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 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

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

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

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

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

Types Shield Cinder cone Composite

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

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

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