Monday, September 1, 2014

Slabby Pahoehoe lava - and lots of it

Flokkar: Volcano
Closeupn of the Holuhraun pahoehoe lava today (Picture courtesy of Armann Hoskuldsson/Univ. of Iceland Institute of Earth Sciences)
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.

The map below shows the area covered by the new lava in Holuhraun, based on infrared radar images from the Icelandic Coast Guard. At the time, the lava covered 4,5 square kilometres. Note how the northern edge of the lava covers the one of the riverbeds of Jokulsa a Fjollum glacial river.

This story, by the Icelandic National Broadcasting Service (RUV), was updated on September 1. 2014, at 20.14 GMT.

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