"Holuhraun eruption not big enough"

03.09.2014 - 15:06
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The magma intrusion feeding the Holuhraun eruption, north of Vatnajokull is getting wider, according to GPS observations. The intrusion has now formed a small rift valley due to increased pressure. This causes concern, says Pall Einarsson, professor of geophysics at the Univ. of Iceland.

Latest update at 16.07 GMT: Scientists and journalists near the Holuhraun eruption have been ordered to leave the area, due to a possible glacial flood from Dyngjujokull. Increased tremor has been detected. A subglacial eruption is considered possible, as a small rift valley (Graben) has formed and extends several kilometres to the south, beneath the glacier. (see below)

According to the conclusions of the latest Scientific Advisory Board of the Civil Protection Agency, the volume of the dike intrusion from Bardarbunga volcano towards the north has increased since the beginning of the current eruption in the Holuhraun lava field. This is taken to signify that more magma is entering the dike than is being erupted. 

This has resulted in a formation of a 0,5 - 1 kilometer wide depression, or rift valley, both north of Dyngjujokull outlet glacier, as well as beneath the glacier itself. Signs of the depression extend about 2 km. into the margin of the glacier. 

"Our GPS measurements of land deformation show that the intrusion has gotten wider," says Dr. Einarsson. "That´s why this Graben, or small rift valley has formed; the intrusion is simply getting more material than it is releasing throught the Holuhraun eruption, and this is a cause for concern, because it increases the likelyhood of something else happening."

The current eruption is an effusive lava eruption on barren land, with little or no explosive activity and no ash production. "This was the best possible scenario for an event of this nature," says Dr. Einarsson. "But the Holuhraun eruption is in effect not large enough, to act as a safety valve for the intrusion; it´s still gettting wider, and magma from it could breach the surface in other places. This causes concern, because other scenarios, among them a subglacial eruption, are possible."

The ongoing eruption in Holuhraun could progress southward under Dyngjujokull, which would lead to a subglacial volcanic activity. The Advisory Board considers this a distinct possibility in light of the GPS, radar and seismic observations. An eruption of that kind would lead to immediate flooding hazard on the floodplains north of Dyngjujokull: a large flood (jokulhlaup) would run down the Jokulsa a Fjollum glacial river towards the north east. 

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