Some 864 volcanologists, representatives of the insurance, building, geothermal and tourism industries, a few medics and the media gathered in Puerto de la Cruz in northern Tenerife for the 6th Cities on Volcanoes meeting. The aim of the meeting was to bring together scientists and engineers, policy makers and members of the public (1,474 members of the public attended various parts of the meeting) to discuss experiences of volcanic eruption crises and the potential benefits of volcanoes from geothermal power production and tourism. There was a lot to discuss in one short week!
The main industry on the Canaries is tourism and while the volcanoes found on each island are a major attraction, an increase in activity would threaten the lives and livelihoods of the inhabitants of the islands and would impact huge numbers of people worldwide. This balance, between the positive and negative effects of volcanoes was foremost in the minds of delegates on Tenerife as the active volcano Teide dominates its skyline.
The recent activity at Eyjafjallajokull in Southern Iceland was a timely reminder of the way in which a relatively small eruption in one part of the world can wreak havoc in the lives of people on the other side of the world. The eventual economic impact of this eruption has yet to be quantified, but the closure of much of European airspace for even a few days had consequences for hundreds of thousands of people in various ways.
On Monday, the opening ceremony was followed by a Plenary talk by Hans-Ulrich Sminck. He has been studying the Canary Islands for half a century and was the ideal person to set the conference into context. The Canary Islands have always been something of a geological enigma, not being on either a tectonic plate boundary or a mantle plume and yet having been active for 20 million years. There has been debate as to whether they are underlain by oceanic or continental lithosphere and the hazards related to future activity have been discussed extensively.
There was a speedy reminder to all scientists at this meeting of the need to temper words carefully at all times. The day after Hans gave his half hour lecture about the origins of the Canary Islands, mentioning very briefly that he felt the response of the Civil Aviation Authorities to the ash cloud from Eyjafjallajokull was an over-reaction, the local newspaper reported that ‘expert believes the closure of air space was exaggerated.’ There was no mention in the report about the rest of his talk or the context of the comment.
There were a dozen or so scientists speaking with the media throughout the meeting, mostly about controversial issues. The vast majority of excellent science went unreported to the general public. This vast body of expert knowledge remains, as always, within the scientific community. The challenge, even at a meeting dedicated to increasing communication between the scientific, business and communications worlds is to strike a balance between sensationalism and reflection.
Over coffee each morning, the freely flowing wine over lunch and the beer with the poster sessions in the afternoons, scientists mingled with decision makers and looked for areas of common understanding and developed new connections.
The local schools were invited to contribute to the meeting, and did so with a magnificent display of volcano models and pictures. Some were very imaginative and some were very accurate. As anyone who has kids will know, there is a lot of work that goes into the construction of these models.
Stories of emergency evacuations and disaster mitigation protocols for densely populated cities and remote islands were exchanged between Civil Defence and emergency response teams from around the world.
On Tuesday, I gave a Plenary talk about my recent work in Iceland where I have identified changes in the plumbing system beneath Askja volcano in the centre of the country.
These maps are taken from Rymer et al., 2010. Map (a) shows the fissure swarms running through Iceland and (b) shows the relative locations of Krafla and Askja volcanoes in the northern fissure swarms. Map (c) shows just the main caldera of Askja and the younger caldera, called Oskjuvatn, which was formed in 1875 by a series of massive explosions that sent ash as far as Europe. The dots are places where I regularly make repeat gravity measurements. There is a cluster of places in the very centre of the main caldera, another to the east, close to the small explosion crater of Viti (shown in the photograph below with the lake filling Oskjuvatn behind, and another cluster of places further north on a lava flow erupted in 1961. Map (d) shows some of the places inside the Krafla caldera where I make repeat gravity measurements.
Image © John Cassidy.
In this paper, which is freely available here, I showed how my gravity measurements, which I have been making on a regular basis at Askja and Krafla since 1985, fit in with the measurements made by my colleagues at the Nordic Volcanological Institute.
Askja is what is known as a central volcano – a large, complex volcano that is the centre of activity over hundreds of thousands of years. It is made of several calderas; Oskjuvatn, the most recent and smallest one, is filled with a beautiful lake 5 km across and 200m deep. It formed after the 29 March 1875 eruption of Askja, which ejected ash and tephra across northern and eastern Iceland. These deposits reached Scotland and Scandinavia, but of course jet air travel was not affected at that time. The eruption lasted several months overall and the explosive phase changed the colour of the landscape in northern Iceland for hundreds of square kilometres from black and grey to a light brown.
Image © Geoff Brown
This picture is taken looking north-east from the top of Dyngjufjoll mountain on the east of the main Askja caldera. The black lava in the middle is the 1961 flow, which travelled through a gap in the caldera wall called Oskjuop. It contrasts in colour with the much lighter tephra from the 1875 explosion which covers the area.
For many years, shallow seismic activity has been located beneath Heidubried mountain to the north-east of Askja, (the table mountain in the background, with a small shield volcano on top - shown above) beneath the Dyngjufjoll mountains of Askja and in the south-east of the main Askja caldera.
More recently, Heidi Soosalu and her colleagues in Iceland have found surprisingly deep earthquakes, not only beneath Heidubried and the northern part of the Askja caldera, but also further north. This is interesting, because we would not usually expect to see deep earthquakes in this region, unless there were magma movements going on.
My measurements show that while the inside of the volcano has been deflating since the 1970s at a rate of 2-5 cm per year, this has occurred with a net decrease in gravity. I measure gravity using a LaCoste and Romberg gravity meter.
I interpret the gravity decrease in terms of magma drainage from the shallow magma storage area beneath the caldera. I have seen variations in gravity over the years at Askja and the dotted red line below is the change in gravity in the centre of the main caldera after corrections for the height changes (deflation of the ground).
From 1988 to 2007, I saw only magma drainage. This would suggest that Askja was unlikely to erupt as magma was actually leaving the plumbing system. Since then though, gravity has increased substantially. In 2008 and 2009, I measured gravity increases at the centre of the Askja caldera (solid red line) as usual, but once I had corrected the data for the height changes, (dashed red line) there was still an increase. Using the data collected across the caldera, I can calculate the amount of new magma that is under Askja that was not there before 2007. It is of the order of 70,000,000,000 kg and it is about 3km below the surface.
My measurements this summer will tell us whether more new magma has moved into the Askja system. Before an eruption, we expect there to be a build up of magma below the surface and it is this that I will be looking for.
From Rymer et al., 2010. Raw and height corrected gravity data for Askja for the period 1998-2008. The raw gravity data are shown by solid lines (red: caldera centre, green: south-east and blue: north). The net gravity changes for each location are shown as broken lines.