Photo: Mauna Loa looms above the city of Hilo and Hilo Bay. This view is from Mokuola, commonly called Coconut Island. Mokuola and the rock in bottom of photograph formed from a lava flow erupted by Mauna Loa about 1,400 years ago. A flow from Mauna Loa entered what is now Hilo in 1881, and another neared the city in 1984. (S.R. Brantley, USGS)

The city of Hilo on Hawaii’s Big Island sits in the shadow of the world’s largest shield volcano, Mauna Loa.

There are many tales about Mauna Loa’s eruptions and the dangers those lava flows posed to the pretty little city by the bay that dates back to about 1100 AD.

This is one of the stranger stories: the time when the US Army Air Corps (USAAC) bombed the volcano to stop a threatening magma flow before it could reach Hilo.

Our story begins with the eruption of Mauna Loa that started on November 21, 1935. It came as no surprise to those working at the Hawaiian Volcano Observatory.

Like most Hawaiian eruptions, it was preceded by two flurries of earthquakes months prior to the outburst of lava. Each flurry tracked the upward migration of lava within the volcano. The largest recorded earthquake was so strong it was felt on Oahu. The actual eruption began at 6:20 PM with 300’ curtains of molten rock fountaining on the northeast side of the volcano’s caldera.

News photo of the lava bombing. (USGS photo.)

By December 8, the vent began producing the smooth, gloopy form of lava called pahoehoe. Following a northerly heading, the pahoehoe flows had ponded in the low area between Mauna Loa and the giant dormant shield volcano Mauna Kea at which point it turned to follow the natural drainage toward Hilo.

On December 26, the flow was moving about a mile per day and Hawaii’s leading volcanologist, Dr. Thomas A. Jaggar, Director of the Hawaiian Volcano Observatory, concluded that the threat to Hilo was limited.

Nearly a month later, however, the situation dramatically changed when ponded lava, located less than 20 miles from Hilo, broke through the natural levees of stone and began a rapid flow directly toward the city.

Jagger, neither a Meister nor Mick, believed something had to be done or the lava flow would cut off Hilo’s water supply and possibly burn the city. Seeking a solution to nature’s wrath, he had been experimenting with using TNT hauled by mules up the side of the volcano to dynamite lava tubes and divert the flows. Problem was, he was running out of time and the mules were not getting any faster. Dr. Jaggar estimated that the lava flow would wipe out Hilo on January 9, 1936, unless it could somehow be stopped.

Practice bomb drop from “Keystone” bombers, the last of the Army Air Corp biplane bombers. (USAAC photo.)

Another volcanologist, Guido Giacometti, suggested using US Army Air Corps bombers to deliver precision explosions more rapidly.

The plan made perfect sense in a “here, hold my beer for a second” Guido-sort of way.

I mean, dropping bombs on an active volcano – what could go wrong?

In any case, as time was of the essence, a call was placed to the 23rd Bomb Squadron, US Army Air Corps in Hawaii where the operational planning was tasked to a Lt. Colonel George S. Patton, who would go on to WWII fame.

It was a gorgeous Hawaii day on December 27, 1935 when the first of two flights of five bombers took off to bomb the volcano. Each plane carried two 300 pound practice bombs and two live bombs with 355 pounds of TNT; in other words, twenty bombs for a total of 7,100 pounds of dynamite. Picky chemists and pedants will note that TNT and dynamite are not exactly the same things but I digress.

The 23rd Bomb Squadron patch showing the bombs dropping into a volcano. Victory was declared.

The USAAC’s “Keystone” bombers themselves were a pretty rag tag group of outdated, obsolete airplanes that the USAAC hoped to replace.

The B3-A was a twin-engine biplane bomber, among the last biplanes used by the United States Army. Each 48 foot-long airplane was operated by a crew of five and had a less than dazzling cruising speed of 98 miles per hour with a service ceiling lower than the 13,679-foot summit of Mauna Loa.

The U.S. Army planes dropped bombs, targeting the lava channels and tubes just below the vents at 8,600 ft hoping to divert the flow near its source. The results of the bombing were immediately declared a success by the good Doctor Jaggar. In the resulting news reels, the USAAC was credited with saving Hilo and its waterworks. To this date, the 23rd Bomb Squadron still officially takes credit for saving Hilo from destruction by lava.

Doctor Jaggar who claimed his plans saved Hilo in 1935 by arranging the bombing of a lava flow.

Jagger wrote that “the violent release of lava, of gas and of hydrostatic pressures at the source robbed the lower flow of its substance, and of its heat.”

Indeed, the lava stopped flowing on January 2, 1936.

However, the efficacies of the lava bombing and the science behind the idea have been disputed ever since the 1930s.

The modern scientific conclusion is that Dr. Jaggar’s assessment was vastly overstated and the lava flow stopped entirely by coincidence.

In effect, the small Mk I bombs were a pointless and futile effort.

Just five months later, in a bizarre twist, the Mauna Loa volcano again erupted, once again threatening Hilo. Once again, US Army aviation assets were called in for the job, this time using more modern B18s. Their bombs proved equally ineffective; in other words, a thorough waste of otherwise good munitions in the view of later scientists who have studied the matters closely. That wasn’t the end of the “bomb the volcano” trend, however, and bombs were similarly used to “thwart” another Hilo-bound Mauna Loa flow in 1942. Mauna Loa can be such a tease.

So, could one successfully use bombs to divert lava flows? The question remains alive today and was floated in discussions relating to the current lava flows from Kilauea Carter than have threatened Pahoa as recently as this year.

The answer is not completely clear. In the late 1970s, a volcanologist from the Hawaiian Volcano Observatory recruited the military to drop thirty-six bombs on historical Mauna Loa flows along the northern part of the mountain, within an Army training area. Doctor Lockwood assumed the strength of the hardened old flows was comparable to active flows, which often develop a solidified exterior mid-eruption.

Look at tiny plane. Now, look at world’s largest shield volcano. It wasn’t a fair fight but Madame Pele has a sense of humor and stopped the flow.

The result of the experiment was awesome demolition, where bombing pockmarked flows with mini craters.

The largest craters formed in areas where the rock was less dense.

It was proof enough that bombing could work using the far more powerful bombs available.

In theory lava bombing might work but frankly today’s residents of Hawaii would never stand for a bombing of what Madame Pele has created. “Let the lava flow” is the only acceptable mantra today.

Final note: to watch a brief newsreel of the actual 1935 lava bombing, please click on this link. I could not afford the fees to embed the nifty video but you can see it at the link for free.

Obligatory dog photo. Max cares little about this topic.