What dangers does Hawaii’s Mauna Loa pose?

HONOLULU (AP) — Lava shoots 100 feet to 200 feet (30 to 60 meters) into the air as Hawaii’s Mauna Loa, the world’s largest active volcano, erupts for the first time in nearly 40 years.

For now, the lava does not threaten any homes or communities and no evacuation orders have been issued. The lava could eventually reach neighborhoods as it flows downhill, though it could take a week or more for molten rock to reach populated areas.

Mauna Loa spews sulfur dioxide and other volcanic gases. They form volcanic smog, or vog, when they mix with steam, oxygen, and dust in the sunlight. As a result, state health officials are urging people to reduce outdoor exercise and other activities that cause shortness of breath.

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


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 is the largest, making up about half of the island’s land mass.

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

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

The Big Island is mostly rural, home to cattle ranches and coffee farms, but is also home to a few small cities, including the county seat of Hilo, which has a population of 45,000.

It is about 200 miles (320 kilometers) south of Hawaii’s most populous island, Oahu, where the state capital Honolulu and the beach resort Waikiki are located.

Mauna Loa’s volume is estimated to be at least 18,000 square miles (75,000 square kilometers), making it the world’s largest volcano when measured from the ocean floor to its summit.

A video from Kailua-Kona, Hawaii shows lava from the volcano erupting. (Source: HAWAII DEPARTMENT OF LANDS AND NATURAL RESOURCES/CNN)


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

These vents are on the northeast side of the mountain, and lava flowing there could be heading toward Hilo, which is on the east side of the island.

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

Mauna Loa also erupted from the northeast in 1984. At this time, the lava headed toward Hilo but stopped a few miles from the city.

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

Lava flows downhill hours after Mauna Loa erupted. (Source: USGS/CNN)


Mauna Loa is not exploding like Washington state’s Mount St. Helens did in 1980, killing 57 people. That eruption sent ash over 80,000 feet (24,384 meters) and raining down as far as 250 miles (400 kilometers) away.

The magma at Mount St. Helens tends to be stickier and traps more gas, making it much more likely to explode when it rises. It is of a variety called composite volcanoes, which form concave cones.

Mauna Loa’s magma tends to be hotter, drier, and more fluid. That allows gas from the magma to escape and lava to flow down the side of the volcano the way it is starting to do now. Mauna Loa is a shield volcano, so named because the long, broad flanks built up by repeated lava flows give it the appearance of a warrior’s shield.

In 1989, Alaska’s Redoubt Volcano, another composite volcano, spewed an 8-mile cloud of ash that clogged all four engines of a KLM Royal Dutch Airlines plane. The plane dropped 13,000 feet before all engines were restarted and the plane landed without injuring all 245 people on board.

Mauna Loa spewed some ash this time, but on a much smaller scale than these examples of composite volcanoes.


-Lava: The molten rock can cover houses, farms or neighborhoods, depending on where it flows. But it will likely take at least a week for lava from the northeast rift zone to reach populated areas, giving people time to evacuate if necessary.

-Volcanic Gas: Mauna Loa is releasing volcanic gases, mainly sulfur dioxide. The gases are present in their highest concentrations in the immediate area around the crater or summit vents. But they also combine with other particles to form vog, which can spread across the Big Island and even reach other islands in the state.

Vog can cause burning eyes, headaches, and sore throats in healthy people. You can send people with asthma or other breathing problems to the hospital.

-Glass Particles: When hot lava erupts from a fissure and cools rapidly, it forms glass particles called “Pele’s hair” and “Pele’s tears” after the Hawaiian goddess of volcanoes.

The particles tend not to travel far from volcanic vents, perhaps only a few hundred meters or a mile, and don’t threaten many people, said Aaron Pietruszka, an associate specialist in the University of Hawaii’s Department of Earth Sciences.

“It literally looks like strands of hair. And that’s where the wind stretches the flowing lava to form long, thin threads,” Pietruszka said.

Glass points, as short as a few millimeters or as long as a few inches, can be sharp.

“You wouldn’t want to put your hands in it because you could cut yourself,” Pietruszka said.

An N95 or KF94 mask would protect against these glass particles but not volcanic gas, said Dr. Libby Char, director of the state Department of Health.

Specimens of “Pele’s hair” from the Kilauea volcano eruption are visible in Hawaii Volcanoes National Park.


Mauna Loa emitted about 15,000 tons of carbon dioxide per day during its 1984 eruption, according to USGS data.

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

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


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