The London VAAC is one of nine centres around the world that are responsible for advising international aviation of the location and movement of clouds of volcanic ash.

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The VAACs are part of an international system set up by the International Civil Aviation Organization (ICAO) called the International Airways Volcano Watch (IAVW).

The IAVW comprises observations of volcanic ash from volcano observatories and other organisations, satellites and aircraft in flight, the issue of warnings in the form of NOTAM and SIGMET messages and, since the mid 1990s, the issue of volcanic ash advisory messages from the VAACs identifying areas of volcanic ash and their predicted movement.

The London VAAC is responsible for monitoring and forecasting the movement of volcanic ash over the United Kingdom, Iceland and the north-eastern part of the North Atlantic Ocean.

Although this is a relatively small area, it covers some of the busiest airways in the world. A volcanic eruption on Iceland can quickly affect a large area of airspace, as strong winds spread the ash downwind from the volcano. Air traffic control organisations need to react quickly to the forecasts issued by the VAAC so that aircraft can be diverted onto alternative safe tracks.

The last major eruption of Hekla, Iceland, started on 26 February 2000. Photo courtesy of Sigurjón Sindrason (sigurjon@ok.is)

During a volcanic eruption on Iceland, the London VAAC liaises closely with the Icelandic met. service, which itself is in close contact with the Nordic Volcano Institute. The London VAAC has access to the latest observational data as they emerge. This may be data from:

• seismic surveys undertaken by the Nordic Institute;
• eye witness accounts of current plume behaviour or volcanic activity;
• analysis of satellite pictures.

Often, visual observations originate from aircraft in the vicinity.

More about volcanic ash forecasting and the satellite detection of volcanic ash