Numerical modelling shows that magma buoyancy is the most important factor in determining the frequency and magnitude of the Earth’s most destructive volcanic phenomena

A new paper by a collaboration from the Universities of Geneva, Bristol and Savoie quantifies the relative contributions of magma supply, mechanical properties of the crust and magma, and tectonic regime in controlling the frequency and magnitude of volcanic eruptions. The team, led by Professor Luca Caricchi, coupled over 1.2 million simulations of a thermomechanical numerical model of magma injection into Earth’s crust with complex statistical analysis to try and replicate the behaviour of melt beneath a volcano.

This work reveals a dichotomy in the causes of volcanic eruptions, which is related to their size. It is known that small, frequent eruptions are triggered by magma replenishment, which imparts stress on the magma chamber walls; eruptions occur when this stress exceeds the strength of the surrounding rock. In contrast, Caricchi et al. demonstrate that bigger, less frequent eruptions are instead driven by the intrinsic buoyancy associated with large magma bodies, a consequence of  the slow accumulation of low-density magma beneath a volcano.

Fountain Geyser Pool, Yellowstone National Park, Wyoming. Yellowstone caldera has experienced three supereruptions in the last 2.1 million years. Credit: US National Archives (79-AA-T19)

These findings are particularly important because this is the first time a physical link between the frequency and magnitude of volcanic eruptions has been established. The findings allow the predictions of the scale of the largest possible volcanic eruption on Earth; the work suggests magma chamber can contain a maximum of 35,000 km³ of eruptible magma, translating to an eruption spewing out approximately 3,500 km³ of rock. This is three times the volume released during the supereruption of Yellowstone around 640,000 years ago.