| 1. |
- Hidalgo, Silvana, et al.
(författare)
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SO2 degassing at Tungurahua volcano (Ecuador) between 2007 and 2013: Transition from continuous to episodic activity
- 2015
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Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273. ; 298, s. 1-14
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Tidskriftsartikel (refereegranskat)abstract
- We present continuous SO2 measurements performed at Tungurahua volcano with a permanent network of 4 scanning DOAS instruments between 2007 and 2013. The volcano has been erupting since September 1999, but on the contrary to the first years of eruption when the activity was quasi-continuous, the activity transitioned in late 2008 towards the occurrence of distinct eruptive phases separated by periods of quiescence. During our study period we distinguish 11 phases lasting from 17 to 527days separated by quiescence periods of 26 to 184days. We propose a new routine to quantify the SO2 emissions when data from a dense DOAS monitoring network are available. This routine consists in summing all the highest validated SO2 measurements among all stations during the 10h of daily working-time to obtain a daily observed SO2 mass. Since measurement time is constant at Tungurahua the "observed" amounts can be expressed in tons per 10h and can easily be converted to a daily average flux or mass per day. Our results provide time series having an improved correlation on a long time scale with the eruptive phases and with quiescence periods. A total of 1.25Mt (1.25×109kg) of SO2 has been released by Tungurahua during the study period, with 95% of these emissions occurring during phases of activity and only 5% during quiescence. This shows a contrast with previous volcanic behaviour when passive degassing dominated the total SO2 emissions. SO2 average daily mass emission rates are of 73±56t/d during quiescent periods, 735±969t/d during long-lasting phases and 1424±1224t/d during short-lasting phases. Degassing during the different eruptive phases displays variable patterns. However, two contrasting behaviours can be distinguished for the onset of eruptive phases with both sudden and progressive onsets being observed. The first is characterised by violent opening of the conduit by high energy Vulcanian explosions; and the second by a progressive, in crescendo, development of the activity. The first case is becoming more frequent at Tungurahua making the volcano more dangerous and less predictable.
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| 2. |
- Aiuppa, Sandro, et al.
(författare)
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Tracking formation of a lava lake from ground and space: Masaya volcano (Nicaragua), 2015-2017
- 2018
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Ingår i: Geochemistry, Geophysics, Geosystems. - 1525-2027. ; 19:2, s. 496-515
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Tidskriftsartikel (refereegranskat)abstract
- A vigorously degassing lava lake appeared inside the Santiago pit crater of Masaya volcano (Nicaragua) in December 2015, after years of degassing with no (or minor) incandescence. Here, we present an unprecedented-long (3 years) and continuous volcanic gas record that instrumentally characterizes the (re)activation of the lava-lake. Our results show that, before appearance of the lake, the volcanic gas plume composition became unusually CO2-rich, as testified by high CO2/SO2 ratios (mean, 12.2±6.3) and low H2O/CO2 ratios (mean, 2.3±1.3). The volcanic CO2 flux also peaked in November 2015 (mean, 81.3±40.6 kg/s; maximum, 247 kg/s). Using results of magma degassing models and budgets, we interpret this elevated CO2 degassing as sourced by degassing of a volatile-rich fast-convecting (3.6-5.2 m3·s-1) magma, supplying CO2-rich gas bubbles from minimum equivalent depths of 0.36-1.4 km. We propose this elevated gas bubbles supply destabilized the shallow (<1 km) Masaya magma reservoir, leading to upward migration of vesicular (buoyant) resident magma, and ultimately to (re)formation of the lava lake. At onset of lava lake activity on 11 December 2015 (constrained by satellite-based (MODIS) thermal observations), the gas emissions transitioned to more SO2-rich composition, and the SO2 flux increased by a factor ~40 % (11.4±5.2 kg/s) relative to background degassing (8.0 kg/s), confirming faster than normal (4.4 vs. ~3 m3·s-1) shallow magma convection. Elevated shallow magma circulation is also supported by gradual increase in irradiated thermal energy, captured by MODIS, from which we calculate that 0.4-0.8 m3·s-1 of magma have been surface-emplaced since December 2015.
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| 3. |
- Arellano, Santiago, 1981, et al.
(författare)
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Long-term monitoring of SO2 quiescent degassing from Nyiragongo’s lava lake
- 2017
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Ingår i: Journal of African Earth Sciences. - : Elsevier BV. - 1879-1956 .- 1464-343X .- 0899-5362. ; 134, s. 866-873
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Tidskriftsartikel (refereegranskat)abstract
- The activity of open-vent volcanoes with an active lava-lake, such as Nyiragongo, is characterized by persistent degassing, thus continuous monitoring of the rate, volume and fate of their gas emissions is of great importance to understand their geophysical state and their potential impact. We report results of SO2 emission measurements from Nyiragongo conducted between 2004 and 2012 with a network of ground-based scanning-DOAS (Differential Optical Absorption Spectroscopy) remote sensors. The mean SO2 emission rate is found to be 13 ± 9 kg s−1, similar to that observed in 1959. Daily emission rate has a distribution close to log-normal and presents large inter-day variability, reflecting the dynamics of percolation of magma batches of heterogeneous size distribution and changes in the effective permeability of the lava lake. The degassed S content is found to be between 1000 and 2000 ppm from these measurements and the reported magma flow rates sustaining the lava lake. The inter-annual trend and plume height statistics indicate stability of a quiescently degassing lava lake during the period of study.
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| 4. |
- Arellano, Santiago, 1981, et al.
(författare)
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Report on volcanic plume measurements on volcanoes in Papua New Guinea
- 2017
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report summarizes the findings of plume gas measurements conducted on volcanoes of Papua New Guinea (PNG) during September 2016, as part of the DECADE project. The total sulfur dioxide (SO2) and carbon dioxide (CO2) gas fluxes of Tavurvur, Bagana and Ulawun volcanoes were determined by combining ground- remote sensing and ground-/airborne direct sampling, depending on the particular conditions on each volcano. During the campaign Tavurvur was degassing passively, without forming a continuous plume, and it was accessible for direct sampling in the crater. Its SO2 emission was found to be 0.19 ± 0.05 kg/s from scanning-DOAS and a stationary wide-field-of-view (WFOV) DOAS monitor, and the fraction of CO2/SO2 molar ratios was 2.6, obtained with a compact multi-GAS instrument. Bagana, on the other hand, had permanent degassing, producing occasional explosions and ash emission. The plume was measured by ground-based scanning-DOAS and a compact multi-GAS instrument aboard a multi-rotor UAV, resulting in a SO2 flux of 13 ± 5 kg/s and a CO2/SO2 of 15. Ulawun presented continuous passive degassing, forming an elevated plume which flux and composition were measured by car-traverses with a mobile-DOAS, a stationary dual-beam scanning DOAS, and a multi-GAS/UAV sensor. The SO2 flux of Ulawun was 11 ± 2 kg/s and the CO2/SO2 equal to 4.8. A stationary WFOV-DOAS instrument was left with the Rabaul Volcano Observatory (RVO) for longer-term monitoring of the SO2 flux from Tavurvur.
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| 5. |
- Battaglia, Jean, et al.
(författare)
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Autopsy of an eruptive phase of Tungurahua volcano (Ecuador) through coupling of seismo-acoustic and SO 2 recordings with ash characteristics
- 2019
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Ingår i: Earth and Planetary Science Letters. - : Elsevier BV. - 1385-013X .- 0012-821X. ; 511, s. 223-232
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Tidskriftsartikel (refereegranskat)abstract
- Eruption style and dynamics are controlled by various parameters including magma supply rate, magma viscosity, volatile content, and the permeability of the conduit. Rapid changes of these parameters can significantly modify the hazards associated to the eruption processes and understanding their relationship with multiparametric geophysical monitoring data can greatly improve our forecasting capacities. From 2008 to 2016, volcanic activity at Tungurahua was characterized by eruptive phases separated by episodes of quiescence. These phases displayed great variability of eruptive patterns including Vulcanian and Strombolian explosions, low pyroclastic fountaining, continuous or sporadic ash emissions and passive degassing. We use the comparison between geophysical data (seismic, acoustic and SO 2 emission), recorded by permanent monitoring networks, and the characteristics of the emitted ash to track changes in eruption dynamics during an eruptive phase that lasted from late December 2009 to March 2010. We show that the correlation between the analyzed parameters allows imaging and interpretation of the conditions at the vent. At Tungurahua, these conditions can rapidly change at the time scale of a single eruptive phase, corresponding to various degrees of opening, plugging and permeability of the conduit. Two magma intrusions could be identified during a single eruptive phase showing transitions between violent Strombolian and Vulcanian activity. Changes in the componentry of the analyzed ash samples, together with the geophysical data, nicely highlight these evolutions. Studying these parameters simultaneously provides a unique insight into the physical processes controlling superficial volcanic activity and offers a potential tool for better understanding volcanoes and detecting changes in their activity. The joint interpretation of multiparametric data which we propose is potentially applicable to multiple andesitic volcanoes.
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| 6. |
- Bobrowski, N., et al.
(författare)
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Gas emission strength and evolution of the molar ratio of BrO/SO2 in the plume of Nyiragongo in comparison to Etna
- 2015
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Ingår i: Journal of Geophysical Research. - : American Geophysical Union (AGU). - 0148-0227 .- 2156-2202 .- 2169-897X. ; 120:1, s. 277-291
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Tidskriftsartikel (refereegranskat)abstract
- Airborne and ground-based differential optical absorption spectroscopy observations have been carried out at the volcano Nyiragongo (Democratic Republic of Congo) to measure SO2 and bromine monoxide (BrO) in the plume in March 2004 and June 2007, respectively. Additionally filter pack and multicomponent gas analyzer system (Multi-GAS) measurements were carried out in June 2007. Our measurements provide valuable information on the chemical composition of the volcanic plume emitted from the lava lake of Nyiragongo. The main interest of this study has been to investigate for the first time the bromine emission flux of Nyiragongo (a rift volcano) and the BrO formation in its volcanic plume. Measurement data and results from a numerical model of the evolution of BrO in Nyiragongo volcanic plume are compared with earlier studies of the volcanic plume of Etna (Italy). Even though the bromine flux from Nyiragongo (2.6t/d) is slightly greater than that from Etna (1.9t/d), the BrO/SO2 ratio (maximum 7x10(-5)) is smaller than in the plume of Etna (maximum 2.1x10(-4)). A one-dimensional photochemical model to investigate halogen chemistry in the volcanic plumes of Etna and Nyiragongo was initialized using data from Multi-GAS and filter pack measurements. Model runs showed that the differences in the composition of volcanic volatiles led to a smaller fraction of total bromine being present as BrO in the Nyiragongo plume and to a smaller BrO/SO2 ratio.
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| 7. |
- Bobrowski, Nicole, et al.
(författare)
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Multi-component gas emission measurements of the active lava lake of Nyiragongo, DR Congo
- 2017
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Ingår i: Journal of African Earth Sciences. - : Elsevier BV. - 1879-1956 .- 1464-343X. ; 134, s. 856-865
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Tidskriftsartikel (refereegranskat)abstract
- Between 2007 and 2011 four measurement campaigns (June 2007, July 2010, June 2011, and December 2011) were carried out at the crater rim of Nyiragongo volcano, DR Congo. Nyiragongo is one of the most active volcanoes in Africa. The ground-based remote sensing technique Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS), which uses scattered sunlight, the in-situ Multi-Component Gas Analyzer System (Multi-GAS) and alkaline impregnated filter were simultaneously applied during all field trips. The bromine monoxide to sulfur dioxide (BrO/SO2) and carbon dioxide to sulfur dioxide (CO2/SO2) molar ratios were determined, among other ratios. During the different field trips variations of the level of the lava lake up to several tens of meters were observed during intervals of the order of minutes up to days and also between the years. The measured gas ratios presented covariations with the lava lake level changes. BrO/SO2 ratios and CO2/SO2 ratios showed similar behavior. Annual CO2/SO2 and BrO/SO2 average values are generally positively correlated. In June 2011 increased BrO/SO2 as well as increased CO2/SO2 ratios have been observed before a sudden decrease of the lava lake. Overall the Cl/S ratio, determined by filter-pack sampling, shows an increasing trend with time, which is accompanied by a decreasing sulfur dioxide flux, the later measured nearly continuously by automated MAX-DOAS instruments since 2004. Mean gas emission fluxes of CO2, Cl and ‘minimum-BrO’ fluxes are calculated using their ratio to SO2. The first two show an increase with time, in contrast to the SO2 fluxes. A simple conceptual model is proposed which can explain in particular the June 2011 data, but as well our entire data set. The proposed model takes up the idea of convective magma cells inside the conduit and the possible temporary interruption of part of the cycling. We propose than two alternatives to explain the observed gas emission variation: 1. It is assumed that the diffuse and fumarolic degassing could have significant influence on measured gas composition. The measured gas composition might rather represent a gas mixture of plume, diffuse and fumarolic degassing than only representing the volcanic plume. 2. It is proposed that the interruption of the convection has taken place in the upper part of the conduit and deep degassing of CO2 and bromine initially continues while mixing already with gas emissions from an ageing source, which is characterized by an already diminishing sulfur content. These complex process but as well as the gas mixing of different sources, could explain general features of our dataset, but can unfortunately neither be confirmed nor disproven by the data available today.
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| 8. |
- Bobrowski, N., et al.
(författare)
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Plume composition and volatile flux of Nyamulagira volcano, Democratic Republic of Congo, during birth and evolution of the lava lake, 2014–2015
- 2017
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Ingår i: Bulletin of Volcanology. - : Springer Science and Business Media LLC. - 0258-8900 .- 1432-0819. ; 79:12, s. 90-
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Tidskriftsartikel (refereegranskat)abstract
- Very little is known about the volatile element makeup of the gaseous emissions of Nyamulagira volcano. This paper tries to fill this gap by reporting the first gas composition measurements of Nyamulagira’s volcanic plume since the onset of its lava lake activity at the end of 2014. Two field surveys were carried out on 1 November 2014, and 13–15 October 2015. We applied a broad toolbox of volcanic gas composition measurement techniques in order to geochemically characterize Nyamulagira’s plume. Nyamulagira is a significant emitter of SO2, and our measurements confirm this, as we recorded SO2 emissions of up to ~ 14 kt/d during the studied period. In contrast to neighbouring Nyiragongo volcano, however, Nyamulagira exhibits relatively low CO2/SO2 molar ratios ( 92% of total gas emissions). Strong variations in the volatile composition, in particular for the CO2/SO2 ratio, were measured between 2014 and 2015, which appear to reflect the simultaneous variations in volcanic activity. We also determined the molar ratios for Cl/S, F/S and Br/S in the plume gas, finding values of 0.13 and 0.17, 0.06 and 0.11, and 2.3·10?4 and 1·10?4, in 2014 and 2015, respectively. A total gas emission flux of 48 kt/d was estimated for 2014. The I/S ratio in 2015 was found to be 3.6·10?6. In addition, we were able to distinguish between hydrogen halides and non-hydrogen halides in the volcanic plume. Considerable amounts of bromine (18–35% of total bromine) and iodine (8–18% of total iodine) were found in compounds other than hydrogen halides. However, only a negligible fraction of chlorine was found as compounds other than hydrogen chloride.
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| 9. |
- Coppola, D., et al.
(författare)
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Shallow system rejuvenation and magma discharge trends at Piton de la Fournaise volcano (La Réunion Island)
- 2017
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Ingår i: Earth and Planetary Science Letters. - : Elsevier BV. - 1385-013X .- 0012-821X. ; 463, s. 13-24
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Tidskriftsartikel (refereegranskat)abstract
- Basaltic magma chambers are often characterized by emptying and refilling cycles that influence their evolution in space and time, and the associated eruptive activity. During April 2007, the largest historical eruption of Piton de la Fournaise (Île de La Réunion, France) drained the shallow plumbing system (>240×106 m3) and resulted in collapse of the 1-km-wide summit crater. Following these major events, Piton de la Fournaise entered a seven-year long period of near-continuous deflation interrupted, in June 2014, by a new phase of significant inflation. By integrating multiple datasets (lava discharge rates, deformation, seismicity, gas flux, gas composition, and lava chemistry), we here show that the progressive migration of magma from a deeper (below sea level) storage zone gradually rejuvenated and pressurized the above-sea-level portion of the magmatic system consisting of a vertically-zoned network of relatively small-volume magma pockets. Continuous inflation provoked four small (
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| 10. |
- Dinger, Florian, et al.
(författare)
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On the link between Earth tides and volcanic degassing
- 2019
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Ingår i: Solid Earth. - : Copernicus GmbH. - 1869-9510 .- 1869-9529. ; 10:3, s. 725-740
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Tidskriftsartikel (refereegranskat)abstract
- Long-term measurements of volcanic gas emissions conducted during the last decade suggest that under certain conditions the magnitude or chemical composition of volcanic emissions exhibits periodic variations with a period of about 2 weeks. A possible cause of such a periodicity can be attributed to the Earth tidal potential. The phenomenology of such a link has been debated for long, but no quantitative model has yet been proposed. The aim of this paper is to elucidate whether a causal link between tidal forcing and variations in volcanic degassing can be traced analytically. We model the response of a simplified magmatic system to the local tidal gravity variations and derive a periodical vertical magma displacement in the conduit with an amplitude of 0.1-1m, depending on the geometry and physical state of the magmatic system. We find that while the tide-induced vertical magma displacement presumably has no significant direct effect on the volatile solubility, the differential magma flow across the radial conduit profile may result in a significant increase in the bubble coalescence rate at a depth of several kilometres by up to several multiples of 10%. Because bubble coalescence facilitates separation of gas from magma and thus enhances volatile degassing, we argue that the derived tidal variation may propagate to a manifestation of varying volcanic degassing behaviour. The presented model provides a first basic framework which establishes an analytical understanding of the link between the Earth tides and volcanic degassing.
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| 11. |
- Dinger, Florian, et al.
(författare)
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Periodicity in the BrO/SO2 molar ratios in the volcanic gas plume of Cotopaxi and its correlation with the Earth tides during the eruption in 2015
- 2018
-
Ingår i: Solid Earth. - : Copernicus GmbH. - 1869-9510 .- 1869-9529. ; 9:2, s. 247-266
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Tidskriftsartikel (refereegranskat)abstract
- We evaluated NOVAC (Network for Observation of Volcanic and Atmospheric Change) gas emission data from the 2015 eruption of the Cotopaxi volcano (Ecuador) for BrO/SO2 molar ratios. The BrO=SO2 molar ratios were very small prior to the phreatomagmatic explosions in August 2015, significantly higher after the explosions, and continuously increasing until the end of the unrest period in December 2015. These observations together with similar findings in previous studies at other volcanoes (Mt. Etna, Nevado del Ruiz, Tungurahua) suggest a possible link between a drop in BrO/SO2 and a future explosion. In addition, the observed relatively high BrO/SO2 molar ratios after December 2015 imply that bromine degassed predominately after sulfur from the magmatic melt. Furthermore, statistical analysis of the data revealed a conspicuous periodic pattern with a periodicity of about 2 weeks in a 3-month time series. While the time series is too short to rule out a chance recurrence of transient geological or meteorological events as a possible origin for the periodic signal, we nevertheless took this observation as a motivation to examine the influence of natural forcings with periodicities of around 2 weeks on volcanic gas emissions. One strong aspirant with such a periodicity are the Earth tides, which are thus central in this study. We present the BrO=SO2 data, analyse the reliability of the periodic signal, discuss a possible meteorological or eruption-induced origin of this signal, and compare the signal with the theoretical ground surface displacement pattern caused by the Earth tides. Our central result is the observation of a significant correlation between the BrO=SO2 molar ratios with the north–south and vertical components of the calculated tideinduced surface displacement with correlation coefficients of 47 and 36 %, respectively. From all other investigated parameters, only the correlation between the BrO=SO2 molar ratios and the relative humidity in the local atmosphere resulted in a comparable correlation coefficient of about 33 %.
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| 12. |
- Dingwell, Adam, et al.
(författare)
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Seasonal and diurnal patterns in the dispersion of SO2 from Mt. Nyiragongo
- 2016
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Ingår i: Atmospheric Environment. - : Elsevier BV. - 1873-2844 .- 1352-2310. ; 132, s. 19-29
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Tidskriftsartikel (refereegranskat)abstract
- Mt. Nyiragongo is an active volcano located in the Democratic Republic of Congo, close to the border of Rwanda and about 15 km north of the city of Goma (~ 1,000,000 inhabitants). Gases emitted from Nyiragongo might pose a persistent hazard to local inhabitants and the environment. While both ground- and satellite-based observations of the emissions exist, prior to this study, no detailed analysis of the dispersion of the emissions have been made. We have conducted a dispersion study, using a modelling system to determine the geographical distribution of SO2.A combination of a meteorological model (WRF), a Lagrangian particle dispersion model (FLEXPART-WRF) and flux data based on DOAS measurements from the NOVAC-network is used. Since observations can only be made during the day, we use random sampling of fluxes and ensemble modelling to estimate night-time emissions.Seasonal variations in the dispersion follows the migration of the Inter Tropical Convergence Zone. In June-August, the area with the highest surface concentrations is located to the northwest, and in December-February, to the southwest of the source. Diurnal variations in surface concentrations were determined by the development of the planetary boundary layer and the lake-/land breeze cycle around lake Kivu. Both processes contribute to low surface concentrations during the day and high concentrations during the night. However, the strong northerly trade winds in November-March weakened the lake breeze, contributing to higher daytime surface concentrations along the northern shore of Lake Kivu, including the city of Goma. For further analysis and measurements, it is important to include both seasonal and diurnal cycles in order to safely cover periods of high and potentially hazardous concentrations.
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| 13. |
- Fischer, Tobias P., et al.
(författare)
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The emissions of CO2 and other volatiles from the world's subaerial volcanoes
- 2019
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 9:1
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Tidskriftsartikel (refereegranskat)abstract
- Volcanoes are the main pathway to the surface for volatiles that are stored within the Earth. Carbon dioxide (CO2) is of particular interest because of its potential for climate forcing. Understanding the balance of CO2 that is transferred from the Earth's surface to the Earth's interior, hinges on accurate quantification of the long-term emissions of volcanic CO2 to the atmosphere. Here we present an updated evaluation of the world's volcanic CO2 emissions that takes advantage of recent improvements in satellite-based monitoring of sulfur dioxide, the establishment of ground-based networks for semi-continuous CO2-SO2 gas sensing and a new approach to estimate key volcanic gas parameters based on magma compositions. Our results reveal a global volcanic CO2 flux of 51.3 +/- 5.7 Tg CO2/y (11.7 x 10(11) mol CO2/y) for non-eruptive degassing and 1.8 +/- 0.9 Tg/y for eruptive degassing during the period from 2005 to 2015. While lower than recent estimates, this global volcanic flux implies that a significant proportion of the surface-derived CO2 subducted into the Earth's mantle is either stored below the arc crust, is efficiently consumed by microbial activity before entering the deeper parts of the subduction system, or becomes recycled into the deep mantle to potentially form diamonds.
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| 14. |
- Gislason, S.R., et al.
(författare)
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Environmental pressure from the 2014–15 eruption of Bárðarbunga volcano, Iceland
- 2015
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Ingår i: Geochemical Perspectives Letters. - : European Association of Geochemistry. - 2410-3403 .- 2410-339X. ; 1:2015, s. 84 - 93
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Tidskriftsartikel (refereegranskat)abstract
- The effusive six months long 2014-2015 Bárðarbunga eruption (31 August-27 February) was the largest in Iceland for more than 200 years, producing 1.6 ± 0.3 km3 of lava. The total SO2 emission was 11 ± 5 Mt, more than the amount emitted from Europe in 2011. The ground level concentration of SO2 exceeded the 350 μg m−3 hourly average health limit over much of Iceland for days to weeks. Anomalously high SO2 concentrations were also measured at several locations in Europe in September. The lowest pH of fresh snowmelt at the eruption site was 3.3, and 3.2 in precipitation 105 km away from the source. Elevated dissolved H2SO4, HCl, HF, and metal concentrations were measured in snow and precipitation. Environmental pressures from the eruption and impacts on populated areas were reduced by its remoteness, timing, and the weather. The anticipated primary environmental pressure is on the surfacewaters, soils, and vegetation of Iceland.
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| 15. |
- Harris, A. J L, et al.
(författare)
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Effusive crises at Piton de la Fournaise 2014–2015: a review of a multi-national response model
- 2017
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Ingår i: Journal of Applied Volcanology. - : Springer Science and Business Media LLC. - 2191-5040. ; 6:1
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Forskningsöversikt (refereegranskat)abstract
- Many active European volcanoes and volcano observatories are island-based and located far from their administrative “mainland”. Consequently, Governments have developed multisite approaches, in which monitoring is performed by a network of individuals distributed across several national research centers. At a transnational level, multinational networks are also progressively emerging. Piton de la Fournaise (La Réunion Island, France) is one such example. Piton de la Fournaise is one of the most active volcanoes of the World, and is located at the greatest distance from its “mainland” than any other vulnerable “overseas” site, the observatory being 9365 km from its governing body in Paris. Effusive risk is high, so that a well-coordinated and rapid response involving near-real time delivery of trusted, validated and operational product for hazard assessment is critical. Here we review how near-real time assessments of lava flow propagation were developed using rapid provision, and update, of key source terms through a dynamic and open integration of near-real time remote sensing, modeling and measurement capabilities on both the national and international level. The multi-national system evolved during the five effusive crises of 2014–2015, and is now mature for Piton de la Fournaise. This review allows us to identify strong and weak points in an extended observatory system, and demonstrates that enhanced multi-national integration can have fundamental implications in scientific hazard assessment and response during an on-going effusive crisis.
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| 16. |
- Hidalgo, Silvana, et al.
(författare)
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Evolution of the 2015 Cotopaxi Eruption Revealed by Combined Geochemical & Seismic Observations
- 2018
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Ingår i: Geochemistry, Geophysics, Geosystems. - 1525-2027. ; 19:7, s. 2087-2108
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Tidskriftsartikel (refereegranskat)abstract
- Through integration of multiple data streams to monitor volcanic unrest scientists are able to make more robust eruption forecast and to obtain a more holistic interpretation of volcanic systems. We examined gas emission and gas geochemistry and seismic and petrologic data recorded during the 2015 unrest of Cotopaxi (Ecuador) in order to decipher the origin and temporal evolution of this eruption. Identification of families of similar seismic events and the use of seismic amplitude ratios reveals temporal changes in volcanic processes. SO2 (300 to 24,000 t/d), BrO/SO2 (5–10 × 10−5), SO2/HCl (5.8 ± 4.8 and 6.6 ± 3.0), and CO2/SO2 (0.6 to 2.1) measured throughout the eruption indicate a shallow magmatic source. Bulk ash and glass chemistry indicate a homogenous andesitic (SiO2 wt % = 56.94 ± 0.25) magma having undergone extensive S-exsolution and degassing during ascent. These data lead us to interpret this eruption as a magma intrusion and ascend to shallow levels. The intrusion progressively interacted with the hydrothermal system, boiled off water, and produced hydromagmatic explosions. A small volume of this intrusion continued to fragment and produced episodic ash emissions until it was sufficiently degassed and rheologically stiff. Based on the 470 kt of measured SO2 we estimate that ~65.3 × 106 m3 of magma were required to supply the emitted gases. This volume exceeds the volume of erupted juvenile material by a factor of 50. This result emphasizes the importance of careful monitoring of Cotopaxi to identify the intrusion of a new batch of magma, which could rejuvenate the nonerupted material.
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| 17. |
- Lages, J., et al.
(författare)
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Volcanic Gas Emissions Along the Colombian Arc Segment of the Northern Volcanic Zone (CAS-NVZ): Implications for volcano monitoring and volatile budget of the Andean Volcanic Belt
- 2019
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Ingår i: Geochemistry, Geophysics, Geosystems. - 1525-2027. ; 20:11, s. 5057-5081
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Tidskriftsartikel (refereegranskat)abstract
- Studying spatial and temporal trends in volcanic gas compositions and fluxes is crucial both to volcano monitoring and to constrain the origin and recycling efficiency of volatiles at active convergent margins. New volcanic gas compositions and volatile fluxes are here reported for Nevado del Ruiz, Galeras, and Purace, three of the most persistently degassing volcanoes located in the Colombian Arc Segment of the Northern Volcanic Zone. At Nevado del Ruiz, from 2014 to 2017, plume emissions showed an average molar CO2/S-T ratio of 3.9 +/- 1.6 (S-T is total sulfur, S). Contemporary, fumarolic chemistry at Galeras progressively shifted toward low-temperature, S-depleted fumarolic gas discharges with an average CO2/S-T ratio in excess of 10 (6.0-46.0, 2014-2017). This shift in volcanic gas compositions was accompanied by a concurrent decrease in SO2 emissions, confirmed on 21 March 2017 by high-resolution ultraviolet camera-based SO2 fluxes of similar to 2.5 kg/s (similar to 213 t/day). For comparison, SO2 emissions remained high at Nevado del Ruiz (weighted average of 8 kg/s) between 2014 and 2017, while Purace maintained rather low emission levels (<1 kg/s of SO2, CO2/SO2 approximate to 14). We here estimate carbon dioxide fluxes for Nevado del Ruiz, Galeras, and Purace of similar to 23, 30, and 1 kg/s, respectively. These, combined with recent CO2 flux estimates for Nevado del Huila of similar to 10 kg/s (similar to 860 t/day), imply that this arc segment contributes about 50% to the total subaerial CO2 budget of the Andean Volcanic Belt. Furthermore, our work highlights the northward increase in carbon-rich sediment input into the mantle wedge via slab fluids and melts that is reflected in magmatic CO2/S-T values far higher than those reported for Southern Volcanic Zone and Central Volcanic Zone volcanoes. We estimate that about 20% (similar to 1.3 Mt C/year) of the C being subducted (similar to 6.19 Mt C/year) gets resurfaced through subaerial volcanic gas emissions in Colombia (Nevado del Ruiz similar to 0.7 Mt C/year). As global volcanic volatile fluxes continue to be quantified and refined, the contribution from this arc segment should not be underestimated.
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| 18. |
- Lübcke, Peter, et al.
(författare)
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Retrieval of absolute SO2 column amounts from scattered-light spectra: implications for the evaluation of data from automated DOAS networks
- 2016
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Ingår i: Atmospheric Measurement Techniques. - : Copernicus GmbH. - 1867-1381 .- 1867-8548. ; 9:12, s. 5677-5698
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Tidskriftsartikel (refereegranskat)abstract
- Scanning spectrometer networks using scattered solar radiation in the ultraviolet spectral region have become an increasingly important tool for monitoring volcanic sulfur dioxide (SO2) emissions. Often measured spectra are evaluated using the differential optical absorption spectroscopy (DOAS) technique. In order to obtain absolute column densities (CDs), the DOAS evaluation requires a Fraunhofer reference spectrum (FRS) that is free of absorption structures of the trace gas of interest. For measurements at volcanoes such a FRS can be readily obtained if the scan (i.e. series of measurements at different elevation angles) includes viewing directions where the plume is not seen. In this case, it is possible to use these viewing directions (e.g. zenith) as FRS. Possible contaminations of the FRS by the plume can then be corrected by calculating and subtracting an SO2 offset (e.g. the lowest SO2 CD) from all viewing directions of the respective scan. This procedure is followed in the standard evaluations of data from the Network for Observation of Volcanic and Atmospheric Change (NOVAC). While this procedure is very efficient in removing Fraunhofer structures and instrumental effects it has the disadvantage that one can never be sure that there is no SO2 from the plume in the FRS. Therefore, using a modelled FRS (based on a high-resolution solar atlas) has a great advantage. We followed this approach and investigated an SO2 retrieval algorithm using a modelled FRS. In this paper, we present results from two volcanoes that are monitored by NOVAC stations and which frequently emit large volcanic plumes: Nevado del Ruiz (Colombia) recorded between January 2010 and June 2012 and from Tungurahua (Ecuador) recorded between January 2009 and December 2011. Instrumental effects were identified with help of a principal component analysis (PCA) of the residual structures of the DOAS evaluation. The SO2 retrieval performed extraordinarily well with an SO2 DOAS retrieval error of 1-2 x 10(16) [molecules cm(-2)]. Compared to a standard evaluation, we found systematic differences of the differential slant column density (dSCD) of only up to approximate to 15% when looking at the variation of the SO2 within one scan. The major advantage of our new retrieval is that it yields absolute SO2 CDs and that it does not require complicated instrumental calibration in the field (e.g. by employing calibration cells or broadband light sources), since the method exploits the information available in the measurements. We compared our method to an evaluation that is similar to the NOVAC approach, where a spectrum that is recorded directly before the scan is used as an FRS and an SO2 CD offset is subtracted from all retrieved dSCD in the scan to correct for possible SO2 contamination of the FRS. The investigation showed that 21.4% of the scans (containing significant amounts of SO2) at Nevado del Ruiz and 7% of the scans at Tungurahua showed much larger SO2 CDs when evaluated using modelled FRS (more than a factor of 2). For standard evaluations the overall distribution of the SO2 CDs in a scan can in some cases indicate whether the plume affects all viewing directions and thus these scans need to be discarded for NOVAC emission rate evaluation. However, there are other cases where this is not possible and thus the reported SO2 emission rates would be underestimated. The new method can be used to identify these cases and thus it can considerably improve SO2 emission budgets.
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| 19. |
- Pfeffer, M. A., et al.
(författare)
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Ground-Based measurements of the 2014-2015 holuhraun volcanic cloud (Iceland)
- 2018
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Ingår i: Geosciences (Switzerland). - : MDPI AG. - 2076-3263. ; 8:1
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Tidskriftsartikel (refereegranskat)abstract
- The 2014-2015 Bárðarbunga fissure eruption at Holuhraun in central Iceland was distinguished by the high emission of gases, in total 9.6 Mt SO 2 , with almost no tephra. This work collates all ground-based measurements of this extraordinary eruption cloud made under particularly challenging conditions: remote location, optically dense cloud with high SO 2 column amounts, low UV intensity, frequent clouds and precipitation, an extensive and hot lava field, developing ramparts, and high-latitude winter conditions. Semi-continuous measurements of SO 2 flux with three scanning DOAS instruments were augmented by car traverses along the ring-road and along the lava. The ratios of other gases/SO 2 were measured by OP-FTIR, MultiGAS, and filter packs. Ratios of SO 2 /HCl = 30-110 and SO 2 /HF = 30-130 show a halogen-poor eruption cloud. Scientists on-site reported extremely minor tephra production during the eruption. OPC and filter packs showed low particle concentrations similar to non-eruption cloud conditions. Three weather radars detected a droplet-rich eruption cloud. Top of eruption cloud heights of 0.3-5.5 km agl were measured with ground-and aircraft-based visual observations, web camera and NicAIR II infrared images, triangulation of scanning DOAS instruments, and the location of SO 2 peaks measured by DOAS traverses. Cloud height and emission rate measurements were critical for initializing gas dispersal simulations for hazard forecasting.
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| 20. |
- Roman, Diana, et al.
(författare)
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Mechanisms of Unrest and Eruption at Persistently Restless Volcanoes: Insights From the 2015 Eruption of Telica Volcano, Nicaragua
- 2019
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Ingår i: Geochemistry, Geophysics, Geosystems. - 1525-2027. ; 20:8, s. 4162-4183
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Tidskriftsartikel (refereegranskat)abstract
- Many of Earth's volcanoes experience well-defined states of “quiescence” and “unrest,” with unrest occasionally culminating in eruption. Some volcanoes, however, experience an unusually protracted (i.e., decades-long) period of noneruptive unrest and are thus categorized as “persistently restless volcanoes” (PRVs). The processes that drive persistently restless volcanism are poorly understood, as our knowledge of PRVs is currently based on a small number of case studies. Here we examine multidisciplinary observations of the 2015 eruptive episode at Telica Volcano, Nicaragua, in the context of its long-term behavior. We suggest that the latter phases of the 2015 eruption were ultimately driven by destabilization of its shallow magma reservoir. Based on previous geodetic-seismic studies of Telica (Geirsson et al., 2014, https://doi.org/10.1016/j.jvolgeores.2013.11.009; Rodgers et al., 2013, https://doi.org/10.1016/j.jvolgeores.2013.08.010 and 2015, https://doi.org/10.1016/j.jvolgeores.2014.11.012) and on multiparameter observations at Telica over a 7-year period, we propose that three distinct states of unrest occur at Telica over decadal timescales: a stable open state involving steady conduit convection and two distinct “unstable” states that may lead to eruptions. In the “weak sealing” state, phreatic explosions result from steady conduit convection underlying a weak seal. In the “destabilized” state, destabilization of the top of the convecting magma in the conduit leads to rapid accumulation of high pressures leading to strong/impulsive phreatomagmatic explosions. Our observations and interpretations suggest that continuous seismic, ground-based deformation, gas emission, and thermal monitoring and interpretation of these data within a paradigm of sustained conduit convection modulated by episodes of sealing and destabilization of shallow magma reservoirs may allow robust forecasting of eruption potential, energy, and duration at Telica and similar PRVs worldwide.
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| 21. |
- Simmons, Isla, et al.
(författare)
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Extended SO2 outgassing from the 2014–2015 Holuhraun lava flow field, Iceland
- 2017
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Ingår i: Bulletin of Volcanology. - : Springer Science and Business Media LLC. - 0258-8900 .- 1432-0819. ; 79:11
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Tidskriftsartikel (refereegranskat)abstract
- The 2014–2015 Holuhraun eruption was the largest fissure eruption in Iceland in the last 200 years. This flood basalt eruption produced ~ 1.6 km3 of lava, forming a lava flow field covering an area of ~ 84 km2. Over the 6-month course of the eruption, ~ 11 Mt of SO2 were released from the eruptive vents as well as from the cooling lava flow field. This work examines the post-eruption SO2 flux emitted by the Holuhraun lava flow field, providing the first study of the extent and relative importance of the outgassing of a lava flow field after emplacement. We use data from a scanning differential optical absorption spectroscopy (DOAS) instrument installed at the eruption site to monitor the flux of SO2. In this study, we propose a new method to estimate the SO2 emissions from the lava flow field, based on the characteristic shape of the scanned column density distribution of a homogenous source close to the ground. Post-eruption outgassing of the lava flow field continued for at least 3 months after the end of the eruption, with SO2 flux between < 1 and 9 kg/s. The lava flow field post-eruption emissions were not a significant contributor to the total SO2 released during the eruption; however, the lava flow field was still an important polluter and caused high concentrations of SO2 at ground level after lava effusion ceased.
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| 22. |
- Theys, N., et al.
(författare)
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Global monitoring of volcanic SO2 degassing with unprecedented resolution from TROPOMI onboard Sentinel-5 Precursor
- 2019
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 9:1
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Tidskriftsartikel (refereegranskat)abstract
- Over the last four decades, space-based nadir observations of sulfur dioxide (SO2 ) proved to be a key data source for assessing the environmental impacts of volcanic emissions, for monitoring volcanic activity and early signs of eruptions, and ultimately mitigating related hazards on local populations and aviation. Despite its importance, a detailed picture of global SO 2 daily degassing is difficult to produce, notably for lower-tropospheric plumes, due largely to the limited spatial resolution and coverage or lack of sensitivity and selectivity to SO2 of current (and previous) nadir sensors. We report here the first volcanic SO2 measurements from the hyperspectral TROPOspheric Monitoring Instrument (TROPOMI) launched in October 2017 onboard the ESA’s Sentinel-5 Precursor platform. Using the operational processing algorithm, we explore the benefit of improved spatial resolution to the monitoring of global volcanic degassing. We find that TROPOMI surpasses any space nadir sensor in its ability to detect weak degassing signals and captures day-to-day changes in SO2 emissions. The detection limit of TROPOMI to SO2 emissions is a factor of 4 better than the heritage Aura/Ozone Monitoring Instrument (OMI). Here we show that TROPOMI SO2 daily observations carry a wealth of information on volcanic activity. Provided with adequate wind speed data, temporally resolved SO2 fluxes can be obtained at hourly time steps or shorter. We anticipate that TROPOMI SO2 data will help to monitor global volcanic daily degassing and better understand volcanic processes and impacts.
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| 23. |
- Tulet, Pierre, et al.
(författare)
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First results of the Piton de la Fournaise STRAP 2015 experiment: multidisciplinary tracking of a volcanic gas and aerosol plume
- 2017
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 17:8, s. 5355-5378
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Tidskriftsartikel (refereegranskat)abstract
- The STRAP (Synergie Transdisciplinaire pour Répondre aux Aléas liés aux Panaches volcaniques) campaign was conducted in 2015 to investigate the volcanic plumes of Piton de La Fournaise (La Réunion, France). For the first time, measurements at the local (near the vent) and at the regional scales around the island were conducted. The STRAP 2015 campaign has become possible thanks to a strong cross-disciplinary collaboration between volcanologists and meteorologists. The main observations during four eruptive periods (85 days) are summarized. They include the estimates of SO2, CO2 and H2O emissions, the altitude of the plume at the vent and over different areas of La Réunion Island, the evolution of the SO2 concentration, the aerosol size distribution, and the aerosol extinction profile. A climatology of the volcanic plume dispersion is also reported. Simulations and measurements showed that the plume formed by weak eruption has a stronger interaction with the surface of the island. Strong SO2 and particles concentrations above 1000 ppb and 50 000 cm−3, respectively, are frequently measured over 20 km of distance from the Piton de la Fournaise. The measured aerosol size distribution shows the predominance of small particles in the volcanic plume. A particular emphasis is placed on the gas-particle conversion with several cases of strong nucleation of sulfuric acid observed within the plume and at the distal site of the Maïdo observatory. The STRAP 2015 campaign gave a unique set of multi-disciplinary data that can now be used by modellers to improve the numerical paramameterizations of the physical and chemical evolution of the volcanic plumes.
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| 24. |
- Vignelles, D., et al.
(författare)
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Balloon-borne measurement of the aerosol size distribution from an Icelandic flood basalt eruption
- 2016
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Ingår i: Earth and Planetary Science Letters. - : Elsevier BV. - 1385-013X .- 0012-821X. ; 453, s. 252-259
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Tidskriftsartikel (refereegranskat)abstract
- We present in situ balloon-borne measurements of aerosols in a volcanic plume made during the Holuhraun eruption (Iceland) in January 2015. The balloon flight intercepted a young plume at 8 km distance downwind from the crater, where the plume is 15 min of age. The balloon carried a novel miniature optical particle counter LOAC (Light Optical Aerosol Counter) which measures particle number concentration and size distribution in the plume, alongside a meteorological payload. We discuss the possibility of calculating particle flux by combining LOAC data with measurements of sulfur dioxide flux by ground-based UV spectrometer (DOAS). The balloon passed through the plume at altitude range of 2.0-3.1 km above sea level (a.s.l.). The plume top height was determined as 2.7-3.1 km a.s.l., which is in good agreement with data from Infrared Atmospheric Sounding Interferometer (IASI) satellite. Two distinct plume layers were detected, a non condensed lower layer (300 m thickness) and a condensed upper layer (800 m thickness). The lower layer was characterized by a lognormal size distribution of fine particles (0.2 mu m diameter) and a secondary, coarser mode (2.3 mu m diameter), with a total particle number concentration of around 100 cm(-3) in the 0.2-100 mu m detection range. The upper layer was dominated by particle centered on 20 mu m in diameter as well as containing a finer mode (2 mu m diameter). The total particle number concentration in the upper plume layer was an order of magnitude higher than in the lower layer. We demonstrate that intercepting a volcanic plume with a meteorological balloon carrying LOAC is an efficient method to characterize volcanic aerosol properties. During future volcanic eruptions, balloon borne measurements could be carried out easily and rapidly over a large spatial area in order to better characterize the evolution of the particle size distribution and particle number concentrations in a volcanic plume.
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| 25. |
- Warnach, S., et al.
(författare)
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Variation of the BrO/SO2 molar ratio in the plume of Tungurahua volcano between 2007 and 2017 and its relationship to volcanic activity
- 2019
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Ingår i: Frontiers in Earth Science. - : Frontiers Media SA. - 2296-6463. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- Recent long-term observations of the bromine monoxide (BrO) to sulphur dioxide (SO2) molar ratio in volcanic plumes have suggested a link between changes in the BrO/SO2 ratio and the volcanic activity. Nevertheless, understanding of the mechanisms determining this link is still limited due to the lack of studies on volcanic bromine release from the melt into the atmosphere. We present the results of 10 years (2007–2017) of observations of the BrO/SO2 molar ratio in the volcanic plume of Tungurahua volcano, Ecuador. Following the nearly continuous eruptive activity from 1999 to 2008, Tungurahua showed alternating phases of eruptive activity separated by periods of quiescence between late 2008 and March 2016, after which degassing intensity decreased below detection. By comparing the BrO/SO2 molar ratios collected from 13 eruptive phases to volcanic activity, this study aims to broaden the global observational database investigating their link. For this purpose, we combine three different methods to retrieve the BrO/SO2 molar ratio to analyse variations over different timescales. We identify a cyclic pattern in BrO/SO2 molar ratios for 11 of the 13 eruptive phases. The phases are initialised by low BrO/SO2 molar ratios between 2 and 6 × 10−5 coinciding with vulcanian-type activity followed by a strong increase to ratios ranging between 4 and 17 × 10−5 when eruptive dynamism shifts to strombolian. For five phases, we additionally observe a progressive decrease to the initial values of 2 to 5 × 10−5 toward the end of the phase. This clear pattern indicates a connection between the BrO/SO2 molar ratio and eruptive dynamics. Based on our new data, we propose a conceptual model of the volcanic processes taking place at Tungurahua during the eruptive phases. Our data furthermore indicate that maximal BrO/SO2 molar ratios observed during each phase could be related to the input of volatile-rich magma into the active part of the volcanic system of Tungurahua. This study shows that long-term BrO/SO2 molar ratios can be used as a proxy for the volatile status as well as temporal evolution of the volcanic system. © 2019 Warnach, Bobrowski, Hidalgo, Arellano, Sihler, Dinger, Lübcke, Battaglia, Steele, Galle, Platt and Wagner.
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