Iceland raised its alert for airlines to the highest level after detecting a fissure eruption north of the Bardarbunga volcano.

The Icelandic Met Office increased the aviation alert over the eruption site to red and air traffic control has closed airspace up to 18,000 feet, the Civil Protection Agency said in a statement. A fissure eruption started in the northern part of Holuhraun lava, between Dyngjujokull Glacier and the Askja caldera, north of Vatnajokull glacier. The fissure is 300 meters (984 feet) long and no volcanic ash has been detected, it said.

“Seismic eruption tremor is low indicating effusive eruption without significant explosive activity,” the Civil Protection Agency said.

Iceland is on alert after the Bardarbunga volcano, one of its largest, started rumbling two weeks ago. Magma has spread to form a dike under the Dyngjujokull glacier, north of the volcano. Bardarbunga, which lies underneath Vatnajokull, Europe’s largest glacier, has been rocked by earthquakes that led to evacuations and road closures.

Airlines are on alert amid concern they may face a repeat of 2010 when the Eyjafjallajokull spewed a column of ash 9 kilometers (5.6 miles) into the air. That eruption shut airspace across western Europe for six days, forcing carriers to cancel more than 100,000 flights. Ash is a danger to jets because the glass-like particles can damage engines.

The magma underneath Vatnajokull had been migrating northwards in a dike which extends beyond the borders of the glacier. An eruption there “would most likely produce an effusive lava eruption with limited explosive, ash-producing activity,” the Met Office said earlier.

To contact the reporter on this story: Jonas Bergman in Oslo at jbergman@bloomberg.net. To contact the editors responsible for this story: Tasneem Hanfi Brogger at tbrogger@bloomberg.net. 

Photo Credit: This is a Saturday, April 17, 2010 file photo of the volcano in southern Iceland's Eyjafjallajokull glacier sends ash into the air . Air travel was crippled and millions of passengers were left stranded for days because the ash cloud was considered too dangerous to fly through. Brynjar Gauti / Associated Press