Why were two apparently unexploded bombs sticking out of a lava tube on Hawaii’s Mauna Loa? That’s what Kawika Singson, a photographer, wondered in February when he was hiking on Mauna Loa, the colossal shield volcano that rises 55,700 feet from its base below the sea to its summit.
Mr. Singson had stumbled upon relics of one of volcanology’s more quixotic disaster response plans. These devices, described in more detail recently in the U.S. Geological Survey Hawaiian Volcano Observatory’s Volcano Watch blog, were two of 40 dropped by the U.S. Army Air Corps in 1935 in an attempt to stop lava from plowing into Hilo, the most populous town on the island of Hawaii.
While Hilo was spared as the lava flow naturally lost its forward momentum, it wasn’t the last time that humanity tried to fight volcanic fire with fire of its own. History is filled with schemes to stop molten kinetic rock, and the ineffective 1935 bombing and others show that lava flows are very rarely “a force we humans can reckon with,” said Janine Krippner, a volcanologist at the Smithsonian Institution’s Global Volcanism Program.
Dense, superheated lava does whatever it wants. It certainly cannot be drained away. Few barriers can stand up to its incandescent anger. If lava threatens a harbor by the sea, pumping billions of gallons of seawater at it may slow it down, as Iceland discovered at Heimaey Island in 1973.
And then there is explosive lava diversion. As far back as 1881, it was considered to stop a lava flow headed toward Hilo. It was never tried; the pile of gunpowder remained unused, and religious conviction was widely credited with stopping the burning river.
The incendiary concept nevertheless struck a chord. Lava often travels long distances in solid tubes or in channels of its own design. Some wondered, why not sever these dangerous volcanic arteries? Bombs delivered by land could work, but aerial bombing could be more accurate and speedier.
It remained nothing more than a concept until an eruption in 1935. That December, a pond of lava breached its levees and advanced on Hilo at a rate of a mile per day. Fearing it would reach the town and its watershed, Thomas Jaggar, the founder and first director of the U.S. Geological Survey’s Hawaiian Volcano Observatory, called on the Army Air Corps. On Dec. 27, 10 Keystone B-3 and B-4 biplane bombers struck the lava flow, targeting its tubes and channels.
Half these bombs were packed with 355 pounds of TNT. The other half were not explosive, and instead designed to emit smoke so the pilots could see where the bona fide bombs landed. Mr. Singson found one of those inert devices last month.
On Jan. 2, 1936, the lava flows ceased. Dr. Jaggar was convinced the bombing worked, but other experts thought it was a coincidence. Pilots did spot several imploded lava tubes, but their collapses were insufficient to block the flow of lava. A similar operation was attempted in 1942, again to not much effect.
Despite its ineffectiveness, this explosive method of diverting lava wasn’t consigned to history. In the 1970s, a multitude of massive bombs were dropped on Mauna Loa’s ancient lava formations to investigate which features succumbed to modern bombing technologies. Spatter cones, which are volcanic mounds built up on top of a vent or fissure emitting profuse amounts of lava, were confirmed to be vulnerable to collapse, suggesting they could be targeted in the future.
And explosives have worked at least once, albeit not those dropped from the sky. During the eruption of Italy’s Mount Etna from 1991 to 1993, nearly eight tons of explosives carefully arranged by engineers were used to carve a hole in a major lava channel. Much of its molten contents then drained into a trench, which saved Zafferana Etnea, a town now of some 9,500 people.
This technique isn’t without problems. As with many volcanoes around the world, said Dr. Krippner, “there’s the cultural aspect: the people’s connection with the land, and the volcanoes, and not wanting to interfere with that.” Many native Hawaiians consider the destruction of volcanic land an affront to their spiritual beliefs.
And even if it works, it cannot guarantee that successfully diverted lava won’t accidentally flow toward another important site.
Jack Lockwood, a geologist now retired from the Hawaiian Volcano Observatory and a lava diversion expert, suspects that this option will remain on the table.
He points to Mauna Loa’s 1984 eruption, which again threatened Hilo. Gov. George Ariyoshi had publicly ruled out using bombs to divert the lava. But Dr. Lockwood said that Mr. Ariyoshi’s staff asked him to draft a bombing raid contingency plan should the situation look grim.
Bombing Mauna Loa’s lava flows will always be a fraught proposition. But in a sufficiently dire situation, Dr. Lockwood said, we may again see a day when a Mauna Loa lava flow is greeted by explosive military might.
“It would require martial law, effectively, and an emergency declaration. But I suspect it would be done,” Dr. Lockwood said. Although, he added, “that might depend on the moxie of the governor, and which brickbats they were willing to tolerate.”