The Cornell Gazel Research Group has developed a rapid and accurate way to determine the depth of magma storage underneath volcanoes. The published research, led by Prof. Esteban Gazel, earth and atmospheric sciences, outlines the methods they used to determine the density of carbon dioxide fluids within volcanic crystals, which they related to the depth of the magma.
The research group was part of a small team of international researchers that visited the Canary Islands following the La Palma eruption in October 2021. They joined a NASA-funded project whose main aim was to collect volcanic ash samples, but they also collected volcanic samples from the eruption zone to aid their study.
One of the main areas of focus in the study of volcanoes is locating the depth of magma reservoirs present under the volcano, though using satellite data often proves ineffective, because signals typically do not penetrate deep enough. The ability to pinpoint the location and size of the magma chamber prior to eruption is a significant development, as researchers can now use this information to predict the likelihood of future eruptions based on the previous activity of volcanoes.
Understanding where magma is stored within volcanoes requires information on the crystals that are expelled by the volcano prior to an eruption. As the magma is expelled by the volcano, it cools, crystallizing once the temperature falls significantly.
Researchers can use chemistry to study the pressure difference between the lava held within the crystal and the crystal itself, but the possible errors in this method are too large for it to be reliable.
This is where fluid inclusions — microscopic bubbles of liquid or gas trapped within a crystal — come in. After decades of study, scientists have been able to use the density of carbon dioxide fluid trapped within these crystals to calculate the depth from which they were expelled. Greater density means that the crystal was trapped deeper inside the earth, helping researchers pinpoint the depth of the magma chamber.
“The thought is that if you have carbon dioxide inclusions, then that gives you the location where the crystals are sitting and the inclusions are being trapped — usually a magma chamber,” said Kyle Dayton, co-author of the paper.
According to Dayton, studying carbon dioxide inclusions is a faster and more accurate method. Previously, researchers studied fluid inclusions using xenoliths, fragments of mantle or crust brought up with the eruption.
The Gazel Group modified this approach as well.
“[W]e targeted crystals directly from the magma to get an idea of where the magma actually is,” Dayton said.
The process of physically identifying these inclusions is complex and requires a considerable level of expertise. The research group adopted a method called Raman spectroscopy — a setup using lasers and detectors — that yields accurate results without significant manual intervention.
“What was unique about our paper is that we used a technique called Raman spectroscopy,” Dayton said. “This allows us to measure smaller inclusions very accurately and much faster.”
The use of a standardized method like Raman spectroscopy allows for increased accessibility to other researchers around the world. By determining the structure of carbon dioxide molecules in the magma crystals, the spectroscope helps determine the density of the fluid inside the crystals.
For the La Palma eruption, the group deduced that the crystals started shallower and then became deeper as the magma chamber emptied over the course of the two-month eruption. This data is highly specific to the volcano the samples were taken from, but it can convey a lot of information about the activity within the volcano.
For example, researchers could be aware that magma is stored approximately seven kilometers under the surface. If the tremors causing an earthquake in the region are recorded at one to three kilometers beneath the ground, they should not be a major cause for concern, as they are not located near the magma.
This technique can not only be applied to hotspot volcanoes like the Canary Islands,but also arc volcanoes like those found in Indonesia.
Ultimately, the results of this study demonstrate significant potential for further research in this area.
“A global study of fluid inclusions of different volcanic settings around the world could provide us with information about past magma storage so that we can get an idea of how these systems have evolved over time,” Dayton said.
Aditya Syam is a staff writer. He can be reached at [email protected]