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PG. 89 Volcanic activity. Magma Temperature beneath the lithosphere causes rock to melt As pressure increases, the melting point of rock increases At.

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Presentation on theme: "PG. 89 Volcanic activity. Magma Temperature beneath the lithosphere causes rock to melt As pressure increases, the melting point of rock increases At."— Presentation transcript:

1 PG. 89 Volcanic activity

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

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  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  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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