January 6, 2014
Two New Studies Shed Light On Supereruptions, Other Volcanic Activity
redOrbit Staff & Wire Reports - Your Universe Online
One team of researchers has uncovered the factors that determine the frequency and magnitude of volcanic activity, while another has identified the triggers for the rare and explosive eruptions experienced by supervolcanoes, according to studies currently appearing in the advanced online edition of the journal Nature Geoscience.
In one paper, ETH-Zurich professor Carmen Sanchez-Valle and her colleagues used an X-ray beam at the European Synchrotron Radiation Facility (ESRF) in France to determine the density of supervolcanic magma. By doing so, they demonstrated that the massive amount of pressure caused by density differences in the magma chamber is capable of triggering a supereruption on its own.
Unlike conventional volcanoes, supervolcanoes are typically active only once every 100,000 years at best, and their eruptions are not triggered just by overpressure due to magma recharge in the magma chamber. Their chambers can be several kilometers thick and up to 100 kilometers wide, making it impossible for sufficient overpressure to be sustained through magma recharge, Sanchez-Valle and her co-authors said.
“Until now, scientists could only speculate about what triggers a supereruption. One possible mechanism was thought to be the overpressure in the magma chamber generated through density differences between the less dense molten magma and the comparatively more dense rock in the surroundings,” ETH Zurich said in a statement. The effect was described as similar to an underwater soccer ball being forced upwards by the denser water surrounding it.
“For the magma to break through the crustal rock above the magma chamber and carve out a path to the surface, it needs an overpressure level that is 100 to 400 times higher than air pressure,” the institute added. To determine whether or not that was possible, the researchers had to directly determine the density of both the magma melt and the rock material surrounding it. The magma density, however, had never actually been gauged.
With the assistance of X-rays, the investigators were able to determine the density of supervolcanic magma, collecting enough data to help them simulate the conditions present in a supervolcano. They discovered that if the magma chamber was large enough, the overpressure caused by density differences alone would be enough to break through the crust above and cause an eruption to occur.
In a separate study, an international team of experts conducted more than 1.2 million simulations in order to determine the conditions that cause different sizes of volcanic eruptions to occur. Using numerical modeling and statistical techniques, the study authors were able to discover what factors control the frequency of volcanic activity, as well as the amount of magma that will be released in an eruption.
“The researchers… showed how different size eruptions have different causes,” the University of Bristol, one of the institutions involved in the research, said in a statement. “Small, frequent eruptions are known to be triggered by a process called magma replenishment, which stresses the walls around a magma chamber to breaking point.”
“However, the new research shows that larger, less frequent eruptions are caused by a different phenomenon known as magma buoyancy, driven by slow accumulation of low-density magma beneath a volcano,” the university added. “Predictions of the scale of the largest possible volcanic eruption on earth have been made using this new insight. This is the first time scientists have been able to establish a physical link between the frequency and magnitude of volcanic eruptions and their findings.”
Based on the team’s analysis, lead researcher Luca Caricchi, assistant professor at the Section of Earth and Environmental Sciences at the University of Geneva, and his colleagues said that they can estimate that a volcano’s magma chamber is capable of containing a maximum of 35,000 cubic kilometers of magma that can be erupted. Of that amount, approximately 10 percent is released during a supereruption.