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David Pyle

David Pyle is a volcanologist, and Professor of Earth Sciences at the University of Oxford. His first encounter with volcanoes was at the age of 7, when he visited Villarrica, Chile, shortly after an eruption. David studied geological sciences at the University of Cambridge, and later completed a PhD on the 'older' eruptions of Santorini, Greece. After a short post-doc at the California Institute of Technology, David returned to a lectureship in Cambridge. In 2006, he moved to his current post in Oxford. David tweets at @davidmpyle

Santorini: a volcano in remission?

Santorini: a volcano in remission?

In January 2011, Santorini volcano in Greece began to show the first subtle signs of stirring after many decades of quiet – or at least many decades without detectable activity. This presented an exceptional opportunity to track the behaviour of a very well-studied volcano at the start of a phase of ‘unrest’. Although it may seem counter-intuitive, volcanologists don’t really have a terribly good idea of how volcanoes behave in the long intervals between eruption. Most of the time, resources are devoted to studying volcanoes that are about to erupt, are already erupting, or that have recently erupted, rather than the slumbering volcanoes that might be thought to pose rather less of an immediate hazard. In the case of Santorini, the signs that the volcano might be awakening that we saw in early 2011 presented a scientific chance not to be missed. With urgency funding from NERC (although we did have to explain what the urgency was, without an eruption having happened) and support from our Greek collaborators, we were able to mobilise quickly and make the most of the opportunity to observe and measure while the episode of ‘unrest’ unfolded. Now, two and half years on, the stirring has subsided, and Santorini seems to be settling back into another period of quiet slumber. With the benefit of this hindsight, we can now take a look back over the ‘pulse’ of unrest, and begin to think about what this tells us about how the volcano works.

At the beginning, in early 2011, the first signs of something stirring came from the tiny earthquakes that began to be detected beneath the centre of the volcano. Shortly afterwards, we were also able to see the signs of ground movement from both satellite and ground-based instruments, as the volcano began to swell. Measurements and modelling of this swelling both pointed strongly to the root cause of the unrest being the arrival of molten rock, or magma, about 4 kilometres  beneath the volcano, at a point somewhere beneath the northern part of Santorini’s sea-filled caldera.

Santorini Vertical Deformation Model

Vertical deformation of Santorini during the period of unrest in 2011 – 2012, determined by Michelle Parks (University of Oxford) from measurements of the deformation field across the islands. The deformation is best explained by the intrusion of magma about 4 km below the red dot.

Over the course of the next 12 – 15 months (until about March – April 2012), ten to fifteen million cubic metres of molten rock slowly squeezed into this subterranean reservoir at depth, while we watched our instruments trace out the gradual changes at the surface. Over the same period we were also able to detect subtle changes in the gases leaking out of the summit craters of the Kameni islands; the young volcanic islands in the centre of the caldera. The Kameni islands are almost barren, formed from the overlapping fields of lava erupted over the course of a series of eruptions during the past 2000 years and more. You can get a sense of this from the aerial photographs captured by the NERC-funded aircraft that surveyed the islands in May 2012.

Right in the centre of the younger of these islands, Nea Kameni, the tourist trails circle around the shallow craters formed during eruptions over the past century. Although there is very little visible evidence, apart from a couple of small steamy vents, this summit area is gradually leaking carbon dioxide and other volcanic gases to the atmosphere. The concentrations of these gases are too low to be measured remotely (from satellites, or automated spectrometers), and instead have to be measured directly during field campaigns.

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Aerial view of the summit area of Nea Kameni, Santorini, Greece, showing the tourist trails (in grey – look for the people) that run around the edges of the Agios Giorgios craters. Photo taken by the NERC Airborne Research and Survey aircraft on flight EU12-12, May 2012.

We were interested in measuring the carbon dioxide that is escaping out of the soil, as this is one of the gases that we expect to be released from magmas as they rise up through the Earth’s crust. Carbon dioxide is quite easy to measure, because it has a couple of strong absorption bands in the infra-red, and there are several tailor-made instruments available that can make these sorts of measurements routinely. Most ‘soil gas flux’ instruments are based on the ‘accumulation chamber’ method, a technique adapted for volcanic applications in the early 1990’s. This involves measuring the rate at which carbon dioxide seeps out of the soil into a small volume chamber, resting on the ground surface.

Soil gas measurement using an accumulation chamber, with a PP systems chamber and portable gas analyser.

Soil gas measurement system using a PP systems accumulation chamber and portable gas analyser. The accumulation chamber sits on a collar, pressed into the soil. This picture is from a field setting on a volcano in Ethiopia.

In the field set up that we adopted on Santorini, Michelle Parks was also able to collect small fractions of the soil gas for carbon isotope analysis in parallel with the measurements she was making of the soil gas flux itself.

LiCOR soil gas accumulation system, ready for deployment. Courtesy of Michelle Parks.

LiCOR soil gas accumulation system on Santorini, ready for deployment. Courtesy of Michelle Parks.

As well as measuring carbon dioxide, we also measured concentrations of the short-lived radioactive gas, radon-222 in the soil gas. Radon is a naturally-occurring radionuclide, which decays by alpha-decay. Radon can be measured using ‘passive’ detectors made of a special plastic (manufactured by TASL), that records the tracks left by the alpha particles that are released from the radon atoms as they decay. After exposure to the soil gas environment for a few days, the plastic detectors are etched to reveal the tracks, ready for counting and calculation of the radon gas concentration. Together, these measurements of carbon dioxide emission rate; of carbon dioxide concentration; of carbon isotopic composition, and the radon concentration – allowed us to tease apart the different sources of carbon dioxide that come together to form the ‘soil gas’. In particular, we distinguish the carbon dioxide produced by bacteria in the soil, from that produced deeper inside the volcanic system; and we can also distinguish between carbon dioxide that has recently escaped from a degassing body of magma, and the carbon dioxide released by reactions between the hot, intruding magma and the limestone rock that forms a part of the ancient basement to the volcano. Our new measurements show that after the intrusion of magma began in early 2011, the pattern of soil-gas carbon dioxide changed, as new gas percolated into and through the shallow parts of the volcano towards the surface, before escaping. This gas pulse has now passed through the system, and all of the signs now suggest that the volcanic system beneath Santorini is returning to a quiet state. We will, though, all be keeping a watchful eye.

Update: February 2015.

Santorini volcano remains in remission, and the episode of unrest has passed. The story of the past 20 years of satellite-observation of the slow ups-and-downs of the volcano has now been documented in another recent paper by Michelle Parks (Parks et al., 2015).

Further reading (non technical): http://santorini.earth.ox.ac.uk

Selected further reading (technical): a selection of the papers that describe some of the features of unrest on Santorini since 2011.

Foumelis, M. et al., 2013, Monitoring Santorini volcano (Greece) breathing from space, GEOPHYSICAL JOURNAL INTERNATIONAL Volume: 193 Issue: 1 Pages: 161-170 DOI: 10.1093/gji/ggs135

Lagios, E et al., 2013, SqueeSAR (TM) and GPS ground deformation monitoring of Santorini Volcano (1992-2012): Tectonic implications, TECTONOPHYSICS 594, 38-59 doi 10.1016/j.tecto.2013.03.012

Newman, AV et al., 2012, Recent geodetic unrest at Santorini Caldera, Greece  GEOPHYSICAL RESEARCH LETTERS 39, L06309 DOI: 10.1029/2012GL051286

Papoutsis, I., et al., 2013, Mapping inflation at Santorini volcano, Greece, using GPS and InSAR GEOPHYSICAL RESEARCH LETTERS 40, 267-272 DOI: 10.1029/2012GL054137

Papageorgiou, E. et al., 2012,  Long-and Short-Term Deformation Monitoring of Santorini Volcano: Unrest Evidence by DInSAR Analysis  IEEE JOURNAL OF SELECTED TOPICS IN APPLIED EARTH OBSERVATIONS AND REMOTE SENSING 5, 1531-1537 DOI: 10.1109/JSTARS.2012.2198871

Parks, MM et al., 2012, Evolution of Santorini Volcano dominated by episodic and rapid fluxes of melt from depth, NATURE GEOSCIENCE  5, 749-754 DOI: 10.1038/NGEO1562

Parks, MM et al., 2015, From quiescence to unrest – 20 years of satellite geodetic measurements at Santorini volcano, Greece. Journal of Geophysical Research (Solid Earth), doi:10.1002/2014JB011540

Tassi, F., et al., 2013, Geochemical and isotopic changes in the fumarolic and submerged gas discharges during the 2011-2012 unrest at Santorini caldera (Greece) BULLETIN OF VOLCANOLOGY 75, 711 DOI: 10.1007/s00445-013-0711-8

M.M. Parks, S. Caliro, G. Chiodini, D.M. Pyle, T.A. Mather, K. Berlo, M. Edmonds, J. Biggs, P. Nomikou, & C. Raptakis (2013). Distinguishing contributions to diffuse CO2 emissions in volcanic areas from magmatic degassing and thermal decarbonation using soil gas 222Rn-delta13C systematics: application to Santorini volcano, Greece Earth and Planetary Science Letters, 377-378, 180-190 DOI: 10.1016/j.epsl.2013.06.046

Timelapse volcanoes in Google’s Earth Engine

With the marvels of technology and the generosity of Google and NASA, we can now sit back and watch the back catalogue of volcanic eruptions using the magnificent Google Earth Timelapse of Landsat images. Here are just a few that I have picked out..

Enjoy, and do send more suggestions!

Anatahan, Marianas, erupted in 2005.  Anatahan Timelapse

Chaiten, Chile. Erupted in May 2008: look for the splash of ash.  Chaiten Timelapse

Miyakejima, Japan – a spectacular caldera-forming event in 2000.  Miyakejima Timelapse

Pinatubo, Philippines. Major eruption in 1991; thanks to Ron Schott for this.  Pinatubo Timelapse

Soufriere Hills Volcano, Montserrat. Erupting since 1995: watch the island grow.  Montserrat Timelapse

Lake Voui, Aoba volcano, Ambae island, Vanuatu, erupted in 2005-6.  Lake Voui Timelapse

Who should set the research agenda in Universities?

Universities are complex, organic institutions. Their heart is the academic hub of scholarship and research, sustained  by the ever-changing life-blood of students who come through to learn, to challenge, to grow, and ultimately to leave,  having left their mark on those who have taught them. The excitement of working in a University environment is the daily experience of being challenged to think in new ways to solve old problems. Teaching  forces you to develop a perspective on problems in a way that then allows you to explain them to students. In turn, this can bring new clarity to your research, giving you new ways to come at the problem, and new ways of seeing things. And then, of course, that new understanding feeds back into the teaching.

To support all of this activity, though, requires money, and a lot of it. Money for people, for buildings, and for the resources that underpin scholarship. To give an idea of scale, Oxford University receives about £1000 M in income every year. Of this billion pounds, less than 20% comes from student fees, while over £400 M arrives in external grants and contracts from research sponsors. Most of this money for research comes in the form of project grants: funding solicited by an investigator, or group of investigators, to solve a problem that they have defined. But of course, there is never enough project grant income to go around. Success rates for applications to the major funding bodies (research councils, charities) are often 20% or lower and, increasingly, it is difficult to find the funding  to replace, overhaul, or even just to maintain the essential services and facilities that everyone relies on to keep the research flowing. With this as a backdrop, and with the global competition for the best scholars and researchers, it is perhaps only natural for Universities to look to diversify their research income.

In the field of science, there is a great deal of high quality research that goes on that is pushing entirely at the ‘blue skies’ frontiers of knowledge. This curiosity-driven research is, perhaps, most likely to be funded by research councils or charities. But scientific research has also always been about solving problems, and about equipping people with the intellectual and other skills to solve ‘real world’ problems. Recent years have seen a huge growth in activities related to identifying and understanding the drivers behind global environmental change. And currently, there are great efforts to understand and to tackle the leading problems that will define the next twenty to thirty years of environmental research: the future of food, of energy, of biodiversity, and natural resources. So who should set the research agenda in this area? And should there be areas that are out of bounds? There are no easy answers, but would it be appropriate for students of Earth Sciences not to explore fully the questions of how natural resources form? Or not to be exposed to the global challenges of how to meet the unsustainable but growing demands for energy and materials that are still being driven by consumption in the developed world? At the heart of it, research in Universities remains in the hands of the researchers. It is they who set the research agenda, and find pathways to the solutions. If Universities have become more effective at facilitating researchers to seek external funding to support their research, is this necessarily a bad thing?

Today sees the formal opening, in Oxford, of the Shell Geoscience Laboratory. This partnership provides £5.9M funding for a small number of staff (a Professorship, and several post-doctoral researchers and graduate research students), and some core laboratory equipment. The sum of money involved (equivalent to ca. £1M/yr over about 5 years) is, indeed, significant in the context of a research group – but is both a tiny proportion of Oxford’s annual research income (< 0.25%), and a small fraction of current external funding received by Oxford for studies into Earth, the Environment and the Climate System: Oxford’s current research portfolio from the Natural Environment Research Council currently exceeds £60 M. This does not look like funding that is buying ‘influence over the research agenda‘.

If we wish to demand greater social responsibility from the major global institutions, would it not be better to focus, as ShareAction are doing, on the rather more significant interests that Universities in general, and the Universities Superannuation Scheme (USS) Pension Fund in particular, hold through their investment portfolios?  In 2012, USS alone held investments of £900 M in the ‘hydrocarbon’ sector, and over £500 M in the minerals and mining sectors. Wisely used, that looks like a lot of leverage.

Chaiten: anniversary of an eruption

Chaiten: anniversary of an eruption

May 1st marks the anniversary of the start of the first historical eruption of Chaiten, a small volcano in southern Chile, in 2008. A lot has been written on the eruption elsewhere, starting with Erik Klemetti’s eruptions blog which first reported on the event at the time. This is an opportunity to share some field photos, which I took during field visits to Chaiten in 2009. At the time of the eruption, Chaiten was not well known,  but it was recognised to be an old dome of obsidian lava, last thought to have erupted about ten thousand years previously. In fact, we now know that Chaiten has a long history of explosive eruptions of  rhyolite magma, and is probably one of the most prolific producers of rhyolite in southern Chile.

The snapshots illustrate some of the transient consequences of explosive, ash-rich eruptions for both people, and the environment; and some of the excitement of  trying to read the deposits before they have been washed away. Enjoy!

Further reading: a special issue of the Open Access journal ‘Andean Geology‘ on the Chaiten eruption was published in May 2013. This issue contains a number of papers that describe the 2008 eruption and its consequences, and others that reconstruct the past history of this volcano.

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Ash and leaf litter

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Prints in the ash

Impressions

Impressions in ash

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Ash in the undergrowth

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“Chaiten will not die”

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“We want to return to Chaiten, our little town”

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Wood shavings

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Chaiten bay, choked with pumice

Approaching Chaiten

Approaching Chaiten

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Survey spot

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Field volcanology

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Evening glow

Acknowledgements: funding for fieldwork on Chaiten and elsewhere in southern Chile was provided by grants from NERC and the British Council. Field collaborators included Fabrizio Alfano, Constanza Bonadonna, Chuck Connor, Laura Connor and Seb Watt.

Further reading:

JJ Major and LA Lara, 2013, Overview of Chaiten volcano, Chile, and its 2008-2009 eruption, Andean Geology 40 (2), 196-215. [Open Access]

SFL Watt et al., 2009, Fallout and distribution of volcanic ash over Argentina following the May 2008 explosive eruption of Chaiten, Chile, Journal of Geophysical Research 114 (B04207).

SFL Watt et al., 2013, Evidence of mid- to late-Holocene explosive rhyolitic eruptions from Chaitén Volcano, Chile,  Andean Geology 40 (2), 216-226. [Open Access]

Earth Day – Thin Ice and the inside story of Climate Science

Earth Day, April 22nd, has been chosen as the day for the global launch of a new film on the science behind global environmental change ‘Thin Ice: the Inside Story of Climate Science‘.  This is an exciting project, as the filmmakers include Simon Lamb, who has had a successful career as an academic geologist at the University of Oxford, UK, and then at Victoria University of Wellington, New Zealand; and David Sington, an experienced filmmaker from DOX productions, who originally trained in Natural Sciences. Simon Lamb and David Sington have previously collaborated on a number of documentary films, most notably Earth Story, which was a fabulous documentary on the story of Planet Earth which first aired in the UK in 1998. I still use the accompanying book ‘Earth Story: The Forces that have Shaped our Planet‘ as one of the introductory readings for first year Earth Science students.

For the next 36 hours or so, you can watch Thin Ice live, and for free, online at http://thiniceclimate.org/watch-the-film.

Update.

Having had a chance to see a live screening of Thin Ice, here are my first impressions. ‘Thin Ice’ is a personal journey of discovery  for the filmmaker, Simon Lamb. He has the ambition of trying to understand what climate scientists do, and how they can be confident that global climate is changing. The result is a film that is visually attractive, and that captures in a charming and disarming way the way that science is done. Although there is a narrative, the story mainly unfolds as individual scientists tell the viewers a little bit about the questions they are trying to answer, and how they go about it – whether by collecting ancient samples of ice (bits of the ‘frozen history of climate’); or by rooting back through archives of past measurements of the weather; or by running computer simulations of past, present and future climate. The ‘laboratory’ shifts from snow pits in Antarctica and the heaving deck of a ship in the Southern Ocean, to the physics and computing laboratories of Potsdam and Oxford. This is not a film that really answers the question of why global warming is happening, but it is instead an account of how scientists gather the evidence to try and understand the workings of the climate system. Above all, it is a lovely film about science, by scientists.

What do you wish that you had learned in Graduate School?

In the UK, the landscape of graduate doctoral training (for the PhD, or DPhil degree) in the field of environmental research is about to be radically reshaped.  The main funding agency for PhD training, the Natural Environment Research Council, is currently running a competition for Universities and other Research Organisations to run coordinated doctoral training programmes from next year (October 2014), built around the idea of  training future environmental scientists in cohorts within a multidisciplinary environment.  This differs from current practice in the UK, where funding for doctoral training from NERC is allocated to individual departments on an annual basis, based on an algorithm that takes into account elements such as grant income.

The move to a programme of Doctoral Training Partnerships, where partnerships will be between both academic and research ‘producers’ and non-academic ‘users’ of NERC-funded science and scientists, offers an opportunity to embed some completely new aspects of training into PhD and DPhil programmes.

Looking back on your own graduate training, what  do you wish that you had learned about, been exposed to, or been encouraged to think about while  in Graduate School, rather than having to catch up later?  Here are a few examples of my own [thinking back to a PhD many years ago], just to get started..

1. How to write: for journals, for the media, for the public.

2. How to work collaboratively.

3. How to write a fundable research proposal, and how to manage the research, researchers and other aspects once funded.

4. How scientific research translates into the ‘real world’: who uses it, why and how.

Conference report – EGU highlights, Day 4

Large international science conferences are extraordinary events. For a week at a time, scientists emerge from their offices and laboratories and join a throng of thousands, negotiating their way through tens of thousands of presentations across multiple parallel sessions. For many of those attending, the scale of the event is less important, though, than the opportunity the meeting presents for smaller clusters of researchers to come together to talk about problems of common interest. This week, the European Geosciences Union General Assembly has been taking place in Vienna; a city that seems to me at least to have one of the best integrated public transport systems in the world. With 13,500 abstracts and 11,000 delegates this year, this is one of the major annual Geoscience meetings worldwide, and it attracts people from across the world. This week, I was one of the convenors of a specialist session on volcanic ash; a session that in the end began in the depths of the volcanic conduit, and ended with the spread of volcanic through the atmosphere. This meeting within-a-conference worked really well: the 45 presentations brought together a mix of specialists from disciplinary backgrounds as diverse as applied mathematics, atmospheric physics, meteorology, geophysics and volcanology and from universities, government agencies and volcano observatories for a whole day of discussion.

This sort of forum offers both a very quick way to ‘catch up’ in areas where one might already be a specialist; and to fill in important gaps in knowledge and understanding in other areas. More importantly, it allows people to network; to gain a keener understanding of ‘how things work’, and of the underlying assumptions and other constraints that influence the way that the science is developing. In my own session, the overwhelming challenges ultimately relate to two themes: scale or size, and accessibility. Size, because both in the volcanic conduit and in the atmosphere, the properties and behaviour both of the magma and of the ash cloud relate intimately to the nature, properties and behaviour of materials at the micron or sub-micron scale. Accessibility, because neither the flowing magma within the conduit nor the transient volcanic ash cloud are particularly easy to sample directly while ‘live’. Instead, researchers rely on using  remote-sensing measurements (e.g. seismicity, ground- or satellite-based 0bservations) to gather real-time data, along with with simulation (experimental and computational), and finally inference and validation from analysis of eruptive products, where any are preserved, in order to piece together a story. It would be hard to bring together a similarly diverse group of specialists in a forum other than a large conference without considerable effort, which is perhaps one explanation of why the General Assembly format is both attractive and successful.

Professor John Barry Dawson, 1932-2013

I learnt this week the sad news of the death of Barry Dawson, Emeritus Professor in the School of Geosciences at the University of Edinburgh. I had the great fortune to accompany Barry into the field in 1988, while I was still studying for a PhD, and had the pleasure of spending many enjoyable moments with him subsequently, whether in the field, at meetings, or just in passing. This seems like an appropriate time to reflect briefly on our first meeting.

Barry Dawson in 1988

Barry Dawson in 1988

In the summer of 1988, Barry heard that a volcano that he had first climbed in about 1960 was erupting again, and he was eager to to put together a team for a field visit. This was no ordinary volcano, though: Oldoinyo Lengai, in the northern part of the Tanzanian Rift Valley, is the only known active volcano to erupt lavas of molten sodium carbonate (or carbonatite). With emergency funding in place from the Royal Society, Barry and I, along with Harry Pinkerton and Gill Norton, set off for Tanzania. This was my first visit both to Africa, and to an erupting volcano. I remember Barry’s delight in regaling us with his reminiscences of his life in Tanzania as a Geologist for the (then) Tanganyika Geological Survey in the early 1960’s.  This job had seen him map the ‘Monduli’ region of Tanzania, and had first taken him to the summit of this enigmatic volcano – and his first paper in Nature.

Barry, always eager to pass on his knowledge and enthusiasm.

Barry, always eager to pass on his knowledge and enthusiasm.

We trundled across the rift valley in a ten-tonne truck, and set up camp at the base of the volcano. This was luxurious field work, with a team of guides, cooks and porters from an outfit, which is still going, called Dorobo Safaris.

lengai 1988 1

Half way up..

Getting to the top was a challenge, even with a safari team to carry most of the equipment, but it was certainly worth it: to see, first, sunrise over Kilimanjaro, and then to arrive at the rim of the active crater, shrouded in mist but with the full cacophony of an eruption in progress coming up from somewhere beneath us. Eventually, the clouds lifted, and we were treated to a display from the coolest (literally) and most fluid lavas ever seen on Earth. The next few days are a blur, but included Barry plane-tabling to produce a map of the active vents of the summit crater; impromptu tutorials on the alkaline igneous rocks (of which Oldoinyo Lengai is built), and many hours watching the astonishing eruptive display of this bizarre volcano. And once it was too dark to stay in the field, we would retreat back to the camp site which, in hindsight was perilously located within the main crater, to enjoy a wee dram and a story or two with Barry.

Early morning shadow across the active crater of Oldoinyo Lengai, November 1988.

Early morning shadow across the active crater of Oldoinyo Lengai, November 1988.

A curious little spatter cone of carbonatite lava, within the active crater of Oldoinyo Lengai.

A curious little spatter cone of carbonatite lava, within the active crater of Oldoinyo Lengai.

Five days later, we stumbled and slid our way back down the slopes, and took the dusty track back into Arusha. Arriving at the hotel to find that there was neither running water, nor food, wasn’t the slightest nuisance to Barry, who settled us all down in the bar to quench our thirst with beer.

View of Oldoinyo Lengai from base camp, with Barry Dawson, Celia Nyamweru and Gill Norton.

View of Oldoinyo Lengai from base camp, with Barry Dawson, Celia Nyamweru and Gill Norton, November 1988.

Since that first field expedition, our paths crossed on many occasions. Barry was not only delightful company, he was hugely generous with his time, his expertise and his rock collection – a collection which must be one of the most important collections of both rocks from the mantle, as well as the East African Rift. I shall never forget the way he would always begin a conversation with ‘Now, David, let me tell you… ‘; my only regret is that I didn’t have time to go for a beer with him on my last fleeting visit to Edinburgh.

Below, I have reproduced the formal citation that I put together for Barry’s nomination for the Collins Medal of the Mineralogical Society, which he was awarded in 2012. This hopefully captures a small snapshot of his academic contributions.

Barry Dawson was a petrologist and mineralogist who devoted his career to further the understanding of igneous rocks.  Over the fifty years of a highly productive career, Barry Dawson made a series of lasting contributions to studies of the mineralogy, mineral chemistry, petrology and geochemistry of the parts of the mantle sampled by volcanic rocks; and to the nature of the melts and magmas involved in continental magmatism.  His work significantly developed the fields of kimberlite and carbonatite magmatism and improved our understanding of the nature of the subcontinental mantle.

Barry Dawson’s career began with a PhD at the newly formed Centre for African Studies in Leeds (1956-1960).  Here, he began his work on kimberlite magmas and their xenoliths, which culminated in the publication twenty years later of the influential monograph ‘Kimberlites and their xenoliths’ (Dawson, 1980).  Amongst his major contributions here were his recognition of wet, pegmatitic rock samples from the upper mantle (the Mica-Amphibole-Rutile-Ilmenite-Diopside or MARID suite); and the discovery of diamond in garnet lherzolite nodules (Dawson and Smith, 1975).  After completing his PhD, Barry worked for as a geologist for the Tanganyika Geological Survey, where he discovered the erupting sodium carbonate lavas of the volcano of Oldoinyo Lengai – aspects of which he continued to work on ever since. Barry returned to the United Kingdom in 1964, where he was lecturer at St Andrews and later Professor in the Universities of Sheffield (from 1978) and Edinburgh (from 1990).  Over the course of his career, Barry published prolifically, and gave his time and samples generously to support the developing careers of his students and other scientists.  He was a fount of knowledge on East African magmatism, and in his retirement, Barry completed an important synthesis on this, published in 2008, as a Geological Society of London Memoir titled ‘the Gregory Rift Valley and Recent volcanoes of northern Tanzania’.

Barry’s notable achievements were recognized by a number of awards: he was elected Fellow of the Royal Society of Edinburgh in 1973; was Hallimond Lecturer of the Mineralogical Society in 1980/1, and was awarded the inaugural Norman L Bowen Award of the American Geophysical Union in 1987 for his outstanding contributions to volcanology, geochemistry and petrology. In 2012, he was awarded the Collins Medal of the Mineralogical Society for his career-long contributions to the field.

Full curriculum vitae

Time to move scientific debate into the open?

A few months ago, I got a routine request to review a paper about the fate of the plume formed during the 2011 eruption of Nabro volcano, Eritrea. The topic looked interesting, and so I agreed and duly reported. A few weeks later, the journal asked if I might write a commentary to introduce the paper, essentially as a bit of advertising. It wasn’t too hard to agree to that either; after all, you don’t often get the chance to write short opinion pieces for journals, and this was an area where I had a few things to say. So I duly wrote a short piece on ‘small volcanic eruptions and stratospheric aerosol‘ and it went live a few days later.

Within a matter of days, the journal editor emailed again. Someone had submitted a comment on my piece, and the editor wished it to be corrected. My first instinct was  surprise – I had written an opinion piece and I thought I had been quite careful in checking the facts.  But the comment picked up on a single throwaway statement in the discussion. In my original article I had widened the discussion about the Nabro plume to bring in the interpretation from a recent paper in Science which had suggested that atmospheric circulation, related to the Asian monsoon, may have helped to loft the initial volcanic plume from the upper levels of the troposphere into the stratosphere. I perhaps gave way when I should not have done, but duly wrote a correction (corrigendum) to clarify the point, and that was eventually published. Now even though my commentary and correction are all in the public domain, there is no record of the discussion that went on behind the scenes. The originator of the comment is not identified, and the comment that prompted the correction was not published. This week, however, it has all become a little clearer: a pair of formal comments to the original Science paper, and a reply, have now been published in Science. The comments were submitted in August, about the time that my original piece came out – which explains why the rebuke arrived so quickly. But of course, as is usual with these things the comments and reply illuminate the problem (did the Nabro plume reach the stratosphere of its own accord, or not?) but not the solution.

The whole process  of writing the response, checking the proofs and signing the copyright forms to write a one paragraph response to an anonymous comment on what was only ever intended as an opinion piece took a few weeks of to-and-fro. This seems both rather archaic, and unneccessarily formal, compared to the ease with which one can have civilised and informed debate in blogs and other social media. Is it time for journals to move this sort of  ‘comment’ and ‘reply’ out of the constraints of formal ‘publication’, and into the public domain?

References:

Bourassa A E et al., 2012 Large volcanic aerosol load in the stratosphere linked to Asian monsoon transport Science 337 78–81

Sawamura P et al 2012 Stratospheric AOD after the 2011 eruption of Nabro volcano measured by lidars over the Northern Hemisphere Environ. Res. Lett. 7 034013

Sea-floor spreading, on land

Sea-floor spreading, on land
Looking north, up the Dabbahu rift, Afar.

Aerial view, looking north along the Dabbahu-Manda-Hararo rift, Afar, Ethiopia. The stratovolcano, Dabbahu, lies in the background. Our new work shows that this rift is opening at about 20 mm/yr. Over the past 200,000 years, opening of this part of the rift has accounted for all of the motion between the Nubian and Arabian tectonic plates. The topography of this rift is thought to be similar to that of the mid-Atlantic ridge. Note the prominent fault scarps that cut through young basalt lava flows.  The rift axis, and locus of current faulting and magmatism lies to the right hand side of the photo.

One piece of evidence that helped to establish the theory of Plate Tectonics in the early-1960’s was the recognition of patterns of magnetisation in the basalts of the seafloor that were symmetrical about the global oceanic ridge system. Fred Vine and Drummond Matthews recognised that this pattern had to be fixed in place as the lavas, that were erupted along the ocean ridge, cooled through a critical temperature (the Curie point). Below this point, they would become weakly magnetized, with a signature reflecting the local magnetic field. On long timescales (millions of years) Earth’s magnetic field changes in both intensity and direction, and it is the major changes in polarity, during which the field reverses, that lead to the striped ‘bar-code’ signature of magnetic stripes on the sea floor.  In turn, the symmetrical pattern of this magnetic chart-recorder requires that most of these seafloor lavas are erupted in a narrow region at the oceanic ridge, which marks the point of separation between two tectonic plates. These observations led to the now well established theory that tectonic plates form at oceanic ridges, where magmas from the mantle below rise, and freeze to form the trailing edges of  the separating plates.

While these processes are well understood for the sea-floor, we still don’t have a very good idea of what happens when a continental plate begins to split apart to form a new plate boundary. Think of the analogy of pulling apart a Mars bar. When you start to pull it from both ends, a number of fractures start to form in the brittle chocolate coating. But at what stage does the stretching become concentrated into the one major fracture, and what controls where that fracture forms? To get a closer understanding of how continents break up, there have been several concerted research efforts in the north-eastern parts of Africa (notably Ethiopia and Eritrea) over the past few decades.  These have teased out the geological and geophysical events of the past 30 million years as the Ethiopian Rift Valley developed, and evolved to its current status, with a ‘triple junction’ forming at the boundaries of three plates (the Nubian Plate, beneath north Africa; and the Somalian and Arabian Plates).

Afar, Ethiopia: en route to Digdigga

Afar, Ethiopia: en route to the field camp at Digdigga

A part of this evolving plate boundary now lies within the Afar region of Ethiopia.  This is an area that is both remote and challenging to work in, but also a place that is geologically and culturally fascinating. It is the location, for example, of the oldest Hominid fossils known including Lucy (Australopithecus afarensis).  With the sort of serendipity that geological fieldwork sometime relies upon, an opportunity to re-examine how a continent breaks up arose in late 2005, when a major segment of the plate boundary ruptured. In a series of events which are now very well documented (see references at the end),  the Dabbahu-Manda-Hararo rift lurched into life. Over the next six years, the rift has experienced at least 14 further rifting events, three of which were associated with eruptions of basaltic magma. A multi-partner and multi-national research team has been working in the Afar since 2005, with the aim of using this active rifting episode to understand better how continents rift apart, and how new basaltic crust, which is typical of the ocean floor, begins to form.

Fieldwork near Badi volcano, Afar

Fieldwork near Badi volcano, Afar

One part of this effort was undertaken by David Ferguson for his PhD research at the University of Oxford. David collected many samples of basalt lava from a section that crossed from the present active rift, and out onto the older margins of the rift.  This meant travelling on foot, 4×4 and helicopter, and the collection of many hundreds of kilogrammes of rock, which were then shipped back to the UK.

Access to remote parts of the field required helicopter support

Access to remote parts of the field required helicopter support

David then identified a small number of samples for dating, using the potassium (K) -argon (Ar) method. This method relies on the fact that all lavas contain small amounts of radioactive (and naturally occurring) K-40, which decays over time Ar-40. Since argon is a gas, is will naturally escape from lavas as they erupt; but once a lava is frozen, any Ar that subsequently forms by the decay of potassium will remain trapped within the finely-crystalline structure of the rock. By carefully breaking the rocks apart, pulling out the finely-crystalline  fraction of the frozen melt and then heating the samples up in a controlled environment, David Ferguson and Andy Calvert, from the US Geological Survey, were able to extract and measure the tiny amounts of young Argon that had accumulated since eruption. Since we can measure the amount of potassium present in each rock; and since the  rate of decay of potassium-40 is well known, these measurements tell us how much time that has passed since each lava sample erupted.

IMG_1354

Packing up rock samples at the Digdigga field camp

As we might expect, David found that the lava samples got progressively older the further away they were from the presently-active part of the rift.  But interestingly, the lava samples all have the same chemical signatures as the present day lavas that have been erupted from the rift – suggesting that each of the dated lava flows were also erupted from the centre of the active rift at the time. This may all sound a little bit obvious, but the conclusions are actually quite interesting: they tell us that for the past 200,000 years most of the volcanic activity in this part of Afar has occurred in a narrow rift, as we see today. The older lavas now lie a few kilometres away from the active rift – and this tells us the rate at which the rift has been opening over this period of time. Here, we find that the spreading rate of the Dabbahu-Manda-Hararo rift is about 20 mm/year (or about 4 km in 200,000 years). This matches quite closely with the independent estimates of the rate at which the Nubian Plate is separating from the Arabian Plate. So in this location, we can be fairly sure that main fracture of the ‘Mars bar’ formed at least 200,000 years ago, and this has effectively become the place where the trailing edges of the two plates are forming and pulling apart. So here we have it – the seafloor-spreading process, and the formation of new basaltic crust, identified on land.

Reference: DJ Ferguson et al., 2013a, Constraining timescales of focussed magmatic accretion and extension in the Afar crust using lava geochronology, Nature Communications, 4, 1416.

Update. July 4, 2013.

David Ferguson has now published a new paper in Nature that brings together information both from petrology (the nature of the erupted lavas, and their chemical compositions) and from seismology to develop a self-consistent explanation of the deep structure of the rift. This new work shows that the compositions of geologically young lavas requires them to have formed relatively deep (greater than 80 km or so), and at relatively higher temperatures than expected for ‘normal’ mantle. This can only be reconciled with other geological and geophysical constraints if the plate beneath the active Afar rift is still relatively thick. This, in turn, is consistent with the idea that the slow rate of spreading at the rift means that plate remains thick because of conductive cooling, while volcanism persists because the mantle at depth is suffiiciently hot to partially melt at depths just a little deeper than the bottom of the plate. In turn, this fits in with ideas about the long-lasting and slowly waning influence of a ‘hot spot’ or plume beneath the region, which is the favoured contender for the burst of magmatism in the region about 30 million years ago.

Reference: DJ Ferguson et al., 2013b, Melting during late stage rifting in Afar is hot and deep, Nature 499, 70-73.

Further reading:

Ebinger, C. et al., 2010, Length and timescales of rift faulting and magma intrusion: the Afar Rifting Cycle from 2005 to present. Annual Reviews of Earth and Planetary Sciences 38, 439–466.

Wright, T. J. et al. 2006, Magma‐maintained rift segmentation at continental rupture in the 2005 Afar dyking episode. Nature 442, 291–294.

Acknowledgements: this work was funded by NERC as a part of the Afar Rift Consortium. It would not have been possible without the excellent support of our colleagues, collaborators and logistical support teams in Ethiopia and elsewhere. We are very grateful to the people of Digdigga for graciously permitting us to share their school buildings and to set up a field camp in their village, and to the people of Digdigga and Teru districts for allowing access to the region.