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Volcanoes

Volcanoes. What is a Volcano?. A volcano is a vent in the earth’s crust through which hot gas, ash and molten rock flows. How do Volcanoes Form?. Subduction Zones. Hot Spots. Magma/Lava. Magma : molten rock located underground Lava: Molten rock that has reached the surface. Viscosity.

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Volcanoes

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  1. Volcanoes

  2. What is a Volcano? A volcano is a vent in the earth’s crust through which hot gas, ash and molten rock flows.

  3. How do Volcanoes Form? SubductionZones

  4. Hot Spots

  5. Magma/Lava Magma: molten rock located underground Lava: Molten rock that has reached the surface

  6. Viscosity Viscosity is the resistance to flow of a fluid. The viscosity of magma is determined by the amount of silica present.

  7. High Viscosity Magma High amounts of silica results in thick slow moving magma with high gas content

  8. Low viscosity Magma Low amounts of silica results in thin, runny magma with low gas content

  9. Types and Characteristics of Magma

  10. Types of Volcanoes Shield Volcano Shield volcanoes are commonly found at divergent plate boundaries and oceanic hot spots. Shield volcanoes are large with gently sloped sides. The magma is mainly composed of basaltic magma which has a low viscosity.

  11. Shield Volcano

  12. Cinder Cone Small steep sided volcano which erupts gas-rich basaltic lava. It is formed when highly viscos magma is thrown into the air from the vent, cooling and breaking into fragments upon hitting the ground.

  13. Cinder Cone

  14. Composite Volcano Composite volcanoes, sometimes called stratovolcanoes are characterized by large steep sides which are a result of repetitive explosive eruptions of andesitic and rhyolitic lava and ash. This type of volcano is mainly located along subduction zones.

  15. Composite Volcano

  16. Pyroclastic Flow Explosive volcanoes can produce avalanches of hot gasses, ash, and rock. Pyroclastic flows can reach speed in excess of 100 km/h with temperatures greater than 10000 C.

  17. Classification of Pyroclastic Material Ash Diameter less than 2 mm

  18. Lapilli Diameter from 2 mm to 64 mm

  19. Lava Block or Bomb Diameter greater than 64 mm

  20. Pyroclastic Flow

  21. Lahars Melted snow or ice creates a mudflow that rushes down the volcano at speeds in excess of 100 km/h

  22. Lahar

  23. Caldera Following an eruption, the walls of a volcano are weakened and collapse into the vent and form a large crater shaped basin called a caldera.

  24. Caldera

  25. Crater Lake

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