Airports across Europe were thrown into chaos today after ash drifting from Iceland's erupting volcano caused several countries to close their airspace, creating delays that that one aviation expert said could linger and strand passengers for weeks.
"This is most significant air traffic control event since Sept. 11 and certainly the most significant that's ever hit all of Europe at one time," said Brent Bowen, the head of Purdue University's aviation technology department.
The potentially dangerous cloud of ash and rock spewed up by the volcano more than 1,000 miles away caused the U.K., Norway, Ireland and Sweden to enforce a nationwide no fly policy, stranding thousands of travelers .
France has also announced some airport closures, and Holland, Belgium, Denmark and Germany are expected to follow suit.
"So we're talking about almost one quarter of the entire European area is closed to aircraft at the moment," Brian Flyn of EuroControl, a European aviation authority, told reporters.
It is not yet clear when the flying restrictions will be lifted, but the Eyjafjallajokull volcano is still erupting and could continue spewing ash into the atmosphere for weeks.
"It is likely that the production of ash will continue at a comparable level for some days or weeks," said Einar Kjartansson, a geophysicist at the Icelandic Meteorological Office. "But where it disrupts travel, that depends on the weather."
As the day wore on some travelers' nerves were fraying.
"It's almost like a joke: Volcano ash? It's almost like, what's the punch line?" said Erin Wilson, an advertising executive stranded at London's Heathrow Airport who was hoping to return to Chicago to celebrate her birthday.
But Bowen said relief is not necessarily on the way. Volcano-related delays that weren't predicted yesterday are now "snowballing seemingly out of control across Europe," he said.
Planes from the U.S., Asia, Africa and elsewhere in Europe are being turned around mid-flight. And British media outlets reported that Eurostar trains between London and Paris and Brussels are sold out.
"You can't get on a train out of England through the Chunnel now to mainland Europe. The ferries are filling up. People are trying to go over to Paris before it gets shut down. Amsterdam is already being affected. Copenhagen is being affected," Bowen said. "This is just having a continuous ripple effect."
The United Kingdom and Scandinavia were the first hit by the vast cloud of ash this morning, and it is now heading for western Europe and could reach Russia early Friday morning. While the cloud itself is not harmful, residents of the northern Scottish island of Shetland complained of a strong smell of sulphur in the air.
U.K. controlled airspace is closed until 7 a.m. Friday, according to a statement on the NATS (National Air Traffic Services) Web site. The situation remains fluid, and the airspace could be closed for longer, Deborah Seymour, a NATS spokeswoman told ABC News.