Scientists declare 2 Hawaii volcanoes have stopped erupting

Lava spews from Hawaii's Mauna Loa volcano Lava spews from Hawaii's Mauna Loa volcano, coming three kilometres from the Daniel K. Inouye Highway.

HONOLULU — U.S. scientists declared Tuesday that two active Hawaii volcanoes -- one where lava destroyed hundreds of homes in 2018 and another where lava recently stalled before reaching a crucial Big Island highway -- have stopped erupting.

"Kilauea is no longer erupting," the U.S. Geological Survey's Hawaiian Volcano Observatory said in a statement Tuesday, followed by a separate one saying, "Mauna Loa is no longer erupting."

Alert levels for both volcanoes were reduced from watch to advisory.

Mauna Loa, the world's largest volcano, began spewing molten rock Nov. 27 after being quiet for 38 years, drawing onlookers to take in the incandescent spectacle, and setting some nerves on edge early on among people who've lived through destructive eruptions.

It was Mauna Loa's longest period of repose, said Ken Hon, the observatory's scientist in charge.

Lava-viewers in Hawaii Volcanoes National Park enjoyed the added rare marvel of being able to see Mauna Loa's smaller neighbor, Kilauea, erupting at the same time.

Kilauea had been erupting since September 2021. A 2018 Kilauea eruption destroyed more than 700 residences.

Mauna Loa lava didn't pose a threat to any communities, but got within 1.7 miles (2.7 kilometres) of a major highway that connects the east and west sides of the island.

Hon called the two-week spectacle, which is a typical timespan for Mauna Loa, "my favorite eruption."

"It was a beautiful eruption, and lots of people got to see it, and it didn't take out any major infrastructure and most importantly, it didn't affect anybody's life," he said at a briefing Tuesday.

Hawaii County Civil Defense Director Talmadge Magno said a one-way route that opened to manage traffic from throngs of people watching the lava would close Thursday.

Magno and other county officials had warned that slow-moving lava could force the closure of Saddle Road, also known as Route 200 or Daniel K. Inouye Highway. That prompted motorists to brace for upheaval from a closure that could add hours to commute times on alternate coastal routes.

"Whatever it is -- luck, chance -- this is probably the best situation that we could ask for from Mauna Loa," Magno said.

For Native Hawaiians, volcanic eruptions have deep cultural and spiritual significance. During Mauna Loa's eruption, many Hawaiians took part in cultural traditions, such as singing, chanting and dancing to honor Pele, the deity of volcanoes and fire, and leaving offerings known as "hookupu."

Lava supply to a Mauna Loa fissure ceased on Saturday, the observatory said, and volcanic tremor and earthquakes associated with the eruption "greatly diminished."

"Spots of incandescence may remain near the vent, along channels, and at the flow front for days or weeks as the lava flows cool," the observatory's activity summary said. "However, eruptive activity is not expected to return based on past eruptive behavior."

Lava supply to Kilauea's Halemaumau lava lake ceased on Friday, the observatory said: "Potential remains for resumption of this eruption or initiation of a new eruption at or near the summit of Kilauea."

The observatory will continue monitoring the volcanoes for signs of renewed activity.

Despite the definitive statements, Hon said there's generally a three-month "cooling off" period before scientists consider the eruption over.

But there's been no history of a Mauna Loa rift eruption pausing and restarting, he said, "So we feel pretty confident that this eruption has in fact, paused and is probably over."

It was unclear what connection there could be to the volcanoes stopping their eruptions around the same time. The volcanoes can both be seen at the same time from multiple spots in Hawaii Volcanoes National Park near Kilauea's caldera.

"So, Kilauea may have been diminishing already and the Mauna Loa eruption may have caused enough physical changes to stop it, or it may have just been headed to stop on its own," Hon said. "So we don't have a really good answer for that right now."

Scientists will look at data to study the relationship between the two volcanoes, he said.