15 meter subsidence in Bardarbunga caldera
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."
Cauldrons signs of small and short eruptions
During the surveillance flight yesterday, a shallow, wide depression was observed on the surface of Dyngjujokull, 10 kilometres from the glacier edge. Another depression, 6 km. from the margin of the glacier, in line with the dike intrusion, has deepened to about 35 metres. Scientists say likely that these cauldrons are signs of small and short-lived eruptions beneath the glacier.
See below the subsidence at the Bardarbunga caldera, as measured during the flight on Sept. 5. Picture from the Institute of Earth Sciences at Univ. of Iceland.
This story, by the Icelandic National Broadcasting Service (RUV), was updated on 6. September 2014, at 15.31 GMT. See the IMO´s status report here.