Types of Volcanoes

Shield Volcano

Locations: form in the ocean (oceanic crust).
Process: hot spots under ocean crust melts oceanic crust
Structure: countless layers of lava erupted from main vent, often with a crater on top (some side vents); broad, huge volcanoes with very gentle slopes.
Eruptive violence: low.
Magma: low SiO₂ and H₂O magma of oceanic crust.
Lava type(s): basalt
Materials ejected: free flowing lava
Examples: Hawaii, Galapagos Islands.

Locations: forms on continents (rift valleys).
Process: continental crust opens up to form a new spreading center (eventually a new ocean)
Structure: layers of individual volcanic rocks (cinders, tephra) build up as blobs of lava are expelled from the one central vent; steep sides; usually very symmetrical; small volcanoes.
Eruptive violence: low to moderate.
Magma: high SiO₂ and H₂O magma from mantle.
Lava type(s): usually basalt, sometimes andesite.
Materials ejected: blobs of lava
Examples: Sunset Crater, AZ

Locations: form on the edges of continents or as a chain of islands in ocean.
Process: at a subduction zone, oceanic crust melts and combines with melting continental crust.
Structure: alternating layers of lava, ash and volcanic debris; normally one central vent; moderately steep sides; mid-sized volcanoes.
Eruptive violence: moderate to high.
Magma: medium to high SiO₂ and H₂O magma.
Lava type(s): mostly andesite with some rhyolite.
Materials ejected: lava, ash, cinders and other volcanic debris.
Examples: Mt. Baker, Mt. St. Helens, Mt. Fuji

Locations: form on the continents.
Process: hot spots under continents melt continental crust.
Structure: huge volcano that does not look like typical volcano, maybe very flat, gigantic crater forms when the top of the volcano collapses into the huge magma chamber.
Eruptive violence: explosive eruptions.
Magma: high SiO₂ and H₂O magma.
Lava type(s): rhyolite
Materials ejected: ash and cinders
Examples: Long Valley Caldera, CA; Yellowstone

The bar in the diagrams represents 1 mile. Images courtesy of USGS