Maarten de Moor and Christoph Kern
The 5th NOVAC (Network for the Observation of Volcanic and Atmospheric Change) meeting and associated workshops took place in Costa Rica from 26 April to 5 May 2015. NOVAC, founded in 2005 through funding from the European Union, is a global network of scanning DOAS (Differential Optical Absorption Spectroscopy) instruments, which monitor volcanic sulfur dioxide emissions. The USGS-OFDA Volcano Disaster Assistance Program (VDAP) supported the meeting in collaboration with the Observatorio Vulcanológico y Sismológico de Costa Rica (OVSICORI) and the Deep Carbon Observatory. 43 scientists from 17 countries attended the conference, arriving in Costa Rica without significant delays despite airport closures due to volcanic ash from Turrialba and Calbuco volcanoes.
The first introductory sessions for new NOVAC community members and the icebreaker took place on 26 April at Hotel Bougainvillea near Heredia, Costa Rica. The meeting was officially opened on 27 April at OVSICORI (Heredia) and included overview presentations by NOVAC founder Bo Galle, USAID/OFDA senior regional director Tim Callaghan, and meeting co-organizer Christoph Kern (VDAP). The group then transferred to Guayabo Lodge located on the slopes of Turrialba volcano, where the bulk of the meeting took place. On the afternoon of 26 April, Geoffroy Avard and Maarten de Moor (meeting co-organizer) presented gas monitoring results from Turrialba and other Costa Rican volcanoes. Santiago Arellano summarized the current status and compiled results from the global NOVAC network, showing that despite the fact that NOVAC has been without official funding since 2010, the network continues to monitor gas emissions from 33 volcanoes (~20% of the world’s active volcanoes).
Researchers presented case studies on NOVAC results from individual volcanoes in 11 countries on 28 April. In many cases, large relative increases in SO2 emission rates preceded or accompanied eruptive activity, and were often correlated with geophysical indicators such as seismic activity. Highlights included long time series datasets from Popocatépetl volcano (Mexico) presented by Hugo Delgado, and correlations between gas fluxes, geophysical signals, and eruptive activity at Tungurahua volcano (Ecuador) by Freddy Vasconez. Results from individual observatories clearly demonstrated the high value of NOVAC data in assessing volcanic activity, as well as the dedication of the NOVAC community in maintaining scanning DOAS stations despite challenging environmental and political conditions.
A fieldtrip to Turrialba volcano on the morning of 29 April provided an opportunity for ground-based remote sensing demonstrations. The group (see photo below) visited the NOVAC stations at La Central and La Silvia (figure 2), located ~2 kilometers from the active vent, and also conducted mobile DOAS traverse and UV camera measurements. Turrialba entered a phase of increased eruptive activity on 29 October 2014, which continues to the present. Ash emissions have affected the Central Valley, which is home to the majority of the Costa Rican population, and caused numerous closures of the international airport. Sulfur dioxide emission rates as measured by NOVAC instrumentation have shown elevated gas fluxes in 2009 (months before the first eruption in 2010) and before and during recent eruptions, thus playing a crucial role in the assessment of volcanic activity. However, the challenging conditions at Turrialba (acid rain, intense corrosion, vandalism, and unstable weather and plume conditions) also embody the difficulties and challenges facing continuous and accurate monitoring of SO2 emission rates.
On the afternoon of 29 April, talks focused on innovative new techniques for measuring volcanic gases, including presentations by Robin Campion and Christoph Kern on UV cameras, Ulrich Platt on future techniques in ground-based remote sensing, and Peter Kelley on Multi-GAS instrumentation. On 30 April, researchers discussed errors and uncertainties in NOVAC measurements. Uncertainties in plume speed were highlighted throughout the meeting as a major source of error that should be addressed to obtain more accurate SO2 emission rates. The group discussed and debated multiple UV scattering in volcanic plumes and light dilution. At many volcanoes clouds and fog can result in unrealistic gas flux data. The group proposed many innovative ideas for improving NOVAC data. These ideas will be the focus of future efforts from the NOVAC community.
The last sessions of the conference focused on interpretation of volcanic systems and degassing behavior based on gas emission data. Highlights included possible correlations between variations in SO2 fluxes and earth tides presented by Thor Hansteen, the transition from hydrothermal to magmatic degassing at Redoubt volcano by Cindy Werner, and degassing behavior of Japanese volcanoes by Toshiya Mori.
The group discussed the future of NOVAC on the final day of the meeting. The NOVAC project officially ended 5 years ago and new sources of funding are needed to support its sustainability as an integrated network. The new collaboration between NOVAC and VDAP provides a potential basis for continuity, but dedicated human resources are required to improve the physical network and data processing methods to improve the accuracy of SO2 emission rate data derived from fixed scanning DOAS stations. This issue is fundamental to the interests of global volcanic gas emissions monitoring community.
Two focused workshops followed the main NOVAC meeting. The first was on radiative transfer and light scattering issues, supported by DCO´s Deep Earth Carbon Degassing (DECADE) program and organized by Robin Campion and Nicole Bobrowski. This workshop (2-5 May) brought together many of the leading experts (14 people in total) in the field to tackle the inherent complications in using scattered UV light measurements to determine SO2 fluxes. Topics of discussion included sophisticated radiative transfer modeling, practical solutions to assess scattering effects using information in DOAS spectra, methods for filtering data drastically affected by poor weather conditions, and strategies to test and validate methods for accurate determination of gas emission rates. The workshop participants are currently working on an extensive document describing the state of the art and potential methods to compensate for radiative transfer effects.
The second post-meeting workshop focused on Multi-GAS instrumentation, calibration, and data processing. This workshop (2-3 May) attended by 11 scientists ,was supported by VDAP, and was organized by Maarten de Moor. The challenges of field deployments of Multi-GAS instruments were a topic of animated conversation, with volcanic eruptions, deep snow, high winds, nesting insects, and highly corrosive volcanic gases all contributing to the narrative. The main focus of the workshop was Multi-GAS calibration and inter-comparison of instruments (figure 3). Standard gas mixtures were introduced into four Multi-GAS instruments (3 INGV type, 1 USGS/CVO type) and the results showed encouragingly consistent results between instruments built and calibrated by different groups. Discussions and demonstrations included data processing techniques, and time series datasets from Turrialba and Poás volcanoes represented examples of variations in gas composition with eruptive activity. The most common question raised in the workshop was “How do I get a Multi-GAS?” demonstrating the enthusiasm from the volcano monitoring community for near real-time in situ measurements of gas composition. This ambition was best exemplified by a prototype Multi-GAS developed in El Salvador and tested at the workshop. Issues identified at the workshop included maintaining Multi-GAS instruments under inherently extreme conditions, calibrating the instruments in countries where standard gases are not readily available, data processing considering variations in sensor response times, and assessment of sensor responses at varying atmospheric pressure.
These dynamic activities were made possible by USAID-VDAP, with additional support from DCO-DECADE and OVSICORI-UNA. The organizers would like to thank Sara Jivanjee and Hazel Lopez for their vital support with logistics, as well as the staff at OVSICORI (especially Geoffroy Avard and María Martínez) and Guayabo Lodge.