Types of Volcanoes
Volcanoes at Divergent Boundaries:
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Plates pull apart
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Lithosphere becomes thinner
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Cracks form/rift zones
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Rock rises, decrease in pressure, rock melts and forms magma
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When magma comes to the surface, it is called lava
*Mid Ocean Ridges
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Volcanic mountain chains form when two tectonic plates are apart.
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Magma moves upward from the mantle
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They are under water
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Some magma erupts as basaltic lava on the floor
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As plates continue to move away from each-other, older oceanic
lithosphere moves away from the mid-ocean ridge
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New crack from, and new lithosphere forms in the rift zone
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This process is called sea floor spreading
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These are non-explosive eruptions/volcanoes continue to get bigger
Volcanoes at Hot Spots:
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Active
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Located over a mantle plume
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Mantle plumes are columns of hot, solid rock that rise through
*Shield

Usually forms at hot spots
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Forms from layers of lava left from many non explosive eruptions
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Layers of lava create volcanic mountains
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The side of a shield volcano are not very steep
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The volcanoes are very large
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The base of a large shield volcano can be more than a 100 km in
diameter
Volcanoes at Convergent Boundaries:
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Two plates push together with one subducting under the other.
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The lithosphere contains water which is released in to the mantle and
the overlying crust.
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This causes the temperature to drop and the rock melts
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The magma that forms comes to the surface of the crust and erupts
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volcanoes form at these plate boundaries forming a parallel chain
*Cinder Cone
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It’s the smallest type of volcano
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They have a wide summit
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They reach no more than 300 meters high
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Form from moderately explosive eruptions
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Made from pyroclastic material
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They erupt only once in their lifetime
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They are the most common type of volcanoes
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They have steep sides
*Composite
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They are the most recognizeable
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They may occur at intervals of 100’s of years or more
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They are also known as strato-volcanoes
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They form from pyroclastic material and quieter flows of lava
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Generate many explosives
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Sides get steeper towards the summit
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Have a broad base