Deep magma storage at Hekla volcano, Iceland, revealed by InSAR time series analysis

Hekla volcano is one of the most active volcanoes in Iceland. The most recent eruption occurred from 26 February to 8 March 2000 when about 0.19 km³ of magma was erupted. We present deformation data from multitemporal analyses of synthetic aperture radar (SAR) images acquired between 1993 and 2008, focusing on pixels with low-phase variance (using persistent scatterer and small baseline approaches). Prior to and after the 2000 eruption, we find a broad area of inflation around the volcano (radius about 20 km), with satellite line-of-sight (LOS) shortening of up to 5 mm/yr. We interpret this signal as the result of pressure increase in a deep-seated magma chamber, which we model as a spherical source at 14-20 km depth increasing in volume by 0.003-0.02 km³/yr. Within a ∼6 km radius of the summit of the volcano, a LOS lengthening is superimposed on the broad inflation signal, which correlates partly with recent lava flows. We interpret this signal as the result of thermally contracting lava flows, combined with viscoelastic yielding due to the load of the volcano and its lavas. Coeruptive deflation during the 2000 eruption was similar to the cumulative inflation from 1993 to 2000 and is consistent with a spherical magma chamber at 14-18 km depth that decreases in volume by 0.04-0.08 km³. Interferograms spanning the 2000 eruption show a local coeruptive deformation signal near the eruptive fissure. This is consistent with a dike opening from the surface to depths up to 5.8 km with a volume of 0.005-0.006 km³.