GMPV9.2

During the last two decades, Sangay has been one of the most active Ecuadorian volcanoes. However, because of its remote location and logistically difficult access, monitoring Sangay is a challenging task. The IG-EPN tackled this problem by expanding its terrestrial monitoring network and complementing it with the available satellite data. On 7^th May 2019, the most recent and ongoing eruptive episode commenced. Compared to the previously monitored and observed eruptive activity at Sangay since the 2000’s, this episode is by far the most intense and the first to affect populated areas due to ash fallouts and numerous lahars. Surface activity is generally characterized by frequent low-to-moderate magnitude ash emissions and a semi-continuous viscous lava flow extrusion. This activity is punctuated by occasional lava flow collapse events, probably associated with pulses of high lava extrusion and that produced long-runout pyroclastic density currents towards the southeastern flank.

Here, we present the most complete data set of long-term instrumental observations performed at Sangay. SO₂ degassing, seismic activity, ground deformation, ash emissions and thermal anomalies are depicted as a multiparametric sequence to better understand the link between these parameters and the dynamism and eruptive style of this isolated volcano.  

Correlations between the depicted parameters are not straight-forward, making it hard to identify patterns that might lead to enhanced eruptive activity. High values of SO₂ recorded by the DOAS instruments as well as the TROPOMI satellite sensor seem to coincide with periods of increased eruption rate. Nevertheless, increases in SO₂ flux do not occur systematically before or after these episodes. Seismic activity, characterized by daily counts of individual seismic events, does not demonstrated a clear precursory pattern either. These results indicate that none of the available monitoring parameters currently allow for a timely forecast of the largest and potentially most dangerous eruptions. However, looking at the entire time series we are able to distinguish a slightly but progressive change in the ground deformation displacement associated with a higher number of earthquakes per day prior to the 20 September 2020 paroxysmic event. This eruption produced regional ash fallout which affected significant swaths of farming lands and livestock. Since then, a different ground deformation pattern has taken hold, and coincides with a step decrease in the number of daily earthquakes and a significant increase in the SO₂ mass measured by TROPOMI.

This behavior matches an open-vent system, where punctual increases in eruptive activity show few precursory signals. The observed increase in all the parameters compared to previous eruptions before 2019 allows us to propose that this eruptive phase is fed by batches of deep and volatile-rich magma which rise to the surface at high ascent rates. The interpretations presented here are an important step towards a better understanding of the dynamism and eruptive style of this very active and isolated volcano. Moreover, the various monitoring parameters from terrestrial to satellite provide a better picture of the behavior of Sangay that could be applied to other remote and open-system volcanoes.

How to cite: Vasconez, F. J., Hidalgo, S., Hernández, S., Salgado, J., Valade, S., Espín, P., Bernard, B., Cárdenas, D., Battaglia, J., Samaniego, P., and Coppola, D.: Multiparametric monitoring of the ongoing eruption of Sangay volcano, Ecuador, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10300, https://doi.org/10.5194/egusphere-egu21-10300, 2021.

Changes in the eruptive dynamics are mainly controlled by the magma gas content, and the degassing processes impacting the magma viscosity and ascending speed. The progressive exsolution of the gas species, their release at different depths, their mutual interaction and the eventual assimilation of crustal rocks are reflected in the volcanic plume composition changes. Combining long-term ground-based FTIR and UV remote measurements of the Popocatepetl's plume, seismic data and visual monitoring, we explore the relationship between the gas composition changes in the volcanic plume and the transition between extrusive and passive degassing regimes.

SO2, HCl, HF, BrO, SiF4 and CO2 are simultaneously measured in the volcanic plume since 2013 from the Altzomoni observatory, located 12 km north of the crater. We capture several phases of lava dome growth, different types of explosions and passive degassing periods. The evolution of the gas species ratios through these events allows deciphering the degassing processes.

How to cite: Taquet, N., Stremme, W., Rivera, C., Bezanilla, A., Grutter, M., Campion, R., Valade, S., Boulesteix, T., Legrand, D., Blumenstock, T., and Hase, F.: Long-term evolution of the gas composition of Popocatepetl's plume, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12242, https://doi.org/10.5194/egusphere-egu21-12242, 2021.

Bromine monoxide (BrO) is a halogen radical capable of influencing atmospheric chemical processes, in particular the abundance of ozone, e. g. in the troposphere of polar regions, the stratosphere as well as in volcanic plumes. Furthermore, the molar bromine to sulphur ratio in volcanic gas emissions is a proxy for the magmatic composition of a volcano and potentially an eruption forecast parameter.

The high spatial resolution of the S5-P/TROPOMI instrument (up to 3.5x5.5km²) and its daily global coverage offer the potential to detect BrO even during minor eruptions and also to determine BrO/SO₂ ratios during continuous passive degassing.

Here, we present a global overview of BrO/SO₂ molar ratios in volcanic plumes derived from a systematic long-term investigation of three years of TROPOMI data.

We retrieved column densities of BrO and SO₂ using Differential Optical Absorption Spectroscopy (DOAS) and calculated mean BrOSO₂ molar ratios for each volcano. As expected, the calculated BrO/SO₂ molar ratios differ strongly between different volcanoes ranging from several 10^-5 up to several 10^-4. In our study of three years of S5P/TROPOMI data we successfully recorded elevated BrO column densities for more than 100 volcanic events and were able to derive meaningful (coefficient of determination, R² exceeding 0.5) BrO/SO₂ ratios for multiple volcanoes.

How to cite: Warnach, S., Sihler, H., Borger, C., Bobrowski, N., Schmitt, S., Schöne, M., Beirle, S., Platt, U., and Wagner, T.: A global perspective on Bromine monoxide composition in volcanic plumes derived from three years of S5-P/TROPOMI data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1696, https://doi.org/10.5194/egusphere-egu21-1696, 2021.

At open-vent basaltic volcanoes, resolving the activity escalation that heralds larger, potentially harmful eruptions is challenged by the persistent mild ordinary activity, which often masks the precursory unrest signals related to heightened magma transport from depth. Gas (SO₂ and CO₂) fluxes at surface are controlled by rate of magma transport and degassing within the magma plumbing system, and thus constitute key parameters to infer deep magma budget and dynamics.

Here, we use several year-long (2014-present) gas observations at Etna and Stromboli volcanoes, in Sicily, to provide new evidence for the utility of long-term instrumental gas monitoring in real-time detecting the early phase of unrest prior eruption, and for characterizing syn-eruptive dynamics. To this aim, we use information from a gas monitoring network of permanent ultraviolet (UV) cameras and automatic Multi-Gas instruments that, combined with geophysical observations, allow characterizing changes in degassing and eruptive dynamics at high temporal/spatial resolution.

Our results show that the paroxysmal (lava fountaining) explosions that periodically interrupted persistent open-vent activity on Etna (during 2014-2020) were accompanied by systematic, repetitive SO₂ emission patterns prior, during, and after eruptions. These allow us identifying the characteristic pre- syn- and post- eruptive degassing regimes, and to establish thresholds in the SO₂ flux record that mark phases of unrest.

On Stromboli, the much improved temporal/spatial resolution of UV cameras allows resolving the escalation of regular strombolian activity, and its concentration toward its North-east crater, that heralds onset of effusive eruptions. During effusive eruption, although magma level drops in the conduit and explosive summit activity ceases, UV camera observations can still detect explosive gas bursts deep in the conduit while no infrasonic activity is detected. Combining the UV camera-derived SO₂ fluxes with CO₂/SO₂ ratio records measured by the Multi-Gas, the CO₂ flux can be inferred. We find that such CO₂ flux time-series can allow tracking degassing of deeply stored mafic magma months before Stromboli’s eruptions. We finally show that remotely sensed gas emission and thermal activity can be combined together to characterize the dynamics of shallow magmatic system prior to and during unrest, ultimately helping to define timing of magma re-charging events driving the eruptions.

How to cite: Delle Donne, D., Aiuppa, A., Bitetto, M., La Monica, F. P., Tamburello, G., Coppola, D., Lacanna, G., Laiolo, M., Coltelli, M., Pecora, E., and Ripepe, M.: Long-term gas observations track the early unrest phases of open-vent basaltic volcanoes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9010, https://doi.org/10.5194/egusphere-egu21-9010, 2021.

Tenerife (2,034 km²) is the largest of the Canary Islands. Its structure is controlled by a volcano-tectonic rift-system with NW, NE and NS directions, with the volcanic system Teide-Pico Viejo located in the intersection. Teide is 3,718 m.a.s.l. high and its last eruption occurred in 1798 through an adventive cone of Teide-Pico Viejo volcanic complex. Persistent degassing activity, both visible and diffuse, takes place at the summit cone of the volcano, being the diffuse degassing the principle mechanism.

During the period 1999-2020, more than 200 diffuse CO₂ efflux surveys have been performed in the summit crater of Teide Volcano. For each survey, 38 sampling sites homogeneously distributed inside the crater covering an area of 6,972 m² were selected. Diffuse CO₂ emission was estimated in each point by means of a portable non dispersive infrared (NDIR) CO₂ fluxmeter using the accumulation chamber method. Additionally, soil gas samples were taken at 40 cm depth and analyzed later in the lab for the He and H₂ content by means of quadrupole mass spectrometry and micro-gas chromatography, respectively. To estimate the He and H₂ emission rates at each sampling point, the diffusive component was estimated following the Fick’s law and the convective emission component model was estimated following the Darcy’s law. In all cases, spatial distribution maps were constructed averaging the results of 100 simulations following the sequential Gaussian simulation (sGs) algorithm, in order to determine CO₂, He and H₂ emission rates.

During the study period, CO₂ emissions ranged from 2.2 to 176.1 t/d, He emissions between 0.013 and 4.1 kg/d and H₂ between 1.3 and 35.6 kg/d. On October 2, 2016, a seismic swarm of long-period events was recorded on Tenerife followed by a general increase of the seismic activity in and around the island (D’Auria et al., 2019). Since then, relatively high values have been obtained in the diffuse CO₂, He and H₂ emission rate the crater of Teide. This increase reflects a process of pressurization of the volcanic-hydrothermal system.

The variations in CO₂, He and H₂ emissions indicate changes in the activity of the system and can be useful to understand the behaviour of the volcanic system and to forecast future volcanic activity. Monitoring the diffuse degassing rates at Teide volcano has demonstrated to be an essential tool for predicting future seismic–volcanic unrest, and has become important to reduce volcanic risk in Tenerife (Melián et al., 2012; Pérez et al., 2013).

D'Auria .L, Barrancos J., Padilla G.D., Pérez N.M., Hernández P.A., Melián G., Padron E., Asensio-Ramos M., García‐Hernández R. (2019). J. Geophys. Res. 124, 8739-8752

Pérez N. M., Hernández P. A., Padrón E., Melián G., Nolasco D., Barrancos J., Padilla G., Calvo D., Rodríguez F., Dionis S. and Chiodini G. (2013). J. Geol. Soc., 170(4), 585-592.

Melián G., Tassi F., Pérez N. M., Hernández P., Sortino F., Vaselli O., Padrón E., Nolasco D., Barrancos J., Padilla G., Rodriguez F., Dionis S., Calvo D., Notsu K., Sumino H. (2012).  Bull. Volcanol, 74(6), 1465-1483.

How to cite: Asensio-Ramos, M., Melián, G., Rodríguez, F., Pérez, N. M., Alonso, M., Martín-Lorenzo, A., Amonte, C., Hernández, P. A., Padrón, E., and D'Auria, L.: Long-term variations of diffuse CO2, He and H2 at the summit crater of Teide volcano, Tenerife, Canary Islands, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14767, https://doi.org/10.5194/egusphere-egu21-14767, 2021.

La Palma Island (708.3 km²) 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

As part of the volcano monitoring program of Cumbre Vieja, diffuse degassing of CO₂ 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 CO₂ 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.

Since its installation, CO₂ emissions ranged from non-detectable (<1.5 gm^-2d^-1) to 1,464.0 gm^-2d^-1. 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 CO₂ emissions trend in the LPA04 geochemical station support the occurrence of an upward magma migration towards a subcrustal magma reservoir beneath La Palma island.

Padrón et al., (2015). Bull Volcanol 77:28. DOI 10.1007/s00445-015-0914-2

How to cite: Barrancos, J., Rodríguez, C., Padrón, E., Hernández, P. A., Padilla, G. D., D’Auria, L., and Pérez, N. M.: Monitoring diffuse CO2 emissions by means of an automatic geochemical station at Cumbre Vieja volcano, La Palma, Canary Islands., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15149, https://doi.org/10.5194/egusphere-egu21-15149, 2021.

Carbon dioxide flux from the soil has been monitored for 20 years at Cava dei Selci, the main degassing site of Colli Albani quiescent volcano. Cava dei Selci gas discharge occurs at the north-western periphery of the volcano, within an old stone quarry crossed by a NW-SE volcano-tectonic lineament. The area around the manifestation has been densely urbanized and lethal accidents by gas inhalation have occurred to a man and to dozens of animals including cows and sheep. Some houses had to be permanently evacuated because of hazardous indoor gas concentrations. Emitted gas is dominated by CO₂ (>90 vol.%) with <1 vol.% of H₂S. Isotopic composition (δ¹³C and ³He/⁴He) suggests a deep magmatic origin. No significant compositional variations have been recorded during the observation period.

Surveyed area includes a fixed grid of 130 points, regularly distributed over an area of about 5500 m², where soil CO₂ flux surveys have been carried out 55 times from May 2000 to August 2020 by accumulation chamber. Collected data have been reprocessed by sequential Gaussian simulation. The total diffuse CO₂ output is highly fluctuating, with a maximum rate of 24.8 t*d⁻¹ in January 2006 and a minimum value of 5.6 t*d⁻¹ in December 2003; the estimated mean±1σ is 12.1±4.5 t*d⁻¹. All the flux maps show typically a highly emissive area in the internal sector of the investigated grid, with NW-SE elongation. Another anomalous zone, with the same elongation, is found in the SW of the survey area. Diffuse degassing rate (total flux normalized by survey area) is similar to that of active volcanic zones.

In the same zone an automatic permanent station continuously measured the soil CO₂ flux and environmental parameters (which may influence the soil gas flux) from 2004 to 2008 and from 2019 to present. Results of timeseries processing by Multiple Linear regression and Principal Component analysis, commonly used to filtrate and clear data from atmospheric inferences (for example at Stromboli and Campi Flegrei), were unsatisfying for Cava dei Selci. Therefore, we reprocessed the timeseries by the stochastic Gradient Boosting Trees regression technique. This allowed to explain up to 55 % of the CO₂ variance by environmental variations; 45 % of the variance therefore reflects deep-seated processes. This technique looks promising for the regression of soil CO₂ flux timeseries. The results of 20 years monitoring confirm that Cava dei Selci is a convenient site for both monitoring a potential unrest of the volcano and assessing the gas hazard in the nearby inhabited zone.

How to cite: Tarchini, L., Carapezza, M. L., Granieri, D., and Ranaldi, M.: Twenty years of CO2-emission monitoring at Cava dei Selci, Colli Albani volcano (Central Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12446, https://doi.org/10.5194/egusphere-egu21-12446, 2021.

Tenerife Island (2034 km²), the largest of the Canarian archipelago, is characterized by three main volcano-tectonic axes: the NS, NE and NW rifts and a central caldera, Las Cañadas, hosting the twin stratovolcanoes Pico Viejo and Teide. Although Teide volcano hosts a weak fumarolic system, volcanic gas emissions from the summit cone consist mostly of diffuse CO₂ degassing. The first continuous automatic geochemical station in Canary Islands was installed at the south-eastern foot of summit cone of Teide volcano in 1999, with the aim of improving the volcanic monitoring system and providing a multidisciplinary approach to the surveillance program of Teide volcano. The 1999-2020 time series shows diffuse CO₂ emission values ranging between 0 and 62.8 kgm^-2d^-1, with a mean value of 4.3 kgm^-2d^-1. Inspection of the CO₂ efflux time series shows significant temporal variations with anomalous values of more than 20 kgm^-2d^-1 centred at years 2000, 2003, 2005, 2007, 2008, 2012, 2015 and 2016, always before a significant increase in the seismic activity beneath Tenerife Island. With the aim to filter out environmental variables, a multiple regression analysis (MRA) was applied to the first 12 years of the diffuse CO₂ flux time series (1999-2011), recorder on an hourly basis by the station, and we found that soil temperature, soil water content, wind speed and barometric pressure explained 16.7% of variability. The comparison between filtered CO₂ efflux (continuous, hourly, automated station) versus the temporal evolution of diffuse CO₂ emission estimated by ground CO₂ efflux surveys of summit cone of Teide (during summer season on an area of around 0.11 km²) for the period 1999-2011 (Pérez et al., 2013), shows a nearly coincident marked peak in December 2001 and a similar shaped evolution from each sampling type as the increase from ~2005 to 2009 and the subsequent decrease from ~2009 to 2011, reaching maximum values of 161.6 and 179.9 t d^-1, respectively. Seismic activity displayed as of monthly earthquakes (M>1) occurring in and around Tenerife island is well correlated with diffuse CO₂ efflux relevant peaks. In average, the seismicity recorded during the study period was mainly preceded by geochemical anomalies of the registered surface CO₂ efflux by about one year. After we analysed the CO₂ efflux time series by using the Continuous Wavelet Transform (Ricker wavelet) to detect relevant time-frequency patterns in the signal, we found at low frequencies quasi-periodical oscillations with periods of 3-4 years, which might reflect the internal dynamics of the magmatic-hydrothermal system. Moreover, during the intervals of highest levels of CO₂ efflux, the analysis evidenced also oscillations with a period of about 6 months during the interval 1999-2011. Our study reveals that continuous geochemical monitoring data is representative of the same trends in flux that are quantitatively captured by annual surveys, and provides the basis for accurate determination of background values. This combined approach offers a useful template for application to other volcanic systems for the purposes of constructing quantitative dynamic models of hydrothermal systems and identifying processes at depth in near-real-time.

How to cite: Padilla, G. D., Perez, N. M., Hernández, P. A., Padrón, E., Barrancos, J., D’Auria, L., Melián, G., Rodríguez, F., and Pankhurst, M. J.: Temporal variations of CO2 efflux continuous monitoring at the summit cone of Teide volcano (Tenerife, Canary Islands) during the period1999-2021, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15190, https://doi.org/10.5194/egusphere-egu21-15190, 2021.