A row of "cauldrons" about 1km wide has been revealed after ice above Iceland's rumbling Bardarbunga volcano melted away, experts have said.
The island's largest volcano system has been hit by more than a thousand tremors in the past 10 days raising fears of an eruption that could spell trouble for air travel.
The country's meteorological office said yesterday that the discovery could be caused by a sub-glacial eruption.
In 2010, an ash cloud from the Eyjafjallajokull volcano closed much of Europe's airspace for six days.
The Met Office said on its website it had not observed an increase in the level of tremors in connection with the discovery of the 4-6km long line of 10 to 15-metre deep "cauldrons".
Palmi Erlendsson, a geologist at the Met Office, said the warning code for possible volcanic disruption to the aviation industry remained orange, the second-highest level.
Red, the highest alert, indicates an eruption is imminent or underway, with a risk of emission of ash.
The Met Office said earlier on Wednesday that seismic activity in the area remained high after two earthquakes measuring more than 5.0 in magnitude hit the volcano overnight and another quake shook a nearby volcano. The night before saw a magnitude 5.7 quake - the biggest earthquake yet at Bardarbunga.
On Sunday, Iceland lowered its warning code to orange from red.