03/23/2019
Many of the preconceived notions we had about the eruptions of our Hawaiian volcanoes have been turned upside down by the observations of USGS scientists. Come holoholo with us and learn more about the wonders of our living planet!
Researchers are re-evaluating early assumptions about the role groundwater played in triggering the explosive eruptions at the summit of Kīlauea Volcano and are now looking at the build-up of gases from retreating magma as a likely trigger.
In February 1924, the surface of the lava lake at Halema‘uma‘u dropped rapidly and disappeared from view. Throughout March and April, the crater floor subsided as magma moved out of the summit reservoir into the East Rift Zone. A series of explosions began during the night of May 10–11, 1924, tossing large chunks of rock onto the caldera floor and sending ash plumes more than 2 km (1 mi) high. The trigger for the 1924 explosions was thought to be heated groundwater flowing into the empty conduit.
Fast-forward to May 2018 (94 years later) when the scene was frighteningly similar. Magma drained from Kīlauea's shallow summit reservoir and moved into the East Rift Zone. The summit lava lake was no longer visible on May 10, and likely dropped below the water table on May 11–12, 2018. Explosive activity was considered a strong possibility given what happened in 1924. But, while moderate explosions and associated ash plumes did occur in 2018, major explosions like those of 1924 did not.
Why not? Researchers have analyzed core samples from a deep well in the area and are using computer models to understand more about how quickly groundwater moves through this volcanic area. The answer is, that it takes months to years for groundwater to reach the conduit.
A currently favored idea is that gas from the retreating magma, rather than groundwater steam, powered the explosions (as viewed in the photo comparison of 1924 and 2018). This idea is being used to reconsider what we understand about the eruptions (and hazards) of Kīlauea Volcano's past, present, and future.
Read more in this week’s edition of HVO’s Volcano Watch, “Did groundwater trigger explosive eruptions at Kīlauea?” at https://volcanoes.usgs.gov/observatories/hvo/hvo_volcano_watch.html?vwid=1404.
