Hawaii’s Mauna Loa volcano is erupting for the first time since 1984

For the first time in nearly 40 years, the world’s largest active volcano erupts in Hawaii, after weeks of increased activity in the caldera


November 28, 2022 , updated November 28, 2022

A thermal camera on the northern rim of the caldera at the top of Mauna Loa captured the eruption

US Geological Survey

The world’s largest active volcano, Mauna Loa in Hawaii, is erupting for the first time in nearly 40 years, with US officials warning nearby residents to prepare for possible evacuation.

The eruption, the volcano’s first since 1984, began at 11:30 p.m. local time on Nov. 27 at Mokuʻāweoweo, the summit caldera in Hawaiʻi Volcanoes National Park on the island of Hawaii.

So far, the eruption has been confined to the summit area, but officials warned the situation could change soon.

Along the volcano’s sides are two so-called rift zones, extending northeast and southwest from the caldera, where the volcano’s surface can crack and split. “Very fluid and fast-moving lava” can quickly pour out of a new fissure and threaten populated neighborhoods downstream, Ken Hon of the Hawaiian Volcano Observatory said in a briefing on Nov. 28.

“At this point, we just don’t know what’s going to happen — whether this stays with a summit-only eruption or goes to one of the rift zones,” he said.

On Nov. 28, U.S. Geological Survey officials said lava had begun to flow from the summit caldera, but said there was no evidence of lava coming from the rift zones.

An ashfall alert has been issued for Hawaii’s Big Island, advising medically vulnerable residents to stay indoors or wear filter masks. Shelters have been opened to provide safety for the islanders, though officials say there is no immediate threat to populated areas.

Mauna Loa is a giant shield volcano, which is about 4 kilometers high and covers a land area of ​​about 5000 square kilometers.

It has erupted 33 times since 1843, the most severe in 1950 when it flooded the coastal town of Ho’ōpūloa within 3 hours, destroying homes, a church and the local highway.

During the last eruption in 1984, lava flows came within 5 miles of the city of Hilo.

Volcanologists have been reporting an increase in activity at Mauna Loa for weeks, with dozens of small, shallow earthquakes recorded around the summit over the past month. “Then it really started erupting right before the eruption started,” says Paul Segall of Stanford University in California.

Deeper earthquakes around the volcano in recent years have indicated that Mauna Loa is about to erupt. “This has been on our radar for a while,” he says.

In a statement, the Hawaiian Volcano Observatory said it will conduct aerial reconnaissance “as soon as possible” to better understand the risks of the current eruption.

Segall says the eruption could help volcanologists understand more about the connection between Mauna Loa and another Hawaiian volcano called Kīlauea. “We don’t really understand the piping system where the magma separates” to flow to the two volcanoes, he says. One theory behind the long delay since Mauna Loa’s last eruption is that magma was diverted to Kīlauea, where a major eruption occurred in 2018 that caused a caldera collapse.

Segall says he sees no indication at this point that Mauna Loa’s eruption could become as powerful as Kīlauea’s 2018 eruption. “Statistically, this thing will be relatively modest,” he says.

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