Hiker Finds Bombs Dropped In 1935 To Divert A Lava Flow From Hawaiian Volcano


This "pointer bomb" has been rediscovered in 2020, having first been photgraphed in 1939 (post-eruption inspection), and again in 1977. Jack Lockwood, 1977 (USGS)

Last month, adventurer Kawika Singson came across some “explosive” objects whilst exploring the lava fields of Mauna Loa, Hawaii. Stuck in the rooves of lava tubes, Singson found two old bombs. A recent blog post by the Hawaiian Volcano Observatory (HVO) confirmed that the “pointer bombs” actually originated from an attempt to divert the lava flow from an eruption of Mauna Loa in late 1935.


Dr Thomas Jaggar, the founder of HVO, had predicted the volcano would erupt several years before, and could potentially cause widespread devastation to the nearby city of Hilo. When his predictions came true in November 1935, Jaggar had already thought about using explosives to disrupt the flow of lava – the first time the procedure would be carried out in Hawaii.


Before the lava could contaminate the nearby Wailuku River used by the city’s residents for drinking water, Jaggar enlisted the help of the U.S. Army Air Corps. On December 27, 1935, they dropped 40 bombs from airplanes to two target areas of the flow, both within 2 kilometers (1.24 miles) of the Mauna Loa vent. According to HVO, Jaggar explained on a radio broadcast after the bombs were delivered that "[their] purpose was not to stop the lava flow, but to start it all over again at the source so that it will take a new course."

Within a couple of days, the flow had stopped. Although Jaggar was convinced the bombing “helped hasten end of flow,” he did not confirm whether the diversion actually happened. In fact, when he visited the bombing site in 1939, he concluded that the smashing of the tunnels had cooled the oncoming lava, essentially plugging the vent.

An aerial view of the bomb detonating on Mauna Loa on December 27, 1935. Army Air Crops, 11th Photo Section (USGS)

However, the HVO note that not everyone was convinced of Jaggar’s claims. United States Geological Survey (USGS) Geologist Harold Stearns, who was on board the last plane to deliver the bombs, believed that the eruption had been waning anyway, and the timing of the bombing was merely “coincidental”. A 1970s investigation of the site also found flaws in Jaggar’s “plugging” hypothesis, as they found no thickening of the vent lava by the bombs.

Yet this was not the only time explosives were used in Hawaii to divert lava flow. In 1942, an operation similar to that of 1935 was carried out but had little impact. Successful lava diversions have been achieved elsewhere, including in Italy and Iceland. These efforts went on for months, not just one day of bombing like the case in Hawaii in 1935. In the 1991-93 Mount Etna eruption, explosives were employed to help redirect the flow into an artificial channel.


Lava diversion is seen as a complex legal, political, technical, and cultural issue in Hawaii – not to mention the controversy that still surrounds the 1935 Mauna Loa lava flow. In some cases, a diversion may work, but in many cases it could only delay the inevitable. Even bombs alone are sometimes not enough to reckon with this powerful force of nature.