As the dust settles

1 July 2010

As the Eyjafjallajökull volcano in Iceland erupted, weather conditions meant that the volcanic ash covered a large proportion of Europe, causing widespread disruption to aviation. Here, we take a look at our role in predicting the spread of the ash and advising the aviation industry.

Low-level volcanic eruptions in Iceland occurring since 20 March 2010 increased significantly on 14 April. On 15 April the bright orange plume of the highest concentrations of volcanic ash extended across Scandinavia, and the Met Office observer at Lerwick in the Shetland Islands reported a reduction in visibility and a slight yellow hue in the sky.

The Met Office's responsibility is to monitor and forecast the spread of ash from the volcano. Weather patterns meant that the volcanic ash spread towards the UK so, in our role as a Volcanic Ash Advisory Centre (VAAC), we issued a Volcanic Ash Advisory.

Safety thresholds

Volcanic ash can have a major impact on aircraft, potentially causing their engines to fail. The International Civil Aviation Organisation (ICAO), the UK Civil Aviation Authority (CAA) and aircraft engine manufacturers set safety thresholds for flying planes through volcanic ash. Our forecasts of the ash plume trajectories are based on these thresholds.

We advise the CAA and National Air Traffic Services (NATS) where the ash will be. They have responsibility for safety within UK airspace and decide whether airspace is open or closed. Airspace was closed on 15 April which meant that many people across Europe had their travel plans disrupted.

Monitoring the spread

To forecast the spread of ash we use dispersion models that have been tested and proven during events such as Chernobyl, Buncefield and the outbreak of the animal disease Bluetongue. Our capability to predict the spread of airborne pollution is delivered by our world-leading atmospheric dispersion model, NAME (Numerical Atmospheric-dispersion Modelling Environment). In addition to being used as an emergency response guidance tool, the model is used for routine air quality forecasting and meteorological research activities.

From the moment the volcano erupted, we used our models to forecast how the ash cloud would move. We have also used satellite imagery, scientific balloons, research aircraft and ground-based radar systems to observe the ash cloud and verify the forecasts. As the Facility for Airborne Atmospheric Measurements (FAAM) and Natural Environment Research Council (NERC) research aircraft were called into action, the importance of research flights when monitoring ash plumes was highlighted.

A comparison of five Volcanic Ash Advisory Centre dispersion models was conducted based on the Grimsvötn volcanic eruption in Iceland in 2004. This concluded that the models all produced very similar results. Locations of the eruption plume simulated by the different models were almost identical to those predicted by the Met Office during the eruption and agreed with the satellite observations.


Until 20 April, ICAO guidance was that aircraft should not fly through any volcanic ash or dust, and our predictions were based on this 'zero tolerance' rule. Subsequently, the CAA changed the guidelines, setting new safety thresholds based on information from engine manufacturers and airlines. In support of the regulator, our guidance displayed the areas where ash concentrations were below the new threshold, as well as airspace affected by the 'zero tolerance' rule.

"We very much appreciated the collaborative approach and responsiveness of all your team who worked very effectively with NATS, airlines, airports and the Civil Aviation Authority to bring matters to a close."

Richard Deakin, Chief Executive Officer, National Air Traffic Services (NATS)

Hot on the heels of the new guidance, a change to weather patterns on 23 April meant that most of the ash moved away from the UK for a week. This was good news for everyone as it gave a significant window for airlines to get people and goods to the right places. However, there were still some traces of ash and aircraft still avoided areas where ash concentrations were above the new threshold. Regulators instructed airlines to conduct a risk assessment before flying and engine inspections before and after each flight.

volcanic ash chart

Volcanic ash chart - the red zones represent the standard safety thresholds, while the black represents ash concentrations that are 20 times higher then the standard (red) threshold. The black zone is the area in which aircraft engine manufacturer tolerances are exceeded.

Support network

Many people were involved from across the Met Office, with different teams working together to deliver a world-class service. Collaboration with NERC and the Universities of Reading and Hertfordshire worked well, while research aircraft and research communities provided us with observations and measurements of the volcanic ash plume. Working closely with the Icelandic Meteorological Service, we also had the full support of the European and global VAAC meteorological community throughout. We maintained close contact with aviation authorities who supported us in discussions with the wider aviation community.

Our advice and hard work has been recognised as exemplary at the highest levels of Government and by the agencies we have supported during the eruption. The Cabinet Office, the then Transport Secretary Lord Adonis and previous Business Secretary Peter Mandelson all praised and thanked the Met Office. So too have NATS, CAA and ICAO.

As a Volcanic Ash Advisory Centre we are very proud to provide advice to inform critical safety decisions. Our Volcanic Ash Advisory Centre is an operational service, on watch around the clock, so as the volcanic activity and weather changes we continue to provide timely advice.

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