A conceptual model for the initiation of flank creep at Pacaya Volcano, Guatemala

Magma emplacement is a recognized trigger of volcanic flank instability. There is also growing evidence for links between magmatic intrusions and accelerating creep on detachment faults within volcanic edifices. This driver was recently proposed at Pacaya, an active basaltic stratovolcano in Guatemala with evidence for past flank collapse, and magma-driven flank instability during major eruptions in 2010 and 2014. In order to understand the conditions under which flank creep can be initiated, sustained, or halted at active volcanoes, we investigate the links between flank creep and eruptive behavior at Pacaya and devise a conceptual model for the initiation of flank creep. Flank creep is quantified through time-series of surface displacements from 2007 to 2020 using seven Synthetic Aperture Radar datasets, and eruptive behavior is described through volcanic activity reports, ash advisories, thermal anomaly time-series, and lava flow maps. We identify large transient flank instabilities coincident with vigorous eruptions in 2010 and 2014, but not during times of similarly elevated activity in 2007 to 2009 and 2018 to 2020. Slower creep takes place during the relatively quiescent 2010 to 2014 and 2015 to 2018 intervals, following the 2010 and 2014 transient instability events. Our analysis suggests that during times of elevated volcanic unrest with persistent thermal anomalies and degassing, attributed to open-vent volcanism, as in 2007 to 2009 and 2018 to 2020, magma movements in an open conduit happen with little associated deformation and flank motion. Conversely, whenever new vents open outside the summit area, irrespective of whether this takes place at the start or during a transition in an eruption, transient flank creep can be initiated, as in 2010 and 2014. Therefore, the opening of new vents away from the main summit cone at Pacaya, especially in a north-northwest to south-southeast alignment, could forewarn an increased likelihood of new or accelerating flank creep.