Nueva visión estructural, hidrogeológica e hidrotermal mediante potencial espontáneo en Cumbre Vieja (La Palma, Islas Canarias)

Abstract

Since last 1 Ma, the La Palma island volcanic activity concentrates at its southern half, on the Cumbre Vieja volcanic rift-zone. During the 1949 San Juan eruption a N-S fault system, facing west, developed close to the rift summit area, indicating a potential zone of deformation on the western flank that may provoke future failures and landslides. In this context, a geophysical Self Potential (SP) study was carried out with the aim of to characterize major structural limits influencing volcanic hydrothermal activity and underground meteoric circulations. Our study, which integrates also the soil temperature measurements, provides new information to characterize and place the limits guiding upward or downward fluid circulation shown as a change in SP polarity and intensity. A clear asymmetry of the self-potential signal was found between the eastern and the western flanks of Cumbre Vieja, where strong infiltration of meteoric water seems to affect most of the summit axis. On the eastern flank, a negative SP values suggest a usual vertical water infiltration. However, the poor variation in the self-potential values observed on the western flank could be explained by a constant thickness of its vadose zone, limited by the presence of an impermeable layer controlling the water inflow in a parallel direction relative to the surface. This boundary could be linked with the interface debris-solid rock created after the previous Cumbre Nueva edifice collapse, above which the new Cumbre Vieja is currently growing. However, if the fault system results from a local extension or from larger scale instability, it remains unclear.