Hawaii’s Mauna Loa volcano is erupting. What do you need to know?

Lava, volcanic gas and smog are the main hazards from eruption of the world’s largest active volcano

Hawaii’s Mauna Loa, the world’s largest active volcano, is erupting for the first time in nearly 40 years – causing spectacular scenes, casting an eerie red glow over the island and shooting lava up to 200ft (60 metres) in the air.

Mauna Loa last erupted in 1984. Its smaller, more active neighbor, Kilauea volcano, has been erupting continuously for more than a year since September 2021.

While the volcano is not posing an immediate threat to communities, the situation is dynamic. Here’s what you need to know.

Where is Mauna Loa?

Mauna Loa is one of five volcanoes that together make up the Big Island of Hawaii, which is the southernmost island in the Hawaiian archipelago.

It’s not the tallest (that title goes to Mauna Kea) but it’s the largest and makes up about half of the island’s land mass. Mauna Loa’s volume is estimated to be at least 18,000 cubic miles (75,000 cubic kilometres), making it the world’s largest volcano when measured from the ocean floor to its summit.

It sits immediately north of Kilauea volcano, which is well known for a 2018 eruption that destroyed 700 homes and sent rivers of lava spreading across farms and into the ocean.

Mauna Loa last erupted 38 years ago. The current eruption is its 34th since written history began in 1843.

Where is Mauna Loa erupting from?

The eruption began on Sunday night at its summit after a series of large earthquakes. It then spread to vents that formed in a rift zone where the mountain is splitting apart and it is easier for magma to emerge.

These vents are on the mountain’s north-east side and lava emerging there could head toward the town of Hilo, which is on the east side of the island.

Ken Hon, scientist-in-charge at the Hawaiian Volcano Observatory, said he doesn’t expect additional vents to form on the volcano’s south-west rift zone during this eruption. That means communities to the west would be spared lava flows this time.

Mauna Loa also erupted from the north-east in 1984. That time, lava headed toward Hilo but stopped a few miles short of the town.

Historically, each Mauna Loa eruption has lasted a few weeks. Hon expects the current eruption to follow this pattern.

Is Mauna Loa exploding?

Mauna Loa is not exploding in the sense of, for instance, Mount St Helens in Washington state in 1980. That eruption sent ash soaring more than 80,000ft (24,384 metres) high and killed 57 people.

The magma in Mount St Helens tends to be stickier and traps more gas, making it much more likely to explode when it rises. By contrast, Mauna Loa’s magma tends to be hotter, drier and more fluid. That allows the magma’s gas to escape and lava to flow down the side the volcano the way it is starting to do now. Mauna Loa is a shield volcano, named because the long, broad flanks built up by repeated lava flows give it the appearance of a warrior’s shield.

Lava from the north-east rift zone will likely take at least a week to reach populated areas.
Lava from the north-east rift zone will likely take at least a week to reach populated areas. Photograph: Andrew Richard Hara/Getty Images

What hazards are posed by the eruption?

Lava is one risk – molten rock could cover houses, farms or neighborhoods, depending on where it flows. But for now, lava is not threatening any homes or communities and no evacuation orders have been issued. Lava from the north-east rift zone will likely take at least a week to reach populated areas, allowing people time to evacuate if needed.

Another risk is volcanic gas. Mauna Loa is spewing sulfur dioxide and other volcanic gases that form volcanic smog, or vog, when they mix with vapor, oxygen and dust in the presence of sunlight. The gases are present in their highest concentrations in the immediate area around the summit crater or vents. But vog can spread across the Big Island and even waft over to the state’s other islands.

Vog can give healthy people burning eyes, headaches and sore throats. As a result, state health officials are urging people to cut back on outdoor exercise and other activities that cause heavy breathing.

Glass particles can also form when hot lava erupts from a fissure and rapidly cools. The particles are named “Pele’s hair” and “Pele’s tears” after the Hawaiian goddess of volcanoes.

The particles tend not to travel far from volcanic vents – maybe only a few hundred yards or a mile – and won’t threaten many people, said Aaron Pietruszka, an associate specialist at the University of Hawaii’s department of earth sciences.

“It just literally looks like hair strands. And that’s where the fluid lava is stretched by the wind to make long, thin strands,” said Pietruszka.

The glass bits – as short as a few millimeters or as long as a few inches – can be sharp.

“You wouldn’t want to be digging your hands in it because you could get a cut,” Pietruszka said.

Lava flows from Mokuaweoweo crater down Mauna Loa’s north-east rift on 28 November.
Lava flows from Mokuaweoweo crater down Mauna Loa’s north-east rift on 28 November. Photograph: Bruce Omori/Paradise Helicopters/EPA

How significant are Mauna Loa’s greenhouse gas emissions?

Mauna Loa released about 15,000 tonnes of carbon dioxide per day during its 1984 eruption, according to US Geological Survey data.

That’s equivalent to the annual emissions from 2,400 sport utility vehicles.

Scientists say all of Earth’s volcanoes combined emit less than 1% of the carbon dioxide that humans produce each year.

• This article was amended on 30 November 2022. A previous version gave the volume of Mauna Loa in miles and kilometres, rather than cubic miles and cubic kilometres.

Staff and agencies

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