Hawaii’s Mauna Loa volcano awoke from a nearly 40-year slumber on Sunday night during an eruption that shot lava hundreds of feet into the air and prompted a warning from officials for residents to begin reviewing emergency plans.

Scientists had been keeping an eye on Mauna Loa over the past few months when the world’s largest active volcano began showing signs of increased seismic activity, including a magnitude 5.0 earthquake that shook Hawaii’s big island in October.

“For the past couple of months, Mauna Loa has been in a state of elevated unrest,” said Wendy Stovall, a volcanologist with the USGS. “We were detecting an increased number of earthquakes as magma moved through the volcano and fractured the ground.”

Stovall also said Mauna Loa was swelling outward as the magma was moving.

“So, we were able to detect that with the instruments that we have on the surface of the volcano,” she said “And then about an hour before the eruption occurred, a very high rate of earthquakes started up that signaled that the magma was moving from a summit storage region up to the surface.”

And then, on Sunday around 11:30 p.m. local time, Mauna Loa erupted, ending the longest quiet period between eruptions on record.

The United States Geological Survey said the eruption began in Moku‘āweoweo, the summit caldera of Mauna Loa, but migrated from there to the Northeast Rift Zone by early Monday morning.

Scientists with the Hawaiian Volcano Observatory (HVO) reported fissures in higher elevations within Hawaii Volcanoes National Park were feeding lava flows upslope of the Mauna Loa Weather Observatory.

Lava flows were not threatening downslope communities, but officials warned volcanic gas, fine ash and “Pele’s Hair” could have been carried downwind.

Emergency officials asked residents at risk of lava flows from Mauna Loa to begin reviewing emergency plans and refer to Hawaii County’s civil defense for further guidance and other important information regarding Mauna Loa’s eruption.

“First and foremost, you just need to follow the directions by the emergency management personnel that are actively monitoring the situation to make sure that they keep everyone safe,” Jon Jelsema, senior forecaster for the National Weather Service in Honolulu, said on FOX Weather Monday morning.