Shallow magmatic intrusion evolution below La Palma before and during the 2021 eruption

Abstract

La Palma, Canary Islands, underwent volcanic unrest which culminated in its largest historical eruption. We study this unrest along 2021 using Interferometric Synthetic Aperture Radar (InSAR) and a new improved interpretation methodology, comparing achieved results with the crustal structure. We reproduce the final phase of La Palma volcanic unrest, highligthing a shallow magma accumulation which begins about 3.5 months before the eruption in a crustal volume charactherized by low density and fractured rocks. Our modeling, together with our improved pictures of the crustal structure, allows us to explain the location and characteristics of the eruption and to detect failed eruption paths. These can be used to explain post-eruptive phenomena and hazards to the local population, such as detected gases anomalies in La Bombilla and Puerto Naos. Our results have implications for understanding volcanic activity in the Canaries and volcano monitoring elsewhere, helping to support decision-making and providing significant insights into urban and infrastructure planning in volcanic areas.

Deep magma storage during the 2021 La Palma eruption

“…On the basis of the record from eroded rift systems of other islands, these eruptions are fed by a tightly packed dyke swarms within the rifts ( 14 , 15 ). The intrusion of one such dyke, or possibly a series of dykes, initiated the eruption on the western flank of the CVR on September 19 ( 16 , 17 ).…”

Tidal modulation of the seismic activity related to the 2021 La Palma volcanic eruption

“…Pressure sources initially located along the border separating the Northern Volcanic Complex and CV 14 enhanced magma movement towards an even shallower reservoir below the Jedey zone (Fig. 1), in a low-density zone at ~1-5 km depth 17 .…”

“…NVC hosts the volcanic buildings of Garafía, Taburiente, Cumbre Nueva and Bejenado, whereas the CV edifice is a younger rift-type structure, along which both recent and historical on-land volcanic activity has taken place. Magma arrives to shallow crustal regions below the island from depth, probably following pre-existing intrusion paths in a zone with low density and weakness [15][16][17] below the Jedey zone. Seismicity that occurred in 2017-2020 appears to be related to rock fracturing below CV 14 , opening the path towards the shallow and short-term reservoir below the Jedey zone 17 (Fig.…”

“…Magma arrives to shallow crustal regions below the island from depth, probably following pre-existing intrusion paths in a zone with low density and weakness [15][16][17] below the Jedey zone. Seismicity that occurred in 2017-2020 appears to be related to rock fracturing below CV 14 , opening the path towards the shallow and short-term reservoir below the Jedey zone 17 (Fig. 1).…”

“…The seismic network detected a volcanic tremor signal which exhibited strong variations in amplitude over time. A cone formed the following day 18 and eruptive vents opened, collapsed, and closed, grouping around a ~700 m long fissure trending NW-SE 17,19 . In the following weeks, intense effusive and explosive activity occurred with phreatomagmatic pulses, the expansion of the lava flows, and daily ash emissions 12,20 .…”