Diffuse He and H2 emissions from Cumbre Vieja volcano before and during the recent eruption, La Palma, Canary Islands

Gladys Melián,Mar Alonso,William Hernández,Cecilia Amonte,Nemesio M Pérez,Simone Aguiar,Daniel Di Nardo,Ana Meire,Maud Smit,Rubén García-Hernández,Leticia Ferrera,Lia Pitti Pimienta,Victoria Leal,Sonia M.M Pereira

doi:10.5194/egusphere-egu22-6345

Abstract

&lt;p&gt;La Palma Island (708 km&lt;sup&gt;2&lt;/sup&gt;) 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 (H&lt;sub&gt;2&lt;/sub&gt;), 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. H&lt;sub&gt;2&lt;/sub&gt; 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 H&lt;sub&gt;2&lt;/sub&gt; 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 H&lt;sub&gt;2&lt;/sub&gt; emission from the studied area. The time series of both diffuse He and H&lt;sub&gt;2&lt;/sub&gt; 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 H&lt;sub&gt;2&lt;/sub&gt; emission were also observed with good temporal agreement with the increase of the volcanic tremor. These increases in diffuse He and H&lt;sub&gt;2&lt;/sub&gt; emission preceded the peak of diffuse CO&lt;sub&gt;2&lt;/sub&gt; 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.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

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