Trench

=Trench !These trenches are formed at a particular place of plate boundary which is known as subduction zone. It happens to form when a plate in ocean hits another ocean plate or it strikes with continental plate. Oceanic plates are made of basalt which is a denser rock while continental plates are formed up of granite which is not as dense as the basalt. Now when one plate hits another plate or continental plate in the ocean then the denser plate between the two of them sinks in the mantle. The place where this plate sinks will create a deep trench on that spot of ocean. They are associated with a chain which is known as island arc or the zones that experience frequent earthquakes. The trenches can be very long up to thousand of kilometers and they may be parallel to island arc volcanoes. =