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Volcanic activity Pg. 89.

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Presentation on theme: "Volcanic activity Pg. 89."— Presentation transcript:

1 Volcanic activity Pg. 89

2 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

3 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- basaltic Mt. St. Helens in Washington are andesitic Dormant volcanoes in Yellowstone are rhyolitic

4 Mt. St. Helens

5 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

6 Basaltic volcano Andesitic volcano Rhyolitic volcano
Andesitic volcano Rhyolitic volcano

7 Intrusive activity When magma cools, it forms structures called plutons Plutons are based on size and shape Largest plutons batholiths and stocks; form beneath earths surface; coarse rock Laccoliths mushroom shaped pluton Sills and dikes smallest pluton

8 Anatomy of a volcano Magma erupts in an opening called a vent
Around the vent is a crater Calderas can form when a volcano collapses into the magma chamber

9 Types of volcanoes Shield volcano Cinder cone volcanoes
Mountain w/ broad gently sloping sides that forms when basaltic rock is layered Cinder 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

10 Types Shield Cinder cone Composite

11 Volcanic Material Tephra- rock fragments thrown into the air
Can be dust, ash, lapilli, volcanic blocks, or volcanic bombs Rapidly moving volcanic material is called pryoclastic flow

12 Volcano occurrences Convergent volcanism Divergent volcanism
At a convergent boundary Usually form in the sea Divergent volcanism Magma forced upward through faults Causes seafloor spreading

13 Pg. 90 Create a foldable of the 3 different types of volcanoes. Include a diagram of each on your foldable ( look on pgs for diagrams) Include the types of magma and how explosive it is

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