Chapter 15

Where do Volcanoes Occur Divergent Boundaries Convergent Boundaries Hoy Spots Subduction boundaries

Eruptions of Volcanoes Two factors that determine whether it is explosive or quiet. 1. Is the amount of water vapor and other gases that are trapped in the magma. 2. The other factor is the flavor of lava which means it is either basaltic or granitic.

Eruptions of Volcanoes Gases that escape from magma gives us quiet eruptions. Gases that stay with the magma and then comes out at same time gives us explosive eruptions (much like shaken pop)

Basaltic magma contains less silica is very fluid and produces quiet explosives eruptions. Granitic magma contains more silica is very thick and causes pressure to build up in vents. When it is released it carries magma and lava with it since it has pressure.

Forms of Volcanoes 3 forms of Volcanoes 1. Shield volcano- are made of basaltic lava which is usually a quiet volcano since it is made of many layers. Get very broad volcanoes with gently sloping sides. Examples would be in Hawaiian islands.

Forms of Volcanoes 2.Cinder cone volcanoes- usually comes from explosive volcanoes made up of tephra. This tephra measures in size from ash to bombs. This is steep sided very loose sides and hard to climb. Example would be Paricutin in Mexico.

Forms of Volcanoes 3. Composite volcano- made of balistic and granitic lava usually in alternating layers. Usually found at convergent zones and subduction zones. Example would be MT ST> Helens.

Volcanic features Intrusive features found in volcanoes- 1. Batholith- largest body 2. Dike- a vertical crack layer of rock 3. Sill- a horizontal crack layer of rock 4. Laccoliths- a dome of rock 5. Caldera