volcanoes. 7.2 volcanic eruptions types of lava mafic lava: rich in magnesium and iron – forms...
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Volcanoes
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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
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What determines the type of Volcanic Eruption?
Composition of lava (mafic or felsic ) determines the type of eruption.
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• Mafic Lava- hot and thin, flows similar to water– Creates quiet eruptions
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• 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
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Journal
• Which lava flows easily creating quiet volcanic eruptions?
• Which lava erupts violently?
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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
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Types of Volcanoes
• Shield• Cinder-Cone (or Dome)• Strato-volcanoes or composite volcanoes
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Shield Volcanoes
• Broad base and gentle sloping sides• Formed by mafic lava
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Cinder-Cone Volcanoes
• Steep slopes • Formed by felsic lava
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Strato-volcanoes (or composite volcanoes)
• Formed by both smooth lava flows and explosive pyroclastic eruptions
• Form high volcanic mountains
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1. Create a quick sketch of the following Volcanoes.2. Name each Volcano type.
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Craters and Calderas
• Crater: funnel shaped pit• Caldera: large depression that occurs when a
volcanic cone collapses
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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
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Journal:
What might an increase in earthquakes near a volcano indicate?
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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
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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 theother moons and Jupiter.
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The End