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| 2. |
- Arellano, Santiago, 1981, et al.
(författare)
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Synoptic analysis of a decade of daily measurements of SO2 emission in the troposphere from volcanoes of the global ground-based Network for Observation of Volcanic and Atmospheric Change
- 2021
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Ingår i: Earth System Science Data. - : Copernicus GmbH. - 1866-3516 .- 1866-3508. ; 13:3, s. 1167-1188
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Tidskriftsartikel (refereegranskat)abstract
- Volcanic plumes are common and far-reaching manifestations of volcanic activity during and between eruptions. Observations of the rate of emission and composition of volcanic plumes are essential to recognize and, in some cases, predict the state of volcanic activity. Measurements of the size and location of the plumes are important to assess the impact of the emission from sporadic or localized events to persistent or widespread processes of climatic and environmental importance. These observations provide information on volatile budgets on Earth, chemical evolution of magmas, and atmospheric circulation and dynamics. Space-based observations during the last decades have given us a global view of Earth's volcanic emission, particularly of sulfur dioxide (SO2). Although none of the satellite missions were intended to be used for measurement of volcanic gas emission, specially adapted algorithms have produced time-averaged global emission budgets. These have confirmed that tropospheric plumes, produced from persistent degassing of weak sources, dominate the total emission of volcanic SO2. Although space-based observations have provided this global insight into some aspects of Earth's volcanism, it still has important limitations. The magnitude and short-term variability of lower-atmosphere emissions, historically less accessible from space, remain largely uncertain. Operational monitoring of volcanic plumes, at scales relevant for adequate surveillance, has been facilitated through the use of ground-based scanning differential optical absorption spectrometer (ScanDOAS) instruments since the beginning of this century, largely due to the coordinated effort of the Network for Observation of Volcanic and Atmospheric Change (NOVAC). In this study, we present a compilation of results of homogenized post-analysis of measurements of SO2 flux and plume parameters obtained during the period March 2005 to January 2017 of 32 volcanoes in NOVAC. This inventory opens a window into the short-term emission patterns of a diverse set of volcanoes in terms of magma composition, geographical location, magnitude of emission, and style of eruptive activity. We find that passive volcanic degassing is by no means a stationary process in time and that large sub-daily variability is observed in the flux of volcanic gases, which has implications for emission budgets produced using short-term, sporadic observations. The use of a standard evaluation method allows for intercomparison between different volcanoes and between ground- and space-based measurements of the same volcanoes. The emission of several weakly degassing volcanoes, undetected by satellites, is presented for the first time. We also compare our results with those reported in the literature, providing ranges of variability in emission not accessible in the past. The open-access data repository introduced in this article will enable further exploitation of this unique dataset, with a focus on volcanological research, risk assessment, satellite-sensor validation, and improved quantification of the prevalent tropospheric component of global volcanic emission. Datasets for each volcano are made available at https://novac.chalmers.se (last access: 1 October 2020) under the CC-BY 4 license or through the DOI (digital object identifier) links provided in Table 1.
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| 3. |
- 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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| 5. |
- 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
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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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| 6. |
- Galle, Bo, 1952, et al.
(författare)
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Network for Observation of Volcanic and Atmospheric Change (NOVAC)-A global network for volcanic gas monitoring: Network layout and instrument description
- 2010
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 115:D5, s. Art. no. D05304-
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the global project Network for Observation of Volcanic and Atmospheric Change (NOVAC), the aim of which is automatic gas emission monitoring at active volcanoes worldwide. Data from the network will be used primarily for volcanic risk assessment but also for geophysical research, studies of atmospheric change, and ground validation of satellite instruments. A novel type of instrument, the scanning miniaturized differential optical absorption spectroscopy (Mini-DOAS) instrument, is applied in the network to measure volcanic gas emissions by UV absorption spectroscopy. The instrument is set up 5-10 km downwind of the volcano under study, and typically two to four instruments are deployed at each volcano in order to cover different wind directions and to facilitate measurements of plume height and plume direction. Two different versions of the instrument have been developed. Version I was designed to be a robust and simple instrument for measurement of volcanic SO2 emissions at high time resolution with minimal power consumption. Version II was designed to allow the best possible spectroscopy and enhanced flexibility in regard to measurement geometry at the cost of larger complexity, power consumption, and price. In this paper the project is described, as well as the developed software, the hardware of the two instrument versions, measurement strategies, data communication, and archiving routines. As of April 2009 a total of 46 instruments have been installed at 18 volcanoes worldwide. As a typical example, the installation at Tungurahua volcano in Ecuador is described, together with some results from the first 21 months of operation at this volcano.
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| 7. |
- Galle, Bo, 1952, et al.
(författare)
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NOVAC – Network for Observation of Volcanic and Atmospheric Change, recent developments and present status
- 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
- The NOVAC project, funded by European Union, was started in October 2005 with the aim to establish a global network of stations for the quantitative measurement of volcanic gas emissions. The network is based on a novel type of instrument, the Scanning Dual-beam mini-DOAS. Primarily theinstruments will be used to provide new parameters in the toolbox of observatories for gas emission estimates, geophysical research and hazard assessment. In addition, data are exploited for other scientific purposes, e.g. global estimates of volcanic gas emissions, regional to global statistical analysis, and studies of atmospheric chemistry. In particular large scale validation of satellite measurements of volcanic gas emissions will be possible, bringing space-borne observation of volcanoes a significant step forward.The Scanning Dual-beam Mini-DOAS instrument is capable of real-time automatic, unattended measurement of the total emission fluxes of SO2 and BrO from a volcano with better then 5 minutes time resolution during daylight. The high time-resolution of the data enables correlations with othergeophysical data, e.g. seismicity, thus significantly extending the information available for real-time hazard assessment and research. By comparing high time resolution gas emission data with emissions from neighboring volcanoes on different geographical scales, or with other geophysical events (earthquakes, tidal waves) mechanisms of volcanic forcing may be revealed.The network today encompasses 58 instruments installed on 24 volcanoes, including some of the most active and strongest degassing volcanoes in the world.In addition a mobile version of the instrument has been developed intended for rapid deployment at a volcano in relation to a volcanic crisis.The project and its present status will be presented.
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| 8. |
- Hidalgo, Silvana, et al.
(författare)
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Correlation between SO2 fluxes and acoustic energy related to explosive activity at Tungurahua volcano (Ecuador)
- 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
- Tungurahua is a steep-sided (5023 m high) andesitic stratovolcano located in the southern part of the Ecuadorian volcanic arc, with its summit crater lying just 8 km to both the touristic town of Baños and to a hydroelectric power plant that supplies 13% of the country’s total electric energy. Activity at Tungurahua resumed in September 1999 after 74 years of quiescence and since this time, the volcano has exhibited cyclic phases of activity. Typically, periods of high explosivity often characterized by strombolian to vulcanian behavior alternate with episodes of low to non explosive activity characterized by passive degassing.The monitoring network deployed at Tungurahua is comprehensive, allowing an extensive record of seismic events, acoustic energy, SO2 emissions and changes in deformation, to be recorded. In July 2006, five broad-band seismic stations with accompanying infrasound receptors were installed, allowing seismic and acoustic energy to be calculated for each discrete explosion event. As well, SO2fluxes have been recorded continuously since 2004 using two DOAS stations, before being enhanced to three sites in 2007. This complete record of both acoustic energy and SO2 fluxes subsequently allows meaningful correlations between the two parameters to be detected. Two clearly different kinds of behavior were distinguished:1.- From July 2007 to August 2008: degassing was most of the time above the normal background levels of passive degassing (1000 ton/day). During this corresponding period, explosive activity was also continuous. Total SO2 released between July 2007 and October 2008 was in the region of 328 kton, giving a daily average emission of 960 ton/day, which was associated with a cumulate meanacoustic energy of 93 kPa, which daily average is 247 Pa.2.- From August 2008 to the present: high SO2 emissions are related to explosive activity.Passive SO2 degassing which corresponds to approximately 65% of the time (during this period) reaches about 247 kton (456 ton/day) and is related to zero acoustic energy production. In contrast, explosive SO2 degassing reaches a total release of 456 kton (1,534 ton/day) and is related to a cumulate mean acoustic energy of 137 kPa, with a daily average of 508 Pa. These trends suggest that before August 2008 magma levels at Tungurahua may have been closer to the surface or that conduit geometry was more favorable for efficient degassing showing moderate explosive activity, displaying conditions reminiscent of an open-vent system. Since this time however, volcanic behavior appears to alter to a more closed or blocked conduit regime with degassing efficiency becoming appreciably reduced. During such activity, explosive behavior dominates within well defined eruptive episodes, characterized by more energetic explosions with associated pyroclastic flows and higher SO2 fluxes, such as May and December 2010 eruptive events.
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| 9. |
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| 10. |
- 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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