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Volcanoes!

Volcanoes!. Volcanism - the formation of volcanoes. A. Molten rock 1. magma – molten rock below the Earth’s surface 2. Where rock will melt - rock melts in the asthenosphere - rock also melts at the plate boundaries due to friction created during plate movements

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Volcanoes!

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  1. Volcanoes!

  2. Volcanism - the formation of volcanoes A. Molten rock 1. magma – molten rock below the Earth’s surface 2. Where rock will melt - rock melts in the asthenosphere - rock also melts at the plate boundaries due to friction created during plate movements B. Movement of magma 1. magma is less dense than solid rock therefore it will rise 2. magma will push thru cracks in crust pushed upwards 3. when it reaches the surface – a volcano forms

  3. Volcanoes - magma affects volcano shape Shield cone volcano • Low, wide based volcanoes • Example : Hawaiian volcanoes • Mafic magma • thinner in viscosity, flows easily • oozes out, forming a shield shape as each layer flows and hardens • fewer gases in this form • eruptions not very explosive • Mafic lava erupts and then flows easily • Produces pahoehoe features (ropey, mafic lava)

  4. Volcanoes – how magma affects volcano shape Cinder cone volcano • Tall, steep, narrow based volcanoes • Example : Mt. St. Helens • Felsic magma • thicker viscosity, slower moving • eruptions are often violent • lava is blocky (aa) features, felsic in nature • Large amounts of gas trapped in magma • carbon dioxide, carbon monoxide, sulfur oxide • All dangerous, poisonous in some cases • Even superheated steam can be formed • Sudden expansion of these gases similar to a soda bottle being shaken!!!

  5. Volcanoes – how magma affects volcano shape When volcanoes erupt violently • Lava fragments called tephra thrown out • ash - less than 2 mm in size - smallest kind • lapilli - 2 mm to 64 mm in size • over 64 mm in size – two kinds • blocks – launched and land as solid chunks • bombs – launched as liquid, solidifies as it falls • Pyroclastic cloud • tephra mixed in with volcanic, superheated gases • can move at very high speeds (200 mph!)

  6. Why Volcanoes are Hazardous!

  7. Volcanoes – how magma affects volcano shape • Examples • Mt. Vesuvius and the end of Pompeii • Krakatoa, Indonesia • Mt. St. Helens, Washington State • Mt. Pinatuba, Philipines

  8. Cities in Dust" by Siouxsie and the Banshees • Water was running; children were runningYou were running out of timeUnder the mountain, a golden fountainWere you praying at the Lares shrine? • We found you hiding, we found you lyingChoking on the dirt and sandYour former glories and all the storiesDragged and washed with eager hands

  9. Cities in Dust" by Siouxsie and the Banshees • Water was running; children were runningWe found you hiding, we found you lyingWater was running; children were runningWe found you hiding, we found you lyingyour city lies in dust • Hot and burning in your nostrilsPouring down your gaping mouthYour molten bodies blanket of cindersCaught in the throes ....... • But ohh oh your city lies in dust, my friendohh oh your city lies in dust, my friendyour city lies in dust

  10. Plutonic Activity – when magma doesn’t reach the surface Trivia - Who was Pluto? What was his name in Greek mythology? • Plutons – igneous intrusions below the surface • Sills – igneous intrusion that are parallel to existing rock layers • Dikes – igneous intrusions that cut across rock layers • Laccolith – igneous intrusion that pushes up existing layers to form a dome shape • Neck – remains of the center of an extinct volcano after outside edges are eroded • Batholiths – massive underground intrusions • Stocks – less massive underground intrusions (under a hundred square miles)

  11. Plutonic Activity – when magma doesn’t reach the surface Trivia - Who was Pluto? What was his name in Greek mythology? • Plutons – igneous intrusions below the surface • Sills – igneous intrusion that are parallel to existing rock layers • Dikes – igneous intrusions that cut across rock layers • Laccolith – igneous intrusion that pushes up existing layers to form a dome shape • Neck – remains of the center of an extinct volcano after outside edges are eroded • Batholiths – massive underground intrusions • Stocks – less massive underground intrusions (under a hundred square miles)

  12. Plutonic Activity – when magma doesn’t reach the surface Trivia - Who was Pluto? What was his name in Greek mythology? • Plutons – igneous intrusions below the surface • Sills – igneous intrusion that are parallel to existing rock layers • Dikes – igneous intrusions that cut across rock layers • Laccolith – igneous intrusion that pushes up existing layers to form a dome shape • Neck – remains of the center of an extinct volcano after outside edges are eroded • Batholiths – massive underground intrusions • Stocks – less massive underground intrusions (under a hundred square miles)

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