CO2-rich emissions from alkalic magmatism in the Canary Islands, Spain

Mafic alkali-rich magmas, such as those which form the Canary Islands, Spain, have been proposed as being CO₂-rich due to low-degree partial melting and the presence of recycled oceanic crust in the mantle source region. A CO₂-rich mantle source of Canary magmas has been suggested from melt inclusions study of the 2011 submarine El Hierro eruption, but this has not been verified yet by directly measuring magmatic CO₂ emissions during a subaerial eruption as the last such event in the archipelago, in 1971, occurred before the advent of modern gas sensing tools. Here we report on the first results for gas emissions from the

2021 eruption of Cumbre Vieja on La Palma island. We determined the chemical composition and mass flux of magmatic degassing during both effusive and explosive activities by combining direct plume measurements with MultiGas sensors from the ground, UAV and helicopter, OP-FTIR remote sensing and satellite-based (TROPOMI) SO₂ flux quantification based on back-trajectory modelling. Degassing mass budgets and the magma volatile concentrations were then derived from microprobe analysis of olivine-hosted melt inclusions and comparing our gas results with best estimates of the magma extrusion rates during both explosive and effusive activities. Based on this approach we obtain a direct quantification of the initial CO₂ content of the magma and of the exsolved pre-eruptive CO₂ gas phase that fed the Cumbre Vieja eruption.

We find unprecedentedly high CO₂ content in the mantle source of La Palma magma, consistent with high volatile contents predicted from petrological analyses. Eruptions of oceanic island alkali-rich magmas produce disproportionately high CO₂ emissions, highlighting the key role mantle heterogeneity plays in determining the impact of intraplate volcanism.