When we sing Auld Lang Syne and raise a glass to 2015 on Wednesday, the eruption of Bárðarbunga volcanic system, Iceland, will have been going for four straight months. In that time, the eruption has covered over 80 km2 (1.3 Manhattan islands) of sandy outwash plain at Holuhraun, to the north of the Vatnajökull glacier, with a jumble of jagged black basaltic rock ranging in thickness from the height of a car to more than the height of a house.
By all measures, the eruption is slowing. The seismic energy released by earthquakes in the dyke (underground crack) that carries the magma to the surface is one ten-thousandth of what it was as the dyke was forming. The subsidence of Bárðarbunga caldera, probably caused by draining of magma away from the volcano and out to feed the lava, dropped from over 80 cm per day to less than 25 cm per day; the accompanying magnitude 5 or larger earthquakes there, which used to happen every day, can now be a week apart or more. Satellite measurements of heat flux show a decline from over 20 gigawatts in early September (to put this amount of energy in context, the average UK electricity demand in 2012 was 36 gigawatts), to fewer than 5 gigawatts by the end of November.
This doesn’t mean that the eruption will stop soon. Like the weakening spray from an aerosol can, the eruption rate declines exponentially. The lower the flow, the more slowly it declines. SSKKKOOOOSSSSSSHHHHH ..ssshhhssshhhssshhhssshhhssss ..sssssssss..ssssss ….sssss……sssss……sss! Icelandic scientists have predicted that it has ‘at least some months’ more to go. From initial rates of up to 1,000 m3/s, an average of 200 m3/s through September, the eruption rate in November was less than 100 m3/s. This still corresponds to a healthy river of lava; the mean flow of the Thames through London is around 60 m3/s. Effusion rates of less than 5 m3/s are typical of recent Hawaiian eruptions.
An interesting development is that the lava is now flowing through covered tubes. These are better insulated than open channels so the lava cools much more slowly (as little as 1°C per kilometre) and can travel further. I’m personally hoping that this means that the lava will extend further to the northeast, reaching Vaðalda and blocking the Svartá river that flows into Jökulsá á Fjöllum from the northwest (see map) to create a new lake.
Holuhraun Fieldwork Videos
The main purpose of this post is to share some videos that I recorded when I joined University of Iceland scientists studying the eruption in September. You can read about the trip and see photos in my Fieldwork at the Holuhraun post.
Fire fountains at the vent
This was filmed over a kilometre from the vent. The craters are over 50 m high, the fire fountains are 50 m above this. The lava sprays in the air powered by expanding gases, just like a Hogmanay champagne bottle. A few days after I filmed this, the craters filled with lava to become a churning lake of molten rock. There is spectacular drone footage of this on YouTube. A river of lava drains from the craters to feed the flow field. At the end of the clip you can see Suðri, a crater that was active at the beginning of the eruption.
In the foreground is the pale grey sand plains that extend north of the Vatnajökull glacier. All the darker material on top was produced by the eruption. The clouds above are mainly steam (+ sulphur dioxide, carbon dioxide, hydrogen chloride and other pollutants). The gas and the magma can easily separate, so there is no ash. This is why the eruption hasn’t affected aircraft or had nearly as much news coverage as it deserves for being Iceland’s largest eruption since 1783.
A ‘breakout’ on the lava flow
Every that you initially see here is lava. The coarse blocks formed as part of an early flow lobe that remains molten inside. Hot lava pours from a ‘breakout’ to form a smaller flow at the edge. The orange-yellow material has a temperature of over 800°C. Even standing 5 m away, the heat was intense. As the surface cools it solidifies to form a crust, like wax from a candle. This is broken by movement of the hot lava beneath and carried on the surface of the flow.
Sampling the lava
A University of Iceland scientist samples the active lava flow. The steel shovel has a melting point of around 1400°C so it doesn’t melt. Also, lava (rock) is a poor conductor of heat. The sample is dropped into a large metal saucepan and quenched by pouring water into it. Analysis of such samples has confirmed that the magma originates in Bárðarbunga volcanic system and estimated that it was last stored at a depth of 9-20 km beneath the surface. Future analysis of such samples will help explain why the eruption has produced so much sulphur dioxide pollution.
GPS mapping of the flow outline
One task at the eruption site was driving around the edge of the lava flow recording the tracks by GPS in order to map the extent of the flow. At the start of the eruption, the flow front advanced by hundreds of meters per day and the lava buried an area the size of a football pitch (soccer field) every 7 minutes. Now, the area of the flow field only increases slowly. This is partly because the eruption rate has declined and partly because much of the new lava flows over or through the older material, contributing to the thickness of the flow instead.
Off road driving is illegal in Iceland, but the scientists obtained special permission to survey the lava. The tracks that you can see have since been buried beneath the extending flow. The most recent maps of the flow field are made from radar data collected by satellites, which has the advantages that it can cover the whole flow field instantaneously and that it works at night or in clouds. The downside is that it can be many days between measurements so it can miss rapid changes.
I like this video because it conveys the scale of the lava flow. You can see its height and the fridge-sized blocks on the original flow lobe. Reactions with the atmosphere have turned the surface pale. You can see all the fresh breakouts, dark and slabby, that still glow red inside in places. You can see how the wall of lava extends on and on into the distance. The NW margin of the flow was over 16 km long and it took 45 minutes to drive its full length.
Four months ago, this whole area was a flat and barren sandy plain. How will it look when we are toasting the arrival of 2016?
Happy New Year!
As always, the best information on the eruption comes from the Icelandic scientists. Check out the Icelandic Met Office and the Institute of Earth Sciences pages for frequent updates from the Bárðarbunga Science Board. There are cool fieldwork photos on the Institute of Earth Sciences Facebook page.