Mauna Loa—the World's Biggest Active Volcano—Erupts After 38 Years of Quiet

Mauna Loa, one of the world's biggest and most active volcanoes, has begun erupting after months of unrest.

The volcano, which is one of the five that make up Hawaii, rises 13,000 feet above sea level, and has been rumbling to life since September.

The eruption began at approximately 11:30 p.m. on November 27, an update from the U.S. Geological Survey (USGS) reported. The body has warned that winds may carry volcanic gas.

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At this time, the eruption is contained to the volcano's caldera summit and is not threatening any downslope communities.

Rebecca Williams, volcanologist and Earth scientist at the University of Hull in the U.K., told Newsweek: "Mauna Loa has been in a state of heightened unrest since mid-September. There had been an increase in earthquakes recorded, and an increase in inflation (ground swelling). This indicated movement of magma beneath the surface, but quite deep. There wasn't any change in the gases being released, or significant tilting of the ground that suggested the magma was making it's way to the surface.

"This unrest meant that the volcano was being very closely watched. But, an eruption was not certain. Sometimes these periods of unrest settle down and nothing happens. Sometimes, as in this case, an eruption happens!"

The Hawaii Volcano Observatory is working with emergency management partners to monitor the nature of the eruption, the USGS said.

Mauna Loa volcano last erupted between March 25 and April 15, 1984, following nearly two years of increased seismic activity. Nobody was hurt in this eruption, but lava flow blocked roads and caused damage to power lines.

"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," an update from the USGS said. "If the eruption remains in Moku'āweoweo, lava flows will most likely be confined within the caldera walls. However, if the eruptive vents migrate outside its walls, lava flows may move rapidly downslope."

It is not yet certain how this eruption will progress.

Mauna Loa eruptions are not as dangerous when compared to other Hawaii volcanoes such as Kilauea, as they do not tend to be as explosive. But Rajeev Nair, Earth science professor at the University of Calgary, previously told Newsweek that its eruptions do have the potential to "cut off communities."

"The flanks of the volcano are steeper and the volume of eruptions historically from Mauna Loa eruptions are larger. This can pose risks to neighboring communities if the eruptions occur along the rift zones," Nair said. "Even if not directly affecting communities, a significant Mauna Loa eruption has the potential to cut off communities. But if the eruption occurs in the summit crater, it could likely be contained within the caldera without significantly impacting communities."

Residents living near to the volcano previously told Newsweek that they were concerned about Mauna Loa's heightened unrest.

Many attended meetings held by the USGS in preparation for an eruption.

Laura Roberts, a resident of Ocean View, a community that lies in the Kaʻū district, towards the volcano's Northeast Rift Zone, told Newsweek that an eruption could result in lava reaching homes in only hours.

"We are on the rift zone so fissures could open [here]. It's a weird feeling to know that there is a possibility of losing your home," Roberts said.

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Updated 11/28/22, 6:40 a.m. ET: This article was updated with additional information.