The 2014-2015 eruption at Fogo volcano: constraining the geometry of the intrusion and erupted volumes with space-geodesy

Abstract:

After twenty years of quiescence, Fogo volcano, the most active in the Cape Verde archipelago, erupted for more than two months between November 2014 and February 2015. Voluminous and fast-moving lava flows were erupted from a linear fissure located at the base of Pico do Fogo cone and inundated the summit area of the volcano, destroying two villages.

In our work we first use interferometric synthetic aperture radar (InSAR) data from the European Space Agency’s Sentinel-1A satellite, which had been operative for only a few weeks at the time of the onset of the eruption, to constrain the geometry of the intrusion that fed the eruption. The InSAR data was acquired in the TOPS (Terrain Observation by Progressive Scans) mode and the eruption at Fogo represents the first volcanic eruption imaged by Sentinel-1 in its standard acquisition mode. To accurately model TOPS data, variations in both incidence and squint angle of the satellite line-of-sight (LoS) vector need to be taken into account when projecting 3D displacements into the LoS direction. Following this approach, we perform a Bayesian inversion of the InSAR data and infer that the measured deformation is best explained by the intrusion of a sub-vertical dike beneath the southwestern flank of Pico do Fogo cone. This intrusion seems to have first propagated upwards beneath the cone and subsequently laterally towards the southwestern flank of Pico do Fogo, where it reached the surface.

Successively, we evaluate differences between pre- and post-eruptive digital elevation models (DEMs) of the volcano to estimate the volume of the most recent lava flows. The DEMs are formed using synthetic aperture radar imagery from the TanDEM-X (TerraSAR add-on for Digital Elevation Measurements) satellite mission and tri-stereo optical imagery from the Pléiades satellite constellation. Preliminary results show that during the 2014-2015 eruption almost 50 million cubic meters of lava were emplaced at the surface of the volcano over an area of ~5 square kilometers.