This 24-hour timelapse from the U.S. Geological Survey Hawaiian Volcano Observatory shows the start of the eruption of Mauna Loa, the world's largest active volcano. Officials say volcanic ash and debris is falling nearby. The eruption began late Sunday night in the summit caldera of the volcano on the Big Island. Early Monday, the USGS said lava flows were contained within the summit area and weren't threatening nearby communities. The agency warned residents at risk from Mauna Loa lava flows should review their eruption preparations. Scientists had been on alert because of a recent spike in earthquakes at the summit of the volcano, which last erupted in 1984.