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Mount Merapi EruptsSmoke rises Monday from Indonesia's Mount Merapi, one of the world's most volatile and dangerous volcanoes. Thousands of people living on the volcano's fertile slopes began evacuating as Merapi started erupting Tuesday, sending hot ash and rocks high in the air. (See an Indonesia map.)Scientists had been warning for days that pressure building in the rumbling volcano has the potential to set off an especially violent eruption. (See related pictures of the ten most dangerous U.S. volcanoes.)"The energy is building up. ... We hope it will release slowly," Indonesian-government volcanologist Surono told reporters, according to the Associated Press. "Otherwise we're looking at a potentially huge eruption, bigger than anything we've seen in years."Meanwhile, officials in western Indonesia are racing to deal with the aftermath of a deadly tsunami that struck the remote Mentawai Islands late Monday, killing at least 113 and leaving hundreds more missing. The killer wave, triggered by a magnitude 7.7 earthquake centered offshore of the island of Sumatra, had many recalling the December 2004 Indian Ocean tsunami, which devastated the same region.While it's unclear whether Monday's earthquake and the Merapi volcano eruption are linked, neither event is uncommon in Indonesia. The archipelago sits along the Pacific Ring of Fire, a series of fault lines that stretches from the Pacific coasts of the Americas through Japan and into Southeast Asia. (See "Deadly Java Quake Highlights "Ring of Fire" Dangers.")

Photograph by Dwi Obli, Reuters