Rapid response petrology for the opening eruptive phase of the 2021 Cumbre Vieja eruption, La Palma, Canary Islands

How and why magmatic systems reactivate and evolve is a critical question for monitoring and hazard mitigation efforts during initial response and ongoing volcanic crisis management. Here we report the first integrated petrological results and interpretation provided to monitoring authorities during the ongoing eruption of Cumbre Vieja, La Palma, Canary Islands, Spain. The first eruptive products comprised simultaneous Strombolian fountain-fed lava flows and tephra fall from near-continuous eruption plumes. From combined field, petrographic and geochemical analyses conducted in the 10 days following sample collection, we infer low percentage mantle melts with a variably equilibrated multimineralic crystal-cargo and compositional fractionation by winnowing during eruptive processes. Hence ‘rapid response’ petrology can untangle complex magmatic and volcanic processes for this eruption, which combined with further study and methodological improvement can increasingly assist in active decision making.

NUMERICAL SIMULATION OF TSUNAMI HAZARDS IN SOUTH ATLANTIC COAST: CASE OF THE CITY OF AGADIR – MOROCCO: PRELIMINARY RESULT

The coastal zone is a highly complex area because of its location at the interface between land and sea and as a preferred location for many forms of development. A mega tsunami from the Canary Islands will hit not only the Atlantic coasts of Morocco, but also Spain, Portugal, Great Britain and even reach US shores.A slight earthquake or possible volcanic eruption can trigger one of the most violent natural disasters in history. Indeed, according to Steven Ward and Simon Day (2001) the west flank of the Cumbre Vieja volcano, located on the island of Palma is unstable and could, as a result of a future eruption, collapse into the ocean. It would be in the worst scenario of a huge piece of 25 km long, 15 wide and 1,400 meters thick that would come off, a total of 500 cubic kilometers of land and rocks. This wave could reach 50 meters of height, once arrived on the Moroccan coasts. In this study, a numerical inundation and vulnerability models are used to identify the location and nature of current and future hazards and risk on the Moroccan coast to better understand the tsunami hazard and vulnerability along the Moroccan coast. We have worked on the correction of coastlines from satellite imagery on Google Earth and the digitization of bathymetric and topographic maps, in order to create digital elevation models (DEM). We have also studied the vulnerability assessment of the buildings by using the BTV model (Building Tsunami Vulnerability) such as a combination of tsunami inundation numerical modelling, field survey data and geographic information system.

Numerical Simulation of the Tsunami Generated by a Potential Submarine Landslide in La Palma (Canary Islands) after the September 2021 Cumbre Vieja Eruption

Cumbre Vieja volcano, located in La Palma Island (Canary Islands, Spain), erupted on 19 September 2021. Some papers have been published in the past in which the tsunamis generated by a potential massive landslide due to a collapse of one of the volcano flanks are investigated. However, a potential slide of the lava flow down the island slope has not been considered yet. A numerical model has been applied to simulate the propagation of the tsunami generated by such slide and to assess its consequences in the near field (Canary Islands and west coast of Africa). The model provides maps of maximum wave heights and arrival times of the tsunami, as well as time series of water surface elevation at several selected locations. Since the volume involved in such potential slide is a priori not known, several values were tested and their effects compared.

Petrology of the opening eruptive phase of the 2021 Cumbre Vieja eruption, La Palma, Canary Islands

The first products of the current Cumbre Vieja eruption comprise simultaneous tephra fall from near-continuous, gas-rich eruption plumes and lava flows. From combined field, petrographic and geochemical analyses we identify: low percentage mantle melts with a variably-equilibrated multimineralic crystal-cargo and compositional fractionation by eruptive processes. Hence petrology can untangle complex magmatic and volcanic processes for this eruption, which through further study can assist in active decision making.

DETECCIÓN DEL INICIO DE REACTIVACIÓN VOLCÁNICA EN LA ISLA DE LA PALMA, ISLAS CANARIAS, Y ESTUDIO DE SU EVOLUCIÓN TEMPORAL

La isla de La Palma es de las de mayor riesgo potencial del archipiélago canario, siendo por tanto importante realizar unestudio en profundidad que permita definir su estado de actividad volcánica. Esto se ha realizado usando observacionesde radar de satélite y una técnica de interpretación original de última generación. Ambas cosas han permitido detectar elinicio de la reactivación volcánica en la isla de La Palma, probablemente décadas antes de una posible erupción. Suevolución temporal muestra una naturaleza cambiante de la deformación volcánica, tanto espacial como temporalmente.El uso de imágenes radar permite obtener resultados con una gran resolución espacial y en un periodo de tiempoprolongado (2009-2020), obteniendo información sobre la naturaleza dinámica de los procesos asociados. Las técnicasgeodésicas empleadas permiten detectar la migración de fluidos inducida por la inyección de magma en profundidad eidentificar la existencia de fuentes de dislocación bajo el volcán Cumbre Vieja que podrían estar asociadas con futurosdeslizamientos, siendo por tanto necesario continuar con la monitorización de este proceso de reactivación utilizandoestas y otras técnicas.

Diffuse H2 degassing studies: a useful geochemical tool for monitoring Cumbre Vieja volcano, La Palma, Canary Islands

<p>Hydrogen (H<sub>2</sub>) is one of the most abundant trace species in volcano-hydrothermal systems and is a key participant in many redox reactions occurring in the hydrothermal reservoir gas. Although H<sub>2</sub> can be produced in soils by N<sub>2</sub>-fixing and fertilizing bacteria, soils are considered nowadays as sinks of molecular hydrogen (Smith-Downey et al. 2006). Because of its chemical and physical characteristics, H<sub>2</sub> generated within the crust moves rapidly and escapes to the atmosphere. These characteristics make H<sub>2</sub> one of the best geochemical indicators of magmatic and geothermal activity at depth. Cumbre Vieja volcano (La Palma, Canary Islands) is the most active basaltic volcano in the Canaries with seven historical eruptions being Teneguía eruption (1971) the most recent one. Cumbre Vieja volcano is characterized by a main north–south rift zone 20 km long, up to 1950 m in elevation and covering an area of 220 km<sup>2</sup> with vents located at the northwest and northeast. Cumbre Vieja does not show any visible degassing (fumaroles, etc.). For that reason, the geochemical volcano monitoring program at Cumbre Vieja volcano has been focused on soil degassing surveys.  Here we show the results of soil H<sub>2</sub> emission surveys that have been carried out regularly since 2001. Soil gas samples were collected in about 600 sampling sites selected to obtain a homogeneous distribution at about 40 cm depth using a metallic probe and 60 cc hypodermic syringes and stored in 10 cc glass vials. H<sub>2</sub> content was analysed later by a VARIAN CP4900 micro-GC. A simple diffusive emission mechanism was applied to compute the emission rate of H<sub>2</sub> at each survey. Diffuse H<sub>2</sub> emission values were used to construct spatial distribution maps by using sequential Gaussian simulation (sGs) algorithm, allowing the estimation of the emission rate from the volcano. Between 2001-2003, the average diffuse H<sub>2</sub> emission rate was ∼2.5 kg·d<sup>−1</sup> and an increase of this value was observed between 2013-2017 (∼16.6 kg·d<sup>−1</sup>), reaching a value of 36 kg·d<sup>−1</sup> on June 2017, 4 month before the first recent seismic swarm in October, 2017 at Cumbre Vieja volcano. Six additional seismic swarms had occurred at Cumbre Vieja volcano (February 2018, July-August 2020; October 8-10, 2020; October 17-19, 2020, November 21, 2020 and December 23-26, 2020) and changes of diffuse H<sub>2</sub> emission related to this unrest had been observed reaching values up to ∼70 kg·d<sup>−1</sup>. Diffuse H<sub>2</sub> emission surveys have demonstrated to be sensitive and excellent precursors of magmatic processes occurring at depth in Cumbre Vieja. Periodic diffuse H<sub>2</sub> emission surveys provide valuable information to improve and optimize the detection of early warning signals of volcanic unrest at Cumbre Vieja volcano.</p>

Monitoring diffuse CO2 emissions by means of an automatic geochemical station at Cumbre Vieja volcano, La Palma, Canary Islands.

<p>La Palma Island (708.3 km<sup>2</sup>) is located at the north-west and is one of the youngest (~2.0My) of the Canarian Archipelago. Volcanic activity has taken place exclusively at the southern part of the island, where Cumbre Vieja volcano, the most active basaltic volcano in the Canaries, has been constructed in the last 123 ky. Cumbre Vieja has suffered seven eruptions in the last 500 years, being the last in 1971 (Teneguía volcano). Since the last eruptive episode, Cumbre Vieja volcano has remained in a relative seismic calm that was interrupted on October 7th and 13rd, 2017, by two remarkable seismic swarms with earthquakes located beneath Cumbre Vieja volcano at depths ranging between 14 and 28 km with a maximum magnitude of 2.7. The frequency of these seismic episodes increased in 2020 with the occurrence of five more seismic swarms</p><p>As part of the volcano monitoring program of Cumbre Vieja, diffuse degassing of CO<sub>2</sub> has been continuously monitored since 2005 at the southernmost part of Cumbre Vieja according to the accumulation chamber method. The monitoring site (LPA04) was selected because it shows anomalous diffuse CO<sub>2</sub> degassing emission values with respect to the background values that had been measured in different surveys (Padrón et al., 2015). Meteorological and soil physical variables are also measured in an hourly basis and transmitted to ITER facilities about 150 Km far away.</p><p>Since its installation, CO<sub>2</sub> emissions ranged from non-detectable (<1.5 gm<sup>-2</sup>d<sup>-1</sup>) to 1,464.0 gm<sup>-2</sup>d<sup>-1</sup>. The time series was characterized by a strong variability in the measured values that are modulated mainly by the atmospheric and soil parameters. Soil moisture is the monitored parameter that explains the highest variability of the data, being the dry season (spring y summer) the period with the highest observed diffuse emission values. This behavior in the time series has changed after 2017 as an increasing trend in being observed in a good temporal agreement with the increase of seismic activity recorded. The observed diffuse CO<sub>2</sub> emissions trend in the LPA04 geochemical station support the occurrence of an upward magma migration towards a subcrustal magma reservoir beneath La Palma island.</p><p>Padrón et al., (2015). Bull Volcanol 77:28. DOI 10.1007/s00445-015-0914-2</p>

Temporal evolution of 3He/4He isotopic ratio at Dos Aguas cold mineral spring, La Palma, Canary Islands

<p>Recent volcanic activity of La Palma island, the fifth in extension (706 km<sup>2</sup>) and the second in elevation (2,423 m a.s.l.) of the Canarian archipelago, has taken place exclusively in the last 123 ka at the southern part of the island, where Cumbre Vieja volcano, the most active basaltic volcano in the Canaries, has been constructed. A total of seven volcanic eruptions have been reported along the main north-south rift zone of Cumbre Vieja in the last 500 years. On October 7<sup>th</sup> and 13rd, 2017, two remarkable seismic swarms interrupted a seismic silence of 46 years in Cumbre Vieja volcano with earthquakes located beneath Cumbre Vieja volcano at depths ranging between 14 and 28 km with a maximum magnitude of 2.7. Five more seismic swarms were registered in 2020.</p><p><sup>3</sup>He/<sup>4</sup>He ratio has been monitored at Dos Aguas cold mineral spring in La Palma Island since 1991 to date as an important volcano monitoring tool able to provide early warning signal of future volcanic unrest episodes. Magmatic helium emission studies have demonstrated to be sensitive and excellent precursors of magmatic processes occurring at depth. The highest <sup>3</sup>He/<sup>4</sup>He ratio reported to date from the Canarian archipelago has been measured at Dos Aguas: 10.24 R<sub>A</sub> (being R<sub>A </sub>the ratio in atmospheric helium) (Padrón et al., 2015). This value is higher than any value found either in the lavas or terrestrial fluid in the Canary Islands, and indicates an important mantle contribution.<sup>  </sup>According to the temporal evolution of the magmatic component of helium at Dos Aguas, we suggest the occurrence of aseismic magma rising episodes beneath La Palma within the upper mantle towards an ephemeral magma reservoir in the period 2007-2017. However, in the period 2017-2020, magma rising have produced seismic swarms that were accompanied also by the highest <sup>3</sup>He/<sup>4</sup>He ratio measured at Dos Aguas (10.42 R<sub>A</sub>); both geochemical and geophysical signals confirm an upward magma migration towards a subcrustal magma reservoir beneath La Palma island.</p><p> </p><p>Padrón et al., (2015). Bull Volcanol 77:28. DOI 10.1007/s00445-015-0914-2</p>

How Would the Potential Collapse of the Cumbre Vieja Volcano in La Palma Canary Islands Impact the Guadeloupe Islands? Insights into the Consequences of Climate Change

Tsunamis are among the deadliest threats to coastal areas as reminded by the recent tragic events in the Indian Ocean in 2004 and in Japan in 2011. A large number of tropical islands are indeed exposed due to their proximity to potential tsunami sources in tectonic subduction zones. For these territories, assessing tsunamis’ impact is of major concern for early warning systems and management plans. The effectiveness of inundation predictions relies, among other things, on processes engaged at the scale of the local bathymetry and topography. As part of the project C3AF that aimed to study the consequences of climate change on the French West Indies, we used the numerical model SCHISM to simulate the propagation of several potential tsunamis as well as their impacts on the Guadeloupe islands (French West Indies). Working from the findings of the most recent studies, we used the simulations of four scenarios of collapse of the Cumbre Vieja volcano in La Palma, Canary islands. We then used FUNWAVE-TVD to simulate trans-Atlantic wave propagation until they reached the Guadeloupe archipelago where we used SCHISM to assess their final impact. Inundation is quantified for the whole archipelago and detailed for the most exposed areas. Finally, in a climate change perspective, inundation is compared for different sea levels and degrees of vegetation cover deterioration using modified friction coefficients. We then discuss the results showing that climate change-related factors would amplify the impact more in the case of smaller inundation along with model limitations and assumptions.