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Chp 18.3 Notes TYPES OF VOLCANOES &
WHERE THEY OCCUR
Main Idea 1: Not all volcanoes are built the same. A volcano’s shape is determined largely by:
1. magma’s viscosity 2. force of any eruptions 3. amount of weathering
Composite Volcano
Describe: Large, symmetric volcano with sharp peaks,& violent eruptions.
Magma: Very viscous
Eruption: Can be slow seeping or violent explosions.
Shield Volcano
Describe: have gradual slopes& peaceful eruptions
Magma: Not very viscous
Eruption: Travels a long distance.
Lava Dome
Describe: volcano that forms from very viscous magma atthe peak of another volcano. Lava domes can act like a cork and can eventually result in explosive pyroclasticflows.
Magma type:Very viscous (thick& resistant to Flow)
Mount St. Helens
Main Idea 2: Volcanoes occur in specific regions of Earth.
Subduction Zone Volcano:
Describe: where oceanic crust isPushing under continental crust.
Magma/Eruption: Very viscous& can lead to violent eruptions.
Examples: Ring of Fire aroundPacific Rim where magma comes rising from mantle.Mt. Pinatubo, AK Aleutian Chain are examples
Rift-Zone Volcano:Where 2 plates are diverging, spreadingapart, at an ocean ridgeor in the middle of a continent.
example: African RiftValley.