A lava eruption at Iceland's Bardarbunga volcano saw officials briefly raise their aviation alert to red, then dropping it down to orange as it was determined the outburst of lava was not creating ash in the atmosphere.

In the eruption that started Sunday and continued through Monday, fountains of lava along a fissure threw molten material 150 feet into the air.

The fissure, running north and south on the volcano's Holuhraun lava field, opened up to almost a mile long, officials said.

There are signs the ice deep below the glacier that covers Bardarbunga and its surrounding area is being melted, Iceland's Meteorological Office says.

An ice cap from around 1,300 feet to 1,900 feet deep covers the volcano.

Swarms of earthquakes shaking the area around the volcano suggested lava was moving upward to the surface, but instead of erupting at the volcano it apparently followed an underground channel and spewed out of the surface south of Bardarbunga at Holuhraun, experts said.

The Holuhraun lava field is from an eruption that occurred in 1797.

It sits between Bardarbunga and the Askja volcano, which sits around 30 miles to the northeast of Bardarbunga.

The underground lava finally opened new cracks in the lava field and widened some older fractures, allowing lava to erupt to the surface, experts said.

"The new fissure eruption is [typical] for what you expect in a Hawaiian-style eruption, with a 'curtain of fire' made of several lava fountains that have been sending lava up to 50 meters in the air," Wired.com volcano expert Erik Klemetti posted on his blog.

Although the lava fountains are estimated to be producing more than 1,000 cubic meters of material per second, creating flows up to 26 feet thick, they are not producing large amounts of ash that could be a threat to aviation.

A concern is a repeat of the Eyjafjallajokull volcano eruption of 2010 that closed down European airspace for a week, disrupting thousands of flights and stranding millions of passengers.

The Iceland Scientific Advisory Board has said there are a number of possible outcomes for the current eruption, one of which could be a massive flood of lava or an violent, ash-producing event from Bardarbunga itself.

It is also possible the current outflow of lava could be reducing pressure with the volcano system and bring the eruption to a halt, they said.

The current activity of Bardarbunga began Aug. 16, when thousands of earthquakes began to be detected.