What happens when two oceanic plates collide?

Answer 1

When two oceanic plates collide, the denser oceanic plate will subduct beneath the other, forming island arcs. One example would be the Solomon Islands.

*Note that the Hawaii island chain is NOT formed by convergent plate boundaries but a hotspot which is located right under Hawaii, or the Pacific plate. The Pacific plate moves and the volcanoes on it becomes extinct when it is cut off from the magma source, and the magma from the hotspot rises, forming a new volcano and island.

when plates collide they also form fold mountains and cause earthquakes

Answer 2

An oceanic trench is created where the more dense plate subducts under the less dense plate. Submarine volcanism, seamounts, and island arcs can result from the subduction and partial melting of the crust.

Answer 3

It depends how they collide. You either get a mid-ocean subduction zone - where one plate 'slides' over the other - forcing one plate down under the Earth's surface... or - you get a mid-ocean ridge - where both plates simply push against each other - creating an underwater mountainous chain.