The 1977 eruption of maar volcano Ukinrek in Alaska. Image by Juergen Kienle Volcanic eruptions produce some stunning scenes, the eruption of the Calbuco volcano in Chile being one recent example. Calbuco fits the stereotypical image of a volcano: a large, angry mountain rising up into the sky, the same kind of volcano as Mount St. Helens or Mount Fuji. But some of the world’s most powerful volcanoes – and the second most common – are hidden from sight and can unexpectedly detonate with the force of a nuclear bomb. Maar volcanoes are strange: they are often invisible for much of their life, before suddenly appearing in enormous explosions. They give no warning of their impending destruction. When they do erupt in a cataclysm of fire and noise, they do not rise above the ground, but instead leave a hole similar to large meteorite impact craters. The 1886 eruption of Rotomahana on the north island of New Zealand was one such eruption. With the only warning coming from a small, insignificant earthquake in the region beforehand, a maar volcano-forming eruption suddenly occurred overnight. The resulting heat blasts and descending hot ash and lava bombs killed at least 150 people.