1.) When two plates collide 2.) When ash (lava) keeps building up over time
Volcanoes may form where two oceanic plates collide or an oceanic plate collides with a continental plate
Volcanoes form near converging plate boundaries primarily through subduction of one plate beneath another, leading to melting and magma formation. This can occur when an oceanic plate subducts under a continental plate, creating land-based volcanoes, or when two oceanic plates converge to form island arcs. Examples include the Andes Mountains and the Japanese archipelago.
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