Meltwater is flooding from the Grimsvotn glacial lake in Iceland and could signal the volcano underneath is about to erupt, a spokeswoman at the Icelandic Civil Protection Department said today.
In April, clouds of ash from an eruption under the Eyjafjallajokull glacier grounded flights across Europe for a week, causing billions of dollars in losses for airlines and other industries.
Water now pouring from Iceland's biggest glacier, Vatnajokull, which sits on top of a number of volcanic hotspots, could be a sign of fresh geological activity, Civil Protection Department spokeswoman Gudrun Johannesdottir said.
Eyjafjallajokull is about 100km southeast of Vatnajokull.
"We have to check if there will be an eruption," Ms Johannesdottir said. "Sometimes it initiates an eruption when a glacial outburst flood starts, but not every the time. So we are monitoring the situation closely."
The last eruption at Grimsvotn, in 2004, caused short-term disruptions to airline traffic into Iceland.