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Download 7.3 Volcanoes continued
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Volcanoes 7.2 Volcanic Eruptions Types of Lava • Mafic Lava: rich in magnesium and iron – Forms much of the oceanic crust • Felsic Lava: rich in silica (less magnesium and iron) – Forms much of the continental crust What determines the type of Volcanic Eruption? Composition of lava (mafic or felsic ) determines the type of eruption. • Mafic Lava- hot and thin, flows similar to water – Creates quiet eruptions • Felsic Lava- thick, viscous and cooler. Contain large amounts of trapped gasses. These gasses boil out explosively. – Creates explosive eruptions – Pyroclastic Material: rock fragments ejected into the air Journal • Which lava flows easily creating quiet volcanic eruptions? • Which lava erupts violently? Pyroclastic Material Classified based on size: • Lapilli- less than 64 mm in diameter • Volcanic ash – less than 2 mm in diameter • Volcanic dust – less than 0.25mm in diameter Types of Volcanoes • Shield • Cinder-Cone (or Dome) • Strato-volcanoes or composite volcanoes Shield Volcanoes • Broad base and gentle sloping sides • Formed by mafic lava Cinder-Cone Volcanoes • Steep slopes • Formed by felsic lava Strato-volcanoes (or composite volcanoes) • Formed by both smooth lava flows and explosive pyroclastic eruptions • Form high volcanic mountains 1. Create a quick sketch of the following Volcanoes. 2. Name each Volcano type. Craters and Calderas • Crater: funnel shaped pit • Caldera: large depression that occurs when a volcanic cone collapses Predicting Volcanic Eruptions • seismographs monitor small earthquakes – number of earthquakes increases prior to volcanic eruptions • slight bulging of the surface of the volcano • composition of gasses given off by the volcano Journal: What might an increase in earthquakes near a volcano indicate? 7.3 Volcanoes not on Earth!!! The moon: Basaltic lava flow on the near side of the moon • No tectonics or convection currents….. so how could the volcanoes have formed…. • May have been caused by intense heat due to meteorite collisions Mars: Seismically active and Crust is not shifting, produces very large volcanoes • These volcanoes may still be active. Io: moon of Jupiter, has active volcanoes. The lava is sulfur based. • The cause of its warm core is the friction as its surface is pulled back and forth due to gravitational pull from the other moons and Jupiter. The End