Bardarbunga volcano slowly sinking.

Bardarbunga volcano slowly sinking.(RUV).

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."

The lava flowing from the fissure north of Vatnajokull is classified as Pahoehoe lava - a type of basaltic lava that is very common in eruptions in Iceland. The term comes from Hawaii and means smooth unbroken lava. The lava at Holuhraun is so thin however, that it forms slabs on the surface.

According to dr. Armann Hoskuldsson, volcanologist at Univ. of Iceland´s Institute of Earth Sciences, who has been observing the eruption from the start, the lava is about 1 metre thick when it exits the fissure. "But at the edges of the lava streams, the lava has reached a thickness of 7-8 metres when the edge collapes and stumbles forward."

The lava is hot - really hot. "About 1200 degrees Celcius at the center of the fissure, but cools down rather rapidly," says dr. Hoskuldsson. "Then the surface layer solidifies and creates a sort of slabs that move with the stream. The lava is so thin and moves rather fast, so that the slabs keep breaking up - which is why this particular form is termed Slabby Pahoehoe."

According to a status report from the Institute of Earth Sciences today, the current eruption is believed to have produced until now about 20-30 million cubic meters of lava at a rate of 100 cubic metres per second. Considerable amount of sulphuric gas rises from the lava, making it essential for scientists in the area to have gas detectors and gas masks available.More info here at Volcano Discovery.