InSAR Time-series Analysis Unravels Persistent Flank Motion During 2010-2014 at Pacaya Volcano, Guatemala

Abstract:

Edifice collapse represents one of the most dangerous volcanic hazards threatening communities and infrastructure near volcanoes. Despite its prevalence across volcanic settings, flank instability has mostly been considered at ocean island volcanoes. In Guatemala, all but one volcano with elevation greater than 2000 m have undergone edifice failure. Pacaya is one of these Guatemalan volcanoes, which experienced at least one past episode of flank collapse and where recent transient motion of its SW flank has been identified. To assess the hazards posed by this volcano and the underlying mechanisms playing a role in its flank instability, a better understanding of its deformation behavior over time is required. Interferometric Synthetic Aperture Radar (InSAR) is a useful tool for remote monitoring of surface deformation. Previous InSAR studies have thus identified episodes of flank motion at Pacaya, associated with eruptions in May 2010, as well as possibly in January-March 2014. To provide further insight into inter-eruptive longer-term flank motion at Pacaya and the evolution of deformation over time, we perform Small BAseline Subset (SBAS) InSAR time-series analysis on RADARSAT-2 and COSMO-SkyMed datasets acquired between 2010 and 2015, which span a major eruptive episode in 2014. Subsequently, the InSAR time-series data were inverted using a Monte Carlo Neighbourhood Algorithm coupled with analytical solutions, to solve for acceptable geodetic models explaining this flank motion. We reveal, for the first time, persistent flank deformation at Pacaya between 2010 and 2014. Results from these inversions and static stress analysis suggest that the observed flank motion could be accommodated by slip on a detachment fault, with an observed increase in slip rate attributed to magma intrusion associated with a major eruption in 2014. This study highlights that persistent volcanic flank instability is likely more widespread than previously recognized and that magma-faulting interactions, as well as the existence structural weaknesses within volcanic edifices, are vital considerations in the assessment of likelihood of flank collapse.