Dynamical models of large volume effusive eruptions and controls on caldera collapse

Abstract:

Deformation data and effusive rates of many volcanic eruptions are explained by the depressurization of a magma reservoir embedded in an elastic medium. Larger events, producing erupted volumes on the order of a cubic kilometer, are not accounted for by this simple model. These eruptions seem, rather, to be controlled by the dynamics of caldera collapse which proceeds as a series of discrete slip events along ring faults. We present here a new model to understand the dynamics of these eruptions. The results show that pressure gradients generated by topography are needed to trigger foundering of the reservoir roof, which in turn maintains high pressures in the chamber with periodic collapses. Different types of behavior are possible depending on the relative magnitude of frictional properties and topographic effects. Importantly, this mechanism is able to produce much larger erupted volumes compared to simple elastic models. For the 2018 Kilauea eruption we use these findings and combine them with InSAR, GNSS, tiltmeter and long-term eruptive rate time-series to constrain the main properties of the magmatic system, such as the number of reservoirs, their volumes, magma compressibility, hydraulic connectivity and frictional properties. Finally, we show that this model not only works for the Kilauea 2018 eruption, it is also consistent with the largest instrumented caldera collapses of the past fifty years.