LONDON — When ash spews from an Icelandic volcano, 10 British scientists using laser sensors, satellite pictures and a specially equipped jet must tell the world where it's going.
The grit can block flight paths and shut airports, so the fate of millions of travelers, and billions in revenue, rides on the projections of the Volcanic Ash Advisory Center in Exeter, about 200 miles southwest of London.
Their British base — one of nine global volcanic ash advisory centers — has been on high alert since Iceland's Eyjafjallajokul volcano erupted in April, shutting down global travel for five days. It has caused sporadic disruption since then, closing London's Heathrow and Amsterdam's Schiphol Airport — two of Europe's busiest hubs — over the weekend.
One rattled airline executive — Ryanair's Michael O'Leary — has already attacked the "imaginary black plumes" predicted by the team's computing models, which he blames for prompting excessive caution and wrongly curtailing air traffic.
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"When you get a big volcanic event it gets very, very busy and very, very stressful," said Tony Hall, director of the National Oceanic and Atmospheric Administration's Alaska Volcanic Ash Advisory Center in Anchorage.
"These things can go on for weeks, or months — it can be a very stressful time," said Hall, who has had contact with his colleagues in London since Eyjafjallajokul's eruption.
Sarah Jackson, the British center's atmospheric dispersion group manager, said the scientific model used to predict the spread of ash — and other dangerous particles — was developed to track contamination from the 1986 Chernobyl nuclear reactor disaster.
The scientists themselves acknowledge their predictions can be sketchy, and warn that long-term forecasts are rarely correct. They caution that all estimates of ash movement can quickly become outdated as wind patterns change.