 feet high); solidified (rhyolitic) lava that was relatively cool and thick; convergent boundries. |
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| Small steep cided, max 1500 feet high; mostly layers of loose pyroclastic material, esp. ash & cinders; some lava flows. |
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| Large eruption of basaltic lava usually not associated with a peak. |
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| Gas emitted during volcanic eruption. |
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| Molten rock flowing on surface. |
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| Violent eruption of pyroclastic material & gases. |
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| High-speed avalanche of searing hot gases, ash, & rock fragments. |
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| A circular depression, much lager than a volcanic vent, that results from a large volcanic explosion and/or from the collapse of a magma chamber. |
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| A rocky spire that represents the throat or pipe of an old eroded volcano. |
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| Large intrusion is now exposed over 100 square km. at surface. |
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| Intrusion exposed less than 100 square km. |
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| Large mushroom shaped intrusion exposed at surface. |
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| Relatively think intrusion that forms when magma is forced between pre-existing strata. |
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| Relatively thin intrusion that forms when magma flows across pre-existing strata; often nearly vertical. |
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