PARIS — As an increasingly large part of European airspace was shut down for the third day on Saturday and the towering fountain of ash from an Icelandic volcano showed no signs of letting up, questions about the long-term impact of the eruption were being raised in a continent trying to recover from recession.

With airports closed from Ireland to Ukraine, officials expressed hope that some air travel could resume Sunday, or possibly Monday, but the workings of Iceland’s volcano were too mysterious to make rational predictions about it. Winds pushed the particulate ash farther south and east on Saturday, as far as northern Italy.

About 17,000 flights were canceled Saturday, and travelers scrambled to find accommodation or land routes home during what is already the worst disruption in international air travel since the attacks of Sept. 11, 2001, when all air travel in and out of the United States was halted for three days.

While the closing of the airways has already laid waste to the immediate plans and business of industry, the arts and world leaders, the possibility that it could drag on for days, if not weeks, is raising concerns about the longer term consequences for public health, military operations and the world economy.