Notes

The third type of convergent boundary occurs when two oceanic plates collide. One of the oceanic plates pushes under the other oceanic plate, forming a deep ocean trench between the plates. The collision between two oceanic plates usually creates volcanoes, produced when rock in the lower plate melts and forms a large magma chamber. Over time, erupted lava can build on the ocean floor and form a chain of volcanic islands, called island arcs. The Aleutian Islands are an example of an island arc that formed from an ocean trench near Alaska.

The second type of convergent boundary occurs when a continental plate collides into an oceanic plate. During this type of interaction, the denser oceanic plate pushes under the lighter continental plate. Geologists call this a subduction zone—an area where an oceanic plate is subducted, or sinks, into the asthenosphere under a continental plate. As the oceanic plate sinks into the asthenosphere, the rock melts and forms a magma chamber, which can develop into active volcanoes.