Spatial probability of vent opening at the active central volcanoes of São Miguel (Azores)

Forecasting the location of future volcanic eruptions is one of the most critical and challenging issues when assessing volcanic hazard. A long-term hazard assessment approach based on past eruptive behaviour is of utmost importance for dormant or low-activity volcanoes, on which sound land-use policies and risk mitigation plans should be based.São Miguel Island in the Azores Archipelago hosts three active central volcanoes (Sete Cidades, Fogo, and Furnas) that produced a large variety of eruptions in the last millennia and even in historical times, including trachytic explosive and effusive events and basaltic flank eruptions. Although these volcanoes are currently in a repose period, the likelihood of future eruptions should not be neglected.  This study focuses on the estimation of the spatial probability of vent opening at the Sete Cidades, Fogo, and Furnas volcanoes separately, using the kernel method. Here, we used the location of past basaltic and trachytic emission centres, in the form of vents or fissures, of each volcano, to explore different kernel functions (Gaussian, Cauchy, Exponential, and Uniform) and calculate the best degree of clustering of vents given by a smoothing parameter (h). This approach was applied to each volcano by considering (1) basaltic and trachytic emission centres (fissures and/or vents) and (2) only trachytic emission centres (vents). This allowed us to estimate the pair (kernel function and h-value) that best fits the empirical cumulative distribution function of the minimum distance between emission centres and compute the final vent opening probability maps conditional to an eruption (or susceptibility maps).For Sete Cidades, the results show that when considering basaltic and trachytic emission centres together, the southeast and west flanks of the volcano have a higher likelihood of hosting a new vent; however, when considering trachytic vents alone, the higher probability is at the west flank and southern sector of the caldera. The susceptibility map generated using Fogo’s basaltic and trachytic emission centres indicates a higher likelihood of hosting a new vent at the northwest flank of the volcano and southeast sector of the caldera. When only trachytic vents are considered, the southeastern sector of the caldera is more likely to host a new vent. For Furnas volcano, the results show that the northwestern part of the caldera has a higher likelihood of hosting a future basaltic or trachytic vent.