The 2015 Wolf volcano (Galápagos) eruption studied using Sentinel‐1 and ALOS‐2 data

Abstract

An energetic eruption started on 25 May 2015 from a circumferential fissure at the summit of Wolf volcano on Isabela Island, western Galápagos. Further eruptive activity within the Wolf caldera followed in mid‐June 2015. As no geodetic observations of earlier eruptions at Wolf exist, this eruption provides an opportunity to study the volcano's magmatic plumbing system for the first time. Here we use interferometric synthetic aperture radar (InSAR) data from both the Sentinel‐1A and ALOS‐2 satellites to map and analyze the surface deformation at four time periods during the activity. These data allow us to identify the two eruption phases and reveal strong coeruptive subsidence within the Wolf caldera that is superimposed on a larger volcano‐wide subsidence signal. Modeling of the surface displacements shows that two shallow magma reservoirs located under Wolf at ~1 km and ~5 km below sea level explain the subsidence and that these reservoirs appear to be hydraulically connected. We also suggest that the transition from the circumferential to the intracaldera eruption may have involved ring fault activity.

Integrated Petrological and Geophysical Constraints on Magma System Architecture in the Western Galápagos Archipelago: Insights From Wolf Volcano

“…Sources with maximum posteriori probability solutions are centered at 7‐, 6.7‐, and 7.6‐km depth, respectively, and comparisons between the observed displacements and those predicted using the maximum posteriori probability solutions are shown in Figures b, e, and h. Our results estimate that this source is ~2‐km deeper than inferred by Xu et al () who, in some cases, used the same InSAR data. This discrepancy is likely due to our use of far field data, which was excluded in the study of Xu et al ().…”

“…Long‐term subsidence, possibly related to crystallization and contraction of a shallow magma body at ~3‐km depth, has also been observed at Alcedo (Hooper et al, ). Evidence for additional, deeper magma storage at >5 km has been identified in InSAR data from Fernandina (Bagnardi et al, ; Bagnardi & Amelung, ; Chadwick et al, ), Cerro Azul (Bagnardi & Hooper, ), and Wolf volcano (Xu et al, ), and by seismicity patterns at Sierra Negra (Davidge et al, ). There are currently no geodetic constraints on magma storage depths beneath volcanoes in the eastern Galápagos Archipelago, due to the infrequency of historic eruptions (Siebert et al, ) and the apparent absence of clear intereruptive deformation.…”

“…We form three Sentinel‐1 independent interferograms (i.e., using different image pairs), one during the circumferential fissure eruptive phase (18–30 May 2015; Figure a), one spanning the caldera‐fill eruptive phase (11–23 June 2015; Figure d), and a third one measuring the displacements associated with both phases (6 May 2015 to 5 July 2015; Figure g). Given the complex deformation pattern within and around the summit caldera caused by the convoluted effect of the opening of the subvertical feeder dikes and shallow source deflation (De Novellis et al, ; Xu et al, ), we mask out a subcircular area around the caldera and only use far field data (e.g., Bagnardi & Amelung, ). The extent of the mask is constrained using source parameters for the shallower source and the feeder dikes estimated by Xu et al ().…”

“…Due to their remoteness, our knowledge of magma storage depths beneath Galápagos volcanoes is largely based on remote sensing data (almost exclusively space‐geodetic data), with limited petrological constraints. On long timescales, most volcanoes in the western archipelago show protracted ground uplift, related to shallow magma accumulation in flat‐topped reservoirs at 1‐ to 2‐km depth beneath the surface (Amelung et al, ; Bagnardi et al, ; Bagnardi & Amelung, ; Chadwick et al, ; Xu et al, ; Yun et al, ). Long‐term subsidence, possibly related to crystallization and contraction of a shallow magma body at ~3‐km depth, has also been observed at Alcedo (Hooper et al, ).…”

Long-range transport of stratospheric aerosols in the Southern Hemisphere following the 2015 Calbuco eruption

“…The SO 2 total mass increased again on 28 May 2015 to reach a secondary maximum (0.13 Tg) on 30 May 2015. This new increase in the SO 2 total mass could be due to the Wolf eruption (Isabela Island, Galapagos), which occurred on 25 May 2015 (Xu et al, 2016). The maximum SO 2 total mass (0.41 Tg) emitted during the Calbuco eruption was about two 2 times lower than the maximum value (0.9 Tg) emitted from the Sarychev eruption (0.9 Tg) in June 2009 ( Jégou et al, 2013).…”