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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).

Upload your 2015 General Assembly presentation

Upload your 2015 General Assembly presentation

This year it is once again possible to upload your oral presentations, PICO presentations and posters from EGU 2015 for online publication alongside your abstract, giving all participants a chance to revisit your contribution  hurrah for open science!

Files can be in either PowerPoint or PDF format. Note that presentations will be distributed under the Creative Commons Attribution 3.0 Licence. Uploading your presentation is free of charge and is not followed by a review process. The upload form for your presentation, together with further information on the licence it will be distributed under, is available here. You will need to log in using your Copernicus Office User ID (using the ID of the Corresponding Author) to upload your presentation.

Presentations and posters will be linked to from their corresponding abstracts. If your presentation didn’t have an abstract (this is the case for Short Courses and others), but you still want to share it with the wider community you can consider uploading your presentation to slideshare or figshare as a PDF to share it instead.

Scientists share new observations from comet-chasing Rosetta Mission

Scientists share new observations from comet-chasing Rosetta Mission

Scientists working on the European Space Agency (ESA) Rosetta Mission provided an update on the comet-chaser and its lander, Philae, at the European Geosciences Union (EGU) General Assembly last week, as well as sharing new science gained from the duo so far. These new results from Rosetta were announced at a press conference on Tuesday 14 April, with additional research presented at the Rosetta scientific session on Monday and Tuesday. Nikita Marwaha reports on some of these new developments revealed in Vienna.

The team started by reporting on the flightpath of the Rosetta spacecraft: it is currently keeping its distance from Comet 67P/Churyumov-Gerasimenko in an attempt to avoid streams of dust from interfering with its systems. The spacecraft is currently flying in a new orbital trajectory around the comet, following problems that arose when it made a Valentine’s Day flyby. Soaring just 6 km above the comet’s surface, the spacecraft’s star trackers, which enable it to navigate, “were getting confused” by dust close to the comet, said Matt Taylor, Rosetta Project Scientist at ESA.

Last month, Rosetta was forced into safe mode following another flyby which resulted in its navigation systems being compromised once more. As a result, the spacecraft had to rapidly retreat to a distance of 200 km. Taylor commented, “It turns out, it’s actually quite difficult to fly a spacecraft around a comet”.

His team are trying to calculate a safe approach distance for Rosetta to fly around the comet, with the craft currently alternating between pyramid orbits and terminator orbits. These new trajectories fly at a distance of 140 km and then 100 km and will allow the scientists to monitor how the spacecraft behaves before moving closer.

As the comet approaches perihelion – the orbital point closest to the sun – during the summer months, even more dust will stream out from it as it warms up and grows its characteristic tail. Meanwhile, the Rosetta spacecraft is slowly inching closer to its comet companion as scientists keep a watchful eye on it to ensure that its navigation systems are coping well.

Mission scientists also revealed their assessment on the potential existence of a magnetic field in the comet. Sensitive magnetometers on board both Rosetta and its lander Philae, which was dropped on to the surface last November, have collected measurements of their local environment. These instruments could sense not only the magnetic field carried in the solar wind flowing off the Sun, but also their interactions with it as they moved.

Such data from Rosetta and Philae suggests that Comet 67/P/Churyumov-Gerasimenko does not possess a magnetic field of its own. This finding is significant because it answers one of the major questions of the mission – did magnetic fields play a role in pulling together the material that makes up comets like 67P? This evidence suggests it did not.

An artist's impression of Philae detaching from the Rosetta spacecraft. Scientists are currently trying to work out a safe distance from which Rosetta can orbit the comet, whilst waiting for Philae to wake up from hibernation. (Credits: ESA)

An artist’s impression of Philae detaching from the Rosetta spacecraft. Scientists are currently trying to work out a safe distance from which Rosetta can orbit the comet, whilst waiting for Philae to wake up from hibernation. (Credits: ESA)

Other formation processes may have played a significant role in the birth of the early Solar System. Combined measurements from both orbiter and lander such as these provide us with a key insight into the primordial Solar System, and will produce further fruitful results once Philae wakes up from hibernation.

Locating the sleeping lander is a task in progress. It touched down very close to its target point last November, however then bounced to where it lies today. Rosetta scientists explained in the press conference that they have a good understanding of where the lander is but cannot identify it clearly from Rosetta’s imaging system, OSIRIS. They know that Philae is currently surrounded by walls and is sitting in a very dark area, riddled with shadows.

Questions still remain on the lander’s current orientation, why its footprints do not fit the landing gear geometry, why it bounced in a sharp angle and whether its feet hit rock or soft material when landing. Unfortunately, the illumination in the final landing site is very poor, with 1 hour and 20 minutes of sunlight per comet day. As a result, Philae is still in hibernation but scientists are optimistic that it will wake up within the next few weeks.

Stephen Ulamec, Philae Project Manager at German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) said, “In order to wake up, Philae’s solar panels should be sufficient to reboot the lander in the coming weeks”.

He also explained that a series of wake-up campaigns were already being launched, with the last attempt two days prior to the press conference. These campaigns involve periodically switching on Rosetta’s communication unit around the clock, so that once Philae gathers enough energy, its signal will be heard by the orbiter overhead. So far, there has been no contact made with the lander but as the comet approaches the sun, the scientists displayed hope for better news in time.

When asked what Philae waking up would mean to him, Matt Taylor said “Philae waking up is a fundamental part of the story. I see the Rosetta Mission as a kind of a soap opera and Philae is currently the cliffhanger. This can’t be the end.”

Rosetta has gripped the world with its fascinating story. This next stage of the mission is vital to unlocking the secrets of the primordial Solar System, yet for now we must wait patiently for Philae to wake up and join Rosetta in their quest to explore their new rocky world.

By Nikita Marwaha, EGU Press Assistant and EJR-Quartz Editor

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