GNGTS 2022 - Atti del 40° Convegno Nazionale

130 GNGTS 2022 Sessione 1.3 MAPPING THE 2021 LA PALMA ERUPTIVE SEQUENCE THROUGH MULTI-SPECTRAL AND SAR IMAGES OF THE SENTINEL SATELLITES C. Braitenberg, T. Pivetta, F. Stefan Department of Mathematics and Geosciences, University of Trieste The volcanic activity bears a hazard to a large portion of the population worldwide: it is estimated that about 8% of the world’s population lives within 100 km from a volcano with at least one recent significant eruptive episode (Freire, 2019). Cohabiting with this hazard requires an extensive knowledge of the structure of the volcano, its historical and geological activity, and a monitoring system able to detect changes in deformation, increase in the seismicity and variation of physical and chemical parameters prior, during and after the event. Mapping the past eruptions and their paths is a fundamental task to assess the risk and to plan possible counter-measures to limit the impact of future episodes. Satellite products, as those provided by the Sentinel missions, offer images with sufficient spatial and temporal resolution to fulfill this objective. Using satellite images in fact the user can rapidly estimate the areas involved by the volcanic activity during the eruption, even discriminating lava flows from the areas subjected to ashes fallout. In case of episodes lasting for weeks, a temporal evolution of the various paths followed by the lava is also obtainable. In this contribution we present a study of the recent “La Palma” eruptive sequence, which lasted for 12 weeks (from19 th September to 13 th December 2021) and that involved the central- western portion of the La Palma Island. We exploited both the multi-spectral observations of Sentinel-2 and the images of the SAR Sentinel-1, obtaining a collection of images of the whole eruptive sequence. The Sentinel-2 data was processed through Google Earth Engine (GEE), which allowed to mosaic the different scenes, to remove the effect of the clouds and to finally create false-color maps using various combinations of available bands. The SAR reflectance images were as well merged with GEE and were employed since the radar band is more penetrative and less sensitive to the ash clouds of the eruption. The short-wavelength infrared (SWIR) bands of Sentinel-2, exploiting the sensitivity to the rock’s temperature, was used to obtain a dynamic picture of the lava flows throughout the period of eruption. The comparison of Sentinel-2 and the SAR images before and after the event allowed to: 1. precisely map the area that was covered by the fallen ashes 2. detect the vent from which the lava originated 3. identify a new portion of land emerging from the sea with area 400000 m 2 or 0.40 km 2 4. the volcanic hazard affected a total area of 12 km 2 . By the comparison with a map of the known volcanic eruptions, we found that the 2021 event is located between two older events occurred in 1470-1492 and 1949. The vent from which the lava flowed out, was formed during this eruption and it is located about 600 m west from the Cumbre Vieja, the axial ridge along which most of the magmatic manifestations occur. References Freire S., Florczyk A.J., Pesaresi M., Sliuzas R.; 2019: An Improved Global Analysis of Population Distribution in Proximity to Active Volcanoes , 1975–2015. ISPRS Int. J. Geo-Inf., 8 , 341 , https://doi.org/10.3390/ijgi8080341