GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 1.2 GNGTS 2024 Geodetc imaging of magma ascent through a bent and twisted dike during the Tajogaite erupton of 2021 (La Palma, Canary Islands) M. Przeor 1,2 , R. Castaldo 3 , L. D’Auria 1,2 , A. Pepe 3 , S. Pepe 3 , T. Sagiya 4 , G. Solaro 3 , P.Tizzani 3 , J. B. Martnez 1,2 , N. Perez 1,2 1 Insttuto Volcanológico de Canarias (INVOLCAN), Granadilla de Abona, Tenerife, Canary Islands, Spain 2 Insttuto Tecnológico y de Energías Renovables (ITER), Granadilla de Abona, Tenerife, Canary Islands, Spain 3 Isttuto per il Rilevamento Eletromagnetco dell’Ambiente (CNR-IREA), Napoli (ITALY) 4 Nagoya University, (JAPAN) On Sept. 19th, 2021, the Tajogaite erupton on the island of La Palma began with short precursors, lastng only eight days. The seismicity started on Sept. 11th with a westward and upward migraton of hypocenters. Permanent GNSS statons started recording deformaton on Sept. 12th on the island's western side, which reached more than 15 cm just before the erupton. Afer the erupton onset, the ground deformaton increased, reaching a maximum on Sept. 22nd and showing a nearly steady defaton trend in the following months. To beter understand the dynamics of the erupton, we exploited a joint dataset of GNSS and Sentnel-1 SBAS tme series along both ascending and descending orbits. To obtain the geometry of the causatve source of the ground deformaton, we combined the result of a preliminary non-linear inversion and the precise locaton of the seismicity. The resultng geometry of the source is that of a twisted dike bending eastward. We performed inverse modelling to obtain the spatotemporal kinematcs of the opening functon of the dike. The forward modelling has been realised using a 3D fnite-element approach considering the island's topography. Our fndings reveal a close correspondence between the magmatc intrusion and pre-eruptve seismicity. The ascent of the magma occurred along two branches, and the rheology of a previously identfed ductle layer strongly afected the magma propagaton process. Finally, we found evidence of an early shallow deformaton, which we interpret as the efect of ascending hydrothermal fuids. Our fndings highlight the need for advanced modelling to understand pre-eruptve processes in basaltc volcanoes. Corresponding author: solaro.g@irea.cnr.it