August 22, 2014

expert reaction to seismic activity in Bárðarbunga volcano

Further expert reaction to the detection of seismic activity in Bárðarbunga, a large sub-glacial volcano in Iceland.

Dr Matt Watson, Senior Lecturer in Natural Hazards at the University of Bristol, said:

Reasons to be cheerful

“It is an inevitable consequence of the impacts of the Ejyafjallajokull eruption that every time alert levels rise at Icelandic volcanoes more interest is paid to them. However, the response to the current ‘crisis’ is, at present, disproportional. The Icelandic Met Office’s statement on 21 August appears to have passed people by, despite its calming tone. Personally, statements like ‘there are no measurements that suggest an eruption is imminent’ and ‘previous intrusion events in Iceland have lasted for several days or weeks, often not resulting in an eruption’ appear unambiguous to me: whilst an eruption cannot be ruled out, it is not by any means a certainty at the moment.

“For impacts like those from Eyjafjallajokull to be seen again several other things also have to line up, even if there is an eruption. Firstly, the eruption could well not generate any ash – either by being more effusive, by only producing lava flows and small explosions, or by not punching through the 700 metre thick glacier. Both those types of eruption are relatively common in Iceland and, while they have the potential to cause severe local hazards, which is why evacuations have taken place, will not affect UK airspace. Secondly, even if ash is generated by a more explosive eruption there is no guarantee that it will impinge on UK airspace at all – the eruptions of Hekla (2000), Grimsvotn (2004, 2011) all generated significant clouds which did not have the same level of impact as Eyjafjallajokull at least partially thanks for favourable winds. Even if ash does reach UK airspace, scientists, engineers and airspace managers are better prepared.

“Finally, the UK and Icelandic governments have invested millions in trying to better understand volcanic ash clouds since 2010, through new monitoring instruments and better computer models, and different rules for flight are now in place. Bandarbunga has had larger eruptions in the recent geological past which could have profound impacts but, at the moment, there is absolutely nothing to suggest that is likely.”

Prof Bill McGuire, Professor Emeritus of Geophysical & Climate Hazards at University College London, said:

“If it eventually blows, Bardarbunga will be the third Icelandic volcano to erupt in the last four years. There is no guarantee, but even a moderate explosive eruption is likely to impact upon aviation in the region. Like Eyjafjallajokull (2010) and Grimsvotn (2011), Bardarbunga sits beneath the Vatnajokull Ice Cap, which is melting rapidly as a result of anthropogenic climate change. Around 12,000 years ago, at the end of the last ice age, the melting of the ice sheet that stretched across Iceland triggered a massive increase in volcanic activity. A volcano storm on such a scale is not expected this time, but modelling does point to a future increase in volcanic activity as the ice cap melts and reduces the load on the crust beneath; another hazardous aspect of climate change that few have considered.”

Detailed update from Prof Dave McGarvie:

Current situation at Bárðarbunga

Stable as at 10:30 GMT on 22 August 2014. No sign that an eruption is about to start.

Events on 21 and 22 August have raised anticipation (amongst some) that an eruption is imminent. Given the absence of escalation, these (i.e. summit earthquakes and slight subsidence) are best regarded as normal.

What’s happened so far?

“A magma filled fissure (dyke intrusion) some 25 km long has formed within the crust at 5-10 km depth. Sitting on top of this 25 km strip of crust is ice c.150-350 m thick. This dyke is on the NE flank of the main volcano, which is good news, as eruptions from beneath the main volcano itself have a higher probability of being powerful and explosive enough to generate sufficient fine ash to cause disruption to air traffic. There is no indication that the magma in the dyke is moving upwards, but if it did start moving upward this would heighten the possibility of an eruption.”

The NE flank zone – where magma is on the move

“Should an eruption occur from this flank dyke, the eruption style will be influenced by the presence or absence of ice above the eruption site, how much magma erupts, and the rate at which magma erupts. The likelihood of the magma currently in this dyke erupting to produce a substantial enough ash cloud to seriously affect international air travel is zero.

In summarising the flank dyke scenario, if this dyke grows at a similar (slow) rate to that of recent days, then it will either stall in the crust where it will cool and solidify, or it will gain access to the surface and erupt. A modest eruption is likely, with spectacular local explosions generated via interactions between magma and ice/water being observed unless the eruption is wholly covered by ice. Any subglacial eruption generates considerable amounts of meltwater as erupting magma can melt more than 10 times its own volume of ice (NB. variable – depends on conditions).”

Local flooding

“The authorities in Iceland have taken the precaution of evacuating everyone from an area where they would be cut off should a vital bridge be destroyed during a flood. The bridge crosses one of Iceland’s largest and most powerful rivers, and so authorities have alerted communities downstream of action they should take in the event of a flood. It should be noted that unlike the spectacular Amazon River sized flood following the subglacial Gjálp eruption of 1996, as there is no similar sub-ice topographic receptacle near the dyke intrusion in which to store meltwater till it escapes in one massive pulse, meltwater should escape rapidly and continuously from underneath the glacier which will help with managing and mitigating the effects of the flood.”

One worst-case scenario

“Although there are a number of ‘worst-case’ scenarios, one worth mentioning (because it is naturally on everyone’s radar because of the Eyjafjallajökull eruption) is a large and powerful explosive eruption from the main volcano itself that produces a sizeable ash cloud. I must stress that this is not even on the horizon at the moment – it’s somewhere well off the edge. Powerful and explosive eruptions from Iceland’s volcanoes are well documented, and there are many of them. Put simply, Icelandic magma contains enough gas to drive powerful explosive eruptions. The most recent  unequivocal evidence of this was the 20 km high eruption plume produced during the 2011 eruption of Grímsvötn. Evidence from ash layers in Iceland indicates that powerful explosive eruptions have occurred in the past from Bárðarbunga.

“The good news is that if a powerful and explosive eruption does happen, then the experience gained during the 2011 Grímsvötn eruption (which involved a relaxation of the rules for flying with volcanic ash in the atmosphere), would result in a carefully managed strategy to minimise the number of flight cancellations and diversions. Despite erupting twice as much  ash as Eyjafjallajökull 2010, flight cancellations during the Grímsvötn 2011 eruption were less than 1% of the number of flights cancelled during the Eyjafjallajökull 2010 eruption. An important factor in reducing the number of flight cancellations in 2011 was a wind direction that was favourable to UK and western Europe.

“In summarising the large and explosive eruption scenario, there are NO indications that this is about to happen. Even if it does happen we would not get a repeat of the disruption caused by the 2010 Eyjafjallajökull eruption, simply because if this same eruption happened tomorrow there would be far fewer flight cancellations (due to revised flight rules, better information on ash concentrations, and experience gained during 2010 and 2011).”

Concluding note

“Finally, volcanoes are complex natural systems, and when we know so little about a volcano such as Bárðarbunga because it hasn’t erupted in the modern era and thus we have no prior understanding of how it behaves when it stirs, it’s difficult to anticipate what might happen. If this current event does not last long then it will be a volcanic speed dating experience. If it lasts longer, then we may get to know Bárðarbunga’s volcanic personality a little better.”

Declared interests

Dr Watson is funded by the Natural Environment Research Council to work on volcanic ash clouds and I am a member of both the goverment’s VAORG (Volcanic Ash Observations Review Group) and the VAAG (Volcanic Ash Advisory Group) and was a member of the Scientific Advisory Group for Emergencies (SAGE).