The predictive power of geochemistry
A WHOI researcher looks for changes in gas molecules to forecast volcanic eruptions
The predictive power of geochemistry
A WHOI researcher looks for changes in gas molecules to forecast volcanic eruptions
BY ELISE HUGUS | DECEMBER 20, 2022
For WHOI petrologist Forrest Horton, the future of hazard prediction is geochemical. When news recently broke that Mauna Loa on the Big Island of Hawai’i was erupting for the first time in 38 years, he immediately got in touch with colleagues in Hawai’i. While the United States Geological Survey (USGS) Hawaiian Volcano Observatory uses a suite of instruments and satellites to monitor active volcanoes, Horton and fellow WHOI geochemist Pete Barry look for changes in ambient gas molecules that might signal an impending eruption, Horton says, because it escapes so rapidly. That means scientists are able to distinguish the molecular signals of helium originating from the deep Earth from the helium coming from shallower magma reservoirs beneath dormant volcanoes.
Once things cool down on Mauna Loa, Horton hopes to find crystals embedded in solidified lavas at the eruption site in order to characterize the gases trapped within them. As he found after a 2021 volcano eruption in Iceland, changes in the helium isotope signature in lavas gathered around the eruption site demonstrate the potential of this method—but it won’t be as easy as placing a sensor on the lip of an active volcano. Still, he hopes geochemical methods could become part of the scientific community’s hazard-prediction toolbox to provide an extra layer of safety for people living on volcanic islands.
While Mauna Loa smolders, Horton shared his insights into the predictive power of geochemistry.
How can we use chemistry to help predict volcanic eruptions? And why use helium specifically?
Horton: There’s an increasing effort to use a variety of methods to monitor hazards. Instead of relying on just earthquakes or just ground swelling, we can inform predictions using geochemical instruments, like monitors that provide 24/7 readings of the gases coming out of volcanoes.
Helium is a noble gas, which means it doesn't create chemical bonds with other elements. And it's the lightest noble gas, so it escapes our atmosphere quickly, which is why helium balloons go up.
Much of the helium leaking out of Earth was trapped during planetary formation. And so, there's this continual degassing or loss of helium from Earth's interior to space. Different layers of the Earth have different isotopic compositions, or slightly different weights, of helium. There’s much more of the light Helium-3 relative to the heavier Helium-4 in the deep Earth compared to shallower portions of the planet.
How can this chemical signature method be used to predict eruptions?
Horton: When a volcano is about to erupt, magma from the deep Earth fills a magma reservoir, which is pretty shallow. So if you're able to detect magma recharge–or the filling of a magma reservoir beneath the volcano–that allows you to better predict the eruption. And because the magmas carry with them this unique helium from the deep Earth, we might detect helium leaking out in volcanic gases. So helium may provide a critical clue about whether magma recharge is happening.
Our goal is to look at the helium trends over the course of previous eruptions and see whether changes in eruptive behavior, such as the discharge rate, or how much lava is coming out, changes with the helium [signature].
Nobody's looked at helium on these timescales in lavas before, so it’s difficult to know whether they can be used to predict an eruption. We know that helium isotopes change over thousands of years, millions of years. But do they change on shorter timescales? In Iceland, after the 2021 eruption, we found helium isotopic changes over the course of months. And so the idea behind our research is to go to a bunch of these volcanoes and look at changes over time to see whether we can develop this into a predictive tool.
What would it look like to take helium measurements from an active volcano?
Horton: If it can be used in a predictive way that's useful for hazard monitoring, then perhaps we can create mobile stations for measuring helium. It's not as easy as just taking an instrument out there. We're talking about perhaps a shipping container full of equipment costing more than $1 million. But compared to the destructive potential of some volcanoes, maybe it's a worthwhile investment if it has predictive power.
I would be really excited if we could continuously monitor helium isotopes on some of the most dangerous volcanoes and use the resulting information in tandem with more established techniques to predict eruptions. But of course, we need to improve our scientific understanding of helium behavior in volcanic systems to realize the potential of this approach.
Funding for this research is provided by a WHOI Interdisciplinary Award.
