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Bardarbunga slowly sinking

01.09.2014 - 15:43
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Strong earthquakes at the Bardarbunga in Vatnajokull are signs that the magma chamber beneath is partly subsiding due to the magma streaming out, says Pall Einarsson professor of geophysics. Since August 16th, 559 earthquakes have been detected; twelve of them Magnitude 5 and over.

During the entire episode of the seismic and volcanic activity in northwestern Vatnajokull, Bardarbunga and north of the glacier, the strongest earthquakes have been detected along rim of the caldera in Bardarbunga, a subglacial volcano.

A 5.3 Magnitude event was detected there shortly before noon today; since August 16, some 559 earthquakes have been detected around the caldera. 26 of them have been larger than Magnitude 4; 12 have exceeded Magnitude 5. 

"These strong earthquakes are the consequence of magna streaming out of the chamber beneath the caldera", says Pall Einarsson, professor of geophysics at University of Iceland´s Institute of Earth Sciences. "The magma chamber is clearly subsiding, thus reacting to the considerable amount of magma that has been streaming out towards the dike intrusion," says Einarsson. "Analysis of these earthquakes supports this conclusion, as well as nearby GPS measurements of land deformation. We call this pressure changes in the roof of the magma chamber; in effect, the top of the volcano is sinking ever so slightly." 

Before the current episode of seismic activity, 18 years had passed since a Magnitude 5 or larger earthquake had been detected in Bardarbunga. Thus far, the strongest one was M5,7 on August 26th. That earthquake was the strongest in Iceland since May 29th. 2008, when a doublet earthquake with a combined magnitude of 6,3 struck near the town of Selfoss in southern Iceland, in what geologists call the South Iceland Seismic Zone. There, two transform faults move horizontally against each other. 

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This story, by the Icelandic National Broadcasting Service (RUV), was updated on September 1. 2014, at 14:47 GMT.

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