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Volcanoes

Volcanoes. Types of eruptions. Viscosity affects how the volcano will erupt, determined by magma’s composition Mafic -runny lava, low viscosity, quiet Felsic - sticky lava, high viscosity, violent Trapped gases likely to cause explosive eruptions. Quiet eruptions.

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Volcanoes

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  1. Volcanoes

  2. Types of eruptions • Viscosity affects how the volcano will erupt, determined by magma’s composition • Mafic-runny lava, low viscosity, quiet • Felsic- sticky lava, high viscosity, violent • Trapped gases likely to cause explosive eruptions

  3. Quiet eruptions • A. Oceanic form from mafic magma • B. Low viscosity- gases easily escape • C. Example Hawaii

  4. Lava flows • Pahoehoe- least viscous, wrinkly, ropy texture, cools on surface • Aa- more viscous, forms sharp rock when it cools, same composition • Different in texture because of gas content, rate, & slope of a volcano • Blocky lava- most viscous, forms chunky rock when cools, high silica content, solidify on top & liquid beneath

  5. Explosive Eruptions • Occur on continents, felsic lava, Mt. St. Helen • Lava tends to be cooler and stickier • Contain trapped gasses, water vapor, CO2 • Gases send rock into air • Pyroclastic material- fragments of rock that from during volcanic eruption

  6. Types of Pyroclastic Material • Volcanic ash- less than 2mm • Volcanic dust-less than .25mm • Lapilli- little stones- near vent • Volcanic bombs- red hot, spindle shaped • Volcanic blocks- blasted rock, can be size of house

  7. Types of volcanoes • Shield- broad cones, gentle slope quiet eruptions- Hawaii • Cinder- steep slope, explosive, pyroclastic material • Composite- stratovolcanoes, alternating layers of lava and pyroclastic layers, both quiet & violent- Mt. St. Helens • Crater- funnel- shaped pit

  8. Calderas • Circular depression formed by ground sinking & magma chamber empties • From when large amounts of magma is expelled.

  9. Predicting Volcanic Eruptions • Earthquake activity • Small earthquakes • Temperature changes, fracturing rock • Increase in strength & frequency a signal

  10. Patterns in activity • Movement in rock to bulge surface • Knowledge of previous eruptions • Difficult to see patterns because of dormant volcanoes

  11. Two Types of magma • Mafic- rich in Mg, Fe, dark in color, oceanic • Felsic- rich in silica, light in color, continental

  12. Explosive eruptions

  13. Quiet eruptions

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