Volcano Watch: Explosive Eruptions from Halemaʻumaʻu in 1924

“Volcano Watch” is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates. This week’s article was written by Hawaiian Volcano Observatory geologist Drew Downs.

May 2023 marks the 99th anniversary of a sequence of explosive eruptions from Kīlauea’s summit that occurred throughout 16 days from May 11-27, 1924. During this eruption, about 60 explosions occurred from Halemaʻumaʻu, with fragments ranging in size from volcanic ash to large blocks as large as cars falling around the summit caldera.

For nearly two decades prior to the explosive eruptions in 1924, Halemaʻumaʻu hosted a large lava lake. In February 1924, this lava lake drained during the course of two days, leaving behind an incandescent crater that was about 380 feet deep by 1,700 feet wide (115 meters deep by 520 meters wide). Halemaʻumaʻu remained an empty crater for the next two months.

April 1924 saw the summit of Kīlauea hit with an earthquake swarm that migrated down the East Rift Zone. Residents of Kapoho in the lower East Rift Zone felt more than 200 earthquakes April 22-23, which resulted in an approximately 4-mile-long by 1-mile-wide (6.5-by-1.6-kilometer) tract of land cracking and subsiding. This included the area near the eastern point of the Island of Hawaiʻi dropping by about 14 feet (4 meters) and the ocean covering nearly a half mile (1 kilometer) of previously dry land. Despite the shaking and subsidence in the lower East Rift Zone, which was associated with lava draining from the summit lava lake, no eruption occurred in the rift zone.

On April 29, 1924, the floor of Halemaʻumaʻu started to subside and eventually reached about 600 feet (180 meters) below the crater rim by the time the first explosions occurred during the nighttime hours of May 10-11. Hot rocks from this explosion were noticed near the rim of Halemaʻumaʻu on the morning of May 11 by a national park ranger. This prompted road closures within Hawai’i National Park (as it was named then), as well as a close call when the park superintendent and two observers were pelted by ash during another explosion that sent ash up to 3,000 feet (nearly 1 kilometer) high. In fact, a 100-pound (45-kilogram) boulder was thrown over the group’s vehicle nearby, prompting the roadblock to be pushed back even farther.

Explosions of ash, lapilli and blocks continued to be ejected from the crater. The largest of these explosions occurred May 18, with lightning-charged ash pluming higher than 4 miles (6.5 kilometers) into the sky, as well as spreading across the crater floor. Several people were near the crater rim when this explosion occurred. Unfortunately, a resident of Pāhala was hit by a block and died that night at the hospital in Hilo. This was the only fatality during these explosive eruptions.

Explosions continued, although smaller than the one on May 18, and by May 27, when the explosions ended, Halemaʻumaʻu was about twice as wide and eight times as deep than prior to the sequence of explosions. Blocks weighing as much as 8 tons (8,000 kilograms, equivalent to 10 cows) were hurled as much as 1,600 feet (500 meters) from the crater.

Scientists originally proposed that the lava lake draining exposed cracks in the crater floor that allowed groundwater to enter the system. This groundwater might have flashed to steam and resulted in the many explosions throughout the 16 days in May 1924. However, new research being undertaken by the Hawaiian Volcano Observatory could reveal other explanations for these explosive events. This research will help us better understand these explosive bursts that occurred nearly a century ago and compare them with the more recent explosions from the summit of Kīlauea in 2018.

Volcano Activity Updates

Kīlauea is not erupting. Its USGS Volcano Alert level is Advisory.

Webcams show no signs of active lava in Halemaʻumaʻu crater, at the summit of Kīlauea in Hawai‘i Volcanoes National Park. During the past week, summit tiltmeters showed inflation and seismicity has been variable. The summit sulfur dioxide (SO2) emission rate was most recently measured May 3, when it totaled 135 tonnes per day.

Mauna Loa is not erupting. Its USGS Volcano Alert Level is at Normal.

Webcams show no signs of activity on Mauna Loa. Seismicity remains low. Summit ground deformation rates show inflation above background levels, but this is not uncommon following eruptions. SO2 emission rates are at background levels.

There were five earthquakes above magnitude 3 and with three or more felt reports in the Hawaiian Islands during the past week: a magnitude-3.5 earthquake at 4:56 a.m. May 10 located about 5.6 miles (9 kilometers) east-southeast of Pāhala at at depth of 19 miles (32 kilometers); a magnitude-3.8 quake at 11:58 p.m. May 7 located about 6.8 miles (11 kilometers) east-northeast of of Pāhala at a depth of 19 miles (32 kilometers); a magnitude-3.3 temblor at 7:35 a.m. May 7 less than 1 mile northeast of Pāhala at at depth of 24 miles (39 kilometers); a magnitude-3.0 earthquake at 4:26 p.m. May 5 located 21 miles (35 kilometers) easth-northeast of Waimānalo Beach at a depth of 5 miles (8 kilometers); and a magnitude-3.7 quake at 1:05 p.m. May 4 located 7 miles (12 kilometers) south-southeast of Fern Forest at a depth of 3 miles (5 kilometers).

HVO continues to closely monitor Kīlauea and Mauna Loa.

Visit HVO’s website for past “Volcano Watch” articles, Kīlauea and Mauna Loa updates, volcano photos, maps, recent earthquake information and more. Email questions to askHVO@usgs.gov.