Ecuador's Tungurahua volcano (satellite map) puts on a spectacular show, as seen from the town of Juive Grande last Monday. The volcano has been erupting intermittently since 1999, but it only recently roared back into a very active phase.
Eruptions have been picking up steam since late November on the 16,479-foot-high (5,023-meter-high) volcano, which towers above the town of Baños—popular with tourists for its thermal baths and scenery. Some 25,000 residents live permanently in high-risk evacuation areas under the mountain's steep flanks.
During the past few days, Tungurahua has been unleashing booming explosions, hurling columns of ash some 9,800 to 16,000 feet (3 to 5 kilometers) above its peak, and issuing flows of lava. (Also see more pictures of seven other volcanoes erupting right now.)
Tungurahua "certainly ranks as one of the volcanoes that keeps people up at night," said Smithsonian Institution volcanologist Richard Wunderman, managing editor of the Bulletin of the Global Volcanism Network. "It's scary."
(Related: "'Sleeping' Volcanoes Can Wake Up Faster Than Thought.")