Abstract

Using ground deformation measurements of high spatial and temporal resolution SAR , the understanding of new vents created during volcanic eruptions can be improved with 3D mapping of the activated shallow magma plumbing system. Interferometric analysis of radar data from ICEYE X -band satellites with daily coherent ground track repeat (GTR) provides unprecedented time series of deformation in relation to the opening of 6 eruptive vents over 26 days in 2021, at Fagradalsfjall, Iceland. Unrest started in this location at the end of February and tens of thousands of earthquakes were recorded during a four week duration. The seismicity was linked to gradual formation of a magma-filled dike in the crust and triggered seismicity along the plate boundary. On 19 March, an eruptive fissure opened near the center of the dyke. New vents and eruptive fissures opened on the 5th, 7th, 10th, and 13th April. The daily acquisition rate of the ICEYE satellite facilitated the observation of the ground openings associated with each new vents. Each event can be observed individually and with minimal loss of signal caused by new lava emplacement, which would occur if images were acquired at a slower rate. Being able to retrieve deformation near the edge of the fissure ensures that we have the optimal constraints needed for modelling the subsurface magma path. The ICEYE dataset consists of Stripmap acquisitions (30×50km) in the period 3-21 March, and Spotlight acquisitions (5×5 km) from 22 March and onward. Images have a resolution of about 2 m x 3 m, and 0.5 m x 0.25 m, respectively. The descending 1-day interferogram covering each individual event is used to invert for the distributed opening along the dike plane. We find that the opening of the conduits in relation to each eruptive vent in April is mostly taking place in the topmost 100 meters of the crust and that opening is less than 0.5 meters. There is almost no re-opening along previously formed magma pathways. There are also indications of new vent locations being influenced by local conditions and stress in the shallow crust.