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The volcanic eruption at La Palma started on September 19, 2021. The eruption was preceded by a seismic swarm that began on September 11, although anomalous seismicity has been observed on the island since 2017. During the co-eruptive phase of the seismic activity, hypocenters depth was generally less than 15 km, save for the period between November 10 and November 27, when hypocenters ranged in the depth from 15 to 40 km. The eruption ended on December 13, 2021. We compute tidal stress for each earthquake at the hypocenter depth and find statistically significant correlations between the occurrence times of the earthquakes and the confining tidal stress values and stress rates. The correlation is depth-dependent, and ocean-loading tides have a stronger effect than body tides. We find that tidal stress variations contribute to the eruption onset and that certain explosive events, typical in Strombolian type volcanoes, seem to occur preferentially when the tidal stress rate is high. Our analysis supports the hypothesis that tides may modulate earthquake activity in volcanic areas, specifically during magma migration at shallow depths. A conceptual model is proposed, which could have a general application in the Canary Islands archipelago and other volcanic islands. [ABSTRACT FROM AUTHOR]

La Palma island is one of the highest potential risks in the volcanic archipelago of the Canaries and therefore it is important to carry out an in-depth study to define its state of unrest. This has been accomplished through the use of satellite radar observations and an original state-of-the-art interpretation technique. Here we show the detection of the onset of volcanic unrest on La Palma island, most likely decades before a potential eruption. We study its current evolution seeing the spatial and temporal changing nature of activity at this potentially dangerous volcano at unprecedented spatial resolutions and long time scales, providing insights into the dynamic nature of the associated volcanic hazard. The geodetic techniques employed here allow tracking of the fluid migration induced by magma injection at depth and identifying the existence of dislocation sources below Cumbre Vieja volcano which could be associated with a future flank failure. Therefore they should continue being monitored using these and other techniques. The results have implications for the monitoring of steep-sided volcanoes at oceanic islands. [ABSTRACT FROM AUTHOR]

Abstract The deep roots of oceanic island volcanoes are poorly known and geophysical models can help to constrain processes such as magma storage and transport before and during eruptions. Lanzarote, Canary Islands, is a volcanic island in post-erosional phase where, in the 18th century, one of the most important historical eruptions, considering duration and volume, of the Canary Islands took place in the Timanfaya area. To improve the knowledge on the structure of Lanzarote and in Timanfaya area, we carry out a gravity determination of the subsurface anomalous 3D density structure, using an improved quasi-automatic inversion methodology. The obtained model presents a 3D morphology of anomalous density bodies. We describe the improvements of the inversion methodology, the adjusted model and interpretative conclusions corresponding to the structure and the long-term cumulative magmatic plumbing system of the island. Three high-density sources are described as resulting in the inference of three main volcanic complexes: a large central complex (San Bartolomé) and two smaller complexes, one in the NE and a third smaller one located in the SW close to the Timanfaya area. The outcrops of Miocene lava flows from the center of the Island can be attributed to the top of the central intrusive model. We infer the local plumbing system for Timanfaya volcano area by means of strongly tilted successive branches of magma departing from the SW intrusive body. The structural results show no evidence of any magma chamber below Timanfaya as proposed by previous works. We also present a comparison of the gravity results and geological observations, showing different cases of correlation in the Island. They go from a good match between the gravity anomaly and the position of the central volcanic structure, to no anomaly associated to the fissural Quaternary volcanic activity. Graphical abstract Unlabelled Image Highlights • We use published and new gravity data with an improved inversion methodology. • 3D density structure is determined solving the inverse gravity problem. • Three high-density sources are described as resulting of main volcanic complexes. • Timanfaya's plumbing system is inferred as branches of magma from SW intrusive body. • Comparison of gravity results and geology gives different cases of correlation. [ABSTRACT FROM AUTHOR]