Time series compositional insights into magmatic evolution during the 2021 Cumbre Vieja eruption, La Palma, Canary Islands, Spain

<p>On 19 September 2021, Cumbre Vieja volcano, La Palma, Canary Islands erupted after 50 years of quiescence. The eruption lasted 85 days through to 13 December. Cone building that initiated from the main fissure vent resolved into discrete emission centres dominated by ash plumes and lava fountains that fed flows that coursed to the west and west-southwest. The lava flow field covers over 1000 hectares and is up to 3.5 km wide and ~6.2 km long. Tephra fall covers over 5,500 hectares with volcanic plume heights reaching up to 6000 m depositing material mainly in the eastern part of the island but, on occasion, reaching other Canary islands: El Hierro, La Gomera, Tenerife and Gran Canaria.</p><p>Significantly, uncertainties exist regarding how such eruptions initiate, evolve and ultimately cease, e.g. changes in magma composition and volume. Here we show time series whole-rock and mineral chemistry variations throughout the eruption from initiation to paroxysm and finally cessation. Bulk chemical trends of erupted products in the first week together with textural and mineralogical observations made within a few weeks of samples&#8217; eruption provide an initial benchmark for understanding the evolution of the eruption. Petrographically, the lavas are hypocrystalline, porphyritic and vesicular. Clinopyroxene is the most common coarse mineral with olivine and amphibole also present. Whole-rock XRF and ICP-MS analyses show that samples have restricted, primitive, metaluminous, alkaline whole-rock compositions; geochemically, lavas plot as basanite-tephrites, but mineralogical observations, for example the absence of feldspathoids, classify them as alkali basalts.</p><p>Time-resolved whole-rock analyses through the eruption show increasing MgO contents and decreasing incompatible element contents, which may reflect changes in melting dynamics or crystal cargos. A jump in whole-rock major and trace element compositions on day 7 to 8 of the eruption coincides with the disappearance of resorbed amphibole crystals in the thin sections, and also the amphibole peak in XRD spectra, as well as transition to the eruption of less viscous lava flows. The whole-rock compositional changes also correlate with variations in geophysical monitoring records of real-time seismic amplitude measurements.</p><p>Our new data has potential to be applied to eruption forecasting, as well as evaluation of volcanic hazards and associated risks for activity in the Canary Islands and other comparable ocean island systems.</p>