The continuous rumbling of an Icelandic volcano has led the country to issue a red alert to the world's airlines over fears of significant ash emissions.
The alert, the highest on the five-step scale of warning codes, was issued after a small eruption of lava occurred under a glacier in the Bardarbunga volcano region in the center of the island nation.
"It is believed that a small subglacial lava-eruption has begun under the Dyngjujokull glacier," the Icelandic Meteorological Office announced. "The aviation color code for the Bardarbunga volcano has been changed from orange to red."
Under a red alert, an imminent eruption with significant emissions of ash is considered possible.
There are concerns about a possible eruption similar to the 2010 eruption of the Eyjafjallajokull volcano, which spewed towering columns of ash that spread over European airspace, leading to the cancellation of thousands of airline flights and the stranding of millions of passengers around the world.
The shutdown of the continent's airspace lasted six days and created an economic loss of around $1.7 billion.
Seismologists have recorded numerous earthquakes under the Bardarbunga volcano over the last week, increasing concerns of a possible major event.
"There has been intense earthquake activity at the volcano," scientist Kristin Jonsdottir at the Met Office said. "We cannot exclude that this could be a big eruption."
The subglacial eruption of lava under Dyngjujokull is thought to be melting the overlying ice, which varies from 330 feet to 1,300 feet thick.
Vulcanologists said they could not predict if, or when, it might completely melt through the covering ice and possibly send plumes of ash and steam into the atmosphere.
How much ash might be produced if that happens would likely be a result of the thickness of the overlying ice, with a thicker ice cover possible crating a more violent and ash-laden eruption, seismic volcanologist Melissa Pfeffer said.
"Because of pressure from the glacier cap it is uncertain whether the eruption will stay sub-glacial or not," authorities said.
Aviation authorities have ordered a no-fly zone in the airspace immediately over the Bardarbunga region, although Iceland's airports have remained open.
Earlier in the week hikers and tourists were evacuated from the area when the biggest earthquake since 1996 rattled the region.
Because the Bardarbunga volcano is so remote, the surrounding area is, for the most part, uninhabited, with just campsites and hiking cabins that tourists, hikers and hunters use in summer months.
