The Danger of Sleeping Volcanoes Revealed by Zircon Crystals
Cathodoluminescence image of Zircon crystals from Nevado de Toluca volcano in Mexico.
A new method shows that it’s now possible to estimate the volume of magma stored below volcanoes providing essential information about the potential size of future eruptions.
Most active volcanoes on Earth are dormant, meaning that they have not erupted for hundreds or even thousands of years, and are normally not considered hazardous by the local population. A team of volcanologists from the University of Geneva (UNIGE), working in collaboration with the University of Heidelberg in Germany, has devised a technique that can predict the devastating potential of volcanoes.
The scientists used zircon, a tiny crystal contained in volcanic rocks, to estimate the volume of magma that could be erupted once Nevado de Toluca volcano (Mexico) will wake up from its dormancy. Up to 350 km3 of magma — about four times the volume of water stored in Lake Geneva — are currently lying below Nevado de Toluca and their eruption could bring devastation. The new technique, applicable to most types of volcano across the globe, is described in the scientific journal Nature Communications.
The largest volcanic eruptions in the last 100 years were sourced from volcanoes that do not erupt frequently and therefore fly under the “radar” of scientists. Yet today, 800 million people around the world live close to volcanoes and are potentially at risk. A determining factor for the dangerousness of volcanoes is the volume of eruptible magma stored in their bellies, as this is related to the magnitude of future eruptions. Unfortunately, this magma is stored at inaccessible depths of 6-10 km and cannot be directly measured.
Tiny watches with a thermometer
The UNIGE volcanologists used a new approach combining zircon geochronology and thermal modeling to determine the volume of potentially-eruptible magma present in the volcanic reservoirs. “Zircon is a small crystal found in rocks erupted by volcanoes, and it contains uranium and thorium,” begins Gregor Weber, a postdoctoral fellow at UNIGE and co-author of the study. “The decay of these radioactive elements allows us to date when they crystallized. Additionally, zircon crystallizes only in a specific temperature range. With these two parameters, we can determine how fast the magma is cooling below a volcano. Like a pot of water, the larger the pot, the more time it takes to cool it. We analyzed the zircons erupted over the last 1.5 million years by Nevado de Toluca thus determining the evolution of temperature of the magma stored below the volcano over time. This information can be converted into a volume of magma using thermal modeling.” This approach has a resolution two times higher than that of existing techniques.