This photo provided by the U.S. Geological Survey shows the summit lava lake of Hawaii's Kilauea ... [+]
By analyzing the dynamics of a string of explosions that happened during the 2018 Kīlauea volcano eruption, researchers described a new type of volcanic eruption mechanism. The explosions were driven by sudden pressure increases as the ground collapsed, which blasted plumes of rock fragments and hot gas into the air, much like a classic stomp-rocket toy.
In May 2018 Kīlauea volcano erupted following a 5.0-magnitude earthquake, sending lava flows down the flanks of the volcano. Those lava flows destroyed thousands of homes and displaced nearly 1,700 residents on the Island of Hawai'i for months.
A lava lake formed in the summit caldera, with explosions sending huge columns of ash into the sky.
For the most part, such explosive eruptions are either primarily driven by rising magma pressure, steam/vaporized groundwater, or some combination of the two, according to Josh Crozier, who as a doctoral student at the University of Oregon studied the 2018 eruption.
"These eruptions are quite interesting in that they don't really seem to involve either of those," Crozier says. "The eruptive material contained very little that looked like fresh magma that was blasted out, but there's no evidence for significant groundwater being involved, either."
"A cool thing about these eruptions is that there were a bunch of them in sequence that were remarkably similar; that's relatively unusual," so Leif Karlstrom, a volcanologist at the UO and study coauthor. "Typically, volcanic eruptions don't happen with as much regularity."
Kīlauea is one of the best monitored active volcanoes in the world. The mountain is covered with scientific instruments, from ground sensors that measure the shaking of the earth to tools that analyze the gases released from the ground. So the researchers had more data than usual to work with, and they could dig deeper into the specific dynamics of the eruptions.
Before each explosion at the summit, magma slowly drained from an underground reservoir, feeding the lava that flowed on the surface. As the reservoir depleted, the ground above it—the crater within the caldera at the volcano's summit—suddenly collapsed as shown by seismic data. That quickly increased the pressure in the reservoir, squeezing gas and bits of rubble through the vent in Kīlauea's crater and forming a column of ash.
The researchers compare the eruption dynamic to a stomp-rocket toy, where stepping on an air bag connected to a hose launches a projectile into the air.
"The 'stomp' is this whole kilometer-thick chunk of rock dropping down, pressurizing the pocket, and then forcing material directly up," Crozier explains. "And the 'rocket' is, of course, the gas and rocks erupting from the volcano."
Caldera collapse is fairly common and a similar mechanism was hypothesized to feed very large eruptions. Observing it directly and repeatedly on a smaller scale shows that volcanic eruptions can be far more complicated than previously believed. Kīlauea's eruption style is generally dominated by a "harmless" effusive activity of lava pouring out from fissures. However, the new study shows that even such volcanoes can quickly switch to a more dangerous explosive eruption style.
The full research paper "Explosive 2018 eruptions at Kīlauea driven by a collapse-induced stomp-rocket mechanism" was published in the journal Nature Geoscience and can be found online here.
Additional material and interviews provided by the University of Oregon.
