Hawaii’s Mauna Loa volcano erupts for first time in 38 years

No evacuation orders were issued, but two shelters were opened as a precaution, Hawaii County officials said. And authorities advised that winds could carry volcanic gas and fine ash downwind.

While the eruption was initially limited to the volcano’s summit, USGS said in a 7:20 a.m. update that lava had also begun flowing out of the northeast side of the volcano, in what scientists refer to as its northeast rift zone.

Wendy Stovall, a USGS volcanologist, said that was good news for the Kona area on the west side of the island, where steep slopes mean it can take just a few hours for lava flows from Mauna Loa’s southeast rift zone to arrive, making it the most vulnerable part of the island during an eruption.

“When Mauna Loa erupts, it stays in one rift zone; it doesn’t typically move from one side to the other,” she said. “The eruption should stay in the northeast rift zone.”

The volcano’s slopes on its northeast side are gradual, meaning it could take weeks or months, and a large volume of lava flows, for any populated areas to face significant danger. Stovall said that lava flows could eventually reach a key road that cuts across the island, Saddle Road, as well as a road leading to an observatory on Mauna Loa’s north flank where measurements of atmospheric gases have been collected since the 1950s, including carbon dioxide and methane, known to cause climate change. The observatory itself is not at imminent risk, Stovall said.

Though there were no immediate signs of dangerous lava flows or earthquake risks, both are common consequences of past eruptions, said Falk Amelung, a professor at the University of Miami who has studied Mauna Loa.

“The worst-case scenario is not good,” Amelung said, urging residents to be prepared for earthquakes and evacuation.

Earthquakes are “not among the highest hazards we’re looking at right now,” said Wes Thelen, a USGS seismologist. Hawaii’s largest earthquake on record, in 1868, was associated with a Mauna Loa eruption, though, and links between volcanic eruptions and earthquakes are “pretty tight,” he added.

“There are cases of earthquakes triggering eruptions and potentially eruptions triggering earthquakes,” Thelen said. “But it isn’t a foregone conclusion that there’s going to be a large earthquake associated with this particular eruption.”

A surge in earthquake activity around Mauna Loa that began in late September provided a hint that the volcano was bound to erupt. Swarms of weak quakes increased in frequency from about 20 per day to 40 to 50 per day. On a couple of occasions there were as many as 100 per day, USGS said last month.

Earthquakes occur as magma rises to the surface, breaking a pathway through Earth’s crust, but are typically small to medium in magnitude, said Ed Venzke, senior data researcher with the Smithsonian Institution’s Global Volcanism Program. Such quakes are different — and far less severe or destructive — than those caused by plate movements along fault lines.

An ash fall advisory expired at 10 a.m. Hawaiian time on Monday, or 3 p.m. Eastern time, for the Big Island and across the Maui Channel to the southeastern shores of Maui. The National Weather Service in Honolulu, which is about 190 miles to the northwest of Mauna Loa, said as much as a quarter of an inch of ash could accumulate across the Big Island, potentially causing respiratory distress for some people, damaging engines and electronics, and harming crops and livestock.

The eruption prompted Southwest Airlines to cancel flights between Hilo and Honolulu, while Hawaiian Airlines flights were continuing.

Eruptions in 1984 and 1950 sent lava flows toward the towns of Hilo and South Kona, respectively, the National Park Service said. The flows can take anywhere from hours to weeks or months to reach communities, according to USGS maps.

“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,” the USGS said.

Mauna Loa, one of the Earth’s most active volcanoes, has erupted 33 times since 1843, according to the USGS.

Kilauea, the other active volcano on Hawaii’s Big Island, has been erupting since September 2021; before that, lava from a 2018 eruption destroyed more than 700 homes. Though Kilauea is more active than Mauna Loa, it typically poses a lesser hazard because it is smaller, and because its lava flows tend to be smaller and move more slowly, according to the Hawaii Center for Volcanology.

Mauna Loa, whose name means “long mountain,” is known as a shield volcano because it is significantly wider than it is tall. Mauna Loa makes up about 51 percent of the Big Island and rises 13,679 feet above sea level and about 30,000 feet from the sea floor, according to the National Park Service.

Images captured by USGS research cameras and Civil Air Patrol flights showed a red glow appearing over Mauna Loa overnight, and lava sweeping down the volcano’s northern slope by Monday morning.

The eruption could also be seen from space, with bursts of heat and sulfur dioxide captured by the National Oceanic and Atmospheric Administration’s GOES West satellite.