Four cauldrons (also known as lows or calderas) have formed in Vatnajökull glacier east-southeast of Bárðarbunga volcano. They are 10-15 meters (33-49 feet) deep and form a 4-6 km (2-3 mile) long line.
This was observed by the Icelandic Coast Guard's TF-SIF flight over the area yesterday.
In addition, fractures have formed north of Dyngjujökull outlet glacier, in the Holuhraun lava field, above the magma intrusion dike.
Specialists at the Icelandic Met Office are now saying that there is no doubt that the cauldrons are a visible sign of ice melting. Specialist Sigurlaug Hjaltadóttir told RÚV that this could be due to an eruption or very great geothermal activity.
Sigurlaug said that an eruption could possibly have started in the last few days, hence causing the icecap to melt. It is estimated that the glacier is 400-600 meters (1,300-2,000 feet) thick in that location.
The big mystery is where the water might flow. A huge flood in Jökulsá á Fjöllum glacial river has been feared, but there is no indication that the water level has increased there. Another possibility is that the water has flooded into Grímsvötn glacial lakes, but then the icecap by the lakes should have risen. Measurements are not available on that yet.
Should melt water have flowed into Grímsvötn it would be collected there before a flood would start to the southwest of Vatnajökull glacier. This happened in the river Gjálp in 1996 when a bridge was swept away, hence closing the Iceland Ring Road.
Víðir Reynisson, director of the Civil Protection Department, told RÚV that the cauldrons are located further to the south than expected. Hence, it is difficult to predict where a possible flood would occur, to the north or south of Vatnajökull.
Víðir said that the weather had made it difficult to make observations during a flight this afternoon, yet stressing that it's difficult to explain the cauldrons by anything else than considerable heat below the ice.
“We might not have the results for certain until tomorrow morning when we can fly over the glacier again,” Víðir said. A new observation flight is scheduled at dawn.
When asked whether an eruption had started Víðir replied:
“It's difficult to say, but if these changes are sudden it's hard to explain them by other reasons than an eruption. Conditions were difficult this evening, but [the cauldrons] were not there on Saturday. What scientists are looking into is that a lot of water should have accumulated when the ice is melting. We are going over the situation.”
Víðir added that the sensors of the Icelandic Met Office indicate great seismic activity.