Fieldwork at the Holuhraun

Posted on September 25, 2014 by John A. Stevenson

Last week I joined the team from the Institute of Earth Sciences at the University of Iceland who are on the ground monitoring the eruption of the Holuhraun. This post is a description of the eruption and the monitoring work taking place. It is based on tweets sent out when I was away.

Surveying the fire fountains

The eruption is a fissure eruption, which began with a curtain of fire as magma sprayed from the ground. By the time I arrived the activity had focussed onto a few main vents. The main vent is named Baugur and has built a cone about 50 m tall. Using surveying equipment gives accurate measurements of the heights of the cones and the fire fountains.

The vents are spectacular once night falls. When bursts of lava fountain into the air they light up the whole surroundings and even from 1 km away you can feel the heat on your face.

Describing the points that we were surveying is easiest with a sketch. It was a geologist’s dream to annotate, too.

Infrared cameras measure the temperatures of distant objects. The fire fountains were over 850°C. This image uses a temperature scale that shows hotter temperatures as brighter. In real life, you can estimate rock temperatures from the colour, too. Red hot = over 600°C, orange = over 800°C.

The hot air above the vent rises quickly, and it carries the smallest, lightest particles with it. These scoria (basaltic pumice) fall to the ground downwind. Sampling them is useful because we know exactly when they formed. Analysing their composition will give a value for that particular time.

Larger particles fall close to the vent and build up the craters. They are often still molten when they land and the deposits are called spatter. The current eruption is referred to as the Holuhraun eruption because it is erupting onto a lava field, originally formed during eruptions in 1797 and 1862, which is called the Holuhraun.  The old cones are still present, and the new eruption has even reoccupied some of them.

Mapping the lava flows

The Holuhraun lava flow is growing amazingly quickly. It’s just three weeks old, but it’s as thick as a 2-storey house is high and to run around it would be about as far as a marathon. Another job is mapping the outline by driving alongside it in a 4×4. GPS data are compared to see the changes each day.

Unfortunately, it is now only possible to do this on the NW side.  The route around the flow front in the NE is blocked by the Jökulsá á Fjöllum river and there are deep cracks in the ground at the SW end near the vents.  This is a big disadvantage: when it seemed to us that the lava flow rate was slowing, it was actually growing more to the east.

Measurements from aircraft or satellites can be used to record growth on the SE side of the flow. These are very useful, but are sometimes limited by weather, resolution or the timing of satellites passing overhead.  Measurements from both methods are combined and published on the Institute of Earth Sciences website.

The front of the lava has stopped advancing since reaching the river where it is cooled by the water. Instead, the flow prefers grow sideways, with lava breaking out from the molten centre of the flow and spreading across the flat plains.

Study of the advancing lava is concentrated on the breakouts. Time lapse video shows how they move. Samples can reveal how the lava has crystallised and lost gas in the interior of the flow. Thermal images record variations in surface temperature. The latter are important because cooling of the lava can limit how far the flow can grow; the hotter the surface, the faster it is losing heat.

Flowing lava is molten rock, so, unsurprisingly, has a similar density to solidified rock. This means that chunks of solidified lava can float in the flow, especially if they have lots of air gaps and most of their bulk is submerged, like an iceberg. A great example of this are balls of spatter over 2 m in diameter that can be found kilometres downstream from the vent. These were originally part of the cone, but must have collapsed and been swept away by the flow.

Sulphur dioxide pollution

A striking feature of the Holuhraun eruption is the amount of gas being released, in particular sulphur dioxide (SO2). The plume is so clear that it was visible from the aeroplane window as I flew over the south coast of Iceland on the way from Edinburgh. It is also prominent on the drive south to the eruption from Mývatn.

Closer in, it rises from the fissure like smoke. Written Icelandic records refer to past eruptions as ‘fires’. It is easy to see why. Back in the 80’s, I remember when farmers in Scotland used to burn stubble and unwanted straw in their fields. Lines of orange flame ran hundreds of metres across the ground, shimmering in the heat haze, while blue curtains of smoke rose above. It turns out that a fissure eruption looks just the same, but on a much bigger scale.

The way the gas dominated the whole experience got me wondering why I hadn’t paid it much attention before.

In fact, it is a really serious concern at the eruption site. The area is closed off to the public, and those with permits to be there have to bring safety equipment.

The concentrations reach dangerous levels near the plume or near breakouts. Many more dead birds have been found in the past week since I got back. Even hundreds of kilometres away across Iceland, people are advised to stay indoors if the gas is blowing their way and the Icelandic Met Office has begun producing forecasts of where the concentration will be highest.

If you don’t feel 100%, it isn’t always easy to identify the cause.

The gas plume had a strong effect on the sun, cutting down the brightness and turing it red/pink. It makes you think that descriptions of ‘blood red’ suns during the devastating 1783 Laki fissure eruption were not exaggerations.

The effect was particularly weird in the middle of the day, when the sun should be high and bright.

Gas-induced tourism

When the gas plume went directly over the mountain hut where we were staying at Askja, about 25 km north of the eruption site, we decided to retreat to Mývatn. This was also an opportunity for much needed vehicle repairs and maintenance. It was also a chance to take in the local geology.  In particular, Hverfell is a tuff cone formed by the explosive interaction of a basaltic fissure eruption with groundwater or a lake.

I was especially pleased to see the Hekla 3 and Hekla 4 tephra layers, as my current research project is reconstructing these two huge ancient eruptions.  This ash had travelled over 200 km to be deposited at Mývatn.

Sources of good information

The best source of information on the ongoing Holuhraun eruption and unrest at Bárðarbunga is the Icelandic Met Office website. Click the links on the top banner for access to the latest monitoring information. I posted other useful links in my last post.

The following are some recent additions.

Acknowledgement

I’d like to thank the Royal Society of Edinburgh and Marie Curie Actions for providing funding for this trip. I’d also like to thank the University of Iceland for having me and for making sure that I got home in time to see Scotland decide its future.

If you enjoyed this post, you can read about the 12 hour glacier crossing and tephra wilderness adventure that I had when I worked with Icelandic scientists on the deposits of the Grímsvötn 2011 eruption.  You can follow the blog on Twitter at @volcan01010.

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7 Comments

  1. Katie says:
    September 25, 2014 at 18:45

    In grad school, one of my proudest moments was being able to explain my stable isotope research and MS project to my mother. She periodically asked very good questions about what I was doing and understood it on a layman’s level. My mother would approve of this blog. I have enjoyed your twitter feed. Hope you make it back to Iceland soon!

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  4. Klaus Kaiser says:
    February 24, 2015 at 17:29

    Are there any measurements available on the full composition of the emitted gas?

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