InSAR-derived thermoelastic lava flow compaction following the 2014-2015 Holuhraun fissure eruption

Abstract

The Icelandic volcano Bárðarbunga experienced a caldera collapse and a fissure eruption at Holuhraun from 16 August, 2014 to 27 February, 2015 (Sigmundsson et al., 2015). This eruption produced about 1.44 km³ of lava deposited over an 84 km² area on the Holuhraun plain north of the Vatnajokull Glacier (Pedersen et al., 2017), making it the second largest Icelandic eruption since the 1783-1784 Laki eruption (Gudmundsson et al., 2016). Since basaltic lava flows erupt at high temperatures (1100 to 1250 °C), they contract as they cool over time, which can manifest as measurable deformation of the lava flow surface. Remote sensing observations with high spatio-temporal resolution afford us with an opportunity to capture and analyze such post-eruptive processes. Here, we use Synthetic Aperture Radar (SAR) observations from 2015-2020 captured by the European Space Agency's Sentinel-I A/B satellite pair to perform Interferometric Synthetic Aperture Radar (InSAR) time series analysis on descending and ascending tracks that cover the Holuhraun lava field. Two Short Baseline Analysis (SBAS) are computed, and modeled deformation from plate tectonics and glacial isostatic adjustment is removed from these line-of-sight (LOS) velocity fields. We leverage the dual-view geometry of the estimated LOS InSAR velocity fields to infer effective vertical and east-west velocities of the lava flow surface. The effective vertical velocity field constrains a model linking lava flow compaction to cooling. The InSAR-inferred average velocities indicate higher rates of motion at lava tubes, eruptive centers, and "distributary centers" (as defined by Pedersen et al., 2017) where lava pooled before entering lava tubes during the eruption. We hypothesize that the different emplacement history of individual lobes and features of the lava field, as well as inconsistent compaction amounts of the Holuhraun alluvial plain, have caused the heterogenous cooling that manifests in a highly varying surface deformation field.