Ch. 8 – Volcanic Activity – Flashcards
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Why are most active volcanoes associated with plate tectonic boundaries?
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Spreading of sinking plates interact at plate boundaries with other materials to produce magma
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Viscosity of a magma is controlled by...
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Temperature and silicon content of the magma
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The shape of shield volcanoes is a function of...
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Lava viscosity
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Why do composite volcanoes consist of alternating lava and pyroclastic layers?
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Composite cones are created by a mixture of explosive activity and lava flows
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Mid-ocean ridge volcanism produces what type of volcanic rock?
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Basalt
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Composite cones typically are associated with what type of plate tectonic feature?
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Subduction zone
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What is the principle difference between craters and calderas?
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Calderas are much larger depressions created by collapse of the upper portions of the volcano
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Why were the citizens of Heimaey, Iceland, successful in stopping the lava flow that threatened their harbor?
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They had a ready supply of water with which to to chill the lava
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The number of fatalities from the Mt. Pinatubo eruption was relatively low because...
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The eruption was predicted successfully, and the area was evacuated
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What is one reason that ash fall is such a significant hazard?
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The weight of the ash can cause structural damage to buildings
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A Lahar is produced when...
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Ash and other pyroclastic ejecta become saturated with water
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Hundreds of residents near a dormant volcano at lake Nyos died when...
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A dense cloud of volcanic gas was released
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Seismic activity serves as a tool of volcanic forecasting because...
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Moving magma causes earthquakes
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Why is the geologic history of a volcano important in hazard prediction?
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The geologic history reveals the frequency and style of eruptions
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Why is topographic monitoring sometimes useful in forecasting a volcanic eruption?
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A volcano sometimes swells as lava moves into the edifice
