Volcanic activity

PG. 89

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

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

Mt. St. Helens

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

Basaltic volcano http://www.youtube.com/watch?v=5hE2DZdl0IA

Andesitic volcano

Rhyolitic volcano

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

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

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

Types

Shield

Cinder cone

Composite

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

Volcano occurrences

Convergent volcanism At a convergent boundary Usually form in the sea

Divergent volcanism Magma forced upward through faults Causes seafloor spreading

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