Supervolcanic eruptions solved?

Supervolcanic eruptions are caused by a change in magma pressure and magma buoyancy suggests two new research papers. Supervolcanoes have a large magma chamber compared to conventional volcanoes, and are located in areas where the heat flow from the interior of the Earth the surface is very high. Its chamber is able to change shape as it fills with magma which allows for greater dissipation of pressure and fewer eruptions. “The driving force is an additional pressure which is caused by the different densities of solid rock and liquid magma,” said Wim Malfait from ETH Zurich. “It is comparable to a football filled with air under water, which is forced upwards by the denser water around it.” In the study, Malfait led an international team of researchers who used X-rays at the European Synchrotron to probe the state and change in density when magma crystallises into rock. They placed speck-sized rock samples in a Paris-Edinburgh press, between the tips of two tungsten carbide anvils and heated with a resistive furnace. Here the samples reached temperatures of up to 1700°C and pressures of up to 36,000 atmospheres. Their results show that the pressure resulting from the density differences is enough to crack the Earth’s surface above the magma chamber, allowing the magma to expand and an eruption to occur. In a second study, a team from the Universities of Bristol, Geneva and Savoie carried out over 1.2 million simulations to determine the frequency and magnitude of volcanic eruptions. “Some volcanoes ooze modest quantities of magma at regular intervals, whereas others blow their tops in infrequent super-eruptions. Understanding what controls these different types of behaviour is a fundamental geological question,” said Professor Jon Blundy from Bristol. The research has for the first time established a physical link between the frequency and magnitude of volcanic eruptions. Smaller frequent eruptions are known to be caused by magma replenishment, but what causes eruptions like those of supervolcanoes was unclear. Using numerical modelling and statistical techniques, the team showed that larger, less frequent eruptions are caused by magma buoyancy – a slow accumulation of low-density magma beneath a volcano. “Our work shows that this behaviour is a result of interplay between the rate at which magma is supplied to the shallow crust underneath a volcano and the strength of the crust itself. Very large eruptions require just the right (or wrong!) combination of magma supply and crustal strength.” Both papers have been published in Nature Geoscience. Supervolcanic eruptions driven by melt buoyancy on large silica magma chambers Frequency and magnitude of volcanic eruptions controlled by magma injection and buoyancy