Will Mauna Loa Erupt Next?

The short answer is yes—but don’t freak out.

mauna loa lava bursting hawaii eruption earthquake

Ira Schwarz/AP/REX/Shutterstock

Kīlauea has been erupting continuously since 1983. But in recent weeks, the Hawai`i volcano noted as the most active in the world amped up big time, becoming a sort of time-lapse photographic record of all possible volcanic events occurring before our eyes. Alerts and warnings have been issued at a rapid-fire pace.

But Kīlauea sits adjacent to the world’s largest active volcano. Could things compound? Could Kīlauea’s robust activity trigger Mauna Loa to erupt?

Let’s recap. On May 4, an earthquake rocked the entirety of Hawai`i’s Big Island, its magnitude 6.9 rating ranking it as the strongest temblor in the archipelago in 42 years. Then, after continual reports of lowering lava level at the 4,000-feet elevation summit, on May 17, an explosion of ash sent a plume at least 30,000 feet high, dropping abrasive particulates on nearby Volcano Village and the U.S. Geological Survey’s Hawaiian Volcano Observatory (HVO). Perched on the summit caldera, HVO, the very team charged with monitoring volcanic activity and reporting pending hazards to county emergency managers, got a front row seat of it.

Warnings of dangerous levels of sulfur dioxide gas and volcanic smog, known as “vog,” were issued, as was the possibility of acid rain—when sulfuric acid droplets mix with rain.

At the volcano’s lower east rift zone, the weeks-long fits and starts of fissures and lava fountains merged to create a confluence of crackling and thundering rivers of faster-moving pahoehoe lava that have since reached the sea. That event triggered the County of Hawai`i Civil Defense to issue a warning of laze—when hot lava hits the ocean and emits hydrochloric acid and steam mixed with particles of glass into the air.

A couple thousand people have been evacuated from their homes, Hawai`i Volcanoes National Park closed, and a geothermal power plant that provides 25 percent of electricity to Hawai`i Island shut down and removed from its premises a flammable gas called pentane, used in the process to turn heat and steam from the Earth’s core into electrical power.

Collectively, Kīlauea’s long-term eruption, since 1983, may add up to more than a single Mauna Loa eruption, but a big Mauna Loa eruption can take out an entire city like Hilo.
Chuck Blay, geoscientist

Meanwhile, sitting like an elder sibling above Kīlauea at more than three times the height, Mauna Loa hasn’t erupted since 1984, but it is most certainly active, having erupted 33 times since its first historically documented event in 1843.

Ken H. Rubin, professor and chair of geology and geophysics at University of Hawai`i, told The Daily Beast that Mauna Loa has been quiet for the past few years. “Mauna Loa has been in a period of low level unrest for much of the past five years,” he said.

The volcano’s Hawaiian name translates to English as “long mountain” an indication of its massive size. From summit to its southern tip, Mauna Loa stretches 74 miles and includes tentacles reaching northwest and northeast. In total, Mauna Loa covers more than half the landmass of Hawai`i Island.

According to geoscientist Chuck Blay, based on Kaua`i, Mauna Loa is “a much larger volcano probably with a much larger summit magma reservoir.” (Scientists refer to molten rock underground as “magma” and as “lava” once it surfaces.)

“When Mauna Loa erupts the much larger volume of magma travels much greater distances, and, in most cases endangers a greater area,” he continued. “Collectively, Kīlauea’s long-term eruption, since 1983, may add up to more than a single Mauna Loa eruption, but a big Mauna Loa eruption can take out an entire city like Hilo.”

In fact, the 1984 eruption came within four-and-a-half miles of Hilo.

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Previous to that, a 23-day eruption in 1950—called a “whopper” by Rubin—broke out of Mauna Loa’s southwest rift zone, adding 492 million cubic yards of lava to the island, equivalent to three-and-a-half year’s worth of production from Kīlauea’s reliable vent on its eastern flank known as Pu`u `Ō`ō. One flow from 1950 made the 15-mile jaunt from eruption site to ocean entry in less than three hours. Unlike Kīlauea, most of Mauna Loa’s eruptions tend to be short and intense.

But let’s not get too carried away just yet.

According to HVO geologist Janet Babb, “There is no indication that Mauna Loa will erupt in the near future.” By that, she means tomorrow or the next few weeks. The reason, she cites, is that seismicity and deformation rates have recently decreased to near background levels. HVO monitors Mauna Loa as well as Kīlauea and two other volcanoes on Hawai`i Island—Hualālai (active) and Mauna Kea (dormant). The fifth volcano that makes up Hawai`i Island is Kohala, considered extinct.

Whereas Kīlauea’s current alert level is a code red, Mauna Loa’s is two levels lower at yellow.

But scientists agree the world’s largest volcano is overdue. Since 1843, Mauna Loa has averaged a flow every five years, making 1984 seem like a very long 34 years ago. In 2015, HVO updated their volcano alert level from “normal” to “advisory” status, indicating an increase in seismic stirrings, ground deformation, and possible magma intrusion.

Turns out volcanoes have individual personalities. Per Blay, “Mauna Loa is famous for acting like it might be ready to erupt, with inflation and more earthquake clusters, and then merely quiets down again.”

Each of the volcanoes has their own summit magma reservoirs—their own plumbing systems—so it would seem they act independently, and history tends to support that. Blay points out the two have more often erupted separately than concurrently. However, maybe that’s because they are influencing each other at a deeper level. A 2012 report by Rice University researcher Helge Gonnermann suggests that as one volcano erupts, the other quiets down (PDF). This theory would suppose that Kīlauea’s current activity is acting as a release valve for Mauna Loa.

“There is one hot spot under Hawai`i [from which magma escapes in the mantle], so at some level, all the active volcanoes are connected at depth,” Rubin said. “What we debate is how much connection there is in the [Earth’s] crust. Is there a physical mingling of magmas? Some say yes. At minimum, there is probably a connectivity in terms of pressure gradients and stresses that affect how magma is fed into the volcanoes where it accumulates and when it might erupt. But it is complex.”

Interestingly, the two volcanoes have erupted concurrently before—in 1984 and 1919. But Blay said, “It seems the few times they have erupted simultaneously was merely coincidental.”

The question is not if Mauna Loa will erupt again but when. Using devices such as tiltmeters, seismometers, and satellite-based technology help volcanologists know when to raise the red flag of a pending eruption; however, their challenge has been pinpointing the exact spot lava will burst from the ground. The same has been true with Kīlauea these last few weeks. And sometimes, an eruption starts in one place and migrates to another like a game of Whac-A-Mole.

But every time a volcano erupts in Hawai`i, more is learned. “Each Hawaiian-style eruption teaches us a little more about the way magmas accumulate, get stored, and erupt and how lava flows and eruption vents change in space and time,” Rubin said. “In these regards, Kīlauea and Mauna Loa eruptions inform each other.”

So, Kīlauea may not be egging on its older sibling Mauna Loa just yet, but it may be helping scientists to predict when and exactly where Mauna Loa will one day erupt.