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Volcanoes

Volcanoes. Volcanoes. C aused by magma (a mixture of liquid rock, crystals, and dissolved gas) expelled onto the Earth's surface . Types of Eruptions: Compare and contrast 1. Explosive (violent) Ex: Mount St. Helens and Pinatubo B egins with a blockage in the crater of a volcano

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Volcanoes

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  1. Volcanoes

  2. Volcanoes Caused by magma (a mixture of liquid rock, crystals, and dissolved gas) expelled onto the Earth's surface. Types of Eruptions: Compare and contrast 1. Explosive (violent) • Ex: Mount St. Helens and Pinatubo Beginswith a blockage in the crater of a volcano • High gas content trapped in highly viscous magma. • The high viscosity of the magma prevents the release of trapped gases. When this type of magma flows towards the surface pressure builds

  3. Eventually causing the blockage to be blasted out in a violent explosive eruption where ever the volcano is the weakest • Explosive eruptions (tephra) can send rocks, dust, gas and pyroclastic material up to 20 km into the atmosphere. • This cloud will then collapse, creating a pyroclastic flow of hot volcanic matter. Primary Effects: A. Pyroclastic flow (hot ash clouds): is a fast moving current of hot gas and rock up to 450 mph and temperatures of 1,830 °F. They hug the ground and travel downhill. Burn everything in path

  4. B. Volcanic Ash • Volcanic ash consists of tiny jagged pieces of rock and glass. Ash is hard, abrasive, mildly corrosive, conducts electricity when wet, and does not dissolve in water. • Ash is spread over broad areas by wind. • Falling ash can turn daylight into complete darkness, destroy vegetation, crops, and kill livestock

  5. 2. Basaltic Eruptions (mild) • Ex: Galapagos Islands • Non explosive eruptions are favored by low gas content and low viscosity magmas • Begins withlava fountains due to release of dissolved gases (up to 400m high) • Lava flows are produced on the surface, and these run like liquids down slope for a long way, cool quickly, smooth C. Lava: when magma reaches surface, type depends on temp, viscosity, gas content

  6. Secondary Effects • Mudflows • Landslides • Tsunami • Atmospheric effects (sulfur and CO2) • Volcanic earthquakes Predicting and Monitoring • Study surrounding geology, gives history of the volcano, look at lava and other deposits. Can forecast likely future eruption patterns on past behavior • Radiometric age dating of deposits gives frequency of eruptions • Changes in gas composition from the vents : increases in the proportions of hydrogen chloride (HCl) and sulfur dioxide (SO2) are seen to increase before an eruption • Earthquake monitoring below a volcano • Deformation of the ground (due to magma) around a volcano can be measured using tilt meters (measure changes in angle of the earths surface)

  7. Responses • Volcano hazard maps- give zones of danger and expected hazard, ex lava flows • Evacuations • Rescue and recovery

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