Question

What happens when oceanic plates collide?

Answer 1

The creation of volcanic chains, called island arcs.

Explanation:

Density is important here.

Oceanic plates are primarily basaltic in composition, meaning the rock that makes up the plate is mostly basalt (an extrusive igneous rock). Basalt is a fairly dense rock, but as it ages it gets colder, therefore it is more dense than the younger plates being formed at the mid-ocean rifts. This means the older plate subducts beneath the younger plate. The result is nearly identical to what happens when an oceanic plate converges with a continental plate. The only difference is that the uplifted arc occurs in the ocean, so it's termed an island arc.

Check out the Aleutian Peninsula of Alaska. It's very active.