The 2021 eruption of Pacaya Volcano, Guatemala – Geophysical analysis through satellite geodesy and seismic noise correlations

Abstract

Pacaya is an active basaltic volcano in Guatemala, that underwent a heightened period of volcanic activity in early 2021, as the culmination of effusive and explosive activity starting in mid-2015. We present an assessment of the geophysical signals associated with this heightened eruptive interval leveraging access to ground deformation data from 9 Synthetic Aperture Radar (SAR) datasets acquired by 5 different radar satellite platforms and seismic data from 4 permanent stations. Given evidence for past vigorous eruptive activity from vents beyond the summit area being associated with initiated or accelerated flank creep, we assess whether this process occurred also in 2021 or not. Further, the availability of a dense SAR dataset with different spatial and temporal resolutions is leveraged as an incomparable opportunity to assess the relative performance of different SAR platforms for monitoring volcanic eruptions. The more limited seismic dataset is used for comparison of peaks in real-time seismic amplitude measurement (RSAM) time-series, as well as velocity variations derived from single-station cross-component correlations (SC) and auto-correlations (AC), with changes in volcanic activity. The SAR time-series results reveal displacements compatible with down-dip motion of the unstable southwest flank (downward vertical and westward horizontal displacements), but there might be contributions to the signal from lava flow compaction and seasonal tropospheric water vapor variations. RSAM peaks appear to reflect vigor of lava effusion at Pacaya but gaps in the data impede the assessment of whether there were recognizable signals during times of change in eruptive behavior. Single-station correlations captured the effects of rainfall variability but were otherwise too noisy to draw clear insights. Overall, this study showcases the challenges of coherence loss during periods with widespread lava effusion and ash fall, and the advantages of performing time-series analysis on shorter subsets of time to retain more pixels in times of lower volcanic activity. Additionally, our results highlight the advantage of high spatial resolution SAR amplitude imagery for mapping surface changes, the vulnerability to geometric distortions of low incidence angle platforms, and the challenge of relying on tasking to obtain timely satellite imagery over active volcanoes.