Oceanic plates create ocean trenches once they collide into each other. These plates are settled beneath the oceans and they are responsible for holding these massive amounts of water into place. Plates are constantly moving at a slow rate of a few inches per year and when they shift they can either collide (converge), separate (diverge) or slide across each other (transform-boundaries). Oceanic plates are not only responsible for developing ocean trenches they are also responsible for creating land masses, volcanoes and earthquakes.
When two plates collide, the leading edge of the heavier plate will bend downward and melt beneath the lighter plate and this is called subduction. Continental and oceanic plates typically converge to form trenches and colliding oceanic plates are also responsible for manufacturing trenches. When oceanic plates move they will always affect other plates. Oceanic plates produce a great deal of force which constantly alters the world's ocean floors.
Many ocean trenches are found along the edges of continents and oceanic plates carry some of this continental land mass. When these oceanic plates collide into another plate the land mass doesn't sink but it fills up a trench until it no longer can move. Once this occurs the leading edge of the continental land mass will begin to crumple and start to form mountains which is opposite of underwater trenches. This process is called trench flipping and some mountain chains are created from this process along the edges of continental plates and they extend into the ocean.
Oceanic plates form trenches near active volcanic chains and they are called volcanic island arcs which are land masses that resemble islands. Oceanic trenches have been known to extend for thousands of miles parallel to volcanic island arcs. Trenches and active subduction zones are found around the Ring of Fire which is a zone of volcanism and earthquake activity that lies within the Pacific Ocean. Subduction is responsible for most of the volcanic activity that takes place around the world. This process is also responsible for causing earthquakes that take place near the edges of continental and oceanic plates.
