REYKJAVIK, Aug 28 (Reuters) - Ice over Iceland's rumbling Bardarbunga volcano has melted to reveal a row of 1-km wide "cauldrons", possibly due to a sub-glacial eruption, the country's meteorological office said late on Wednesday.
Rumblings at Iceland's largest volcano system for about a week have raised worries of an eruption that could spell trouble for air travel. 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 to 6-km 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. (Reporting by Robert Robertsson, additional reporting by Anna Ringstrom in Stockholm; Editing by Jeremy Laurence)