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Chapter 9

Chapter 9 Notes.docx

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Department
Geological Sciences
Course Code
GEOL 2390
Professor
William M.Last

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Chapter 9 Notes Volcanic Activity Magma molten rock including a small component of dissolved gasses (mostly water vapor and CO )2 Lava Magma that has emerged from volcano onto earths surface Volcano Types Shape Silica Viscosity Rock Eruption content type type formed Shield Volcano Gentle arch or low Low Basalt Lava flows, shield with tephra shallow slopes ejections Composite Cone-shaped Med Med Andesite Combination volcano or steep sides, of lava flows stratovolcano build up of and lava flows and explosive pyroclastic activity Volcanic dome Dome shaped High High Rhyolite Highly explosive Cinder cone Cone shaped, low low Basalt Tephra steep sides (mostly ash) often with ejection summit crater Volcano Origins Volcanism at mid-oceanic ridges form shield volcanoes with basaltic rock Above hot spots located below the lithospheric plates forms shield volcanoes with basaltic rock Subduction zones associated with andesite rock form composite volcanoes producing rock with intermediate silica when mixed with crusts basalt rock Caldera-forming eruptions are extremely explosive and violent, associated with rhyolitic rocks, associated with volcanic domes inland of subduction zones Craters Depressions commonly found at the top of volcanoes formed by explosion or collapse of the upper portion of the volcanic cone and may be flat floored or funnel shaped (usually a few km) Calderas Gigantic often circular depressions resulting from explosive ejection of magma and subsequent collapse of the upper portion of the volcanic cone Volcanic vents Openings though which lava and pyroclastic debris are erupted, may be circular or elongated Hot springs Ground water that comes into contact with hot rock becomes heated and in some cases this heated water discharges at the surface Geyser Subsurface ground water involving circulation and heating pattern that produce periodic release of steam and hot water at the surface Volcanic Hazards Primary effects Effects that are the direct result of the eruption e.g. lava flows, pyroclastic activity, ash fall, ash flows, lateral blasts and release of gasses Lava flows Result when magma reaches the surface and overflows the crater or a volcanic vent along the flanks of the volcano, can be basaltic, andesitic and rhyolitic Basaltic lava Fifty percent silica with a range of viscosities Pahoehoe Basaltic lava with lower viscosity and higher eruptive temperatures the fastest moving (velocity of 1 m or so per hour) have a smooth ropy surface Aa Basaltic lava that is cooler, more viscous and flows at a few meters per day leaving a blocky texture Methods for - Hydraulic chilling: cooling the f
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