The Volcano.

[Sonic_the_Hedgehog]

All possibilities. Here's another one:
The volcano may not even erupt in it's current cone. If the volcano is hot-spot related (typical of Hawaii-style volcanos), the earth may have moved over the top of it. If so, the path of least resistance for the lava could be somewhere unsuspected like, say, Bearded Rock for example. Disaster!!!

Although having the existing formation go bang would be so much more dramatic and we must never underestimate the value of a well-designed cinematic...

I think the volcano may be hot-spot related considering there aren't any noticeable island arcs, so it's not made by convergence.