Mauna Loa wakes up after almost 40 years; eruption’s duration uncertain, say scientists

Mauna Loa, the world’s largest active volcano situated in the US state of Hawaii, erupted for the first time November 28, 09:30 UTC (3 pm IST) after waking from its almost 38-year-long slumber.

In the initial hours of the eruption, the lava emerged from the summit, flowing out of a crater or bowl-shaped depression called the caldera. 

But now cracks have opened up outside the caldera, allowing the lava to flow downhill, experts told Down To Earth.

“This, unfortunately, means there is an increased probability of the lava reaching inhabited places, as most of the population lives lower down the flanks of the volcano and on the coast,” Carmen Solana, Reader in Volcanology and Risk Communications at the University of Portsmouth, told DTE.

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However, “there is still not a big risk to human life because the lava is flowing slow enough for people to be evacuated,” Jessica Johnson, associate professor in Geophysics at the University of East Anglia, told DTE.

But, she added, if the flows continue, they could threaten infrastructure and buildings.

If the eruption had stayed within the caldera, the lava would have remained confined within its walls for a while, experts told DTE. The eruption of Mauna Loa moved from the summit to the Northeast Rift Zone, an update November 28, 2022, from the Hawaiian Volcano Observatory read.

Most eruptions originate in Hawaii’s summits and rift zones of Hualālai, Mauna Loa, and Kīlauea.

Rift zones are areas that have weak cracks, allowing magma to push against the rock above, making its way to the surface and flowing downhill, according to the University of Hawaii.

As of November 29, eruptions occurred at three fissures. Two of them have now stopped, Johnson said. The United States Geological Survey warned that additional fissures could open up along the Northeast Rift Zone.

Was it expected?

The volcano showed signs of unrest. “Before the current eruption, there was deformation in the volcano and small earthquakes,” Solana said. Both deformation and earthquakes occur due to magma pushing up the rocks above, she added.

However, Solana and Johnson said they were not entirely expecting Mauna Loa to strike this year as the volcano has been showing signs of unrest for some time now. “Scientists did not know that it would definitely erupt this year, but they knew it was likely to happen soon,” Johnson said.

Scientists said it is hard to tell whether Mauna Loa will stay active for hours, weeks or months. 

“Typically, an eruption of this type, with lava fountains and lava flows, will last for weeks and even a couple of months, but as the volcano has not erupted for such a long period, we might be looking at a longer eruption,” Solana noted. The Hawaiian Volcano Observatory is currently monitoring the situation.

Scientists also measured sulphur dioxide (SO2) emissions from the eruption. Satellite images showed a strong signature of SO2 within the volcanic cloud, according to a blog from scientists and researchers at US National Oceanic and Atmospheric Administration’s Cooperative Institute for Meteorological Satellite Studies.

In the eruption’s initial phase, SO2 drifted northeast of Hawaii, Simon Carn from Michigan Technological University wrote on Twitter. Satellite data suggests 0.2 Teragrams (Tg) of SO2 were emitted on November 28. Carn added that the 1984 Mauna Loa eruption emitted roughly 1.2 Tg SO2.

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