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What Would Happen If a Hurricane Hit an Erupting Volcano?

The Atlantic logo The Atlantic 21-10-2017 Jim Nash
a close up of a colorful wall © Trong Nguyen / Shutterstock / Juan Cevallos / Getty

In addition to the cars flipped, the roofs collapsed, and the streets flooded, this season’s unprecedented string of devastating hurricanes also hit a much grander target: a volcano. The Caribbean island of Montserrat, home to the active Soufrière Hills volcano, twice suffered blows: first an almost-direct hit by category-5 Hurricane Irma, then a direct hit by category-5 Hurricane Maria.

The volcano’s peak this year was, thankfully, more noisy than explosive. No volcano-related calamities were reported from the storm. But the collision of the two disaster-movie terrors reveals the possibility of unnerving scenario: What happens when a superstorm lands on a volcano that’s exploding?

While there’s no record of a top-of-the-scale category-5 hurricane or super typhoon ever running over such a volcano, there are hundreds of active volcanoes in the tropics—including 20 in the Caribbean—where some of the worst storms start tearing things apart. And evidence suggests a warming climate only intensifies these storms. No one is certain about what would happen in a matchup, but most likely neither of the two primeval forces could take the stuffing out of the other. Even so, the battle could prove especially deadly for people caught nearby.

Some meteorologists and geologists speculate that the collision would be like a pair of agitated gorillas: two giants making a lot of noise, shaking the ground, and then parting ways. It’s unlikely the volcano would make much of a dent in this battle. “As massive as the impact of a volcanic eruption can be, it’s hard to grasp the scale of a hurricane,” says David Nolan, an atmospheric scientist at the University of Miami. “The eye wall of a hurricane typically has a radius of 30 miles. Off the top of my head, I'd say the primary updraft from a volcano is just one mile across.”

Scenic air shot of Calbuco Volcano erupting © Getty/gadaian Scenic air shot of Calbuco Volcano erupting

As a result, he explains, almost anything a volcano can do to disrupt a storm would be localized and likely erased as it moved along. Tracy Gregg, a geologist at the University at Buffalo, also emphasizes how little impact typical volcanic eruptions would likely have on such a powerful storm. “A volcano punching up through [a hurricane] would be a smudge on the windshield,” she says.

Nevertheless, there are certain circumstances that could be much more extreme. It’s possible that a volcano’s intense heat—lava can register 2,200 degrees Fahrenheit—could intensify a tropical cyclone. Heat evaporates seawater, which rises to create thunderstorms. No heat, no storm. And an explosive eruption might still temporarily disrupt areas within a hurricane. For instance, dust shot into the atmosphere could delay or accelerate rainfall, Nolan says. One study suggests the dust would contribute to more lightning. In fact, massive eruptions often generate cinematic lightning within their boiling black clouds.

More intriguing—and terrifying—is a theory that a submerged, massive volcano could heat enough ocean water to supercharge a category-5 hurricane or super typhoon. Heating the already abundant heat of tropical waters would make storms bigger, stronger, and do it in less time. Jeff Masters, the meteorology director at The Weather Channel, says such an underwater eruption might even spin up something called a hypercane, with winds reaching the speed of sound.

It would take “an awful big coincidence” for this to happen, Masters reassures: The volcano would have to be big enough and hot enough to heat hundreds of miles of the ocean’s surface to 122 degrees. Standard weather dynamics would take it from there. “It’s theoretically possible,” Masters says. So is the possibility that a hypercane could inject enough water into the stratosphere to block the sun, creating a years-long global winter.

© Getty/RomoloTavani

Team Hurricane’s fever dream is more mundane. Some think the low air pressure in a hurricane’s eye might weakly draw up the contents of a volcano, like a TV cowboy sucking venom from his cowpoke friend's snakebite wound. But “that’s really unlikely,” Gregg says. After all, volcanoes begin 1,800 miles down, where temperatures exceed 6,700 degrees, and liquid rock (or magma) is squeezed by pressures that are 1.4 million greater than air at sea level. A change in air pressure over a volcano is like a fly buzzing off an elephant’s back.

The feet of water that a storm can drop also isn’t likely to have any effect. The entire state of Hawaii, for example, is a collection of gurgling volcanoes that rose through 20,000 feet of water from the floor of the Pacific. Volcanoes experiencing a category-5 hurricane might as well be enjoying a music-festival mist station.

Major hurricanes slamming into volcanoes could still have a devastating impact, but victims would be the environment below the crater—and anyone who lives there. As often happens even with lesser hurricanes, rain soaks into the enormous deposits of fine ash resting precariously on a steep volcano’s flank until the resulting warm mud suddenly breaks free. The rush of debris, known as a lahar, roars down the slope at 120 m.p.h. like a runaway freight train. Anything—and anyone—not washed away is encased in the mud.

Volcanic eruption in Holuhraun Iceland © Getty/GISBA Volcanic eruption in Holuhraun Iceland

In 1991, Typhoon Yunya hit Mt. Pinatubo on the Philippines island of Luzon and triggered lahars that, according to Masters, killed as many as 300 people. Yunya, barely a typhoon at the time, delivered a glancing blow to Mt. Pinatubo as the mountain—coincidentally—ended almost a year of fitful activity with the 20th century’s second-most-monstrous volcanic explosion. The lahars easily inflicted more damage than the eruption.

At lease one positive could result from a geological-meteorological grudge match, Gregg points out. The hurricane likely would act like an air filter, trapping motes of dust in raindrops. Dust then would fall to earth almost immediately, instead of into the atmosphere, as typically happens with all large, explosive volcanoes. Up there, the dust would circle the globe, reflecting sunlight back into space and measurably disrupting air temperatures for years.

Asked if he would ever buy a ticket to Montserrat, the island struck by Irma and Maria, to witness such a matchup, Masters paused a surprisingly long time before laughing. “Maybe when I was younger, I would. I don't know.” It sounded like a “no,” but as with hypercanes, he couldn’t rule it out completely.

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