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Surface geothermal exploration by means of soil carbon dioxide and radon degassing in Jedey, La Palma, Canary Islands

Ana Gironés1,2, Nemesio M. Pérez1,2, Eleazar Padrón1,2, Gladys V. Melián1,2, María Asensio-Ramos1, Pedro A. Hernández1,2

  • Affiliations: 1Instituto Volcanológico de Canarias (INVOLCAN), Puerto de la Cruz, Tenerife, Canary Islands, Spain 2Instituto Tecnológico y de Energías Renovables (ITER), Granadilla de Abona, Tenerife, Canary Islands, Spain   

  • Presentation type: Poster

  • Presentation time: Tuesday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 13

  • Programme No: 5.1.19

  • Theme 5 > Session 1

Abstract

Cost-effective surface geochemical surveys, like measurement of diffuse CO2 efflux, soil radon (222Rn) and thoron (220Rn) gases activities, have demonstrated to provide relevant information on defining potential geothermal systems boundaries by highlighting permeable areas and potential up-flow zones. A detailed surface geochemical study was carried out in Jedey (25 Km2), an area of interest for geothermal exploration, located at the west coastline to the western side of the Cumbre Vieja Volcanic Rift Zone in La Palma Island and southwards from the recent lava flows of Tajogaite Volcano. A total of 968 diffuse CO2 efflux and radon and thoron measurements (~39 sample sites/Km2) were performed between 2023 and 2024 surveys. Data analysis showed an average CO2 efflux of 4 g∙m-2/day, ranging from 0 to 106 g∙m-2/day, an average 222Rn value of 994 Bq/m3, ranging from 0 to up to 27,000 Bq/m3, and an average 222Rn/220Rn ratio of 1.5, ranging from 0 to a maximum of 49. Both 222Rn and 222Rn/220Rn ratios were plotted together, enabling limiting areas with higher values, which might indicate zones of interest. These variables were used to produce spatial distribution maps showing the main CO2 and radon gases anomalies along the coastline, but also in some areas following a northeast trend. The CO2 diffuse degassing might have controlled the migration and transport of the radon trace gas towards the surface. In summary, geochemical surveys have revealed to be a useful technique for surface exploration, allowing identify a potential geothermal system and permitting a posterior subsurface exploration.