Colossal volcanic eruption could destroy Japan: study
It's certainly true a large enough volcanic explosion would destroy Japan. A large enough meteorite striking us would as well. A nuclear war between the US and China or Russia would do the trick, too. Or an airborne illness with no possibility of a cure and a 100% mortality rate. If Crayon Shin-chan lit a powerful enough fart, he could incinerate all of Honshu. One day the sun will consume the inner planets, including the earth.
It's best to be prepared, but in the event of a disaster of this magnitude, you should just kiss your ass goodbye. In other words, pointing out the obvious-- a vast disaster we have no control over and for which no amount of preparation can save us kills everyone dead, dead, dead-- doesn't really help anyone do anything. Makes for interesting news copy, though.