​MELIÁN, G., MEIRE, A., AMONTE, C., PITTI PIMIENTA, L., DI NARDO, D., ALONSO, M., SMIT, M., LEAL, V., GARCÍA-HERNÁNDEZ, R., HERNÁNDEZ, W., PEREIRA, S., AGUIAR, S., FERRERA, L., PÉREZ, N. M. (2022). Diffuse He and H₂ emissions from Cumbre Vieja volcano before and during the recent eruption, La Palma, Canary Islands. EGU General Assembly 2022, Vienna, Austria, 23-27 May 2022, EGU22-6345, https://doi.org/10.5194/egusphere-egu22-6345.

​La Palma Island (708 km²) is located at the north-west and is one of the youngest (~2.0My) of the Canarian Archipelago. On September 19, 2021, a new volcanic eruption occurred at Cumbre Vieja volcanic system at the southern part of the island, the most active basaltic volcano in the Canaries. The erupting fissure (~1.0 km-length) is characterized by lava effusion, strombolian activity, lava fountaining, ash venting and gas jetting. After 85 days of eruption finished on December 13, 2021. We report herein the results of an intensive soil gas study, focused on non-reactive and/or highly mobile gases such as helium (He) and hydrogen (H2), in Cumbre Vieja. He has unique characteristics as a geochemical tracer: it is chemically inert and radioactively stable, non-biogenic, highly mobile and relatively insoluble in water. H₂ is one of the most abundant trace species in volcano-hydrothermal systems and is a key participant in many redox reactions occurring in the hydrothermal reservoir gas. Since 2002, soil gas samples were regularly collected at ~40 cm depth using a metallic probe at 600 sites for each survey. He content was analysed by means of a quadrupole mass spectrometer (QMS; Pfeiffer Omnistar 422 and HIDEN QGA) and H₂ concentrations by a micro-gas chromatograph (microGC; VARIAN CP490). Spatial distribution maps have been constructed following the sequential Gaussian simulation (sGs) procedure to quantify the diffuse He and H2 emission from the studied area. The time series of both diffuse He and H₂ emission show significant increases before and during the occurrence of seismic swarms that took place in the period 2017-2021. During the eruptive period, significant increases in diffuse He and H₂ emission were also observed with good temporal agreement with the increase of the volcanic tremor. These increases in diffuse He and H₂ emission preceded the peak of diffuse CO₂ emission as expected by the characteristics of these gases. The absence of visible volcanic gas emissions (fumaroles, hot springs, etc.) at the surface environment of Cumbre Vieja, makes this type of studies in an essential tool for volcanic surveillance purposes.