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Volcanic Eruptions and Volcano Type What is a volcano? •A volcano is any place where gas, ash, or melted rock come out of the ground. Anatomy of a Volcano • Crater – Lava collects in the crater, the bowlshaped area that forms around the volcano’s vent. Vent Crater Lava Flow Side Vent Pipe Magma chamber Volcano Menu • Vent – The point on the surface where magma and gas leave the volcano’s pipe. Vent Crater Lava Flow Side Vent Pipe Magma chamber Volcano Menu • Pipe – A narrow, almost vertical crack in the crust through which magma rises to the surface. Vent Crater Lava Flow Side Vent Pipe Magma chamber Volcano Menu • Magma Chamber – A large underground pocket of magma that forms from magma rising to the surface. Vent Crater Lava Flow Side Vent Pipe Magma chamber Volcano Menu • Lava Flow – The river of lava that pours down a volcano over the land. Vent Crater Lava Flow Side Vent Pipe Magma chamber Volcano Menu • Types of Volcanic Eruptions – A volcano’s magma determines its volcanic cone and influences how the volcano erupts. – The silica content helps determine whether the volcanic eruption is quiet or explosive. Shield Cones and Quiet Eruptions (Examples: Grimsvotn of Iceland and Kilauea of Hawaii) *Form as a result of sea-floor spreading or “hotspots” in the Earth’s mantle. • Shield Cones and Quiet Eruptions – Magma flows easily. – Dissolved gases in the magma bubble out easily. – Thin runny lava oozes from the vent and flows • Volcanic Hazards of Quiet Eruptions – Quiet Eruptions: • Lava flows- set fire and bury everything in their path. Composite Volcanoes and Explosive Eruptions (Examples: Mount Vesuvius of Italy and Mount Saint Helens Washington State) *Form as a result of subduction. • Volcanic Hazards – Time between eruptions for composite cones can span hundreds of years. (Dormant Volcano) – Example: Mt. St. Helens 123 years. – People may be unaware of the danger. • Explosive Eruptions • Magma is thick and sticky. • Thick magma builds up in the pipe, plugging it like a cork in a bottle. • Pressure builds up due to the gases in the magma until the volcano explodes. • Volcanic Hazards of Explosive Eruptions – Lahar: • A mud flow caused by melted snow. – Carries ash, trees and rocks. • Explosive Eruptions • The gases push the magma out with incredible force. • The explosion breaks lava into fragments that quickly cool and harden into different sizes. • Explosive Eruptions • Fragments: – Volcanic Ash » fine, rocky, grain of sand sized particles. – Cinders» pebble sized particles – Bombs» large pieces of rock (baseball to the size of a car) • Explosive Eruptions • Pyroclastic Flow – Occurs when an explosive eruption hurls out ash, cinders and bombs as well as gases. (400mph, 1,800˚F)