Updated Sunday, August 24 at 10:00 a.m.
A subglacial eruption is underway at Iceland's Bardarbunga volcano, where there have been thousands of earthquakes in the past week, Iceland's Meteorological Office said Saturday.
Seismic data suggests that volcanic lava is melting ice beneath the Vatnajokull glacier, said seismic vulcanologist Melissa Pfeffer, Reuters reports. It's unclear whether the eruption will break through the ice and shoot steam and ash into the atmosphere. The amount of ash produced in a larger eruption would depend on how thick the ice is, Pfeffer said, with thicker ice likely to cause a more explosive and ash-rich eruption.
On Sunday, Iceland lowered its aviation alert level to orange from red, saying there is no sign of an eruption at the Bardarbunga volcano. Iceland had said the day before that an eruption could cause "significant emission of ash into the atmosphere" and set its alert level for the volcano to the highest degree, red.
Ash clouds can cause a massive headache for international airlines, as aircraft have to be rerouted to avoid them. More than 100,000 flights were cancelled in 2010 after the eruption of Eyjafjallajokul, an Icelandic volcano that produced a cloud so large it obstructed air travel.