Good Morning!
Well, first of all, when a oceanic plate hits another, an earthquake is usually about to pass. The problem though, is that after, the earthquake, a tsunami is expected and tsunamis are know to destroy cities and flood them with lots of water. Note, that also in this same manner, islands are sometimes formed, or even underwater volcanoes! Cool, right?
Well happy studying and tag me if you need something! :)
Thank you,
Darian D.