What Happens When a Hurricane Meets a Volcano?

When Iselle crosses the Big Island of Hawaii, it will offer a rare glimpse at a clash of the titans

Hawaii hurricanes
A NASA satellite image shows Hurricane Iselle approaching Hawaii, with Hurricane Julio hot on its heels. NASA image by Jeff Schmaltz, LANCE/EOSDIS Rapid Response

In Hawaii, hurricanes hardly happen. That means when Hurricane Iselle crosses the Big Island tonight, scientists will have a rare chance to see how the monster storm interacts with another extreme force of nature: an active volcano.

Even now, the Kilauea volcano in Hawaii Volcanoes National Park is erupting from two vents, oozing lava and sending up white plumes of volcanic gases. The rarity of hurricanes in this area means that not much is known about how the oncoming storm will affect the volcano, says Jim Kauahikaua, scientist-in-charge at the USGS Hawaiian Volcano Observatory on the Big Island.

“We don't expect that the hurricane will have much effect on the eruption itself, because recent past storms with a lot of rainfall have not significantly affected lava eruption,” Kauahikaua says.

Instead, gases and particles pouring out of the volcano could make aspects of the hurricane more intense, says Steven Businger at the University of Hawaii. A June 2014 study about Tropical Cyclone Flossie showed that fine particles from volcanic emissions can cause water in storm clouds to divide into smaller droplets, which get carried higher into the clouds by updrafts. This creates a charge imbalance in the cloud that causes more lightning in the storm.

Animation by Cameron Beccario

But the experts are still debating whether volcanic emissions will make a storm’s winds stronger or help break up the tempest, Businger says. “There are several different effects working together that make it difficult to predict what will happen.”

It’s also possible the approaching hurricane played a role in the 4.5-magnitude earthquake that struck the Big Island ahead of landfall, says Michael Manga, a geophysicist at the University of California, Berkeley.

“The change in pressure from a large storm can promote earthquakes, but this stress change is still very small, so the earthquake is likely to have occurred anyway – just later,” says Manga. In a similar vein, volcanologist John Lockwood and geologist Richard Hazlett have suggested that low atmospheric pressure from Typhoon Yunya may have helped trigger the massive eruption of Mount Pinatubo in the Philippines in 1991.

But Eric Dunham at Stanford University isn’t so sure. “Most of the action in a volcano happens deep underground, where the changes in air pressure from the hurricane would not be significant,” he says.

Hawaii’s sleeping volcanoes pose yet more quandaries for Hurricane Iselle. The dormant peaks of Mauna Kea and Mauna Loa will affect wind circulation as the hurricane sweeps across the island, according to the National Weather Service. That could help break up and weaken the storm as it moves on towards Maui and Oahu but it could also accelerate the storm’s already strong winds.

“When it strikes its going to be ferocious, but as it passes over it’s going to be very disrupted,” says Businger.

Update: Elizabeth Cottrell, director of the Smithsonian’s Global Volcanism Program, adds that the effect of surface pressures on eruptions is an active area of research, and lowering the pressure should cause greater volumes of lava to erupt. But she does not think the scale of the pressure drop from a hurricane would be enough to influence an eruption. Instead, the dousing from a big storm’s precipitation could be a bigger worry.

“Heavy rains are always capable of generating mudslides and other slope instabilities,” says Cottrell. “As Hawaii has enormous topographic relief due to the volcanoes, there is certainly potential for heavy rain to cause slope failure.”

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