Final Report Summary - SLIM (Strain Localisation in Magma)
In this interdisciplinary study, combining field investigations and monitoring of active volcanoes with laboratory testing, we aimed to understand how magma flows, and in particular, provide a description of Strain Localisation in Magma (SLiM). The tendency of geomaterials to localise deformation is a measure of “the fragility of the Earth” – a threshold to the occurrence of geological hazards. At volcanoes, the remarkable, unpredictable and alarming occurrence of eruptions, switching from low-risk effusive to high-risk explosive eruptive behaviour is a direct consequence of strain localisation in magma. Our experimental findings show that the presence of crystals and bubbles in magmas result in a complex deformation where melt, crystals and gas bubbles deform differently. This strain localisation facilitates the rupture of magma, allowing gas to escape or magma to fragment, causing an explosive eruption. These volcanic scenarios are preceded by contrasting monitoring signals (seismicity, ground deformation, outgassing), which may be used to forecast volcanic activity. We find that the accuracy of forecasting methods is dependent on the fraction of heterogeneities (crystals and bubbles) in a system. Following rupture, magma may heal at a rate proportional to its viscosity; but if slip takes place along the rupture interface, heat is generated which lowers the viscosity of magma (increasing the ability of fractures to heal), causes crystals to melt and gas bubbles to grow, thus impacting the mobility of the magma and gas phases that dictate the development of an eruption and its associated signals. The combined field and laboratory descriptions, augmented by analysis of monitored signals performed in SLiM provide important solutions and targeted questions for the future of volcanological research.