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Science, Maths & Technology

The case of the shrinking volcano

Updated Thursday 19th November 2009

In an area of Iceland, one volcano is sinking while others are rising. Is magma moving from one place to another, and if so, where’s it going to?

Askja is a huge volcano in Central Iceland. The youngest caldera formed in 1875 when a massive explosion threw rock with a lot of gas in it (rather like the froth on the top of a bottle of fizzy drink) as far as Scandinavia and Scotland. More recently, Askja has erupted lava flows several km long and even now there are hot springs in the caldera.

View across Askja from the SW. In the foreground is the explosion crater Viti and the larger lake Öskjuvatn, both formed in 1875. Copyrighted image Icon Copyright: Used with permission

Above: View across Askja from the south-west. In the foreground is the explosion crater Viti and the larger lake Öskjuvatn, both formed in 1875.

 

View looking NE from Askja at the table mountain Herdubreid and the ridge Herdubreidartogl in the distance. The black lavas in the foreground were erupted from Askja in 1961.

Above: View looking north-east from Askja at the table mountain Herdubreid and the ridge Herdubreidartogl in the distance. The black lavas in the foreground were erupted from Askja in 1961.

For the last 40 years or so, the centre of the largest caldera at Askja, which is about 10 kilometres across has been sinking at a rate or between 4 and 6 centimetres per year. This may be because the unerupted magma beneath is cooling and contracting, or because the ground is caving in on top of hollow chambers, or because the unerupted magma is draining away. Using the ground deformation information with my 4D-gravity measurements (minute changes in the acceleration due to gravity through time), I have shown that the amount of material beneath Askja is decreasing with time. This is probably because magma is draining away. The big question now is, ”Where is this magma draining to?”

If the magma is draining downwards, it must be accumulating in some big reservoir beneath Askja. I don’t think this can be the whole explanation, because we have not found any evidence for deep accumulation. In fact, our models show that 2 regions, about 3 kilometres and 16 kilometres depth, are actually shrinking. All the time that Askja has been sinking, two other regions, one to the north and the other to the south of Askja, have been rising. A volcano called Grímsvötn to the south of Askja erupted beneath Vatnajökull icecap in 2004 and before that, Gjalp erupted in 1996, and to the north, Krafla erupted between 1975 and 1984. These big ‘central’ volcanoes in Iceland all have broadly north-south trending fissure swarms associated with them and it is possible that magma can travel underground along these fissures between volcanoes.

Damage to a bridge following flooding caused by the 1996 eruption of Gjalp through the Vatnajokull icecap. Copyrighted image Icon Copyright: Used with permission

Damage to a bridge following flooding caused by the 1996 eruption of Gjalp through the Vatnajokull icecap.

Picture © Antoaneta, used under Creative Commons licence.

Recent work by colleagues at the University of Cambridge has shown that there are deep earthquakes in a region just to the north of Askja. It may be that these relate to magma moving from Askja, possibly towards Krafla. The main objective of this work is to discover whether magma draining from beneath Askja is travelling north. I then want to find out how much magma is moving and then to see whether I can detect it accumulating beneath Krafla. If this is the case, I will need to consider where and when a future eruption at Krafla may occur as this information is essential for hazard warning and mitigation.

Icelandic colleagues have a comprehensive network of GPS stations in the region of interest in the north and central part of Iceland. I have measured 4D-gravity changes at some of these stations in the past and now plan to re-occupy these stations and to extend the networks to cover the region where the earthquakes have been detected in more detail. By looking for gravity changes at the places where we have GPS data, I can quantify any mass changes beneath the surface. I will also make continuous gravity measurements at a few key locations so that at these places, I will be able to see the rate of any magma movement. By combining these methods, I will be able to see how much magma is moving, where to and at what rate. I should be able to detect magma leaving the Askja system and accumulating beneath Krafla if this is indeed what is happening.

This project is important from a scientific point of view, as we have very little information on how volcanoes of this type work. We do not know much about the processes that occur beneath the surface in advance of an eruption. By understanding these processes better, we will understand many other volcanoes better, including the vast majority of volcanoes which are below sea level. From a hazards perspective, these volcanoes have the power to be devastating locally, but their ash and even acidic haze can reach as far as the UK. They have had environmental and health impacts on the UK in the past. If we can better understand the causes of these eruptions, and predict when they will occur, we will be in a stronger position to mitigate their effects.

This research is linked to my work in Central America at Poás and Turrialba volcanoes in Costa Rica and Telica and Masaya volcano in Nicaragua. If you are interested in participating in this work as a volunteer (no previous experience needed!), then do think about signing up for my forthcoming expedition.

If volcanology is not the fieldwork you are interested in doing, or you can’t manage the dates this time, you might also be interested in participating in a project aimed at conserving the Amazon Basin’s pink dolphins, giant river otters, monkeys, turtles, fishes, macaws and more. Have a look at Amazon Riverboat Exploration.

 

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