Hawaii’s Mauna Loa, the largest active volcano in the world, has erupted for the first time in nearly 40 years, US authorities said, as emergency crews went on alert early Monday. Flows of lava remained “contained” within the summit caldera of Mauna Loa, but the eruption could pose a threat to nearby residents should conditions change, the United States Geological Survey (USGS) reported at 11:45 pm local time Sunday (9:45 GMT Monday) some 15 minutes after the eruption inside Hawaii Volcanoes National Park. “At this time, lava flows are contained within the summit area and are not threatening downslope communities,” the USGS said on its website, noting that residents of the area should review preparedness procedures. While the eruption on the main island of the remote US state in the Pacific remains confined within the basin at the top of the volcano, called the caldera, “if the eruptive vents migrate outside its walls, lava flows may move rapidly downslope,” according to the USGS.