MULTIDIMENSIONAL SMALL BASELINE SUBSET (MSBAS) FOR VOLCANO MONITORING IN TWO DIMENSIONS: OPPORTUNITIES AND CHALLENGES. CASE STUDY PITON DE LA FOURNAISE VOLCANO

Space-borne Synthetic Aperture Radar (SAR) provides an opportunity for monitoring ground deformation at active volcanoes with high temporal and spatial resolutions. Modern SAR satellites acquire very large volumes of data that no longer can be effectively and efficiently processed and interpreted manually. The development of novel automatic processing methodologies is warranted in order to fully utilize big data. The Multidimensional Small Baseline Subset (MSBAS) methodology is an example of the semi-automatic processing system for computing temporally dense two-dimensional, horizontal east-west and vertical time series of ground deformation from ascending and descending SAR imagery acquired by various satellites. Here MSBAS is used for mapping ground deformation at the Piton de la Fournaise volcano (La Réunion Island, France) during the February 2012 - April 2016 period from RADARSAT-2 data. Five volcanic eruptions occurred during the June 2014 - October 2015 period, producing over 60 cm of horizontal and over 30 cm of vertical ground deformation, well-resolved in the MSBAS-derived time series. Validation of DInSAR results by comparison with GNSS observations and modeling of the two last and largest eruptions was performed. Validation showed good overall agreement between DInSAR and GNSS observations while revealing the benefits and limitations of both techniques. Modeling of fault and dike geometries attempted to explain the dis-proportionally large eastward motion of the eastern flank of the Piton de la Fournaise volcano that occurred during these eruptions. We demonstrated that the simple elastic model consisting of two dikes and a sliding surface can account for the observed ground deformation.