On March 20, Iceland’s Eyjafjallajokull volcano woke from its nearly 200-year slumber to change the way the world viewed volcanoes forever. Bringing almost all transatlantic air travel to a halt for the first time in modern history, this volcano reminded humanity of the powers these forces of nature contain — and of our relative inability to understand them. Researchers have studied this event and other massive volcanic eruptions and their atmospheric consequences in the past in North America.