During an oceanic plate convergence, the plate will sink. 2. The West Coast of the United States has features formed by 3. During the of two tectonic plates, magma fills the space between the plates. 4. The only volcanic activity that's not formed at tectonic plate boundaries is Respond to the following based on your reading. 5. Why does underwater hot-spot volcanism tend to form chains of islands? For that matter why doesn't it form one huge, single island?