Iceland's meteorology office has said that Iceland's volcano roared back to life Thursday, shooting a plume of ash 4 1/2 miles high and appearing ready to blow again.

The Icelandic Meteorological Office and the Institute of Earth Sciences at the University of Iceland said in a statement, "The eruption has changed back to an explosive eruption, lava has stopped flowing and most of the magma gets scattered due to explosions in the crater."

The statement further said, "The ash plume rises high above the crater (2 1/2 to 4 1/2 miles) and considerable ash fall can be expected in wind direction. No signs of the eruption ending soon."

The statement came as authorities started rerouting trans-Atlantic flights and the Irish Aviation Authority announced six western Irish airports would be shut until at least 1 p. m. local time Friday due to a "massive ash cloud" 1,000 miles long and 700 miles wide drifting into the country's airspace.

The agency also said that the affected airports are Shannon, Donegal, Sligo, Ireland West (Knock), Galway and Kerry.

British and Irish authorities had just reopened the skies to planes several hours earlier after shutting airports in Scotland, Ireland and Northern Ireland Tuesday and Wednesday.

It was further reported that ash from Iceland's Eyjafjallajokull volcano, located beneath a glacier in southern Iceland, first forced authorities across Europe to ground an estimated 100,000 flights and 10 million passengers April
14-20 in the worst peacetime air travel disruption in history.

Its passenger numbers dropped by almost a quarter last month as a result of the volcano-related flight bans, which forced the carrier to ground its fleet for the first time in its history, British Airways said on Thursday. (With Inputs from Agencies)