The composition of the gases could warn of increased volcanic activity.
Volcanic eruptions are dangerous, but unfortunately also difficult to predict. Now a team of scientists from the University of Tokyo has discovered that the ratio of atoms in certain gases released from volcanic fumaroles (holes in the Earth’s surface) can provide an indicator of what’s happening to the magma deep below. It works much like a blood test to check your health. This may indicate when things could be volcanically “heating up.”
In particular, changes in the ratio of argon-40 and helium-3 can indicate how frothy the magma is, indicating the risk of different types of eruptions. Understanding which ratios of which gases indicate a particular type of magma activity is a big step. Next, the researchers hope to build a 24/7 monitoring and early warning system for volcanic activity by developing wearable devices that enable real-time on-site measurements.
Does the thought of standing on a volcano make you tremble with excitement or fear? For many people, living in the shadow of a volcano is part of everyday life. Japan has 111 active volcanoes and an average of 15 volcanic “events”, including eruptions, each year. However, these events — which can be deadly — are notoriously difficult to predict.
Mount Ontake, Japan’s second highest volcano and a famous tourist spot, unexpectedly erupted in 2014, sadly killing 58 people and missing five. Although earthquake activity is typically an early warning sign, some eruptions (including that at Ontake) can occur without clear earthquake signals. Therefore, disaster management agencies like the Japan Meteorological Agency would benefit from other reliable ways to warn residents of the next potential disaster.
Fumaroles are holes and fissures in the Earth’s surface (the crust) that release gas and steam, and often form near volcanoes. The emitted gas consists of a mixture of chemicals. Its composition can give us a glimpse of what is happening beneath the Earth’s crust in the mantle, where magma (molten rock) forms and pushes up to eventually erupt as lava. Researchers already know that the ratio of isotopes (atoms of an element with the same chemical properties but different masses) in certain gases can indicate latent magma activity.
“We knew that the isotopic ratio of helium occasionally changes from a low value, similar to helium in the crust, to a high value, like that in the mantle, as magma activity increases. This was based on an observation of the helium isotope ratio of cold source gas on El Hierro Island in the Canary Islands (in the Atlantic Ocean off the northwest coast of Africa), where an eruption occurred in 2011,” explained Professor Hirochika Sumino of the Research Center for Advanced Science and Technology. “But we didn’t know why we had more mantle-derived helium during magmatic upheavals.”
Hirochika Sumino (dark green jacket), Tomoya Obase (blue jacket), and Hiroshi Shinohara (orange jacket) collect gas samples from fumaroles in the Tateyama Jigokudani (“Hell Valley”) geothermal area in Toyama Prefecture, Japan. Collecting gas samples from fumaroles is dangerous due to the toxic gas and hot steam, so a gas mask, goggles, helmet, and gloves are required. But according to Sumino, the results of this study show that the insights gained from the samples are worth the challenge. Credit: Yuki Hibiya
To gain more insight, Sumino and the research team decided to monitor gases from six fumaroles around the active Kusatsu-Shirane volcano, located about 150 kilometers (90 miles) northwest of Tokyo in Gunma Prefecture. The team collected samples every few months for seven years between 2014 and 2021. After collection, they brought the samples back to the lab and analyzed them using state-of-the-art equipment called noble gas mass spectrometers. This allowed them to precisely measure isotopic compositions, including those of ultratrace (tiny but important) isotopes like helium-3, which is typically more abundant in the mantle than in the crust or air.
“We have been able to detect changes in the magma-derived argon-40/helium-3 ratio associated with magmatic turmoil. Using computer modeling, we found that the ratio reflects how much the underground magma foams, forming bubbles of volcanic gases that separate from the liquid magma,” Sumino explained. “How much magma foams controls how much magmatic gas is fed into the hydrothermal system beneath a volcano and how buoyant the magma is. The former is related to the risk of a phreatic eruption, where an increase in water pressure in the hydrothermal system causes the eruption. The latter would increase the rate of magma rise, leading to a magmatic eruption.
“If you compare a volcano to a human body, the conventional geophysical methods represented by observations of earthquakes and crustal deformation are akin to chest-listening and measuring body size. In these cases, without a thorough medical exam, it’s difficult to determine what health problem is causing your chest noise or sudden weight gain. On the other hand, analyzing the chemical and isotopic composition of elements in fumarol gases is like a breath or blood test. That means we’re looking at actual material taken directly from magma to know exactly what’s going on with the magma.”
Currently, gas samples must be collected in the field and returned to the laboratory for analysis, a challenging and time-consuming process. However, Sumino has experience improving noble gas mass spectrometers and hopes to develop a new tool that would allow them to perform the same analysis, but in real time and in the field.
“We want to be able to detect changes in magma activity as quickly as possible,” Sumino said. “Now we are developing a portable mass spectrometer for on-site real-time monitoring of noble gas isotopic ratios of fumarole gases. Our next step is to set up an inert gas analysis protocol with this new instrument to allow all active volcanoes — at least those that have the potential to cause disaster for local residents — to be monitored 24 hours a day, seven days a week on the weekend .”
Reference: “Monitoring of the magmatic-hydrothermal system by noble gas and carbon isotope compositions of fumarole gases” by Tomoya Obase, Hirochika Sumino, Kotaro Toyama, Kaori Kawana, Kohei Yamane, Muga Yaguchi, Akihiko Terada and Takeshi Ohba, November 21, 2022, Scientific Reports.
Funding: This work was supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan under its Integrated Next Generation Volcano Research and Human Development Program (Program Grant Number JPJ005391) and The Second Earthquake and Volcano Hazard Observation and Research Program (Research to reduce earthquake and volcanic hazards).
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