Mauna Loa Volcano in Hawaii Erupts for the First Time in Nearly 40 Years

Mauna Loa, located on the Big Island of Hawaii, erupted for the first time in 38 years late Sunday night, following a series of striking eruptions in recent years of the smaller and nearby Kilauea volcano.

“I have been waiting for Mauna Loa, Earth’s largest active volcano, to erupt since I first learned of it in college,” said Kenneth Rubin, a volcanologist at the University of Hawaii at Manoa. “And despite thirty-plus years of living in Hawaii and witnessing many spectacular things from Kilauea, I am watching this eruption closely and hoping for no substantial impacts on Hawaii’s communities.”

At 11:30 p.m. local time, an eruption began at Mauna Loa’s summit, inside Hawaii Volcanoes National Park, according to the U.S. Geological Survey. Lava flowing from the volcano was confined to the summit area, moving in the early hours of the morning to a rift zone on the northeast side.

Although there are few current safety risks to nearby communities, which are mainly placed downhill on the southwest side of the volcano, the location and direction of lava flow can shift rapidly, and residents who are at risk were advised to review their preparedness plans.

“Mauna Loa eruptions in particular tend to be very dynamic in their earliest days,” Dr. Rubin said. “Conditions on the ground can change fairly quickly.”

Other threats to the public could include winds that carry volcanic gas, fine ash and thin glass fibers known as Pele’s hair.

Earlier on Monday, the Hawaii County Civil Defense Agency raised the volcano alert level from an advisory to a warning. Mitch Roth, the mayor of Hawaii County, said in a statement on Facebook that there were no evacuation orders or threats to the community. Two shelters were opened along the South Kona coast for people who voluntarily left their homes, officials said.

While officials say that there are no risks for air travelers, Southwest Airlines canceled flights to Hilo International Airport and the Hawaii Department of Transportation issued a travel advisory.

Mauna Loa covers an area of more than 2,000 square miles, mostly under water, and stretches about 10 miles from base to summit. It is covered with scientific instruments that measure seismicity, gas and thermal activity, and the eruption offers an important opportunity to gather data to help predict future eruptions.

“We knew that the volcano was pressurizing, we knew that magma was moving into the system, and we’re seeing that play out now,” said Wendy Stovall, a volcanologist with the U.S. Geological Survey. She added that safety for people nearby had to be prioritized over scientific excitement around the eruption for the moment. But, “right now, there’s not a huge concern,” she said.

Jim Kauahikaua, a volcanologist with the U.S.G.S. Hawaiian Volcano Observatory, added that experts are conducting aerial surveys of the eruption to assess any hazards and “installing additional monitoring equipment to better document the activity.”

Earlier research suggests that volcanic activity at Mauna Loa can probably be attributed to a plume of molten rock and minerals from Earth’s mantle that flows up through the crust, creating a volcanic “hot spot” under moving tectonic plates.

A period of heightened seismic unrest for Mauna Loa began in mid-September when the number of earthquakes below its summit increased from 10 to 20 per day to between 40 and 50 per day. Those were early signals of a potential eruption. In mid-October, scientists recorded a 5.0-magnitude earthquake on Mauna Loa’s southeastern flank, setting off near-daily updates on the volcano’s status.

The day before the eruption, low magnitude earthquakes were detected about every hour near the volcano. Despite this vigilant data gathering, Dr. Stovall said that experts only noticed the eruption had started an hour before magma reached the volcano’s surface. “We knew we didn’t have much time,” she said.

Mauna Loa has erupted 33 times since its activity began to be recorded in 1843, but a majority of these eruptions occurred before 1950. In the following years, there have been only two outbursts — a summit eruption in 1975, and an eruption in 1984 when lava flow approached the city of Hilo. This last eruption caused volcanic air pollution across the state and prompted the authorities to close Highway 200 as lava flow destroyed utility poles and power lines.

Dr. Kauahikaua noted that there seems to be some relationship between activity at Mauna Loa and Kilauea, which share the same magma source.

Kilauea erupted almost continuously from 1983 until 2018. That year, a monthslong eruption produced 320,000 Olympic-sized swimming pools’ worth of lava that transformed the surrounding landscape and destroyed around 700 homes.

“When Mauna Loa is frequently active, Kilauea tends to be less active, and vice versa,” he said, adding that this relationship is somewhat speculative given the limited scope of recorded data.

“Mauna Loa is a really old volcano, it’s hundreds of thousands of years old, and we’ve only been tracking its activity for a few hundred years,” Dr. Stovall said.

Dr. Kauahikaua also said that observers are watching Mauna Loa for unexpected risks.

“Right now, we have to know where lava is erupting and how fast the lava flows are advancing,” he said. “But there is also the possibility that new vents will open up and erupt new flows.”

And while eruptions pose risks, the size of both Mauna Loa and the power of its eruptions, “are all scientifically intriguing attributes for volcanologists,” Dr. Rubin said.