pg. 89 volcanic activity. magma temperature beneath the lithosphere causes rock to melt as pressure...
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PG. 89
Volcanic activity
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Magma
Temperature beneath the lithosphere causes rock to melt
As pressure increases, the melting point of rock increases
At any pressure, a wet rock will melt at a lower temp
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Types of magma
Magma formed from the 3 major types of igneous rock- basalt, andesite, and granite
Major types of magma: basaltic, andesitic, and rhyolitic
Hawaiian volcanoes- basalticMt. St. Helens in Washington are andesiticDormant volcanoes in Yellowstone are
rhyolitic
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Mt. St. Helens
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Magma composition
The viscosity of magma is based on silica content more silica, higher viscosity
Basaltic magma Volcanoes erupt quietly About 50% silica Made from rocks in the upper mantle Oceanic and continental crust
Andesitic magma found along subduction zones Made from oceanic crust and sediments 60% silica, eruptions are in the medium range
Rhyolitic magma Comes from water rich continental crust Very explosive 70% silica content
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Basaltic volcano http://www.youtube.com/watch?v=5hE2DZdl0IA
Andesitic volcano
Rhyolitic volcano
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Intrusive activity
When magma cools, it forms structures called plutons
Plutons are based on size and shapeLargest plutons batholiths and stocks; form
beneath earths surface; coarse rockLaccoliths mushroom shaped plutonSills and dikes smallest pluton
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Anatomy of a volcano
Magma erupts in an opening called a ventAround the vent is a craterCalderas can form when a volcano collapses
into the magma chamber
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Types of volcanoes
Shield volcano Mountain w/ broad gently sloping sides that forms when
basaltic rock is layeredCinder cone volcanoes
Forms when material is ejected high in to the air and piles up around a vent
Has steep sides More explosive
Composite volcanoes Much larger than cinder cone Dangerous to humans Lava alternates with volcanic fragments
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Types
Shield
Cinder cone
Composite
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Volcanic Material
Tephra- rock fragments thrown into the airCan be dust, ash, lapilli, volcanic blocks, or
volcanic bombsRapidly moving volcanic material is called
pryoclastic flow
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Volcano occurrences
Convergent volcanism At a convergent boundary Usually form in the sea
Divergent volcanism Magma forced upward through faults Causes seafloor spreading
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Pg. 90
Create a foldable of the 3 different types of volcanoes. Include a diagram of each on your foldable ( look on pgs. 482-483 for diagrams)
Include the types of magma and how explosive it is