It's a scenario tailor-made for a cheesy disaster film. The next big thing on Netflix, say, or a soon-to-be Syfy network classic:
A rumbling volcano on a remote tropical island. A monstrous hurricane barreling relentlessly toward it. Lava. Lightning. Stinging rain. Flooding. Man-eating sharks dropping out of the sky.
Wait. This isn't Sharknado. But this odd coupling of active volcano and hurricane still can be pretty cool — and scary. And very real.
When a hurricane meets a volcano — it happens probably more often than you think — some strange and wondrous natural sparks begin to fly. How big those sometimes literal sparks become depends on a few key factors, of course, including the strength of the hurricane, how active the volcano is and the topography surrounding the volcano, to name the more obvious.
Because of those variables, it's almost impossible to accurately predict what will happen when a big storm settles over a big volcano. But lightning, lava, rain and winds all are possibilities.
"We always get excited when a hurricane comes by," admits Steven Businger, a professor in the department of meteorology at the University of Hawaii (UH).
Volcanoes Can Supercharge a Storm
In Hawaii, the volcano Kilauea, on the island of Hawaii (known as the Big Island), has been actively spouting off since 1983, spewing lava and claiming houses with scary regularity. But its latest stretch, which began in mid-May 2018, has spewed lava from the volcano destroying 700 houses and adding more than 850 acres (343 hectares) of new land to the Big Island. On Aug. 5, 2018, researchers from the U.S. Geological Survey described activity from Kilauea's fissure No. 8 — the largest and most active — had decreased to "only a glow."
It's not just the lava that makes volcanoes dangerous, though. Volcanoes shoot vast amounts of ash into the sky that can contribute to a lot of rain and flooding. From Oregon State University's Volcano World:
The main effect on weather right near a volcano is that there is often a lot of rain, lightning and thunder during an eruption. This is because all the ash particles that are thrown up into the atmosphere are good at attracting/collecting water droplets.
When a tropical cyclone or hurricane, heavy with rain and strong winds, is added to that already volatile volcanic weather mix, things become even dicier.
"Its circulation is more vigorous," says Businger, who has a Ph.D. in atmospheric sciences from the University of Washington and has been tracking storms — including ones that interact with volcanoes — at UH for some 25 years. "People can get killed by the ... heavy winds that result, or the lightning that results."
In 1991, Mount Pinatubo in the Philippines blew its top, the second-largest volcanic eruption of the 20th century. When Typhoon Yunya brought heavy rains as the volcano was erupting, the volcanic ash and rock that Pinatubo coughed up was washed down the volcano's slopes in flows known as lahars. Over the next four years, those lahars, originally prompted by Yunya and later egged on by other storms and rainy seasons, eventually caused more damage than the eruption itself.
After observing Tropical Storm Flossie roll over Kilauea in 2013, Businger and colleague Andre Pattantyus measured something else: a marked increase in lightning. They explained it in a paper in the journal Geophysical Research Letters in 2014.
"In the clean atmosphere, you have large droplets form around few particles. And those large droplets tend to fall out before these large droplets have a chance to get up into the upper atmosphere where freezing takes pace. It is freezing that is required for electrification," Businger says. "When you have pollution from a volcano that is producing lots of condensation particles — cloud condensation nuclei; CCN, we call it — then you get many droplets. Those smaller droplets don't rain out, and they're more easily lofted above the freezing level. And then you do get charge separation — electrification."
A Once-in-a-while Fling
By early August 2018, just before Hurricane Hector swung near the southern side of the Big Island, seven tropical cyclones had already made landfall across the Hawaiian Islands since Kilauea began its latest run of eruptions. The three most recent, according to the Weather Channel, were Flossie in 2013, Hurricane Iselle in 2014 and Hurricane Darby in 2016. Now meteorologists are concerned about Hurricane Lane. On Aug. 21, 2018, it was packing 150 mph (241 kmh) winds, presenting a rare direct threat to Hawaii. Lane could become the first hurricane to make direct landfall in Honolulu since Hawaii became a state in 1959.
With Kilauea showing few signs of abating, Hawaii may be facing several more chances at hurricane vs. volcano meetings. But even if a tropical storm doesn't directly strike the Big Island, even if it doesn't make landfall and glide over Kilauea, even if the rains and lightning are somehow held to a minimum, it still can stir up things around the 50th state.
Some of those byproducts, given the alternative, might even be welcome in Hawaii. The heavy, moist air of a hurricane can help clean the air of the bigger ash particles from a volcanic eruption. And a good, windy storm is always welcome by some types in the islands.
"It's going to kick up some hellacious surf," Businger says.
Now That's Interesting
Using high-speed video footage and advanced acoustics, researchers in Germany recently measured volcanic lightning in Sakurajima Volcano in Japan; that is, lightning that occurred right in the ash cloud, just a few hundred meters above the rim of the crater of the volcano. The constantly roiling magma in the volcano electrifies the ash above it until it builds up enough charge to create lightning.
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