At many dormant volcanoes, magmatic gases are not channeled through preferential degassing routes as fumaroles and only percolate through the flanks of the volcano in a diffuse way. This type of volcanic gas emission provides valuable information, even though the soil matrix contains an important atmospheric component. This study aimed to demonstrate that chemical ratios such as He/CO2 in soil gases provide excellent information on the evolution of volcanic unrest episodes and help forecast the volcanic eruption onset. Before and during the occurrence of the October 2011–March 2012 submarine of El Hierro, Canary Islands, more than 8500 soil He analyses and diffuse CO2 emission measurements were performed. The results show that the soil He/CO2 emission ratio began increasing drastically one month before eruption onset, reaching the maximum value 10 days before. During the eruptive period, this ratio also showed a maximum value several days before the period with the highest magma emission rate. The He/CO2 ratio was also helpful in forecasting the eruption onset. We demonstrate that this tool can be applied in real-time during volcanic emergencies. Our results also encourage a reevaluation of the global He emission from the subaerial volcanism.

The recent eruption of Tajogaite volcano occurred between September and December 2021 at La Palma Island is considered the most devastating of Europe since that of Vesuvio in 1944. The post-eruptive period is being characterized by the appearance of high outdoor and indoor CO2 concentrations at inhabited areas such as La Bombilla and Puerto Naos (Hernández et al., 2022), forcing the eviction of numerous homes. However, anomalous concentrations of CO2 have not only appeared in inhabited areas, but also in cultivated lands. In fact, the highest CO2 concentration values measured in the outdoor environment during the entire post-eruption period have been in a banana plantation of approximately 4,200 m2 that INVOLCAN has been monitoring since June 2022, named Las Hoyas.Since June 2022, 26 scientific observation surveys have been carried out at Las Hoyas consisting of the measurement at 39 homogeneously distributed sites of the CO2 and O2 concentration at two heights, 40 and 170 cm from the ground, as well as sampling of atmospheric air in 19 sites at 40 cm for carbon isotope ratio of air CO2. Air CO2 and O2 concentrations are measured with a hand portable Dräger X-am® 8000 meter and the carbon isotope ratio of air CO2 (expressed as δ13C-CO2 ‰ vs. VPDB) is analyzed at ITER/INVOLCAN lab by a Thermo Finnigan MAT 253 mass spectrometer. Spatial distribution maps have been constructed following the sequential Gaussian simulation (sGs) to evaluate the spatial distribution of the air CO2 concentration. Observed air CO2 concentration values ranged from air value (412ppm) up to 69%, the highest ever measured during the post-eruptive period, with an average value of 7.1%. Air O2 concentration values ranged between 7.9% to air value (20.9%), with an average value of 19.2%. δ13C-CO2 values ranged between –8.90 to -2.66‰, with an average value of -4.87‰, indicating a clear volcanic-hydrothermal origin for the anomalous CO2 emitted from Las Hoyas banana plantation and ruling out a single biogenic origin.In order to investigate the temporal evolution of the observed high CO2 concentrations in Las Hoyas, a Sinclair statistical graphic analysis was applied to the data from each survey. Time series of background and peak populations does not show a clear trend, with the occurrence of peaks and valleys throughout the entire series, and maintaining values much higher than those of the air. Likewise, the temporal evolution of the δ13C-CO2 values shows a trend towards heavier values, indicating that the volcanic-hydrothermal contribution increases with time. The spatial distribution of the air CO2 concentration measured at 40 cm shows that in most of the surveys, the anomalous values (>10%) are located mainly along the walls of Las Hoyas and in the NW sector, where in more than a year after the eruption, the banana plants are still withered and dead terrestrial and aerial fauna constantly appear due to poisoning and suffocation from CO2 inhalation. Hernández et al. EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7705, https://doi.org/10.5194/egusphere-egu22-7705, 2022.

Abstract The explosive activity of the 2021 Tajogaite eruption eludes pigeonholing into well‐defined eruption styles, with a variety of pyroclast ejection modes occurring both alternately and simultaneously at multiple vents. Visually, we defined four endmembers of explosive activity, referred to as fountaining, spattering, ash‐poor jets and ash‐rich jets. To capture the physical parameters of these activities, we deployed a camera array including one high‐speed camera and three high‐definition cameras in two field campaigns. Transitions between and fluctuations within activity occurred at the time scale of minutes to hours, likely driven by the same shallow conduit and vent processes controlling Strombolian activity at other volcanoes, but at higher gas and magma fluxes. From a physical standpoint, mean pyroclast rise velocity ranged 5–50 m/s, maximum ejection velocity 10–220 m/s, and sub‐second mass flux of lapilli to bomb‐sized pyroclasts at the vent 0.2–200 × 103 kg/s. The largest mass flux occurred during fountaining, which contributed by far more than other activities to cone building. All explosive activity exhibited well‐defined pyroclast ejection pulses, and we found a positive correlation between the occurrence rate of ejection pulses and maximum pyroclast ejection velocity. Despite orders of magnitude variations, physical parameters shift gradually with no boundary from one activity endmember to another. As such, attributing this explosive activity specifically to any currently defined style variations is arbitrary and potentially misleading. The highly variable explosive activity of the Tajogaite eruption recalls previous definitions of violent Strombolian eruptions, an eruption style whose pyroclast ejection dynamics, however, were so far largely undefined.

The 2021 eruption at Tajogaite (Cumbre Vieja) volcano (La Palma, Spain) was characterized by Strombolian eruptions, Hawaiian fountaining, white gas-dominated and grey ash-rich plumes, and lava effusion from multiple vents. The variety of eruptive styles displayed simultaneously and throughout the eruption presents an opportunity to explore controls on explosivity and the relationship between explosive and effusive activity. Explosive eruption dynamics were recorded using ground-based thermal photography and videography. We show results from the analysis of short ( < 5 min) near-daily thermal videos taken throughout the eruption from multiple ground-based locations and continuous time-lapse thermal photos over the period November 16 to November 26. We measure the apparent radius, velocity, and volume flux of the high-temperature gas-and-ash jet and lava fountaining behaviors to investigate the evolution of the explosive activity over multiple time scales (seconds-minutes, hours, and days-weeks). We find fluctuations in volume flux of explosive material that correlate with changes in volcanic tremor and hours-long increases in explosive flux that are immediately preceded by increases in lava effusion rate. Correlated behavior at multiple vents suggests dynamic magma ascent pathways connected in the shallow (tens to hundreds of meters) sub-surface. We interpret the changes in explosivity and the relative amounts of effusive and explosivity to be the result of changes in gas flux and the degree of gas coupling.

&lt;p&gt;After the Tajogaite eruption at Cumbre Vieja volcano (La Palma, Canary Islands), volcanic gas hazard continues to affect the inhabited coastal areas of Puerto Naos and La Bombilla, as well as the nearby agricultural fields, which are located about 6 km distance from the eruptive vents. This gas hazard is primarily due to CO&lt;sub&gt;2&lt;/sub&gt; (Hern&amp;#225;ndez et al. 2022) and persist during the post-eruptive phase of the eruption. According to long-term geochemical studies conducted by INVOLCAN, the high levels of CO&lt;sub&gt;2&lt;/sub&gt; emissions in these coastal areas were first recorded approximately three weeks before the end of the Tajogaite eruption on December 13, 2021.&lt;/p&gt;&lt;p&gt;To monitor this anomalous diffuse CO&lt;sub&gt;2&lt;/sub&gt; degassing at La Bombilla, 46 surveys consisting of approximately 84 sampling observation sites have been regularly conducted since December 2021, covering an area of 0.033 square kilometers. In-situ measurements of soil CO&lt;sub&gt;2&lt;/sub&gt; efflux and ground temperature as well as collection of samples of the soil gas atmosphere at a depth of 40cm for chemical and isotopic analysis were carried out at each sampling site. Soil CO&lt;sub&gt;2&lt;/sub&gt; efflux measurements have been performed following the accumulation chamber method. Soil gas chemical analysis were carried out by means of a microGC and the carbon isotope ratio of soil gas CO&lt;sub&gt;2&lt;/sub&gt; (expressed as &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C-CO&lt;sub&gt;2&lt;/sub&gt; &amp;#8240; vs. VPDB) was analyzed also in our geochem lab by a Thermo Finnigan MAT 253 mass spectrometer. Spatial distribution maps have been constructed following the sequential Gaussian simulation (sGs) to evaluate the spatial distribution of the soil CO&lt;sub&gt;2&lt;/sub&gt; efflux measurements and quantify the diffuse CO&lt;sub&gt;2&lt;/sub&gt; emission from the studied area. Observed soil CO&lt;sub&gt;2&lt;/sub&gt; efflux values ranged from &lt;0.5 (detection limit) to 449,500 gm&lt;sup&gt;-2&lt;/sup&gt;d&lt;sup&gt;-1&lt;/sup&gt; with a mean value of 513 gm&lt;sup&gt;-2&lt;/sup&gt;d&lt;sup&gt;-1&lt;/sup&gt;. Diffuse CO&lt;sub&gt;2&lt;/sub&gt; emission values ranged between 4.0 and 170 td&lt;sup&gt;-1&lt;/sup&gt;, with an average value of 16 td&lt;sup&gt;-1&lt;/sup&gt;. &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C-CO&lt;sub&gt;2 &lt;/sub&gt;values ranged between -8.63 to -4.31 (&amp;#8240; vs. VPDB) with an average value of -5.68 (&amp;#8240; vs. VPDB). The temporal evolution of the diffuse CO&lt;sub&gt;2&lt;/sub&gt; emission rate at La Bombilla shown a rapid initial decrease from the first survey (170 td&lt;sup&gt;-1&lt;/sup&gt;) remaining relatively stable between 55 and 4 td&lt;sup&gt;-1&lt;/sup&gt;. Since November 2022, the time series seems to show a progressive decreasing trend. However, the temporal evolution of the &amp;#948;&lt;sup&gt;13&lt;/sup&gt;CO&lt;sub&gt;2&lt;/sub&gt; values shows that volcanic-hydrothermal contribution to these diffuse emanations continues to be important. In order to evaluate other potential geochemical parameters as indicators of a possible mitigation of this problem related to the CO&lt;sub&gt;2&lt;/sub&gt; hazard, we are investigating the temporal evolution of the La Bombilla / Cumbre Vieja diffuse CO&lt;sub&gt;2&lt;/sub&gt; emission ratio normalized per area unit.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Hern&amp;#225;ndez, P. A., Padr&amp;#243;n, E., Meli&amp;#225;n, G. V., P&amp;#233;rez, N. M., Padilla, G., Asensio-Ramos, M., Di Nardo, D., Barrancos, J., Pacheco, J. M., and Smit, M.: Gas hazard assessment at Puerto Naos and La Bombilla inhabited areas, Cumbre Vieja volcano, La Palma, Canary Islands, EGU General Assembly 2022, Vienna, Austria, 23&amp;#8211;27 May 2022, EGU22-7705, https://doi.org/10.5194/egusphere-egu22-7705, 2022.&lt;/p&gt;

During and after the end of the 2021 Tajogaite eruption (La Palma, Canary Islands), anomalous CO2 degassing has been detected in the neighborhoods of La Bombilla and Puerto Naos, located around 5 km distance southwestern of the 2021 Tajogaite eruption vents. The aim of this study is to determine the indoor air quality of the houses of the aforementioned neighborhoods. For that purpose, from August 11 to October 24, 2022, air samples were taken, for further analysis, from indoors of 10 locations in Puerto Naos, on a weekly basis. In addition, on September 22, 2022, a discrete survey of the indoor ambient air was carried out in 10 houses of La Bombilla, consisting on in-situ measurements and gas sampling for further analysis.Gas samples were taken for a complete geochemical characterization (i.e., He, Ar, Ne, H2, N2, O2, CH4, CO contents) by micro-gas chromatography (micro-GC) and quadrupole mass spectrometry (QMS) and, as well as for carbon isotopic analysis of the CO2 (δ13C-CO2) by isotopic ratio mass spectrometry (IRMS). In-situ measurements of CO2, O2, 222Rn, 220Rn, H2S and Hg0 were conducted in La Bombilla with and without natural ventilation.National Health Systems in the European Union reflect that the upper limit of the acceptable CO2 concentration range for long-term exposure in the indoor ambient air of buildings for residential use should be of the order of 1,000-1,200 ppm to guarantee people health. The concentrations of CO2 registered in the indoor ambient air of the 10 houses of La Bombilla determined by the in-situ measurements showed relatively high values -above 5,000 ppm- even reaching a maximum of 183,900 ppm in conditions without natural ventilation. In these conditions of absence of ventilation, a certain displacement of O2 was observed, which dropped to 18.7% in the worst case. Under conditions with natural ventilation for a period of 2 hours, the range of CO2 concentration fell to a range between 1,050 and 14,200 ppm and the O2 concentration registered was 20.9%. These results reflect that natural ventilation, and even more forced ventilation, would contribute to reduce CO2 concentration in the ambient air inside buildings. Regarding the results of the indoor gas samples analysis from Puerto Naos, the CO2 concentration and the δ13C-CO2 mean values ranged from 1,190 to 230,952 ppm and -7.9 to -4.8‰ vs. VPDB, respectively. These results of the chemical and isotopic composition of the indoor ambient air of Puerto Naos and La Bombilla demonstrate the importance of these studies to monitor and manage these silent hazards that pose a threat to the population and restrict access to their houses.

During the main phase of the 2021 eruption of the Cumbre Vieja volcano (La Palma, Spain), eruptive activity was characterized by Strombolian eruptions, fire fountaining, white and grey ash and gas-dominated plumes, and lava effusion from multiple events. Over the period November 16 to November 26, we recorded continuous time-lapse IR images and opportunistic visible and IR videos of the vent from multiple ground-based locations. We measure the apparent area of the high-temperature gas-and-ash jet and fire fountaining from time-lapse images recorded between 1 and 60 frames/min to investigate the evolution of the explosive activity and of these plumes on minutes to days time scales. We compare plume size estimates from two different angles and vent-camera distances. We will explore periodicity and relationships between neighboring vents and discuss the implications for processes occurring in the shallow-most plumbing system of the volcano.

Cumbre Vieja (220 km2) is the most active volcano in the Canary Islands. It has been the location of 8 of the 17 historical eruptions in the archipelago during the last 600 years. The establishment of a geochemical monitoring program by our research group for the volcanic surveillance of Cumbre Vieja started in 1997. This program was mainly focused on diffuse degassing monitoring because of the absence of visible volcanic degassing manifestations (fumaroles, plumes, etc.) as well as other obvious geothermal features at Cumbre Vieja up to the 2021 eruption which started on September 19, ended on December 13 and lasted 85 days. The INVOLCAN’s soil degassing monitoring at Cumbre Vieja is carried out by means of a geochemical instrumental permanent network (soil CO2 efflux, soil gas 222Rn and soil C isotope ratio) and regular geochemical surveys covering the entire area of Cumbre Vieja (diffuse CO2, He and H2 emissions). Several soil degassing anomalies have been observed and some of them years before the 2021 eruption, which illustrates the importance of diffuse degassing monitoring for volcanic surveillance. The single visible manifestation of volcanic degassing at La Palma is a cold CO2-rich site at Taburiente volcano. Regular helium-3 emission monitoring of this observation site has been carried out since 1991 in collaboration with Tokyo Univ., and provided a clear early warning signal of the 2021 Cumbre Vieja eruption. Because of the registration of seismic swarms, and to strengthen the INVOLCAN geochemical monitoring program of Cumbre Vieja volcano, regular sampling of groundwater for chemical and isotopic analysis started in October 2017. The results of this hydrogeochemical monitoring also showed significant changes related to the recent volcanic unrest of Cumbre Vieja. Since the 2021 eruption onset, INVOLCAN performed daily observations of SO2 emissions using a miniDOAS in traverse mode, on terrestrial (car), sea (ship) and air (helicopter) mobile position recording relatively high SO2 emissions (> 50.000 t/d). Static scanners and satellite instruments were used also to monitoring the SO2 emission released by this eruption; a task lead by the volcano research group of Manchester University. Additional plume geochemical monitoring was carried out using OP-FTIR spectrometers and UAV, helicopter and ground-base MultiGas units to characterize the chemical composition of the plume degassing in collaboration with scientists from Manchester Univ., Palermo Univ., UCL, INGV, IPGP and Azores Univ. Carbon isotope analysis of the CO2 gas plume was also undertaken in collaboration with New Mexico Univ. Analysis of pristine ash leachates has been also performed in collaboration with Durham Univ. and Tokyo Institute of Technology since it is often used to estimate the composition of the gas phase during volcanic eruptions and provides important information on the eruption processes was also performed. The results of these geochemical observations during the inter-eruptive, pre-eruptive, eruptive and post-erupive phases have been tremendously useful to understand the recent magmatic reactivation of Cumbre Vieja volcano.

The 2021 Cumbre Vieja eruption has provided powerful insights not only on the pure research field, but as well on the communication side. From INVOLCAN we´ve developed a clear strategy on how to communicate what was going on, and about the role of science on this eruption. But there is as well a long road to let the different audiences understand the ultimate goal of an institutional profile, that is telling about science and nothing else related to the drama lived by the population. That strategy led us to show anything but science, discarding tons of footage of destruction of infrastructure and properties. Through the eruption our Twitter and Facebook profiles published the same content, with a clear divergence on the output. While Facebook followers remained almost stagnant all over the 3 months period, the Twitter account skyrocketed to a +-5000% increase on followers, and almost 100M tweet impressions. We focused on working on a single profile rather than in personal profiles of researchers, where part of the message and the influence can be lost in time All our graphic material was released as public domain, what resulted in hundreds of INVOLCAN TV hours, and led to hundreds of interviews on media from anywhere in the world. The impact of the INVOLCAN brand is literally unaccountable and we believe strengthens the Institute reputation all over. But we have discovered some flaws as well on the “relationship” established between the “speaker” (INVOLCAN) and the “audience”. As massive attention was driven to the INVOLCAN account, the number of trolls and eccentric characters emerged. This is a well-known behaviour on social media, but never happened before to us on that scale. A clear ignorance of the objectives of INVOLCAN may explain part of some feedback received, which perhaps did not understand well that INVOLCAN was not responsible for emergency tasks such as evacuations, or that it was not responsible for showing the destruction of private property or that at least it wasn't our job. But there is still an important part of the work to be done, insofar as it is exhausting to see the proliferation of "experts" capable of demanding information that does not make any sense to the population or that directly accused of hiding information. There is a long way to go in the world of social networks, and this eruption, the same as that of the COIVD-19 pandemic, has revealed the multiple menaces that threaten science lurking in the shadows, which may end up losing its voice in a tower of Babylon where anyone thinks they know the language of volcanoes

The 2021 Cumbre Vieja eruption has provided powerful insights not only on the pure research field, but as well on the communication side. From INVOLCAN we´ve developed a clear strategy on how to communicate what was going on, and about the role of science on this eruption. But there is as well a long road to let the different audiences understand the ultimate goal of an institutional profile, that is telling about science and nothing else related to the drama lived by the population. That strategy led us to show anything but science, discarding tons of footage of destruction of infrastructure and properties. Through the eruption our Twitter and Facebook profiles published the same content, with a clear divergence on the output. While Facebook followers remained almost stagnant all over the 3 months period, the Twitter account skyrocketed to a +-5000% increase on followers, and almost 100M tweet impressions. We focused on working on a single profile rather than in personal profiles of researchers, where part of the message and the influence can be lost in time All our graphic material was released as public domain, what resulted in hundreds of INVOLCAN TV hours, and led to hundreds of interviews on media from anywhere in the world. The impact of the INVOLCAN brand is literally unaccountable and we believe strengthens the Institute reputation all over. But we have discovered some flaws as well on the “relationship” established between the “speaker” (INVOLCAN) and the “audience”. As massive attention was driven to the INVOLCAN account, the number of trolls and eccentric characters emerged. This is a well-known behaviour on social media, but never happened before to us on that scale. A clear ignorance of the objectives of INVOLCAN may explain part of some feedback received, which perhaps did not understand well that INVOLCAN was not responsible for emergency tasks such as evacuations, or that it was not responsible for showing the destruction of private property or that at least it wasn't our job. But there is still an important part of the work to be done, insofar as it is exhausting to see the proliferation of "experts" capable of demanding information that does not make any sense to the population or that directly accused of hiding information. There is a long way to go in the world of social networks, and this eruption, the same as that of the COIVD-19 pandemic, has revealed the multiple menaces that threaten science lurking in the shadows, which may end up losing its voice in a tower of Babylon where anyone thinks they know the language of volcanoes

A variety of eruptive styles concurred to define the explosive activity of the 2021 Cumbre Vieja eruption (La Palma, Canary Islands, Spain). These styles include, as broadly defined, lava fountaining, Strombolian explosions, rapid Strombolian, spattering, ash-rich jets, and ash venting, and occurred both alternately and simultaneously at the multiple vents that hosted the activity during the more-than-three-months-long eruption. In order to capture the defining features and the underlying processes of these styles and of their transitions, we deployed FAMoUS (Fast, MUltiparametric Setup) during two field campaigns, between 22 September-1 October and between 5-9 November 2021. FAMoUS includes one high-speed camera (frame rate 250 to 500 frames per second (FPS) and 0.021-0.147 m/pixel resolution at the vent), one thermal camera (up to 50 FPS and 0.2-0.8 m/pixel .ca), three high-definition cameras (25 FPS, 0.03-1.2 m/pixel ca.), and one microphone (flat response between 0.5 and 10000 Hz, sampling rate 20 kHz). Preliminary video processing results, obtained using both manual tracking and Optical Flow routines, reveal ejection velocities of pyroclasts in the 20-220 m/s range, with the highest and the lowest values of peak velocity being recorded during Strombolian explosions and ash venting, respectively. All activity styles display ejection velocity fluctuations and variably marked ejection pulses, which are more pronounced during Strombolian explosions. Lava fountains feature the highest mean ejection velocity and a variety of fluctuation patterns, with larger-amplitude and more abrupt ones when transitioning towards Strombolian explosions. The maximum settling velocity of bomb-to lapilli-sized pyroclasts in the vicinity of the vent is remarkably stable around 50 m/s. The transition between the different styles of activity is marked by changing rates of ejection pulse frequency/amplitude and relative proportions of ash and bombs, pointing to a feedback between the volume, ascent rate, and frequency of gas pockets rising in the conduit, and the changes induced by their transit through the magma residing in the uppermost termination of the conduit.

Two remarkable 2021 eruptions – Fagradalsfjall (Reykjanes, Iceland) and Cumbre Vieja (La Palma, Spain) – have been captured in imagery and videography at unprecedented spatial and temporal resolution by tourists, volcano-enthusiasts, and media organizations. We propose this represents the start of a new era for observational volcanology, with the abundance of eruption imagery leveraged for scientific use. This study explores the scientific potential of crowdsourced observations during volcanic eruptions, using the 2021 Fagradalsfjall (Iceland) and Cumbre Vieja (Canary Islands) events as case studies.

On September 19, 2021, a volcanic eruption began at the west flank of Cumbre Vieja, La Palma, the most northwestern of the Canary Islands. The lava flows caused the evacuation of thousands of residents living in the vicinity of the volcano, and 1,219 hectares were covered by lava flows. After 85 days of activity, the eruption ended on December 13, 2021. Since visible volcanic gas emissions (fumaroles, hot springs, etc.) do not occur at the surface environment of Cumbre Vieja, the geochemical program for the volcanic surveillance has been focused mainly on diffuse (non-visible) degassing studies. Since 2001, diffuse CO2 emission surveys have been yearly performed in summer periods to minimize the influence of meteorological variations. Measurements of soil CO2 efflux have been performed following the accumulation chamber method in about 600 sites and spatial distribution maps have been constructed following the sequential Gaussian simulation (sGs) procedure to quantify the diffuse CO2 emission from the studied area. In the period 2001-2016, the diffuse CO2 output released to the atmosphere from Cumbre Vieja volcano ranged between 320 to 1,544 t·d-1. During pre-eruptive period (2016-2021), time series of the diffuse CO2 emission showed a change with an increasing trend from 788 t·d-1 up to 1,870 t·d-1, coinciding with the beginning of the seismic swarms. This increase of diffuse CO2 emission is interpreted as a geochemical precursory signal of volcanic eruption of Cumbre Vieja, on September 19, 2021. The observed increase on the diffuse CO2 emission during this time window suggests that in October 2017 a process of magma ascent began from the upper mantle to depths between 35-25 km, at which the seismic swarms were recorded for four years. During eruption period, diffuse CO2 emission showed strong temporal variations with a minimum value of the diffuse CO2 emission in October 21, followed by an increase trend of up to 4,435 t·d-1 on December 14, the highest of time series and coinciding with the end of the eruption. During the post-eruptive period, the diffuse CO2 emission has shown a descending trend. Our results demonstrate that periodic surveys of diffuse CO2 emission are extremely important in the volcanic surveillance tools of Cumbre Vieja to improve the detection of early warning signals of future volcanic unrest episodes.

Ground surface diffuse degassing and heat flow surveys were conducted at the summit crater of Teide volcano (Tenerife) on a roughly monthly basis from 2013 to 2017 to evaluate their degree of temporal variation and compare with seismovolcanic activity in and around Tenerife Island. We report that significant changes in survey physicochemical and chemical parameters through time were observed. Several geochemical signals record the occurrence of magmatic fluid injections in the hydrothermal system of Tenerife: during June‐August of 2016 there were increases in diffuse H 2 S emission, observed relatively higher values of diffuse H 2 S/CO 2 He/CO 2 , and CO 2 /CH 4 degassing ratios and changes in the carbon isotopic ratio of diffuse CO 2 degassing. Convective mixing within a magma reservoir triggered by an injection of fresh magma is confirmed as the most plausible scenario to explain the source of fluid injection into the hydrothermal system of Teide.

(1) Instituto Volcanológico de Canarias (INVOLCAN), 38320 La Laguna, Tenerife, Canary Islands, Spain (nperez@iter.es), (2) Agencia Insular de la Energía de Tenerife (AIET), 38600 Granadilla de Abona, Tenerife, Canary Islands, Spain, (3) Instituto Tecnológico y de Energías Renovables (ITER), 38600 Granadilla de Abona, Tenerife, Canary Islands, Spain, (4) Dipartimento di Scienze della Terra, Università degli Studi di Firenze (UniFI), Firenze, Italy, (5) Istituto di Geoscienze e Georisorse – CNR, Pisa, Italy, (6) Department of Geological Sciences, Ohio University, Athens, USA

We report the results of 49 soil CO2 efflux surveys by the accumulation chamber method at the North West Rift (NWR) Zone of Tenerife Island, Canary Islands. The surveys were carried out from 2000 to 2016 to evaluate the temporal and spatial variations of CO2 efflux and their relationships with the volcanic and seismic activity at Tenerife. Soil CO2 efflux values ranged from non-detectable (<0.5 g m−2 day−1) up to 141 g m−2 day−1, with the highest values measured in May 2005, whereas total CO2 emission rates ranged between 52 and 867 t day−1 (metric tons per day). Isotopic analyses of soil gas in carbon dioxide (δ13C–CO2) suggest a mixing between organic and atmospheric CO2 with a small contribution of deep-seated CO2. The main temporal variation in the total CO2 output does not seem to be driven by external factors; it shows a clear temporal correlation with the onsets of seismic activity. Subsurface magma degassing affecting the central part of the island is proposed as a cause for the observed changes in the total output of diffuse CO2 emission, as well as for the spatial distribution of soil CO2 efflux.