Mount Ontake, a towering Japanese stratovolcano about 200 kilometers (125 miles) west of Tokyo, erupted unexpectedly on September 27, 2014. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua and Terra satellites captured these views of gas and steam rising from the volcano on September 27 (top) and September 28 (bottom). Early reports suggest this may have been a steam-driven phreatic eruption. Such eruptions can cause underground water to boil and flash to steam, generating explosions of steam, water, and ash with little warning. As many as 36 hikers are presumed dead, according to media reports.