Earth safe from supervolcanoes, for now
The term's used to describe explosive volcanic eruptions that eject about ten thousand times the quantity of magma and ash as Mount St Helens, one of the most explosive eruptions in recent years.
There's evidence that there have been many in the past. Layers of ash are to be found across large portions of many continents, and craters as big as 60 miles across are to be found in Indonesia, New Zealand, the United States and Chile.
But, says NASA, there's one thing that all experts agree on: supereruptions are very, very rare. The most recent one occurred in New Zealand about 26,000 years ago, and the next most recent, Mount Toba, some 50,000 years earlier.
In all, geologists have identified the remnant of about 50 supereruptions. While there may have been quite a few more, it appears that they happen at a rate of around 1.4 per every million years.
They do appear to occur in clusters, but the clusters aren't regular enough to serve as the basis for predictions of future eruptions.
"Scientists have no way of predicting with perfect accuracy whether a supervolcano will occur in a given century, decade, or year – and that includes 2012," says NASA.
"But they do keep close tabs on volcanically active areas around the world, and so far there's absolutely no sign of a supereruption looming anytime soon."