U.S. bombed some volcanic eruptions

It is known that, as early as 1669, an attempt was made to divert the lava from Etna that threatened Catania, but it was not until 1881 that an attempt was made to solve the same problem in the most American way possible: with explosives. However, it was not until the eruption of Mauna Loa in 1935 that the plan was put into practice in the Territory of Hawaii.

Background

During the previous century, the coastal town of Hilo had been threatened by four volcanic eruptions of Mauna Loa, coming within a mere 2 km of Hilo Harbor during the 1881 eruption despite rock walls built to prevent it. Fortunately, the large amount of gunpowder that had been sent by the Hawaii Department of Public Works for the same purpose did not have to be used.

In 1920, Lorrin Thurston, president of the Hawaii Volcanic Research Association, published in a newspaper how explosives could be used to alter the flow in the lava tubes. In 1931, T. A. Jaggar, director of the Hawaiian Volcano Observatory, focused exclusively on lava tube explosions, noting that a couple of men, a couple of mules, and a volcanologist would be successful. However, in 1935, he himself decided that it was better to go all out.

1935 Eruption

In the 1935 eruption, the vents opened on November 21 and 27 did not threaten Hilo, but on December 22 lava overflowed the natural levees and headed toward the city. In just four days, it had already covered a quarter of the distance. At the suggestion of Guido Giacometti of Ola'a, Jaggar directed the use of Keystone B-3 and B-4 light bombers. On December 26 they flew with Jagger to decide on the bombing site and the next day dropped 36 to 40 bombs on the pahoehoe, i.e., the wash whose surface is coagulating but still retains a liquid interior. Half of them were only for targeting purposes, while the other half were MK I demolition bombs with 161 kg of TNT. While the bombs that exploded on more solid surfaces left craters 6.7 m in diameter and 2 m deep, the damage of the rest was immediately covered.

Although the lava flow stopped within a week, Jaggar claimed that the bombing thickened the pahoehoe by blocking fumaroles, cooling the lava and solidifying it. However, it was later observed that it did not increase the density of the flow, but that the eruption ended coincidentally.

1942 Eruption

On April 28, 1942, it erupted again. This time, the flow dropped 10 km in 6 hours. The lava continued its path rapidly and on May 1 threatened the artificial water channel of the city of Mountain View, the highway around the island and part of Hilo. In this case it was Ruy Finch, a volcanologist with the Hawaiian Volcano Observatory, who flew in that morning to select impact sites, choosing a pahoehoe channel below the mouth of the volcano to reduce the flow of channels, which later converged into one. Bombardments followed between the afternoon of May 1 and the morning of the next day.

As in the previous case, Finch claimed that the detachment of the main cone three days later was a consequence of the bombardment, although it was later estimated that it was not possible. However, the slowing and widening of the collapse prevented further bombing with 900 kg bombs. In addition, the collapse of the cone also slowed and diverted the lava flow.

Eruptions in 1975 and 1976

Although local authorities asked federal military agencies to prepare contingency plans to divert the lava, the brevity of the eruptions prevented them from materializing. Nevertheless, the U.S. Army and Air Force conducted tests on prehistoric lavas. Training focused on a cone, lava channels, and lava tubes, which were the primary targets in active eruptions.

Aim

The objective of these bombardments was not to completely stop the lava from descending to populated areas and strategic structures, but to attack the cone, channels and lava tubes to slow the flow of the main lava flow, dispersing it and allowing it to cool down without reaching as far. Of course, the idea is designed for the type of lava emitted in Hawaii and it may be that in other volcanoes the results would be different. Tests in 1975 made it possible to define what type of bombs to use, how to bomb the targets and what results are obtained from them according to their characteristics.

This method was presented as an economical mechanism that could adapt to changing conditions and prevent the lava from destroying government land or valuable habitats. On the other hand, in addition to religious offenses, there was the possibility that the targets might not be visible during the eruption, the effects on the molten rock might not be as expected, or the weather might not favor the operation.

Regardless, the success of the bombing is questionable and has produced a division of opinion between those who believe it is a good method of containment and those who believe it is as effective as the prayer of Princess Ruth Keʻelikōlani of Hawaii, which stopped the 1881 eruption.

Source

• Lockwood, J. P., & Torgerson, F. A. (1980). Diversion of lava flows by aerial bombing—lessons from Mauna Loa volcano, Hawaii. Bulletin Volcanologique, 43(4), 727-741.