Ground displacement assessment on Pico Volcano, Azores, by multitemporal InSAR data

Interpreting the signal deriving from interferometric synthetic aperture radar (InSAR) analyses in volcanic islands, characterized by strong regional deformations and recurrent seismicity, is a complex and challenging issue. In these zones, the secondary effects connected to the SAR acquisition system cannot be neglected, and it is important to consider that delay phenomena of the electromagnetic waves, due to the propagation in the tropospheric layer and loss of SAR coherence because of dense vegetation, could affect the interferometric phase. This work focuses on Pico, the second largest and the youngest island of the Azores Archipelago (North Atlantic Ocean). This island consists of a central volcano and a fissure zone. These systems are inactive but recurrent microseismicity occurs in a rock volume host- ing a partially crystallized magma storage system, which fed the recent activity of the central volcano. In the same area affected by microseismicity, the main volcanic edifice shows flank instability. All these elements support the hypothesis of possible reactivation of the shallow magmatic system. Aiming to check potential active ground displacements and to define their source, we collected two datasets of C-band Sentinel-1 SAR data, both in descending and ascending acquisition geometry, from January, 2017, to December, 2020. The application of the small baseline subset method of differential InSAR allowed drawing the mean ground velocity maps over the island and the displacement time series, useful to understand the defor- mation evolution. InSAR data only evidence areas affected by small-scale subsidence at the cinder cones of the fissure zone and along the southeastern slope of Pico volcano, where local debris flows activate during rainy periods.