The Holuhraun lava in late October (Photo: Egills Aðalsteinsson, Iceland Magazine)
The first sign of activity was an earthquake swarm at the Bárðarbunga central volcano that began on August 16 (about a week after I left Iceland, having taught my annual volcanology field camp there). There was concern that an eruption might occur under the Vatnajokull icecap which would likely be explosive, potentially disrupting trans-Atlantic air traffic. However, a dike, manifested by a propagating linear belt of seismicity, fed magma laterally in the subsurface ever farther northeast from Bárðarbunga until the magma reached the surface on August 29 at Holuhraun, site of a late 18th century crater row and lava field. The lateral drainage of magma from under Bárðarbunga is evident from the dramatic subsidence of the caldera at Bárðarbunga, 56 m as of December 19. This kind of lateral dike propagation has been demonstrated to be significant in other historic and prehistoric eruptions in Iceland.
Seismicity at Bárðarbunga and propagating along the dike that fed the Holuhraun eruption (Iceland Met Office)
This basaltic lava eruption is the largest since Laki 1783-1784. The Laki eruption emitted voluminous volcanic gases which resulted in famine in Iceland (fluorine killing livestock) killing ~25% of the population and volcanic fogs (sulfur dioxide) in Europe that killed 10,000's. Sulfur dioxide emissions during the current eruption have been substantial, resulting in visible atmospheric effects and warnings in downwind parts of Iceland. However, the volcanic gas emissions have been lower than Laki, sulfur dioxide emissions are estimated to be 7-20% of the Laki emission rates.
At the margin of the Holuhraun lava flow October 2014 (Photo: Karolina Michalczewska, Univ. of Iceland Twitter)
Will the eruption still be going on in summer 2015, for the next offering of the Iceland Volcanology Field Camp? Only time will tell, and even if the eruption it is unlikely that there will be ready access to the site (currently there is a travel ban in the area). But we can dream.
Extent of the Holuhraun lava as of December 28, 2014 (Iceland Met Office)