GeoLog

Holuhraun

Imaggeo on Mondays: Hints of an eruption

Imaggeo on Mondays: Hints of an eruption

The photograph shows water that accumulated in a depression on the ice surface of Vatnajökull glacier in southeastern Iceland. This 700m wide and 30m deep depression [1], scientifically called an ‘ice cauldron’, is surrounded by circular crevasses on the ice surface and is located on the glacier tongue Dyngjujökull, an outlet glacier of Vatnajökull.

The photo was taken on 4 June 2016, less than 22 months after the Holuhraun eruption, which started on 29 August 2014 in the flood plain north of the Dyngjujökull glacier and this depression. The lava flow field that formed in the eruption was the largest Iceland has seen in 200 years, covering 84km2 [2] equal to the total size of Manhattan .

A number of geologic processes occurred leading up the Holuhraun eruption. For example, preceding the volcanic event, a kilometre-wide area surrounding the Bárðarbunga volcano, the source of the eruption, experienced deformation. Additionally, elevated and migrating seismicity at three to eight km beneath the glacier was observed for nearly two weeks before the eruption [3]. At the same time, seven cauldrons, like the one in this photo, were detected on the ice surface (a second water filled depression is visible in the upper right corner of the photo). They are interpreted as indicators for subglacial eruptions, since these cauldrons usually form when geothermal or volcanic activity induces ice melt at the bottom of a glacier [4].

Fracturing of the Earth’s crust led up to a small subglacial eruption at the base of the ice beneath the photographed depression on 3 September 2014. This fracturing was further suggested as the source of long-lasting ground vibrations (called volcanic tremor) [5].

My colleagues and I studied the signals that preceded and accompanied the Holuhraun eruption using GPS instruments, satellites and seismic ground vibrations recorded by an array of seismometers [2, 5]. The research was conducted through a collaboration between University College Dublin and Dublin Institute for Advanced Studies in Ireland, the Icelandic Meteorological Office and University of Iceland in Iceland, and the GeoForschungsZentrum in Germany.

The FP7-funded FutureVolc project financed the above mentioned research and further research on early-warning of eruptions and other natural hazards such as sub-glacial floods.

By Eva Eibl, researcher at the GeoForschungsZentrum

Thanks go to www.volcanoheli.is who organised this trip.

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

Imaggeo on Mondays: A Bubbling Cauldron

Imaggeo on Mondays: A Bubbling Cauldron

Despite being a natural hazard which requires careful management, there is no doubt that there is something awe inspiring about volcanic eruptions. To see an erupting volcano up close, even fly through the plume, is the thing of dreams. That’s exactly what Jamie  Farquharson, a researcher at Université de Strasbourg (France) managed to do during the eruption of the Icelandic volcano Bárðarbunga. Read about his incredible experience in today’s Imaggeo on Monday’s post.

The picture shows the Holuhraun eruption and was taken by my wife, Hannah Derbyshire. It was taken from a light aircraft on the 11th of November of 2014, when the eruption was still in full swing, looking down into the roiling fissure. Lava was occasionally hurled tens of metres into the air in spectacular curtains of molten rock, with more exiting the fissure in steady rivers to cover the surrounding landscape.

Iceland is part of the mid-Atlantic ridge: the convergent boundary of the Eurasian and North American continental plates and one of the only places where a mid-ocean ridge rears above the surface of the sea. It’s situation means that it is geologically dynamic, boasting hundreds of volcanoes of which around thirty volcanic systems are currently active. Holuhraun is located in east-central Iceland to the north of the Vatnajökull ice cap, sitting in the saddle between the Bárðarbunga and Askja fissure systems which run NE-SW across the Icelandic highlands.

Monitored seismic activity in the vicinity of Bárðarbunga volcano had been increasing more-or-less steadily between 2007 and 2014. In mid-August 2014, swarms of earthquakes were detected migrating northwards from Bárðarbunga, interpreted as a dyke intruding to the east and north of the source. Under the ice, eruptions were detected from the 23rd of August, finally culminating in a sustained fissure eruption which continued from late-August 2014 to late-February of the next year.

My wife and I were lucky enough to have booked a trip to Iceland a month or so before the eruption commenced and, unlike its (in)famous Icelandic compatriot Eyjafjallajökull, prevailing wind conditions and the surprising lack of significant amounts of ash from Holuhraun meant that air traffic was largely unaffected.

At the time the photo was taken, the flowfield consisted of around 1000 million cubic metres of lava, covering over 75 square kilometres. After the eruption died down in February 2015, the flowfield was estimated to cover an expanse of 85 square kilometres, with the overall volume of lava exceeding 1400 million cubic metres, making it the largest effusive eruption in Iceland for over two hundred years (the 1783 eruption of Laki spewed out an estimated 14 thousand million cubic metres of lava).

Numerous “breakouts” could be observed on the margins of the flowfield as the emplacing lava flowfield increased in both size and complexity. Breakouts form when relatively hot lava, insulated by the cooled outer carapace of the flow, inflates this chilled carapace until it fractures and allows the relatively less-viscous (runnier) interior lava to spill through and form a lava delta. Gas-rich, low-viscosity magma often results in the emission of high-porosity (bubbly) lava. My current area of research examines how gases and liquids can travel through volcanic rock, a factor that is greatly influenced by the evolution of porosity during and after lava emplacement.

Flying through the turbulent plume one is aware of a strong smell of fireworks or a just-struck match: a testament to the emission of huge volumes of sulphur dioxide from the fissure. Indeed, the Icelandic Met Office have since estimated that 11 million tons of SO2 were emitted over the course of the six-month eruption, along with almost 7 million tons of CO2 and vast quantities of other gases such as HCl. These gases hydrate and oxidise in the atmosphere to form acids, in turn leading to acid rain. The environmental impact of Holuhraun as a gas-rich point source is an area of active research.

By Jamie Farquharson, PhD researcher at Université de Strasbourg (France)

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

Iceland’s Bárðarbunga-Holuhraun: a remarkable volcanic eruption

Iceland’s Bárðarbunga-Holuhraun: a remarkable volcanic eruption

A six month long eruption accompanied by caldera subsidence and huge amounts of emitted gasses and extruded lavas; there is no doubt that the eruption of the Icelandic volcano in late 2014 and early 2015 was truly remarkable. In a press conference, (you can live stream it here), which took place during the recent EGU General Assembly, scientists reported on the latest from the volcano.

Seismic activity in this region of Iceland had been ongoing since 2007, but in late August 2014 a swarm of earthquakes indicated that the activity at Bárðarbunga-Holuhraun was ramping up a notch. By August 18th, over 2600 earthquakes had been registered by the seismometer network, ranging in magnitude between M1.5 and M4.5. Scientist now know that one of the main drivers of the activity was the collapse of the ice-filled Bárðarbunga caldera.

Caldera collapses -where the roof of a magma chamber collapses as a result of the chamber emptying during a volcanic eruption – are rare; there have only been seven recorded events this century. The Bárðarbunga eruption is the first caldera collapse to have occurred in Iceland since 1875. They can be very serious events which result in catastrophic eruptions (e.g. the Toba eruption of 74,000 BP). In other cases the formation of the large cauldron happens over time, with the surface of the volcano slowly subsiding as vast amounts of magma are drained away via surface lava flows and the formation of dykes. Bárðarbunga caldera subsided slowly and progressively, much more so than is common for this type of eruption, to form a depression approximately 8km wide and 60m deep.

“The associated volcanic eruption, which took place 40km away from the caldera, was the largest, by volume and mass of erupted materials, recorded in Iceland in the past 230 years”, described Magnus T. Gudmundsson, Professor at the Institute of Earth Sciences at the University of Iceland, during the press conference.

If the facts and figures above aren’t sufficiently impressive, the eruption at Holuhraun also produced the largest amount of lava on the island since 1783, with a total volume of over 1.6 km3 and stretching over more than 85 km4. In places, the lava flows where 30 m thick!

The impressive figures shouldn’t detract from the significance of the events that took place during those six months: scientists were able to observe the processes by which new land is made on Earth! Major rifting episodes like this “only happen once every 50 years or so”, explained Gudmundsson.

So what exactly have scientists learnt? Most divergent boundaries – where two plates pull apart from one another – are found at Mid-Ocean Ridges, meaning there is little opportunity to study rifting episodes at the Earth’s surface. The eruption at Bárðarbunga-Holuhraun offered researchers the unique opportunity to take a closer look at how rifting takes place; something which so far has only been possible at the Afar rift in Ethiopia.

New crust is generated at divergent plate margins, commonly fed by vertical sheet dykes – narrow, uniformly thick sheets of igneous material originating from underlying magma chambers. Dykes at divergent plate boundaries are common because the crust is being stretched and weakened. One of the clusters of seismic activity at Bárðarbunga-Holuhraun was consistent with the formation of a dyke. The seismic signal showed that the magma from the Bárðarbunga caldera, rather than being transported vertically upwards to the surface, was in fact being transported laterally, forming a magma filled fissure which stretched 45 km away from Bárðarbunga. This video, from the Icelandic Met Office, helps to visualise the growth of the dyke over time.

The figure shows all the earthquakes which took place in the region in and around Bárðarbunga, from 16 August 2016 until 3 May 2015. The bar on the right counts days since the onset of events, and it gives a colour code indicative of the time passed. The dark blue colour implies the oldest earthquakes whereas the red colour implies the youngest earthquakes. The earthquakes clearly show the growth of a lateral dyke, headed northeast, away from the Bárðarbunga caldera. Click here to enlarge the map. (Credit: Icelandic Meteorological Office)

The figure shows all the earthquakes which took place in the region in and around Bárðarbunga, from 16 August 2016 until 3 May 2015. The bar on the right counts days since the onset of events, and it gives a colour code indicative of the time passed. The dark blue colour implies the oldest earthquakes whereas the red colour implies the youngest earthquakes. The earthquakes clearly show the growth of a lateral dyke, headed northeast, away from the Bárðarbunga caldera. Click here to enlarge the map. (Credit: Icelandic Meteorological Office)

Further study of the dyke using understanding gained the from propagating seismicity, ground deformation mapped by Global Positioning System (GPS), and interferometric analysis of satellite radar images (InSAR), allowed scientists to observe how the ground around the dyke changed in height and shape. The measurements showed the dyke was not a continuous feature, but rather it appeared broken into segments which had variable orientations. Modelling of the dyke revealed that it was the interaction of the laterally moving magma with the local topography, as well as stresses in the ground cause by the divergent plates, that lead to the unusual shape of the dyke.

On average, magma flowed in the dyke at a rate of 260 m3/s, but the speed of its propagation was extremely variable. When the magma reached natural barriers, it would slow down, only picking up momentum again once pressure built up sufficiently to overcome the barriers. Shallow depressions observed in the ice of Vatnajokull glacier (the white area in the map above) – known as Ice cauldrons – were caused by minor eruptions underneath the ice at the tips of some of the dyke segments. The dyke propagation slowed down once the fissure eruption at Holuhraun started in September 2014.

What has the Bárðarbunga-Holuhraun taught scientists about rifting processes? It seems that at divergent plate boundaries, in order to create new crust over long distances, magma generated at central volcanoes (in this case Bárðarbunga), is distributed via segmented lateral dykes, as opposed to being erupted directly above the magma chamber.

 

By Laura Roberts Artal, EGU Communications Officer

 

Further reading and references

You can stream the full press conference here: http://client.cntv.at/egu2015/PC7

Details of the speakers at the press conference are available at: http://media.egu.eu/press-conferences-2015/#volcano

The speakers at the press conference also reported on the gas emissions as a result of the Holuhraun fissure eruption and the implications for human health. You can read more on this here: Bardarbunga eruption gases estimated.

Sigmundsson, F., A. Hooper, Hreinsdóttir, et al.: Segmented lateral dyke growth in a rifting event at Bárðarbunga volcanic system, Iceland, Nature, 517, 191-195, doi:10.1038/nature1411, 2015.

Sigmundsson, F., A. Hooper, Hreinsdóttir, et al.: Segmented lateral dyke growth in a rifting event at Bárðarbunga volcanic system, Iceland, Geophys. Res. Abstr.,17, EGU2015-10322-1, 2015 (conference abstract).

Hannah I. Reynolds, H. T., M. T. Gudmundsson, and T. Högnadóttir: Subglacial melting associated with activity at Bárdarbunga volcano, Iceland, explored using numerical reservoir simulation, Geophys. Res. Abstr.,17, EGU2015-10753-2, 2015 (conference abstract).