2 Magma Temperature beneath the lithosphere causes rock to melt As pressure increases, the melting point of rock increasesAt any pressure, a wet rock will melt at a lower temp
3 Types of magmaMagma formed from the 3 major types of igneous rock- basalt, andesite, and graniteMajor types of magma: basaltic, andesitic, and rhyoliticHawaiian volcanoes- basalticMt. St. Helens in Washington are andesiticDormant volcanoes in Yellowstone are rhyolitic
5 Magma compositionThe viscosity of magma is based on silica content more silica, higher viscosityBasaltic magmaVolcanoes erupt quietlyAbout 50% silicaMade from rocks in the upper mantleOceanic and continental crustAndesitic magmafound along subduction zonesMade from oceanic crust and sediments60% silica, eruptions are in the medium rangeRhyolitic magmaComes from water rich continental crustVery explosive70% silica content
7 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
8 Anatomy of a volcano Magma erupts in an opening called a vent Around the vent is a craterCalderas 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 layeredCinder cone volcanoesForms when material is ejected high in to the air and piles up around a ventHas steep sidesMore explosiveComposite volcanoesMuch larger than cinder coneDangerous to humansLava alternates with volcanic fragments
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