So, it appears that there is to be no Bárðarbunga ash cloud after all.
On Sunday, 24 August, the civil authorities in Iceland reduced the alert on the Bárðarbunga volcano from red (“Eruption is imminent or in progress – significant emission of ash into atmosphere likely”) to orange (“Volcano shows heightened or escalating unrest with increased potential of eruption”).
Some roads are open, although other roads in the immediate vicinity of the volcano remain closed, and there has been no disruption to air traffic.
But it’s a mistake to assume that this is the end of the matter.
There may be nothing visible on the webcams but Bárðarbunga, the beast beneath the Vatnajökull icecap, is unquestionably stirring and the regular updates from the Iceland meteorological office indicate that this episode is by no means over.
Was There a Bárðarbunga Eruption?
Vatnajökull is Iceland’s – and Europe’s – larger ice cap, hundreds of metres thick and covering not just Bárðarbunga but also three other volcanoes — Grímsvötn (the country’s most active), Kverkfjöll and Esjufjöll. That thickness of ice means that it isn’t possible for volcanologists to see for certain when the magma has reached the surface – which constitutes an eruption.
On 23 August, news media reported that a small eruption had started, although there was no physical evidence above the volcano. If indeed an eruption did occur, it was small and short-lived – not large enough to melt the overlying ice.
What’s Happening Now?
Even if there was no actual eruption, there has certainly been major movement of magma beneath the volcano. Recent days have seen an intensification of seismic activity: Up to the 25 August, there were around 1,200 tremors in the immediate vicinity of the volcano, most of them small but including several over magnitude 3.
In the early hours of 26 August, the largest tremor yet occurred – an M5.7 was the latest in a sequence of significant earthquakes (at least M4.5) which began on the 22 August and which included two other tremors of at least M5.0.
From the location and depths of these earthquakes, volcanologists are able to interpret what is happening below ground. The earthquake epicentres show migration of magma along a long narrow path to form an intrusion known as a dike.
The dike is currently more than 30 km in length and extends beyond the northern edge of the ice sheet, a direction in which it appears still to be propagating. It remains beneath the surface, however, so that the activity is not classed as an eruption.
Bárðarbunga’s Future: What Might Yet Happen?
So while all is quiet on the aviation front, the volcano rumbles on. As to what happens next, the authorities are uncertain. Volcanoes in general are unpredictable and Iceland’s seem to be particularly so.
According to the Iceland Meteorological Office (IMO) and the University of Iceland, Institute of Earth Sciences, there are a number of possible options, three of which appear more likely.
The first is a gradual slowing of magma movement with accompanying reduction in seismicity. Alternatively, the magma may reach the surface towards the end of the dike in which case an eruption would occur but, because it would be away from the ice cover (which enhances fragmentation of rock) the likelihood of a major ash cloud is low.
If the magma were to each the surface beneath the ice (the third of these more likely scenarios) the chance of a significant ash cloud, along with the near-certainty of major flooding as the ice melts, is increased.
What happens thereafter is also unclear, with some speculation that the extension of the dike might lead it into the fissure system associated wit another volcano further to the north, at Askja. And Askja is know for its major, explosive eruptions.
At the moment we can be certain only that volcanic activity at Bárðarbunga is not over. But whether it dies down quietly or progresses to a major and possibly disruptive eruption, remains to be seen.