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Volcanic Activity Earth Science Ch. 18
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Factors affecting magma formation ► Pressure ► Temperature ► Water-causes rock to melt at a lower temp ► YouTube - Volcano Eruptions YouTube - Volcano Eruptions YouTube - Volcano Eruptions
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Map of volcanoes Fig. 18-2
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Viscosity-resistance to flow ► Honey has a high viscosity ► Water has a low viscosity
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► The hotter the magma, the lower the viscosity ► YouTube - Ol Doinyo Lengai Volcano YouTube - Ol Doinyo Lengai Volcano YouTube - Ol Doinyo Lengai Volcano
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► Magma=below surface ► Lava=above surface ► Vent-what lava erupts through ► Crater-depression around the vent ► Caldera-collapsed volcano
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Caldera (in AK)
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Crater Lake, OR (caldera)
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Types of Volcanoes ► 1. Shield Volcanoes -broad slope -largest type of volcano -usually nonexplosive eruptions Ex. Hawaiian Islands ► Fig. 18-12
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Hawaii
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Cinder-cone volcanoes ► Smallest type of volcano ► Less than 500m ► More viscous magma, lots of gases, so it makes it very explosive
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Cinder cone antomy
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Composite volcanoes ► Layers of ash/volcanic fragments and lava ► Violent eruptions ► Ex. Mt St. Helens and Mt. Rainier in USA
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layers
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► Cinder cones=smallest; steepest slopes ► Shield=largest ► volcanic eruption - Google Video volcanic eruption - Google Video volcanic eruption - Google Video ► HowStuffWorks Videos "Mt. Saint Helens' Powerful Erruption" HowStuffWorks Videos "Mt. Saint Helens' Powerful Erruption" HowStuffWorks Videos "Mt. Saint Helens' Powerful Erruption"
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Mt. St. Helens
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Tephra ► Fragments thrown in air from eruption ► Pyroclastic flows- clouds of ash, gas, and tephra down slope up to 150 mph. Temp can exceed 700 C.
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Distribution of volcanoes is not random ► Found along plate boundaries (Ring of Fire), mid-ocean ridges ► Fig. 18-16 ► Some found at hot spots, where plumes of mantle (magma) rise up-ex. Hawaii ► Fig. 18-17
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