The world’s largest active volcano, Mauna Loa, has erupted in Hawaii for the first time in nearly four decades. The U.S. Geological Survey (“USGS”) said Mauna Loa erupted at 11:30 p.m. local time Sunday (4:30 a.m. ET Monday). It was the first eruption since 1984.  The volcano, whose name means “Long Mountain,” covers half of the island; and prior to its most recent eruption, it erupted 33 times, beginning in 1843, making it among the world’s most active volcanoes. It is one of six volcanoes in the state of Hawaii, according to the agency.

The USGS said the eruption began in Moku‘āweoweo, the summit caldera of Mauna Loa, inside Hawaii Volcanoes National Park, who upgraded the volcano’s alert level from an “advisory” to a “warning.” The USGS said in a news release: “At this time, lava flows are contained within the summit area and are not threatening downslope communities. Winds may carry volcanic gas and possibly fine ash and Pele’s hair downwind.”  Residents at risk from Mauna Loa lava flows were advised to “review preparedness and refer to Hawai’i County Civil Defense information for further guidance … Based on past events, the early stages of a Mauna Loa eruption can be very dynamic and the location and advance of lava flows can change rapidly … However, if the eruptive vents migrate outside its walls, lava flows may move rapidly downslope.”

The eruption of Mauna Loa follows weeks of warnings from officials that an eruption was possible given a recent spike in earthquakes at the volcano’s summit and that residents of the Big Island should be prepared to evacuate. The USGS previously said that “heightened unrest” began in mid-September, when earthquakes beneath the summit increased from 10 to 20 per day to 40 to 50 per day. That unrest prompted Hawaii Volcanoes National Park to close the summit backcountry until further notice.

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