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An opening in the crust out of which magma, ash, and gases erupt. The shape of the volcano depends very much on the type of lava. Cone volcanoes are associated with thick lava and much ash. Shield volcanoes are formed when less thick lava wells up and spreads over a large area, creating a wide, gently sloping landform. Most volcanoes are located at destructive or constructive plate margins.

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