The Big Picture has a great series of photos of a recent eruption from an undersea volcano near Tonga, located a few hundred kilometers southeast of Fiji.
This afternoon an earthquake in the region triggered a brief tsunami warning that blew over. It may very well be that a small tremor a few days ago is what triggered this eruption, too.
In case you ever wonder just how much energy is involved even in a small blast, consider this: the plume of ash and rock goes up several hundred meters. OK, go outside and find a rock that masses about 10 kilos. Now climb a flight of steps with it and see how tired you get. Now imagine climbing 100 flights of stairs with it.
Now imagine doing that with, say, a million of those rocks. That's how much energy it takes to blast the plume into the sky.
Never misunderestimate planet Earth. There's a lot of energy just sitting there under our feet, and sometimes it struggles free.