| 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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Degassing patterns of Tungurahua volcano (Ecuador) during the 1999–2006 eruptive period, inferred from remote spectroscopic measurements of SO2 emissions
- 2008
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Ingår i: Journal of Volcanology and Geothermal Research. - 0377-0273. ; 176, s. 151-162
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the results of 7 years (Aug. 1999–Oct. 2006) of SO2 gas measurements during the ongoingeruption of Tungurahua volcano, Ecuador. From 2004 onwards, the operation of scanning spectrometers hasfurnished high temporal resolution measurements of SO2 flux, enabling this dataset to be correlated with otherdatasets, including seismicity. The emission rate of SO2 during this period ranges from less than 100 to35000 tonnes/day (t/d) with a mean daily emission rate of 1458 t/d and a standard deviation of ±2026 t/d.Average daily emissions during inferred explosive phases are about 1.75 times greater than during passivedegassing intervals. The total amount of sulfur emitted since 1999 is estimated as at least 1.91 Mt, mostlyinjected into the troposphere and carried westwards from the volcano. Our observations suggest that the rateof passive degassing at Tungurahua requires SO2 exsolution of an andesitic magma volume that is two orders ofmagnitude larger than expected for the amount of erupted magma. Two possible, and not mutually exclusive,mechanisms are considered here to explain this excess degassing: gas flow through a permeable stagnant magma-filled conduit and gas escape from convective magma overturning in the conduit.We have found thatreal-time gas monitoring contributes significantly to better eruption forecasting at Tungurahua, because it hasprovided improved understanding of underlying physical mechanisms of magma ascent and eruption.
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| 4. |
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| 5. |
- 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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| 6. |
- Arellano, Santiago, 1981, et al.
(författare)
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New developments on remote sensing studies of volcanic gas emissions by solar infrared spectroscopy
- 2011
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Ingår i: 11th IAVCEI-CCVG Gas Workshop, September 1 - 10, 2011, Kamchatka, Russia.
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Konferensbidrag (refereegranskat)abstract
- In this contribution, we will present some recent developments made by our group on the application of solar occultation remote sensing to the measurement of volcanic gas emissions in the infrared spectral region. These include the automation of Fourier Transform Spectrometers (FTS) and novel methods for radiation collection and spectrometric analysis.Solar FTS is a proven and versatile method for measuring volcanogenic gases. However, its relatively high cost and complexity on data collection and analysis have precluded its wider use by observatories as a permanent monitoring tool. We will present some results of a field experimentperformed at Popocatépetl volcano (Mexico) within the FIEL-VOLCAN project in April 2010, to show the feasibility of automating a solar FTS on volcanic settings to measure SO2/HCl molar ratios. The system includes a compact solar tracker for automatic radiation collection from a stationary point as well as an embedded computer for data acquisition. Data is evaluated off-line by using e.g., the Chalmers-QESOF program.Further simplifications of the transfer optics and spectroscopic analysis have been investigatedby our group and their operation principles and preliminary results will be presented.
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| 9. |
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| 10. |
- Arellano, Santiago, 1981, et al.
(författare)
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Prospects of a global network for studies of volcanic plumes
- 2009
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Ingår i: CEV-IAVCEI Workshop on Advances in studies of volcanic plumes and pyroclastic density currents, Clermont-Ferrand, France, Oct. 2009..
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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