1935 Eruption of Mauna Loa

What would it take to stop an eruption from one of Earth’s largest and most active volcanoes? That question was tested during the 1935 eruption of Mauna Loa and the first aerial bombing of an active lava flow. But should man interfere with the natural processes of the volcanic deity Pelehonuamea at all?
Black and white photo of a molten lava flow steaming and moving through a sparse forest
A rapidly moving lava flow from Mauna Loa on December 30, 1935. The flow reportedly moved 600 feet in 25 minutes. (NPS Photo, 17707 Image Collection, Box 33, Folder 3, Image 11)
On November 21, 1935, a fissure of high fountaining lava marked the beginning of one of the frequent summit eruptions of Mauna Loa. Within a few days, a new vent opened on the mountain’s northern flanks. Pāhoehoe lava flowed downhill and gathered on the saddle between Mauna Loa and Mauna Kea before moving east towards Hilo, the population center of the Island of Hawaiʻi. The lava quickly moved down-slope at a rate of one mile (1.6 km) per day as local residents watched pensively. There was a growing concern that lava flows would reach the Wailuku Rver and cut the town's water supply. Pressure was on Dr. Thomas A. Jaggar, the founder of the Hawaiian Volcano Observatory (HVO), to take some sort of action.

Jaggar called on the United States Army Air Service and Lieutenant Colonel George S. Patton (who later gained fame during World War II) to send military planes to detonate bombs near the eruptive vent. His hope was to use bombing to disrupt the lava channels by diverting lava from the advancing flow. However, this wasn’t the first time that the idea of using explosives to alter the path of lava had been raised. Bombing had first been suggested as a method of lava diversion in Hawaiʻi when the 1880-1881 eruption threatened Hilo, though it was never acted upon.
Black and white photo of three bombs on the ground next to a plane and the back of two people in flight suits
Plane preparing to bomb 1935 flow (USGS Photo/Kenichi Maehara)
On December 27, 1935, a cluster of bombs were deployed with astounding technical accuracy. According to a 1980 study by retired USGS Hawaiian Volcano Observatory geologist Jack Lockwood and F.A. Torgerson of the U.S. Air Force, 20 of these bombs were 600-pound MK I demolition bombs, featuring 355 pounds of TNT and armed with a 0.1 second time-delay fuse. The other 20 were "pointer bombs" that contained only small black powder charges.

The 1935 eruption ended six days after the bombing campaign and Dr. Jaggar himself considered the operation a success. He declared that the bombing, "helped hasten end of the flow,” and that, “in a natural end, the lava would not cease so abruptly.”

However, Howard Stearns, a USGS geologist, who was on board the last plane to deliver bombs was doubtful. In his 1983 autobiography Stearns wrote, "I am sure it was a coincidence..." Other studies also show that the 1935 bombing, as well as another in 1942, had limited impacts.

Whether the bombing stopped the 1935 lava flow remains unknown, though many geologists today cast doubt. The 1935 flow did not stop immediately, but rather waned over the course of days, and did not change paths dramatically.

Even with the doubtful success of previous endeavors, the possibility of using air power to divert lava flows should they threaten population centers is still occasionally discussed today. Technology has advanced significantly since previous efforts. However, the use of such tools raises additional questions. Should man interfere in these natural events at all? To some, these actions may be viewed as an affront to the volcano deity Pelehonuamea and the processes of rejeuvenation that she represents. After all, these lava flows were occurring long before the presence of man and contribute to the continued growth of the Island of Hawaiʻi.

Regardless, today the USGS Hawaiian Volcano Observatory continues to monitor the active volcanoes in Hawaiʻi by assessing their hazards, issuing warnings, and advancing scientific understanding to reduce impacts of volcanic eruptions.

See video of the 1935 Mauna Loa eruption, courtesy of the USGS Hawaiian Volcano Observatory.

Black and white photo of a bomb stuck in lava
A bomb from 1935 stuck in the Humuʻula lava flow, discovered and photographed by Jack Lockwood (USGS Photo/J. Lockwood)
In recent years, local media reports have mentioned the “discovery” of one of the unexploded bombs from the 1935 event one of the smaller “pointer bombs” that were used. However, the bomb has been photographed and documented in 1939, 1977, and again in 2020.

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Last updated: March 12, 2021

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