Volcano Types and Volcano Types and FormationFormation

Shield VolcanoShield Volcano

Typically occur at divergent Typically occur at divergent boundaries and hot spots.boundaries and hot spots.

Molten rock pushes its way up to the Molten rock pushes its way up to the surface as the plates spread.surface as the plates spread.

Oceanic crust passes over a hot spot Oceanic crust passes over a hot spot in the mantle.in the mantle.

Very large in scale.Very large in scale. Erupt in gentle lava flows ( mainly Erupt in gentle lava flows ( mainly

basaltic lava)basaltic lava)

Formation over a hot spot.Formation over a hot spot.

Haleakala, HI Haleakala, HI

Mauna Loa, HIMauna Loa, HI

Cinder ConeCinder Cone

Usually Small in scale.Usually Small in scale. Formed from cinders piling up on Formed from cinders piling up on

itself.itself. Typically felsic lava.Typically felsic lava.

Pyroclastic LayersPyroclastic Layers

PyroclastsPyroclasts

Rock fragments from a volcanic Rock fragments from a volcanic eruption.eruption.

Smallest = AshSmallest = Ash Medium = CinderMedium = Cinder Largest = BombsLargest = Bombs Which is the most deadly?Which is the most deadly?

Composite VolcanoesComposite Volcanoes

Contain granite lavas that are very viscous.Contain granite lavas that are very viscous. These lavas can trap gas and act as “plugs” These lavas can trap gas and act as “plugs”

in the vent of a volcano.in the vent of a volcano. Pressure builds up and can cause explosive Pressure builds up and can cause explosive

eruptions.eruptions. Formed from alternating layers of lava flows Formed from alternating layers of lava flows

and pyroclastic eruptions.and pyroclastic eruptions. Mixture of felsic and basaltic lava.Mixture of felsic and basaltic lava. Continent-Oceanic convergent boundariesContinent-Oceanic convergent boundaries

Dissected StratovolcanoDissected Stratovolcano

Mt. Hood, WashingtonMt. Hood, Washington

Mt. Egmont, New ZealandMt. Egmont, New Zealand

CalderasCalderas

Formed from the largest and most Formed from the largest and most explosive volcanic eruptions.explosive volcanic eruptions.

Extremely large volumes of magma Extremely large volumes of magma are removed from below the ground.are removed from below the ground.

The empty chamber then collapses.The empty chamber then collapses.

Crater Lake, Oregon Crater Lake, Oregon

YellowstonYellowstone National e National Park, WYPark, WY