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Volcanoes

Volcanoes. Volcano. Repeated eruptions of lava and pyroclastic material Often separated by long inactive periods Often forms a mountain. What causes volcanoes?. Magma forms deep inside Earth Less dense than rock above it, so slowly forced upward

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Volcanoes

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  1. Volcanoes

  2. Volcano • Repeated eruptions of lava and pyroclastic material • Often separated by long inactive periods • Often forms a mountain

  3. What causes volcanoes? • Magma forms deep inside Earth • Less dense than rock above it, so slowly forced upward • Magma reaches Earth’s surface and flows through opening called a vent

  4. Volcano vent

  5. Volcano Crater • Steep-walled depression around a volcano’s vent • Formed as lava flows out of vent, quickly cools and hardens • A large crater is called a caldera

  6. Volcano Crater

  7. Form in one of three places Divergent plate boundary Convergent plate boundary Hot spot Where do volcanoes occur?

  8. Divergent Boundaries • Plates separate (move apart) and magma flows up from the rifts. • Can rise above sea level to form islands • Ex: Mid-Atlantic Ridge, Iceland

  9. Divergent Plate Boundary

  10. Plates move together Create subduction zone where several volcanoes may form Ex. Ring of Fire Convergent Boundaries

  11. Pacific Ring of Fire

  12. Hot Spots • Areas away from plate boundaries where magma is forced to the surface • Ex: Hawaii

  13. Hawaiian Hot Spot

  14. Factors affecting type of eruption • Viscosity of magma • Magma composition • Magma temperature • Amount of dissolved gases in magma

  15. Viscosity= Resistance to flow The higher the viscosity of magma the greater the eruption Temperature affects viscosity higher temps = lower viscosity Chemical composition of magma also has an effect Higher silica content = greater viscosity

  16. Dissolved Gases Trapped gases provide the force to eject material from the vent 2 main gases- Water vapor and Carbon Dioxide More dissolved gases = greater eruption

  17. Magma Composition

  18. Types of Volcanoes • Shield • Lava quietly flows from vent • Mountain covers large area and dome-shaped • Sides gently sloped • Ex: Mauna Loa, Hawaii

  19. Mauna Loa • Earth’s largest volcano

  20. Types of Volcanoes • Cinder Cone • Cinders and rock particles blown into air • Mountain small with steep sides • Ex: Paricutin, Mexico

  21. Paricutin, Mexico

  22. Types of Volcanoes • Composite • Violent eruption sends up volcanic bombs, cinders and ash • Quiet volcanic flow follows explosion • Alternating layers form mountain • Mountain large and cone-shaped with steep sides • Ex: Mt. St. Helen’s, Washington

  23. Mt. St. Helen’s

  24. Worlds most active volcano: • Kilauea in Hawaii • Most recent series of eruptions 1993 • 1990 destroyed most of Kalapena Gardens, Hawaii

  25. Kilauea

  26. Monserrat • Caribbean Island • Erupted 1997 • 19 killed

  27. Mt. St. Helen’s • May 1980 • 57 killed

  28. Mount Pinatubo • In the Philippines • June 1991, • Almost 900 killed • 27 million metric tons of sulfur dioxide and ash thrown into Earth’s upper atmosphere

  29. Mount Pinatubo

  30. Nevado del Ruiz • Armero, Colombia destroyed • Erupted 1985 • 23,000 killed

  31. Armero, Colombia

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