Long-term observation of volcanic degassing: methods, findings and challenges

Volcanic degassing plays a central role in the dynamics of volcanic activity, both during and between eruptions. In order to understand longer-term trends and to detect transitions in the style of volcanic activity it is necessary to sustain permanent monitoring of the composition and flux of different volcanic gases over several years. Only during the last few decades has this task been attainable due to the implementation of a growing suite of instrument networks or global observing systems around volcanoes, for example through in-situ or remote sensing techniques around volcanoes or by space-based sensors. The aim of this session is to gather contributions from long term (>1year) instrumental records of volcanic degassing that show unique information that can only be obtained by long-term observation of volcanic emissions. This includes presentations of technological advancements with proven capabilities for long-term operation, as well as findings obtained from these records, which are relevant for understanding volcanic activity or to assess the impact of emissions on the environment, or to quantify global geochemical cycles of volcanogenic species. We also welcome discussions regarding challenges posed by long-term monitoring of volcanic emissions.

Convener: Silvana Hidalgo | Co-conveners: Santiago ArellanoECSECS, Christoph Kern, Agnes Mazot, Sebastien Valade
vPICO presentations
| Mon, 26 Apr, 15:30–17:00 (CEST)

Session assets

Session materials

vPICO presentations: Mon, 26 Apr

Chairpersons: Santiago Arellano, Sebastien Valade, Agnes Mazot
Remote sensing from ground
Bo Galle and the The NOVAC Collaboration

We present a detailed global data-set of volcanic sulphur dioxide (SO2) emissions during the period 2005-2017. Measurements were obtained by scanning-DOAS instruments of the NOVAC network at 32 volcanoes, and processed using a standardized procedure. We reveal the daily statistics of volcanic gas emissions under a variety of volcanological and meteorological conditions. Data from several volcanoes are presented for the first time. Our results  are compared with yearly averages derived from measurements from space by the Aura/OMI instrument and with historical inventories of GEIA. This comparison shows some interesting differences which reasons are briefly discussed. Data is openly available through the web repository at

How to cite: Galle, B. and the The NOVAC Collaboration: The NOVAC database of volcanic SO2 emissions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7577,, 2021.

Fredy Apaza, Christoph Kern, Mayra Ortega, and Rafael Miranda

Ubinas is a stratovolcano located in the Central Volcanic Zone of the Andes. It is one of the most active volcanoes in Peru, with more than 26 eruptive episodes recorded in the last 500 years (VEI 1-3). Its latest eruption began in early 2019, whit the occurrence of some distal VT seismicity accompanied by low levels of LP seismicity and in sometimes high frequency seismic signals associated with rockfalls. Concurrently, SO2 emissions increased from a few hundred to over 1,000 t/d between January and June while no significant ground deformation could be detected. Throughout the month of June, SO2 emissions climbed further to over 4,000 t/d, proximal VT swarms began to occur beneath the volcanic edifice, and deformation measurements indicated a pressurization of the system. This ramp-up in activity culminated with an explosive eruption on 19 July 2019 (07:28:49 UTC). The eruption released a cumulative energy of 336 MJ and vented an estimated 4.6x106 m3 of volcanic ash, making this one of the most energetic eruptive events of the last decade. Filled with hot gas and ash, the eruptive column reached 6,500 meters above the volcanic vent, with blocks and ballistic projectiles that reached 3.5 km from the crater and fragments up to 2.5 cm in diameter reported in the Ubinas town, 6.5 km to the southeast. By the time the eruption ended, up to 4 kg/m2 of tephra had fallen at this distance. Most of the plume was dispersed in east to southeast directions, crossing the regions of Moquegua, Puno. Ashfall was observed as far as Oruro, Bolivia, some 180 km from the volcano. Subsequent analyses of monitoring data and eruptive products allow classification of this event as a VEI 2 eruption caused by a rapid magmatic intrusion to shallow depths below the volcanic edifice.

How to cite: Apaza, F., Kern, C., Ortega, M., and Miranda, R.: The July 2019 explosive activity of Ubinas Volcano, Peru, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3529,, 2021.

Francisco Javier Vasconez, Silvana Hidalgo, Stephen Hernández, Josué Salgado, Sébastien Valade, Pedro Espín, Benjamin Bernard, Daniel Cárdenas, Jean Battaglia, Pablo Samaniego, and Diego Coppola

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 7th 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,, 2021.

Syegi Kunrat, Hilma Alfianti, Christoph Kern, Sofyan Primulyana, Allan Lerner, Moh. Nurul Asrori, Armen Putra, and Deri Al Hidayat

After more than 800 years of dormancy, phreatic explosions occurred at Sinabung Volcano in North Sumatra, Indonesia, on August 27, 2010. These marked the beginning of a period of unrest at Sinabung that continues through the present. Phreatic activity temporarily ceased in September 2010, however a more explosive phase of the eruption began again in September 2013, sending ash columns as high as 9 km above the volcano’s summit. A lava dome breached the surface on 17-18 December 2013 and subsequent collapses of this dome have produced numerous pyroclastic density currents reaching up to 5 km from the vent. Eruptive activity has waxed and waned since 2013, and the eruption entered period of especially vigorous activity beginning in February 2019 that is continuing through the present.

Between 2010 and 2013, the Indonesian Center for Volcanology and Geological Hazard Mitigation (CVGHM) significantly ramped up its monitoring efforts at Sinabung by installing seismometers, GPS instruments and electronic distance measuring benchmarks. In August 2016, the volcano observatory then installed a network of 3 scanning Differential Optical Absorption Spectrometers (DOAS) on the eastern side of Sinabung at distances between 4 and 6 km from the volcano’s summit. These DOAS instruments are part of the Network for Observation of Volcanic and Atmospheric Change (NOVAC), and autonomously measure the emission rate of sulfur dioxide (SO2) from Sinabung during typical west-wind conditions.

Since its installation, the DOAS network has provided useful monitoring information at Sinabung. The collected data indicate that the average SO2 emission rate lies between 100 and 400 metric tons per day (t/d), but emissions up to 2,400 t/d are common throughout the measurement period. The maximum emission rate recorded since 2016 was 4,500 t/d, measured in July 2019. However, the NOVAC instruments are not able to accurately capture the SO2 emissions associated with large explosive eruptions, and satellite data indicate that plumes associated with such events have sometimes contained significantly more SO2 than during the more typical passive degassing behavior. Here, we present excerpts of the long-term SO2 data from Sinabung and compare these with complimentary records of the timing and frequency of explosions, gas exhalations, rockfalls, and pyroclastic flows. These combined datasets provide insights into the active volcanic processes ongoing at Sinabung.

How to cite: Kunrat, S., Alfianti, H., Kern, C., Primulyana, S., Lerner, A., Asrori, Moh. N., Putra, A., and Al Hidayat, D.: Continuous monitoring of SO2 emissions from Sinabung Volcano, Indonesia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3711,, 2021.

Xochilt Gutiérrez, Nicole Bobrowski, Thorsten Hoffmann, Eduardo Gutiérrez, Florian Dinger, Francisco Montalvo, and Demetrio Escobar

Volcanic degassing plays an important role in a volcano’s behavior. Going from large emissions at craters and fumaroles, to invisible degassing at vents and soil; a volcano releases H2O, CO2, SO2, HCl, HF, H2S, CO, H2, HBr, HI, Hg and noble gases.

SO2 emissions are considered a basic monitoring tool, mainly measured by remote-sensing techniques. The Differential Optical Absorption Spectroscopy (DOAS) is a well-established method currently used to regularly measure volcanic SO2 emission rates with about 80 scanning DOAS operating in 37 volcanoes within the framework of the global "Network for Observation of Volcanic and Atmospheric Change" (NOVAC) (Galle et al., 2010). Typically, SO2fluxes are often combined with in-situ gas measurements of SO2 and other volatiles (CO2, H2S), to evaluate the degassing regime. In-situ sampling can be made by collecting the gases directly in evacuated flasks or solution-filled bottles (alkaline traps), or by sampling with a multi-sensor instrument (MultiGAS) that enables real-time measurements of several gases at once (Aiuppa et al. 2005b; Shinohara 2005, Roberts et al. 2017).

Santa Ana and San Miguel are the most active volcanoes in El Salvador, with an average SO2 emission rate of 220 and 326 t/d, respectively during 2018. Both volcanoes arise along the Central American Volcanic Arc – CAVA, where the magmatism, fundamentally basaltic, is related to the convergence of the Caribbean Plate and the subducting Cocos Plate (Leeman and Carr 1995). Also, Santa Ana and San Miguel are part of the NOVAC group since 2008 with just a few published gas data (Rodriguez et al. 2004, Cartagena et al. 2004, Olmos et al. 2007, Colvin et al. 2013, Laiolo et al. 2017). The most recent studies were performed by Granieri et al. 2015 and Hasselle et al. 2019. The first, reported CO2/SO2, HCl/SO2 and HF/SO2 mass ratios (0.95, 0.13 and 0.016, respectively) measured at San Miguel volcano in early 2014; while the second, presented CO2/SO2, H2S/SO2 and H2O/SO2 ratios (<3-37.9, 0.03-0.1 and 32-205, respectively), measured in 2017-2018 at Santa Ana’s crater lake and rim.

In this study, we present an SO2 long-time data series (2008-2018) for San Miguel and Santa Ana obtained from the DOAS stations of each volcano, and complement with data collected during regular monitoring (2018-2020) and field campaigns in El Salvador (2019 and 2020) by means of MultiGAS devices. The aim of the study is to extend the characterization of these two volcanoes in El Salvador and the establishment of SO2 and CO2 baselines and inventories for them.

How to cite: Gutiérrez, X., Bobrowski, N., Hoffmann, T., Gutiérrez, E., Dinger, F., Montalvo, F., and Escobar, D.: Variation of SO2 and CO2 in the volcanic gas plumes of Santa Ana and San Miguel volcanoes: an overview by real-time measurements , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4606,, 2021.

Noemie Taquet, Wolfgang Stremme, Claudia Rivera, Alejandro Bezanilla, Michel Grutter, Robin Campion, Sebastien Valade, Thomas Boulesteix, Denis Legrand, Thomas Blumenstock, and Frank Hase

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,, 2021.

Christoph Kern, Patricia Nadeau, Tamar Elias, Peter Kelly, Allan Lerner, Laura Clor, Miki Warren, Hannah Dietterich, and Taryn Lopez

Kīlauea Volcano (Hawaii, USA) had been in a state of quiescence since the end of the historic 2018 eruption on its lower East Rift Zone. Tapping the volcanic plumbing system at elevations around 300 m well below the volcano’s 1200 m summit, the 2018 eruption drained magma from the volcano’s summit reservoir and East Rift Zone, causing the drainage of a decade-old subaerial lava lake followed by widespread caldera collapse. Two years later, on the evening of 20 December 2020, the Hawaiian Volcano Observatory (HVO) once again detected a glow within the now vastly deepened Halemaʻumaʻu Crater at Kīlauea’s summit. A new eruption had begun. Observations over the next few days revealed lava flowing from three vents in the wall of the crater and into its base. A water lake, which had formed in 2019 – 2020 from groundwater infiltration, boiled off within hours and the crater began rapidly filling with lava. Over the first 3 days of the eruption, the new lava lake filled the lowermost ~150 m of the summit crater, and sulfur dioxide (SO2) emission rates sometimes exceeded 30,000 metric tons per day (t/d) as measured by Differential Optical Absorption Spectroscopy (DOAS) traverses recorded both from the ground and by helicopter. These vigorous SO2 emissions were also clearly detected by the Tropospheric Monitoring Instrument (TROPOMI) aboard the Sentinal-5 Precursor satellite, and comparisons of the ground-based data with those collected by TROPOMI are the topic of ongoing research. Lava effusion and gas emission rates then tailed off and, from 26 December to 2 January, DOAS measurements indicated SO2 emissions of ~5,000 t/d, similar to the average emission rate from Kīlauea’s summit lava lake throughout most of the volcano’s 2008-2018 eruption. Data from a continuous Multiple Gas Analyzer System (MultiGAS) installed approximately 1.3 km downwind of the active vents indicate that the carbon dioxide (CO2) to SO2 molar ratio of the emitted gas is low (0.3 ± 0.1), consistent with a model in which the erupted lava has been previously degassed in carbon dioxide but is only now degassing the more soluble sulfur as it reaches the surface. Further MultiGAS measurements performed with an unoccupied aircraft system (UAS) show that the gas composition varies throughout the emitted plume, but that the primary constituents are water vapor (~80-90% molar), carbon dioxide (~3%), and sulfur dioxide (~7-16%), while hydrogen sulfide is below the detection limit of the instrumentation. As of 11 January 2021, lava effusion and gas emissions appear to be slowly decreasing in vigor, but it is as yet unclear whether the eruption will continue to weaken and end within the coming weeks, or whether Kīlauea Volcano will once again harbor a sustained subaerial lava lake for months or years to come.

How to cite: Kern, C., Nadeau, P., Elias, T., Kelly, P., Lerner, A., Clor, L., Warren, M., Dietterich, H., and Lopez, T.: Gas emissions from the resumption of eruptive activity at Kīlauea Volcano’s summit in December 2020., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3470,, 2021.

Remote sensing from space
Adrian Jost, Steffen Beirle, Steffen Dörner, and Thomas Wagner

With a nearly continuously effusive eruption since 1983, the Kilauea volcano (Hawaii, USA) is one of the most active volcanoes in the world. At the beginning of May 2018, a sequence of eruptions on the Lower East Rift Zone (LERZ) caused an enhanced outbreak of volcanic gases and aerosols, releasing them into the troposphere. Since these gases and particles affect climate, environment, traffic, and health on regional to global scales, a continuos monitoring of the emission rates is essential.

As satellites provide the opportunity to observe and quantify the emissions remotely from space, their contribution to the monitoring of volcanoes is significant. The TROPOspheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5 Precursor satellite was successfully launched by the end of 2017 and provides measurements with unprecedented level of details with a resolution of 3.5 x 7 km2. This also allows for an accurate retrieval of trace gas species such as volcanic SO2.

Here, it will be shown that the location and strength of SO2 emissions from Kilauea can be determined by the divergence of the temporal mean SO2 flux. This approach, which is based on the continuity equation, has been demonstrated to work for NOX emissions of individual power plants (Beirle et al., Sci. Adv., 2019).

The present state of our work indicates that emission maps of SO2 can be derived by the combination of satellite measurements and wind fields on high spatial resolution. As the divergence is highly sensitive on point sources like the erupting fissures in the 2018 Kilauea eruption, they can be localized very precisely. The obtained emission rates are slightly lower than the ones reported from ground-based measurements in other studies like the one from Kern et al. (Bull. Volcanol., 2020). The effects of suboptimal conditions like high cloud fractions on the method probably affect the derived emission rates and have to be further analyzed.

How to cite: Jost, A., Beirle, S., Dörner, S., and Wagner, T.: Quantification of SO2 emission rates from the Kilauea volcano in Hawaii by the divergence of the SO2 flux using S5P-TROPOMI satellite measurements, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4069,, 2021.

Pauline Verdurme, Simon Carn, Andrew Harris, Diego Coppola, Andrea Di Muro, Santiago Arellano, and Lucia Gurioli

Piton de la Fournaise (La Réunion, France) is one of the most active volcanoes in the world, producing frequent effusive basaltic eruptions of varying duration. These eruptions are accompanied by strong thermal infrared (TIR) signals and significant sulfur dioxide (SO2) emissions detected by satellite instruments. The high frequency of eruptions provides an extensive dataset, which allows us to explore the relationships between eruptive heat, mass and gas fluxes. Five eruptions with different temporal trends of erupted mass flux have been selected for this study: April 2007, May 2015, August-October 2015, February 2019 and April 2020. For each of them, we estimated SO2 emission from three ultraviolet satellite instruments (the Ozone Monitoring Instrument OMI, the Ozone Mapping and Profiler Suite OMPS and the Tropospheric Monitoring Instrument TROPOMI). The total SO2 emission for each eruption has been estimated for an extensive range of sulfur (S) content within melt inclusions and the matrix using a petrological approach and the erupted magma masses obtained from MODIS TIR satellite data. Preliminary results show that, assuming the estimated SO2 emission falls within the 30% error of the SO2 mass detected by each satellite instrument, the implied magmatic sulfur contents are in good agreement with expected values for basaltic eruptions. Given pre-eruptive S contents between 200 and 750 ppm, estimated SO2 emissions for the May 2015 eruption are consistent with an eruption largely fed by degassed magma. However, for the February 2019 eruption, there is a discrepancy between the three satellite sensors. Whereas the TROPOMI and the OMI instruments provide almost the same range of magmatic sulfur content (300-1100 ppm), the OMPS gives a higher range (700 to 1900 ppm) suggesting that fresh, undegassed magma was also involved in this eruption. Petrologic analysis of the pre-eruptive sulfur content will allow us to validate the satellite data and, in turn, to validate the ground-based SO2 data from the NOVAC network operated by the Observatoire Volcanologique du Piton de la Fournaise (OVPF). Our approach yields insights into the characteristics of the magma reservoir supplying effusive events (e.g., eruptive degassing processes and the ratio of intrusive to extrusive magma) from space-based sensors.

How to cite: Verdurme, P., Carn, S., Harris, A., Coppola, D., Di Muro, A., Arellano, S., and Gurioli, L.: Gas and heat fluxes during multiple effusive eruptions of Piton de la Fournaise (Réunion) and their implications for magmatic processes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9992,, 2021.

Simon Warnach, Holger Sihler, Christian Borger, Nicole Bobrowski, Stefan Schmitt, Moritz Schöne, Steffen Beirle, Ulrich Platt, and Thomas Wagner

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,, 2021.

Simon Carn, Vitali Fioletov, Chris McLinden, Nickolay Krotkov, and Can Li

Effective use of volcanic gas measurements for eruption forecasting and hazard mitigation at active volcanoes requires an understanding of long-term degassing behavior as context. Much recent progress has been made in quantifying global volcanic emissions of sulfur dioxide (SO2) and other gas species by expanding the coverage of ground-based sensor networks and through analysis of decadal-scale satellite datasets. Combined, these advances have provided valuable constraints on the magnitude and variability of SO2 emissions at over 120 actively degassing volcanoes worldwide. Being less constrained by the style or location of volcanic activity, satellite measurements can provide greater insight into trends in volcanic degassing during eruption cycles. Here, we present an analysis of ~15 years of volcanic SO2 measurements by the ultraviolet (UV) Ozone Monitoring Instrument (OMI) aboard NASA’s Aura satellite, focused on observed trends in SO2 emissions spanning eruptions of varying magnitude. The Aura/OMI measurements have been used to estimate annual mean SO2 emissions at ~100 volcanoes active between 2005 and 2020, around 80 of which erupted during the 15-year period. Superposed epoch analysis (SEA) of SO2 emission trends for the erupting volcanoes (with eruption magnitudes ranging from Volcanic Explosivity Index [VEI] 2 to 4) provides evidence that volcanoes exhibiting higher levels of SO2 emission in the years prior to eruption typically produce eruptions of lower magnitude, and vice versa. Post-eruptive SO2 degassing exceeds pre-eruptive emissions for several years after eruptions with VEI 3-4 and may scale with eruption size; perhaps consistent with larger eruptions being supplied by larger magma intrusions which continue to degas in subsequent years. The SEA is most robust for eruptions of intermediate magnitude (VEI 3) which are the most common events in the recent global eruption record covered by the OMI measurements. Limited observations of larger eruptions (VEI 5+) suggest significant differences in degassing trends during these larger events. Future work will extend the satellite-based estimates of volcanic SO2 emissions both forward and backward in time using other UV satellite instruments, generating longer records of SO2 degassing (extending back to 1978 for the strongest volcanic sources of SO2) that will be used to further explore and constrain these relationships.  

How to cite: Carn, S., Fioletov, V., McLinden, C., Krotkov, N., and Li, C.: Trends in volcanic degassing through eruption cycles: insights from satellite measurements, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14092,, 2021.

Remote and In-situ monitoring
Dario Delle Donne, Alessandro Aiuppa, Marcello Bitetto, Francesco Paolo La Monica, Giancarlo Tamburello, Diego Coppola, Giorgio Lacanna, Marco Laiolo, Mauro Coltelli, Emilio Pecora, and Maurizio Ripepe

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,, 2021.

María Asensio-Ramos, Gladys Melián, Fátima Rodríguez, Nemesio M. Pérez, Mar Alonso, Alba Martín-Lorenzo, Cecilia Amonte, Pedro A. Hernández, Eleazar Padrón, and Luca D'Auria

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,, 2021.

Severine Moune, Roberto Moretti, Arnaud Burtin, David Jessop, Tristan Didier, Vincent Robert, Magali Bonifacie, Giancarlo Tamburello, and Jean-Christophe Komorowski

Fumarolic gas survey of dormant volcanoes is fundamental because the compositional and flux changes in gas emissions are recognised signals of unrest and may even be precursors of eruptions on several dormant volcanoes in hydrothermal unrest [1-5].

Here we report on the chemical compositions (CO2, H2S, SO2, H2) and mass fluxes of fumarolic gas emissions from the low-temperature (from 97° to 104°C) volcanic-hydrothermal system of La Soufrière de Guadeloupe (Lesser Antilles). This present study covers the period 2016 to present, encompassing the peak activity of April 2018. Long-term trends are acquired from both portable MultiGAS measurements (performed monthly) and two permanent MultiGAS stations (4 automated 20’ measurements per day). These MultiGAS data are discussed along with other geochemical and geophysical parameters monitored at OVSG, such as complete fumarole chemistry via Giggenbach bottles, fumarole temperatures, volcanic seismicity and deformation in order to track the deep-sourced magmatic signal contribution compared to the one of the hydrothermal system and detect potential signs of unrest [6].

Dealing with MultiGAS data from a low-T fumarolic system in a tropical environment is not straightforward due to external forcing effect of meteoric water on gas composition. Hence, interpretation of the observed chemical changes must consider (i) the role of water-gas-rock interactions and gas scrubbing processes by the hydrothermal system and the perched volcanic pond [7], which particularly affect sulphur precipitation and remobilization and (ii) how these processes vary with rainfall and groundwater circulation (i.e. rainy vs non-rainy seasons, extreme events).

[1] Giggenbach and Sheppard, 1989; [2] Symonds et al., 1994; [3] Hammouya et al., 1998; [4] De Moor et al., 2016; [5] Allard et al., 2014; [6] Moretti et al., submitted; [7] Symonds et al., 2001

How to cite: Moune, S., Moretti, R., Burtin, A., Jessop, D., Didier, T., Robert, V., Bonifacie, M., Tamburello, G., and Komorowski, J.-C.: Gas monitoring of a hydrothermal-magmatic volcano in a tropical environment: the example of La Soufriere de Guadeloupe (FWI), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8391,, 2021.

José Barrancos, Claudia Rodríguez, Eleazar Padrón, Pedro A. Hernández, Germán D. Padilla, Luca D’Auria, and Nemesio M. Pérez

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,, 2021.

Luca Tarchini, Maria Luisa Carapezza, Domenico Granieri, and Massimo Ranaldi

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,, 2021.

Germán D. Padilla, Nemesio M. Perez, Pedro A. Hernández, Eleazar Padrón, José Barrancos, Luca D’Auria, Gladys Melián, Fátima Rodríguez, and Matthew J. Pankhurst

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,, 2021.