As far as a VEI-7 level eruption, that's harder to know. According to the USGS, the likelihood of a VEI-7 eruption coming from Mount Tambora anytime soon is relatively small. An eruption of that ...

VEI-6s are colossal eruptions every 100 years. The 1883 explosion of Krakatoa was the most famous of these. VEI-7 eruptions occur every 1,000 years. The most recent was Indonesia's Mt. Tambora in ...