Integrating satellite-derived rainfall data into models of stress evolution at active volcanoes

Several studies have highlighted an increased likelihood of eruptive activity during or after precipitation events at active volcanoes, and a wide range of mechanisms have been proposed to account for this. Nevertheless, the influence of rainfall on the likelihood or magnitude of regional volcanic activity is a poorly-understood phenomenon. Here, we focus on the potential triggering of primary volcanic activity due to deep-seated stress perturbations caused by rainfall infiltration into the edifice. By classifying historical eruption catalogues, we observe that a significant proportion of eruptions at many tropical volcanic centers coincide with their respective wet seasons. For example, at Gunung Merapi (Indonesia), >80 % of historical eruptions occur during the wet season of Central Java (October-March). Binomial probability analysis highlights that the temporal distribution of eruptions throughout the year at Merapi is statistically anomalous: the probability of the observed pattern of eruptions occurring by chance is just 0.013 (just over 1 %). This ratio (wet season:dry season) becomes even more pronounced when considering larger events, and is a pattern echoed across many other volcanic systems in the tropics. Mechanical failure at the wall of a magma chamber—and hence, the likelihood of eruption—is a function of the local and regional stresses and the interstitial pore fluid pressure. The combination of these factors gives us a conceptual average stress, termed the effective stress. In order to explore how the pore pressure and effective stress at depth are perturbed by rainfall infiltration into the edifice of different volcanic systems, we extract rainfall time series data from the NASA/JAXA Tropical Rainfall Measuring Mission and Global Precipitation Measurement mission datasets. We use these data to impose boundary conditions in a pressure diffusion model, whereby pore pressure is a function of daily rainfall amounts—related to the initial pressure head perturbation by density and gravity—and evolves as a function of time, depth, and diffusivity (itself a function of rock and fluid physical properties). We anticipate that a combination pore pressure evolution models and inversion-based deformation modeling will yield insight into complex eruptive sequences involving a rainfall component.