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Volcanic activity

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Volcanic activity. Pg. 89. 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. Types of magma. - PowerPoint PPT Presentation
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PG. 89 Volcanic activity
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Page 1: Volcanic activity

PG. 89

Volcanic activity

Page 2: Volcanic activity

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

Page 3: Volcanic activity

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

Page 4: Volcanic activity

Mt. St. Helens

Page 5: Volcanic activity

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

Page 7: Volcanic activity

Intrusive activityWhen magma cools, it forms structures called

plutonsPlutons are based on size and shapeLargest plutons batholiths and stocks; form

beneath earths surface; coarse rockLaccoliths mushroom shaped plutonSills and dikes smallest pluton

Page 8: Volcanic activity

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

Page 9: Volcanic activity

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

Page 11: Volcanic activity

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

Page 12: Volcanic activity

Volcano occurrences

Convergent volcanism At a convergent boundary Usually form in the sea

Divergent volcanism Magma forced upward through faults Causes seafloor spreading

Page 13: Volcanic activity

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


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