NOVAC Network for Observation of Volcanic and Atmospheric Change
B. Galle1, U. Platt2, M. Van Roozendael3, C. Oppenheimer4, T. Hansteen5, G. Boudon6, M. Burton7, H. Delgado8, A. Muños9, E. Duarte10, G. Garzón11, D. Escobar12, M. Kasereka13, S. Carn14, L. Molina15, S. Hidalgo16, E. Sánchez17, S. Inguaggiato7, F. Gil18, K. Vogfjord19, C. Newhall20 and R. Vaquilar21, K.Mulina22, P. Masias23, R. NOVAC instrument installed at San Cristóbal volcano, Nicaragua. Solidum24 and C. Thomas25
1. Chalmers University of Technology, SE-412 96 Gothenburg, Sweden
Incoming Light 2. Heidelberg University, Germany
Beam 1 Beam 2 3. Belgian Institute for Space Aeronomy, Belgium Computer 4. Cambridge University, United Kingdom 5. IFM-GEOMAR Research Center, Germany 6. Instutut de Physique de Globe du Paris, France Radio modem 7. Istituto Nazionale di Geofisica e Vulcanologia, Italy More than 9 million GPS 8. Universidad Nacional Autonoma de Mexico, Mexico measurements until Compass Optional Electronics Solar power 9. Instituto Nicaragüense de Estudios Territoriales, Nicaragua Tilt August 2017 Temperature 10. Observatorio Volcanológico y Sismológico de Costa Rica
11. Instituto Colombiano de Geología y Minería, Colombia 12. Servicio Nacional de Estudios Territoriales, El Salvador Window Spectrometer 1 13. Observatoire Volcanologique de Goma, D.R. Congo Optical fibers 14. Massachusetts Institute of Technology, USA Motor Spectrometer 2 15. University of Maryland, Baltimore County, USA 16 Instituto Geofísico de Escuela Politécnica Nacional, Ecuador Protective cover 17. Instituto Nacional de Sismología, Vulcanología, Meteorología e Hidrología, Guatemala Mirror Lens Temperature stabilisation 18. Servicio Nacional de Geología y Minería, Chile Spectrometer unit Scanning unit 19. Icelandic Meteorological office, Iceland 20. Singapore Earth Observatory Figure 1. Schematic view of the optical layout of the Dual-Beam scanning mini-DOAS instrument. The 21. Philippines Volcano Observatory mirror and the protective cover is rotated around the optical axis of the telescope, thereby scanning the 22. Rabaul Volcano Observatoty, Papua New Guinea field-of-view of the instrument in a plane perpendicular to the optical axis. 23. Instituto Geológico Minero y Metalúrgico, Peru Figure 7. Number of measurements made on each volcano in the NOVAC network , Oct. 2006 – Sept. 2014. 24. Centre for Volcanology and Geological Hazard Mitigation, Indonesia 25.Montserrat Volcano Observatory, Montserrat, West Indies 10 [email protected]
)
-1 8 Introduction The NOVAC project, funded by European Union, started in 2005 with the aim to establish a global 6 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, developed within the EU-project 4 DORSIVA. Primarily the instruments will be used to provide new parameters in the toolbox of the observatories for risk assessment, gas emission estimates and geophysical research on the local scale. In
emission (kgs 2 addition to this, data are exploited also for other scientific purposes, e.g. global estimates of volcanic gas 2 SO emissions, large scale volcanic correlations, studies of climate change and studies of stratospheric ozone wind measurement depletion. In particular large scale validation of satellite instruments for observing volcanic gas emissions Data from 2005 -2013 0 will be possible for the first time, allowing bringing observation of volcanic gas emissions from space a 12:30 13:00 13:30 14:00 14:30 15:00 15:30 16:00 significant step forward. Time The Scanning Dual-beam Mini-DOAS instrument represents a major breakthrough in volcanic gas monitoring; it is capable of real-time automatic, unattended measurement of the total emission fluxes of Figure 2. Time-resolved measurement of emissions from San Cristóbal volcano 23 November 2002, SO2 and BrO from a volcano with better than 5 minutes time resolution during daylight. The high time- calculated using plume height and wind speed from Dual Beam mini-DOAS measurements. resolution of the data enables correlations with other geophysical data, e.g. seismic data, thus Figure 8. There is about 150 degassing volcanoes globally. NOVAC presently monitors approximately
significantly extending the information available for real-time risk assessment and research at the 25% of these. GEIA: 9.66 (tropos) + 3.7 (stratos) TgSO2/y. NOVAC: 12.77 +- 1.9 TgSO2/y. volcano. By comparing high time resolution gas emission data with emissions from neighbouring volcanoes on different geographical scales, or with other geophysical events (earthquakes, tidal waves) mechanisms of volcanic forcing may be revealed. The spectra recorded by the instrument will also be used to derive data that complement global observation systems related to climate change and stratospheric ozone depletion research. The Dual-Beam Scanning mini-DOAS instrument The mini-DOAS system consists of a pointing telescope fiber-coupled to a spectrometer. Ultraviolet light from the Sun, scattered from aerosols and molecules in the atmosphere, is collected by means of a telescope. Light is transferred from the telescope to the spectrometer using an optical quartz fiber. The spectra are analyzed using Differential Optical Absorption Spectroscopy (DOAS) and the slant column of Figure 3. Left, the speed of the plume can be determined by collecting two time series of column data, various gases in the plume is derived. In the Scanning mini-DOAS the telescope is attached to a scanning one further upwind than the other. Right, measurement of the speed of the SO plume from San 2 device consisting of a mirror attached to a computer-controlled stepper-motor, providing a means to scan Cristóbal volcano, Nicaragua. the field-of view of the instrument over 180o, Figure 1. In a typical measurement the instrument is located under the plume, and scans are made, from horizon to horizon, in a plane perpendicular to the wind-direction. Typically a 3 seconds integration time is used, with 3.6o angular resolution, providing a full emission measurement every 5 minutes. By adding a second spectrometer and fiber, simultaneous measurements can be made in two viewing directions. In Figure 2 is shown a time resolved measurement of the gas emissions from San Cristóbal volcano in Nicaragua. A 3-fold increase in gas emission is seen over a time scale of 1 hour. Correlating these gas Figure 9. Comparison between NOVAC data and data from previously published studies, for selected data with other geophysical data, e.g. seismic data, is likely to substantially increase our understanding of NOVAC volcanoes, (data from 2005 - 2015). the status and behavior of this volcano. Volcano 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 San Cristobal Tungurahua Plume speed and plume height Masaya Popocatepetl The main source of error in both mobile and scanning mini-doas measurements is determination of wind- Nyiragongo Piton de Fournaise Cotopaxi speed at plume height. In the scanning measurements, also knowledge of the plume height is crucial in Galeras Colima Figure 4. Two-dimensional vertical concentration measurement performed on the plume from Mt Etna order to correctly calculate the number of gas molecules in a cross-section of the volcanic gas plume. For Santa Ana San Miguel on 18 September 2004. The altitude in the figure is relative to the scanning systems, which were situated Fuego de Guatemala the wind measurements the dual spectrometers of the instrument are used to make simultaneous total Santiaguito 6 km apart at 950 m above sea level. From the plot one can conclude that the centre of the plume is at Turrialba column measurements of SO2 in two different viewing directions, one beam pointing upwind and the Etna 3 Harestua around 4000 meters height above sea level. The concentration is presented in mg/m . Villarrica other downwind the plume. A time series of total column variations are registered in both directions, and Nevado del Huila Nevado del Ruiz from the temporal delay in variations in the total column, the wind speed can be calculated, Figure 3. For Stromboli Llaima Arenal the plume height measurement the plume is simultaneously monitored by 2 scanning mini-DOAS Nyamuragira Volcano instruments separated by some distance, and a vertical cross section of the gas concentration is derived Concepcion Mayon Telica using tomography, Figure 4. Besides giving the plume height, these data can be used to study the plume Ejyafjallajokul Hekla dynamics and in combination with a dispersion model assess the impact of the gas emissions on the local Bardarbunga Lascar Sangay environment. Ubinas Katla Cayambe Volcano risk assessment Chillan Copahue Isluga The primary use of the instruments is to provide time-resolved SO2 gas emission as a new parameter for Tavurvur Sabancaya geophysical research and risk assessment. Data is provided in real time at the local volcano observatory Sinabung
and has proved to be a very valuable tool for risk assessment. In Figure 5 is shown the SO2 emission Table 1. Availability of data from the NOVAC network, until end of 2016. The different colours denote from Nevado del Ruiz volcano in Colombia, famous for its eruption in 1985, with a lahar killing 23000 different projects that has been supporting the data monitoring. people. This volcano today shows a strong increase in gas emission, rising serious concern at the local volcano observatory.
Global assessment of volcanic SO2 emissions A secondary objective of the network is to provide improved statistics on SO2 quiescent degassing from Figure 5. Sulfur dioxide emission from Nevado del Ruiz volcano, Colombia, Dec 2009 – Jan 2017. active volcanoes. The archive today comprises more than 9 million individual measurements from 42 of (Data; SGC). the most strongly degassing volcanoes in the world, Figure 6. These data presently are re-evaluated using a consistent methodology to take into account plume height, plume speed and scattering conditions. The ambition is to make all the data available via an open data base (after approval from the respective Volcano Observatories). This work is expected to be finalized during 2019, and will provide a unique data
base on SO2 emission from volcanoes, a parameter important for global aerosol formation and climate modelling, Table 1 and Figure 10. Satellite Validation Many volcanoes with strong gas emission are located in remote places with no regular gas measurements, Also in the initial phase of a major eruption it may take time before any ground-based measurements may be undertaken. In these situations satellites may provide the only way to obtain estimates of the gas emissions. This project will provide an excellent opportunity to validate both the total column data derived from the satellites and the algorithms used to estimate the emissions. Figure 10. During 2017 – 2019 a data base will be set up at Chalmers that facilitates access to evaluated The Consortium emission data from the NOVAC volcanoes. The consortium presently encompasses observatories of 42 volcanoes from five continents, including some of the most active and strongest degassing volcanoes in the world, Figure 6 and Table 1. As our This project was initially funded by The European Union, FP6, ambitions are to expand the network, additional observatories are invited to join. Figure 6. Map showing the volcanoes involved in NOVAC in April 2017. Not shown is Katla (Iceland), Global Change and Ecosystems, Natural Disasters program. Sabancaya (Peru), Sinabung (Indonesia) and Soufriere Hills (Montserrat). Contact: [email protected]