Experts at Discover The World and Ari Trausti Guðmundsson
19/10/2014
The lava outpouring from the short fissure at Holuhraun has now remained steady for weeks. Three interconnected vents (300-400 m long) are what remains of the original 1.9-km-long, once active fissure. The height of the crater hill around the vents exceeds 100 m, taking the form of a lava shield (also known as a shield volcano) - see the image from the Geoscience institute by geoscientist Morten Riishuus. The big regional dyke is still going strong and the eruption could remain active for many years or die down within a few weeks or months. Further breaching of the surface along the dyke leading to a subglacial eruption in the Dyngjujökull outlet glacier is still possible.
The lava flow now has an area of roughly 60km² and a volume of approximately 800 million cubic metres (0.8 cu. km). The Hekla lava flow is somewhat similar in size but was generated in 13 months. Therefore, the highlands will soon become the largest lava flow occurring within such a short interval in Iceland - since the late 18th century. New trace elements and isotope analysis are said to indicate a magma source at a depth of at least 15 km.
The included map is from the Geoscience Institute and the Coast Guard (October 17th).
The Bárðarbunga central volcano continues to shudder, with dozens of earthquakes every day. On October 18th, two earthquakes were recorded with a magnitude 4.7 and 5.0, with a further two on the 19th with a magnitude of 5.2 and 4.5. Currently, the depression in the caldera ice dome is over 35 m deep. The main earthquake location is at the northern rim of the caldera or at the volcano flank in the north. GPS-readings over a period of a few days show both dilation and/or doming of the volcano.
Reverse faulting has been detected from some earthquakes. Another earthquake location is at the south-eastern rim. Practically no earthquakes originate in the caldera floor. With time, a simple model of caldera floor subsidence and a direct link between a Bárðarbunga magma chamber and the big dyke seems more and more unlikely.
I have stressed before, as have prof. Águst Guðmundsson (Royal Holloway – University of London) and prof. Þorvaldur Þórðarson (University of Iceland) in talks and in an article (in the Bulletin of Volcanology), that a large magma reservoir, is the possible site of the magma influx into the dyke.
Independently of this, the roots and the non-verified (but naturally alleged), shallow magma chamber remains beneath the caldera, a theory consistent with chemical signals in the magma. The magma from a deeper reservoir is probably being injected into the volcano, even as ring dykes. It remains to be seen if this hypothesis is correct but many indications are present.
There is no way to predict what will happen at Bárðarbunga; small or large eruptions may occur, and similar tectonic movements or a sudden caldera collapse could become the result of the processes in the volcano.
The many scenarios presented by the Civil Protection and its Scientific council are still valid.
The nearby Tungnafellsjökull central volcano (with a caldera), west of Bárðarbunga, has been the site of over 150 earthquakes (with the majority of them with magnitude less than 3.0). Most of them have loci at shallow depth but some originate much deeper, at up to 20 km plus. This probably indicates an influx of magma but the GPS-readings do not support that, so far. Magma intrusions in a volcano do not automatically lead to eruptions.
It is interesting to note that the Kverkfjöll central volcano (with two calderas), the next neighbour of Bárðarbunga in the east is showing very little tectonic activity. Only a few dozen quakes have originated there and the same story can be said about the very active Grímsvötn central volcano southeast of Bárðarbunga. It is, at any rate, important to follow the development of all nearby volcanoes with care.
More elaborate seismic and GPS monitoring would help in revealing the processes at hand below the earth´s surface in this very active part of Iceland.
Map base: The Geodetic Survey.
Dates: 28th of Sept. and 15th of Oct.
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