Iceland today raised an aviation alert level to reflect growing concern over underground rumblings at its Bardarbunga volcano in the central part of the island nation.
A sub-glacial eruption caused Icelandic authorities to raise the aviation alert level to red, indicating "significant emission of ash into the atmosphere," The Associated Press reports.
The AP notes: "Seismic data indicated that lava from the volcano was melting ice beneath the Vatnajokull glacier, Iceland's largest, Met Office vulcanologist Melissa Pfeffer said."
"She said it was not clear when, or if, the eruption would melt through the ice — which is between 100 to 400 meters (330 to 1,300 feet) thick — and send steam and ash into the air."
Iceland, located along a seismically and volcanically active mid-ocean ridge, saw the eruption of another volcano, Eyjafjallajokul, in 2010. The eruption four years ago spewed an ash cloud into the sky that wreaked havoc on international air travel in the region for a week, cancelling more than 100,000 flights to and from Europe.
And, in 2011, Iceland's Grimsvotn volcano erupted, briefly threatening a repeat of Eyjafjallajokul.