LONDON — A lingering volcanic ash plume forced extended no-fly restrictions over much of Europe on Saturday, as Icelandic scientists warned that volcanic activity had increased and showed no sign of abating — a portent of more travel chaos to come.

Scientists say that because the volcano is situated below a glacial ice cap, the magma is being cooled quickly, causing explosions and plumes of grit that can be catastrophic to plane engines if prevailing winds are right.

An expansive cloud of grit hovered over parts of western Europe on Saturday, triggering extended flight bans that stranded people around the globe. Continued volcanic activity could produce more plumes if the weather patterns stay the same.

Aviation experts say the volcanic plume has caused the worst travel disruption Europe — and the world — has ever seen.

"I've been flying for 40 years but I've never seen anything like this in Europe," said Swedish pilot Axel Alegren, after landing his flight from Kabul, Afghanistan, at Munich Airport; he had been due to land at Frankfurt but was diverted.