Fifteen hundred years ago, Ilopango, a caldera volcano in what is now El Salvador, erupted in one of the largest events of its kind in recorded history. Known as the Tierra Blanca Joven eruption, it shot 10.5 cubic miles’ worth of tephra—pumice and ash—into the air, more than 100 times the amount produced by the Mount St. Helens eruption of 1980. The solids that resettled blanketed the valley below; those that didn’t are thought to have contributed to a cooler climate throughout the Northern Hemisphere.

The eruption has long been credited with hastening the end of the ancient Maya civilization that flourished throughout Mexico and Central America. But a new study in the