Gas emissions from the Bárðarbunga volcanic eruption
October 2015 - A year on from the start of the eruption at Bárðarbunga, Iceland, a new study by Met Office and University of Leeds scientists combines dispersion modelling, satellite data and surface observations to review the impact of the gas emissions on the UK and estimate the amount of volcanic sulphur dioxide that was emitted in the most vigorous phase of the eruption.
On 29 August 2014 a large lava-producing eruption started in the Bárðarbunga volcanic system in Iceland. This followed 13 days of increasing seismicity under the Vatnajökull ice-cap. The eruption site itself was called Holuhraun and is situated just to the north of the ice-cap. From 31 August 2014 to 28 February 2015 lava was continuously erupted at Holuhraun making it the largest "flood lava" eruption in Iceland since the 1783-1784 Laki eruption. However, the Holuhraun eruption was still just a fraction of the Laki eruption, producing 1.5 km3 of lava versus the 14.7 km3 erupted by Laki over the course of 8 months.
No significant amounts of volcanic ash were erupted at Holuhraun, but large amounts of volcanic gases were emitted, including sulphur dioxide. High concentrations of sulphur dioxide posed a health hazard to the local population and impacted ecosystems in Iceland (as documented by Gislason and co-workers in a recent paper), whilst lower concentrations reached parts of Europe including the UK.
During the eruption, the Met Office as home to the London Volcanic Ash Advisory Centre (VAAC) and as part of the UK's civil contingency sector was in close and regular contact with the Icelandic Meteorological Office, the state volcano observatory for Iceland. Scientists at the Met Office tracked the dispersion of the sulphur dioxide plume from the Holuhraun eruption using satellite imagery. (Further information on how we monitor volcanic plumes from satellites is provided in a Monitoring volcanic plumes from space )
Gases detected in the UK
On 5 September 2014 satellites showed that northerly winds were transporting the sulphur dioxide plume towards Ireland. On 6 September the ground-based air quality monitoring network in the Republic of Ireland detected short-lived (up to 24 hours) increases in sulphur dioxide levels. On 20-22 September elevated levels of sulphur dioxide were also detected at the surface by monitoring sites maintained by the Scottish Environmental Protection Agency (SEPA) and by sites in the UK's automated air quality monitoring network.
Air pollution regulations introduced in the 1980s mean that pollution from industrial sources of sulphur dioxide rarely exceeds baseline levels at monitoring sites, so these raised levels in September 2014, which reached "moderate" on Defra's Air pollution scale, were particularly unusual.
Modelling the gas plume
Atmospheric dispersion modelling undertaken using the Met Office's dispersion model Met Office Dispersion Model (which is also the model used for volcanic ash), confirmed that the raised surface levels during both occasions were associated with emissions from the Holuhraun eruption (figure below). The NAME model differs from many other volcanic dispersion models in that it is able to simulate the chemical conversion of sulphur dioxide in the atmosphere, allowing more accurate representation of the plume's evolution.
Initialising the NAME model requires estimates of quantities such as the emission rate of sulphur dioxide and the height of the gas release. During September 2014, preliminary data for these parameters were derived from observations in Iceland by colleagues at the Icelandic Meteorological Office, the University of Iceland and through the EU FP7 FUTUREVOLC Project.
Building on previous collaborative research following the 2010 Eyjafjallajokull and 2011 Grimsvotn Icelandic eruptions, the Met Office has since been working with researchers at the University of Leeds to improve our understanding of the total sulphur dioxide emissions and emission rates as well as the dispersion of the volcanic plume from the eruption at Holuhraun.
A scientific paper led by Anja Schmidt at the University of Leeds has just been published in the Journal of Geophysical Research which compares NAME simulated emissions from Holuhraun to satellite detections of sulphur dioxide and the surface measurements. In the study, data from the Ozone Monitoring Instrument (OMI) provided by the Belgian Institute for Space Aeronomy and the Infrared Atmospheric Sounding Interferometer (IASI) provided by the University of Oxford have been used. The researchers combined satellite data, ground observations from across Northern Europe and model simulations in order to refine estimates of the height and amount of gas being emitted from the eruption during September 2014.
"We were able to constrain sulphur dioxide emission rates to up to 120 kilotons per day during early September 2014 when the eruption was most powerful; that means that in the beginning the eruption emitted about eight times more sulphur dioxide per day than is emitted from all man-made sources in Europe per day. Our research also shows that the NAME model simulates the location of the volcanic sulphur dioxide plume in very good agreement with satellite instruments" explains Anja Schmidt.
The research highlights that despite the Holuhraun eruption emitting sulphur dioxide only into the lower atmosphere (less than 6 km above the ground) the gas was transported and detected over distances of 2500 km. This demonstrates that volcanic gases from relatively low altitude non-explosive volcanic emissions in Iceland can reach the UK and Europe.
"The resulting pollution events have provided us with a unique dataset and serve as excellent case studies for the verification of atmospheric dispersion models and satellite retrieval algorithms" said co-author Claire Witham from the Met Office.
Although monitoring and forecasting volcanic gases do not fall under the remit of the Volcanic Ash Advisory Centres, the Met Office has provided advice on sulphur dioxide to the UK Government during the Holuhraun eruption and is leading work to assess the wider hazard from gas-rich eruptions to the UK.
More details can be found in the article by A. Schmidt et al., "Satellite detection, long-range transport and air quality impacts of volcanic sulfur dioxide from the 2014-2015 flood lava eruption at Bárðarbunga (Iceland)", published in the Journal of Geophysical Research (see Schmidt et al. (2015)).
The paper by Gislason et al on "Environmental pressure from the 2014-15 eruption of Bárðarbunga volcano, Iceland" is published in Geochemical Perspectives Letters.