Seismoacoustic monitoring of La Palma 2021 volcanic eruption (Canary Islands): first results

We present first results on the continuous monitoring of the 2021 La Palma volcanic eruption (Canary Islands, Spain), from September 2021 to December 2021. During the eruption we installed a 8 level 3-component geophone string and 15 m spacing between geophones in Las Manchas within the restricted area and less than 2 km away of the volcanic edifice. The string was installed on the ground surface, in a straight line pointing towards the volcano. The 24 channels were sampled at 250 Hz, and data acquisition was performed in real-time and continuously till the end of the eruption with occasional minor gaps. The resulting seismoacoustic dataset is a sample of elastic energy propagating in both the subsurface and the atmosphere, allowing us to improve our understanding of the eruptive subsurface and subaerial processes. We use these seismoacoustic records to identify and characterize the different phases and signals of the volcanic activity. For the first analysis of the dataset we performed the calculation and graphing of spectrograms during the acquisition. We identify eruptive signals and correlate them with different events that can be directly observed on the basis of frequency content and relative timing. Explosive events like those derived from destruction of conduit plugs and ash-rich plumes emission, ash-rich explosions, volcanic lightning and degassing events are being analysed.

Finally, we study the correlation of seismic and seismoacoustic records for the same event by comparing with seismic data recorded on land stations. Results show that a good correlation exists between seismic and seismo-acoustic data for the main activity observed in the surface: the activity at the various vents and events like episodes of ash emission and bursts, indicating that this methodology can be successfully applied to monitor remote eruptions. Coupled seismoacoustic observations have turned out to be useful because they provide a comprehensive record of subsurface and subaerial eruptive activity.