The volcanic island chains associated with the trenches follow the trenche's curvature and are called island arcs. When two oceanic plates collide, one of the plates dips beneath the other to form the trench. Again the trench is associated with earthquakes and volcanoes. The volcanoes may rise from the sea floor to create chains of volcanic islands.

The examples of island arcs include the Aleutian and Mariana islands. The Himalayas, for example, were formed when India collided with the rest of Asia. Two continental blocks push against each other with such tremendous force that the two continents become"welded" together.