Caldera collapse: In a nutshell, multiple vents on the lower side of the volcano can partially empty the topmost magma chamber, leaving the walls of the volcano with nothing under them. When they collapse inward, it's kind of like squeezing a plastic water bottle, and the lava can shoot out explosively.
There are other things that can happen, namely, seawater getting into the chamber and creating an explosive situation that blows the side of the volcano out.
Lots of ways it could happen. Look at Mount St. Helens -- if all that earth had gone into a body of water, there would've been further problems.
That isn't to say it will happen, but there's certainly the possibility. I won't go to probability at this point because I don't think there's a high chance of it happening, so... possibility.