15 meter subsidence in Bardarbunga caldera.(RUV).
About 250 million cubic meters of magma have flowed out of the chamber, belived to be under the Bardarbunga caldera, leading to a 15 meter subsidence of the caldera itself. These changes are clearly observed on the surface of the glacier covering the volcano, say scientists.
This was observed yesterday with radar measurements during a surveillance flight over Bardarbunga, and the Dyngjujokull outlet glacier to the north.
According to a status report issued today by the Icelandic Civil Protection Agency´s Scientific Advisory Board, those measurements show dramatic changes on the surface of the glacier. In the center, the Bardarbunga caldera, beneath, has subsided by up to 15 meters. This corresponds to a volume change of 0.25 cubic kilometres, or 250 million cubic meters. According to the report, the shape of the subsidence matches the elevation of the caldera floor under the 7-800 meter thick ice having lowered by that amount.
Never seen before
"This much subsidence has never before been measured in Iceland," says geophysicist Magnus Tumi Gudmundsson, a professor at University of Iceland´s Institute of Earth Sciences in an interview. "We believe that the strong earthquakes in Bardarbunga are signs of this subsidence. We see no signs of eruptions or geothermal activity in the caldera itself, but this subsidence does however not decrease the likelyhood that something could happen in Bardarbunga," says Gudmundsson. "One theory is that the bottom of the caldera kind of floats on the magma below, and helps to push it out towards the dike intrusion, which is feeding the eruption in Holuhraun."
Not since 1875
"We have not measured an event like this before in Iceland," says Gudmunsson. "We probably have to go back to the formation of the Öskjuvatn caldera in Askja, in 1875, when a large explosive eruption occurred there. That event was of course much larger, with subsidence of about 300 meters, but the current one in Bardarbunga is ongoing, and very significant."
Within 24 hours, lava flowing from the Holuhraun fissure will enter the one of the branches of Jokulsa a Fjollum glacial river, if the advancement rate remains the same, says volcanologist Thorvaldur Thordarson. Volcanic activity in Holuhraun has not diminished since yesterday.
"The lava field has been advancing towards the westernmost outlet of Jokulsa a Fjollum glacial river, with a rate of about 40 metres per hour," says Thordarson, who is observing the eruption in Holuhraun along with collagues from the University of Iceland´s Institute of Earth Sciences and the Icelandic Met Office.
"If the lava flow remains steady, we should see the lava entering the riverbed sometime in the afternoon tomorrow," he says. "I do not expect much explosive activity, but we should however see some violent magna/water interaction when the lava meets the glacial runoff."
The glacial river runs from the Dyngjujokull outlet glacier in several branches; the branch which the lava is heading for is one of the larger ones.
More here. And here at Volcano Discovery.
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