Maria Jose Blanco

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.

This paper describes the development of a low-cost multiparameter acquisition system for volcanic monitoring that is applicable to gravimetry and geodesy, as well as to the visual monitoring of volcanic activity. The acquisition system was developed using a System on a Chip (SoC) Broadcom BCM2835 Linux operating system (based on DebianTM) that allows for the construction of a complete monitoring system offering multiple possibilities for storage, data-processing, configuration, and the real-time monitoring of volcanic activity. This multiparametric acquisition system was developed with a software environment, as well as with different hardware modules designed for each parameter to be monitored. The device presented here has been used and validated under different scenarios for monitoring ocean tides, ground deformation, and gravity, as well as for monitoring with images the island of Tenerife and ground deformation on the island of El Hierro.

El Hierro eruption started on 10 October 2011 after an unrest episode that initiated on 17 July 2011. This is the first eruption in the Canary Islands that has been tracked in real time. Although being submarine and not directly observable, the data recorded allowed its reconstruction and to identify its causes and mechanisms. Seismicity, surface deformation, and petrological data indicate that a batch of basanitic magma coming from a reservoir located at a depth of about 25 km below the El Hierro Island was emplaced at shallower depth creating a new reservoir about 10–12 km above, where magma evolved until the initiation of the eruption. The characteristics of seismicity and surface deformation suggest that the necessary space to accumulate magma at this shallower position, which coincides with the crust/mantle boundary beneath El Hierro, was created in about 2 months by elastic deformation and magma‐driven fracturing of the crust. After this first intrusion episode, part of the magma started to migrate laterally toward the SE for nearly 20 km, always keeping the same depth and following a path apparently controlled by stress barriers created by tectonic and rheological contrasts in the upper lithosphere. This lateral migration of magma ended with a submarine eruption at about 5 km offshore from the southern corner of El Hierro Island. The total seismic energy released during the unrest episode was of 8.1 × 10¹¹ J, and the total uplift previous to the onset of the eruption was of 40 mm. Combining geological, geophysical, and petrological data and numerical modeling, we propose a volcanological model of the causes and mechanisms of El Hierro eruption that shows how the stress distribution in the crust beneath El Hierro, which was influenced by rheological contrasts, tectonic stresses, and gravitational loading, controlled the movement and eruption of magma. We also discuss the implications of this model in terms of eruption forecast in the Canary Islands.

On 10 October 2011, a submarine volcanic eruption started 2 km south from El Hierro Island (Spain). Since July 2011 a dense multiparametric monitoring network was deployed all over the island by Instituto Geográfico Nacional (IGN). By the time the eruption started, almost 10000 earthquakes had been located and the deformation analyses showed a maximum deformation of more than 5 cm. Earthquake migration from the north to the south of the island and acceleration of seismicity are in good correlation with changes in the deformation pattern as well as with some anomalies in geochemical and geomagnetic parameters. An earthquake of local magnitude 4.3 at 12 km depth (8 October 2011) and shallower seismicity a day after, preceded the onset of the eruption. This is the first time that a volcanic eruption is fully monitored in the Canary Islands. Data recorded during this unrest episode at El Hierro will contribute to understand reawakening of volcanic activity in this region and others of similar characteristics.

On October 10 2011 an underwater eruption gave rise to a novel shallow submarine volcano south of the island of El Hierro, Canary Islands, Spain. During the eruption large quantities of mantle-derived gases, solutes and heat were released into the surrounding waters. In order to monitor the impact of the eruption on the marine ecosystem, periodic multidisciplinary cruises were carried out. Here, we present an initial report of the extreme physical-chemical perturbations caused by this event, comprising thermal changes, water acidification, deoxygenation and metal-enrichment, which resulted in significant alterations to the activity and composition of local plankton communities. Our findings highlight the potential role of this eruptive process as a natural ecosystem-scale experiment for the study of extreme effects of global change stressors on marine environments.