Ground deformation induced by the horizontal sill intrusion associated with the 2018 Sierra Negra eruption using satellite synthetic aperture radar data

The Sierra Negra volcano on the Galapagos Islands erupted in June 2018, which induced both the caldera to subside by 8 m and lava to flow from vents on the northwestern caldera rim. Some previous studies have reported deformation signals at the caldera using satellite synthetic aperture radar (SAR) data and discussed physical mechanisms for the caldera deformation, while few interpretations have discussed the deformation signals on the northwestern flank where the magma intruded. The goals of this study are to detect the spatiotemporal variation of deformation signals on the volcanic flank using ALOS-2/PALSAR-2, Cosmo-SkyMed, and Sentinel-1 data, and to understand the physical mechanism of the detected deformation signal associated with the eruptive episode on the Sierra Negra volcano in 2018.

The results of the SAR pixel offset approach show deformation signals on the northwestern flank, decorrelations on the extents of lava flows, and the caldera subsidence associated with the 2018 eruption. The co-eruptive deformations on the volcanic flank were detected from the northwestern caldera rim to the initiation point of the lava flow, which showed a stream-like distribution. The pixel offset results revealed a line-of-sight (LOS) shortening of 4 m observed from both ascending and descending orbit, implying uplift. This deformation characteristic contract with that induced by dike intrusions, which causes subsidence at the center and extensions with uplift on the side. Using analytical solutions of surface displacements associated with the opening of a rectangular plane, we inferred the geometry of the propagated magma by fitting the extracted profiles of the pixel offset on the flank based on the particle swarm optimization algorithm. The modeling results suggested that the horizontal opening sill underlies at 650 m below sea level near the summit, while the opening planar at a similar depth tilts in the northwest direction with a dip angle of ~30 degrees. Based on the results of our observation and simple modeling, the magma implies to have intruded along a horizontal crack during the northwestward propagation direction and along a northwest-dipping plane after the bending of the propagation direction to the northeast.