Dublin ? Iceland’s volcano has produced a 1,000-mile-wide ash cloud off the west coast of Ireland that will force western Irish airports to shut down again today, the Irish Aviation Authority announced.

The authority said shifting winds, currently coming from the north, had bundled recent days’ erupted ash into a massive cloud that is growing both in width and height by the hour.

Eurocontrol, which determines the air routes that airliners can use in and around Europe, says the ash accumulation is posing a new navigational obstacle — because the cloud is gradually climbing to 35,000 feet and into the typical cruising altitude of trans-Atlantic aircraft. Until recent days, the ash had remained below 20,000 feet.

The Irish Aviation Authority said the engine-wrecking ash would skirt Ireland’s western shores today, forcing a half-dozen airports to ground flights for much of the day. However, the airports in Dublin, Cork in the southwest and Waterford in the southeast will remain open.