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The triggering of sub-Plinian and Plinian eruptions: insights from three decades of InSAR observations in the Andean Southern Volcanic Zone (1991-2024) and a global compilation

Francisco Delgado1, Pablo León-Ibáñez1, Juan Carlos Báez2, Sofía Parra1

Abstract

Volcanic eruptions are triggered by increases in the overpressure of the regions where magmas are stored.  Hence, observations of ground deformation provide insights on the triggering mechanisms of eruptions, and in particular of sub Plinian and Plinian eruptions which are the most hazardous eruptions with a global impact. We present a compilation of ~30 years observations of ground deformation from InSAR geodesy spanning a sequence of four VEI 4-5 eruptions in the Southern Andes: Hudson 1991, Chaitén 2008-2009, Cordón Caulle 2011-2012 and Calbuco 2015. Only Cordón Caulle displays the theoretical pattern of pre-eruptive uplift, co-eruptive subsidence and post-eruptive uplift. For the rest of the volcanoes we observe co- or post-eruptive ground deformation, but the data temporal resolution is low and did not sample well all the eruptions. On a global scale, a compilation of geodetic data in subduction volcanoes that experienced eruptions of similar magnitudes indicates a dearth of data, but in a few cases geodetic data recorded the last episodes of pre-eruptive reservoir pressurization (Taal, Soufrière St. Vincent). This implies that most of the magma that increased the overpressure must have been emplaced in the decades or centuries prior to eruption. Only Okmok volcano display a ground deformation pattern similar to that of Cordón Caulle. The longer time scales of recharge in subduction volcanoes compared with those in hot spots could be indicative of larger storage regions. This compilations calls for the acquisition of InSAR data with longer wavelengths in heavily vegetated volcanoes.