The ring of fire is dotted with volcanoes, because the Pacific plate is surrounded with subduction zones and the Pacific plate is slowly sinking into the mantle, since it is a lot denser than its neighboring plates. The Marianas trench and the Philippine trench are parts of this subduction zone. Now as the crustal plate slowly sinks in subduction zone and into the mantle, pressure began to build up in the mantle and there are only one way to release all that pressure, through releasing some matter out of the mantle and out into the crust. The result is the birth of a volcano.
