The main cloud of ash from an Icelandic volcano swept north of Scandinavia on Monday, disrupting flights over Greenland, while a second, smaller plume stretched south toward the coasts of Scotland and Ireland European officials warned that ash from the Grimsvotn volcano could affect the airspace over western Scotland and Ireland starting on Monday but it was not immediately clear how many flights, if any, would be disrupted.

The April 2010 eruption of another Icelandic volcano prompted aviation officials to close Europe’s airspace for five days out of fear that the ash could harm jet engines. Thousands of flights were grounded, airlines lost millions of dollars and millions of travellers were stranded, many sleeping on airport floors across northern Europe.

The impact of Grimsvotn was expected to be far smaller because the larger cloud was moving far north of most flight paths. Travellers and aviation officials were still watching nervously.

Danish air traffic officials said the main ash plume reached eastern Greenland, a semiautonomous Danish territory. Air Greenland said its Monday flight between the island’s main airport and Copenhagen was cancelled as a result.

Aviation officials in Norway said the cloud might also affect flights to and from the Arctic islands of Svalbard on Monday.

The European air traffic control agency said the smaller ash plume was not expected to move further east than the western coast of Scotland. It said in a Twitter feed that Scotland could be affected by Tuesday morning.

The ash plume was unlikely to affect President Barack Obama, who arrived in Ireland on Monday. Most trans-Atlantic flight paths run far south of the ash cloud’s projected path.

Iceland shut its main airport after Grimsvotn, about 200 km east of Reykjavik, erupted on Saturday. The airport remained closed on Monday morning, but officials hope to reopen it later in the day.

Eurocontrol’s models of ash concentration showed the main plume of ash at heights from 20,000 feet to 35,000 — the normal altitudes for passenger airliners — gradually extending northward from Iceland over the next two days. The cloud is predicted to arch its way north of Scandinavia and possibly touch the islands off the northern Russian coastline within the next two days.

Neither plume is projected to reach the European mainland.

“We are not in a position to say as yet as to whether there would be any disruption of European aviation,” said Brian Flynn, deputy head of operations. “In any event, we are very confident that if there were to be some disruption it would be at a much smaller scale than that we witnessed last year.”

Mr. Flynn said that about 50-60 of the approximately 500 daily flights between Europe and North America fly over the Arctic. But they too were not likely to be affected because the height of the ash cloud was several thousand feet below their normal cruising altitudes.

EU spokeswoman Helen Kearns noted that differences in the nature and size of the ash cloud meant that “we are far from where we were a year ago.”

Some airline chiefs complained that regulators had overreacted last year. But a study last month in the Proceedings of the National Academy of Sciences concluded the shutdown had been justified. It said the hard, sharp particles of volcanic ash blasted high into the air could have caused jet engines to fail and sandblasted aeroplane windows.

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