Kinematic indicators in the Green Tuff Ignimbrite: can they tell us about the timing of caldera collapse?

By Dr Rebecca Williams (@volcanologist) & Jodie Dyble

In the summer of 2014 I have had a Nuffield Foundation student, Jodie, working with me towards a Gold CREST Award, which we blogged about the other week. Here, I’m going to talk a bit about the research she did.

Jodie looked at the Green Tuff Ignimbrite on the island of Pantelleria, Italy. The Green Tuff Ignimbrite is a rheomorphic ignimbrite which was emplaced during an eruption about 45 thousand years ago. An ignimbrite is the deposit from a pyroclastic density current. Rheomorphic means that the deposit was still hot when it was formed, so that the shards of ash welded together and was able to be deformed ductiley. Rheomorphic ignimbrites are common on places like Gran Canaria, in the Canary Islands (where the classic work of Schmincke & Swanson 1967 was done) and the Snake River Plain in the western US. You can get two types of rheomorphism, that which occurs during deposition of the ignimbrite (e.g. the overriding current exerts a shear on the underlying deposit) and rheomorphism which occurs after the deposit has been fully formed (e.g. the deposit starts slumping under gravity). I’m avoiding using primary vs secondary here, as actually the historical meaning of those words and their relative timings can be difficult to disentangle. For a very good, concise overview take a read of (Andrews & Branney 2005). Either way, rheomorphic structures within the deposit like lineations, folds, tension gashes and rotated crystals or clasts, can tell us about this sense of movement. Volcanologists interpret these kinematic indicators in the same way a structural geologist would interpret verging folds, or rotated porphyroclasts in a mylonite (e.g. Passchier & Simpson 1986). You can even determine the direction a pyroclastic density current flowed if you map out these kinematic indicators across the ignimbrite (e.g. Andrews & Branney, 2011).

Schematic diagram of the development of rheomorphic structures in a syndepositional shear zone during the deposition of an ignimbrite. Taken from Andrews & Branney, 2005.

The Green Tuff eruption was said to have been a caldera forming eruption, but the details of this have been debated. Two different calderas have been proposed: the Cinque Denti caldera (Mahood & Hildreth 1986) and the Monastero caldera (Cornette et al. 1983; Civetta et al. 1988). These share the same scarps to the east, west and south but while the Cinque Denti caldera has exposed scarps in the north (the Costa di Zinedi scarp, the Kattibucale scarp and the Cinque Denti scarp), the Monastero caldera has a buried northern scarp. During my PhD on the Green Tuff (Williams 2010; Williams et al. 2014) I found that the Costa di Zinedi scarps, the Kattibucale scarps and the Cinque Denti scarps were extensively draped by the Green Tuff, right down to the bottom of the exposed caldera walls.

The map shows the two different proposed calderas for the Green Tuff eruption. Panoramics and sketches show the draping Green Tuff down the three disputed scarps. Localities used in this study are highlighted. From Williams, 2010.

What Jodie set out to determine this summer was when that draping occurred. My work on the chemical stratigraphy of the Green Tuff already determined that those drapes represented the earliest part of the eruption. So, did caldera collapse happen after the deposition of the Green Tuff and did those drapes represent the rheomorphic slumping of the deposit down a newly formed caldera wall? Or, did the caldera wall exist before the emplacement of the Green Tuff, and those drapes represent a deposit formed by an overriding current? In the field, macro indicators (such as large scale folds) suggested that the deposit slumped down the caldera wall. We went in search of micro kinematic indicators to see if they would tell the same story.

 Some of the micro-kinematic indicators seen in the thin sections from the Green Tuff Ignimbrite, including verging folds and rotated clasts (δ and σ–objects). From Dyble & Williams, 2015.

What Jodie found was compelling evidence for upslope flow in the thin sections that she analysed. Thus, those deposits were formed by the Green Tuff pyroclastic density current flowing up the caldera scarps, depositing and shearing the underlying deposit as it went. Which means that those caldera scarps must have existed before the Green Tuff ignimbrite did, so we support the idea that those scarps had nothing to do with the Green Tuff eruption. We think that’s pretty neat and we’re presenting the work at the Volcanic and Magmatic Studies Group annual conference, which in January 2015 will be held in Norwich. Jodie has already made the poster we’ll be presenting as part of the assessment required to achieve a Gold CREST Award, so we’ve decided to publish that online before the conference. I’d like to thank Jodie for some stellar research this summer, despite only having done 1 year of Sixth Form (AS level) geology (she’s 17!), and answering some questions I’ve been pondering for about 6 years. Hopefully, this data will go into a couple of papers I’m working on too!

Andrews, G. & Branney, M., 2005. Folds, fabrics, and kinematic criteria in rheomorphic ignimbrites of the Snake River Plain, Idaho: Insights into emplacement and flow. In J. Pederson & C. . Dehler, eds. Interior Western United States: Field Guide 6. Bouldor, Colorado: Geological Society of America, pp. 311–327.

Andrews, G.D.M. & Branney, M.J., 2011. Emplacement and rheomorphic deformation of a large, lava-like rhyolitic ignimbrite: Grey’s Landing, southern Idaho. Geological Society of America Bulletin, 123(3-4), pp.725–743.

Civetta, L. et al., 1988. The eruptive history of Pantelleria (Sicily Channel) in the last 50 ka. Bulletin of Volcanology, 50, pp.47–57.

Cornette, Y. et al., 1983. Recent volcanic history of pantelleria: A new interpretation. Journal of Volcanology and Geothermal Research, 17(1-4), pp.361–373.

Dyble, J.A., Williams, R., 2015. Micro kinematic indicators in the Green Tuff Ignimbrite: can they tell us about caldera collapse? VMSG Meeting, Norwich, 5th-7th January 2015. http://dx.doi.org/10.6084/m9.figshare.1160476

Mahood, G. & Hildreth, W., 1986. Geology of the peralkaline volcano at Pantelleria, Strait of Sicily. Bulletin of Volcanology, 48, pp.143–172.

Passchier, C. & Simpson, C., 1986. Porphyroclast systems as kinematic indicators. Journal of Structural Geology, 8(8), pp.831–843.

Schmincke, H. & Swanson, D., 1967. Laminar viscous flowage structures in ash-flow tuffs from Gran Canaria, Canary Islands. The Journal of Geology, 75(6), pp.641–644.

Williams, R., 2010. Emplacement of radial pyroclastic density currents over irregular topography: The chemically-zoned, low aspect-ratio Green Tuff ignimbrite, Pantelleria, Italy. University of Leicester. http://dx.doi.org/10.6084/m9.figshare.789054
Williams, R., Branney, M.J. & Barry, T.L., 2014. Temporal and spatial evolution of a waxing then waning catastrophic density current revealed by chemical mapping. Geology, 42(2), pp.107–110.

How I Became a Music Geographer

by Dr Kevin Milburn (@kevmilburn)

Oxbow lakes. That’s the first thing people tend to say to me when I mention that I’m a geographer. Occasionally this is followed by ‘glacial moraine’, or, much rarer still, by ‘Christaller’ and ‘central business districts’. I then helpfully correct them by saying that I’m a music geographer, but invariably that just confuses matters further.

Me. Next to a river. 2013

So, I will try here to explain what it is that I tend to spend my days doing – an exercise likely to prove at least as beneficial to me as to anybody else. But before I do so, a quick detour, a circumlocutory ramble concerning how I reached this point. I was born in the town of… no, too far back, no one cares… Secondary school (onto education at least, vaguely relevant) was divided between Essex and Detroit, two places not well known for being linked, unless that is you had a family member working for the Ford Motor Company. Perhaps being schooled in a different culture gave me a lasting interest in notions of similarity and diversity, in what connects and divides us, core ideas that continue to generate considerable levels of discussion within human geography. More likely is that that is just psychoanalytical babble but it did perhaps stimulate an interest in American subject matter which continues to inform my teaching, as on the World Cities (New York) module, as well as my research (as detailed below).

New York, New York. 2006

Next up, came the ‘geography years’; three years studying the subject as an undergraduate at the University of Manchester. The courses offered back then were interesting up to a point, although truth be told, there was a slight sense that rather too many lecturers were counting down the days till their retirement, and I encountered a more dynamic research environment in the geography department at University College Dublin, where I spent an enjoyable term as a student on the EC’s Erasmus scheme. However, one member of staff at Manchester who certainly was not coasting along at that time was Gill Valentine.  Valentine, now a pro-vice chancellor at the University of Sheffield, was the academic who encouraged me, along with other students, such as John Wylie, now a highly regarded professor of geography at the University of Exeter, to engage with a relatively fresh approach / set of ideas / way of thinking — fresh at least in the 1990s — called ‘new cultural geography’.  Interest in this branch of the subject inspired me to do a dissertation with the badly punning title, ‘On the Road with Jack Kerouac and the New Cultural Geography’.

Jack Kerouac, On the Road, 1957. Penquin Books

A decent mark for the Kerouac dissertation prompted me to decide to stay in academia for a bit longer and I successfully applied to do a Masters in Media Culture, taught jointly by the Universities of Strathclyde and Glasgow. The start date of that wouldn’t be for another year however, so in the interim I spent a year working in, and travelling across, Canada (a summer dressed as a monk in a monastic themed restaurant called ‘Brothers’) and Australia (telemarketing to Outback truck drivers, a ‘character building’ experience, and fruit picking in the Bush. The latter was one of the worst jobs imaginable, especially bad were the days spent wrestling with oranges – who knew the trees were so prickly? – and grapes – the juice squirts, the flies descend. Not good).

Once safely ensconced in Glasgow, my longshore drift away from geography and towards popular culture began (years later, I cunningly began to devise various ruses to bring the two together).  On my Media Culture course students had the option of focusing either on TV and film or on popular music. I chose the latter; I'd always been a music nut and had spent a good deal more time than I should have as an undergraduate writing music reviews for Manchester's student paper.  Extended essays on topics of such pressing social concern as the semiotics of New Romantic fashion followed. The culmination of this period of wrapt self-absorption was my dissertation: The production, marketing and consumption of popular music as high art: a case-study of David Sylvian’. Somewhat miraculously, all of this training in becoming a pop pub bore actually led to me landing a job. I know, amazing right?!

David Sylvian, Brilliant Trees, 1984. Virgin Records

A couple of months after leaving Glasgow I was in the capital, doing marketing (still not a term I fully understand) on an event called London Music Week, an exhibition, conference and live music event co-sponsored by Music Week (the music industry’s trade magazine), Radio 1 and MTV. After this I joined the Mercury Music Prize, the annual prize and awards ceremony for the best album of the year from the UK and Ireland, http://www.mercuryprize.com/ Joining the Prize saw me reunited, sort of, with my Masters supervisor from Strathclyde, Simon Frith, who has been chair of the Mercury Prize judging panel since the prize started in 1992 and is widely acknowledged as the world’s foremost academic when it comes to popular music. I worked full-time at the prize for many years, most of them as a director; I stopped working full-time for it in 2008 but have continued my long association with it, to varying degrees, ever since. This year's shortlisted albums are announced a week today (10th September) in Covent Garden, whilst the decision on who will follow the likes of PJ Harvey, The xx, Alt-J and James Blake in becoming the overall winner of the Prize, will be made at the show at the Roundhouse, north London on 29th October.

Working for the Prize, and by extension, with the music and media industries was enjoyable and very rarely dull; my role included: getting the entries in; choosing and liaising with the judges; running retail campaigns in HMV, Fopp, Virgin and so on; writing press releases, website copy and also event scripts for hosts Jools Holland and Lauren Laverne; presenting to sponsors, hosting media announcements and doing lots of press and broadcast interviews. Here’s one that I did with BBC 6Music (with my name mis-spelt most of the way through!) that explains a bit more about how the prize works: http://www.bbc.co.uk/6music/news/20080722_mercury.shtml and here's another with The Independent, one that was also syndicated to the Belfast Telegraph: http://www.belfasttelegraph.co.uk/entertainment/music/news/the-night-of-the-unknowns-the-mercury-music-prize-28062460.html  Quite a lot of my time at the Prize was spent talking about, and talking up, the shortlisted albums, such as here, in relation to Thom Yorke’s solo album, Eraser: http://www.bbc.co.uk/oxford/content/articles/2006/07/19/eraser.shtml

Mercury Prize Albums of the Year Launch, 2013 (t); A Mercury Prize / HMV retail display, 2009 (b) 

However, after a few years at the Mercury, and some might say rather inexplicably,
I began to miss academia. So I did what any sane person would do and started another Masters, this time in Japanese Cultural Studies. I undertook the degree on a part-time basis at Birkbeck, University of London whilst still working at the prize. Here I am talking about combining the two in an interview I did for The Guardian at that time:
http://www.theguardian.com/money/2006/oct/09/careers.theguardian8

My considerable interest in Japan was prompted by a few trips I made to the country in quick succession at the turn of the century. The degree was, as its name suggests, essentially Cultural Studies but with a Japanese emphasis. Debate and ideas encountered there, most notably surrounding issues of identity, representation, and Orientalism, have continued to inform my research and my teaching, most notably in Hull on the Imagining Place, Cultural and Historical Geography and World Cities (Tokyo) modules.  The course was wide ranging and I covered topics as diverse as Tokyo’s 1920s café culture and jazz age, Okinawan modes of cultural protest, Japanese food and identity, and representations of Japan in travel writing and western films. Again, when it came to my dissertation I focused on popular music, this one had the snappy title of: ‘Self-reflexive Orientalism and Cultural Hybridity: a Case Study of Ryuichi Sakamoto and the Yellow Magic Orchestra’.   

Yellow Magic Orchestra, Yellow Magic Orchestra, 1979. A&M Records

As with my earlier Kerouac dissertation, the enjoyment I derived from writing this, allied to some positive feedback, encouraged me to think about pursuing such things in more depth. Therefore, in 2008, I began to scale back my involvement with the Mercury and started a PhD in the Department of Geography at the University of Nottingham. I chose this department principally because Andrew Leyshon and David Matless, two out of the three editors of a book that had captured my attention, The Place of Music, were based there. Andrew became one of my PhD supervisors (along with Alex Vasudevan), whilst David would be one of my viva examiners, the other being Simon Rycroft, also a contributor to that still important collection of writings on music and geography.

Andrew Leyshon, David Matless and George Revill (eds), The Place of Music, 1998. Guilford Press

The content and focus of my PhD thesis evolved during the course of its gestation, as it seems do most, but at its core was an investigation into why and how the city, particularly the nocturnal city, has been aestheticized in certain forms of (generally male authored) romantic balladry and electronica.  Initially, the plan was to produce a kind of 50 year sweep of this topic but it soon became apparent that even a work of 100,000 words would struggle to accommodate all I wanted to say. Sadly, contemporary musicians whose work I reflected on, including Burial, Carl Craig and Richard Hawley, were put to one side (to be ‘re-mobilised’ years later as examples in undergraduate lectures years…) Instead, the focus congealed around two case studies, Frank Sinatra and The Blue Nile, the latter a trio most active in the 1980s, acts with sufficient similarities and differences to warrant being studied together in a comparative fashion in an extended piece of work. Not only were there clear links between the music of both, but there was also no shortage of cultural connections, particularly musical ones, between the cities with which the two artists were most readily identified: New York (Sinatra) and Glasgow (The Blue Nile), something which the thesis explored in some depth when exploring relationships between notions of place and the production and reception of popular music. As is often the way, the title came quite late, and again brevity was not its strong point: ‘Songs of the City: geographies of metropolitanism and mobility in the music of Frank Sinatra and The Blue Nile’.

The Blue Nile, Hats, 1989. Linn Records (l); Frank Sinatra, In the Wee Small Hours, 1955. Capitol Records (r)

Writing the PhD was great fun; no misery memoir here concerning my experience of doing it. Besides the actual writing and editing, one of the most enjoyable aspects of doing the doctorate was getting the opportunity to travel and to attend conferences in many different places, including London, Exeter, Aberystwyth, Durham, Edinburgh, and, easily the most exciting of the lot, Kyoto.

Kyoto Railway Station, 2001

Following completion of my PhD there followed a spell in which I divided my time between the Research and Higher Education Department at the RGS-IBG in Kensington and convening a 3rd year module on Auditory Cultures in the Department of Culture, Film and Media at the University of Nottingham. I got to know the East Midlands Trains timetable better than I ever wished to.

Next, and we are nearly at the end destination now, I took up a Research Fellow position for a few months in the Department of Geography at the University of Exeter, working on two AHRC (Arts and Humanities Research Council) funded public engagement projects, both of which were led by Nicola Thomas, who I first encountered at the Kyoto conference. Given that I am writing this a few days after attending the RGS-IBG conference, it reaffirms the importance of being present at such events (especially if they are held somewhere nice…)

The first of the projects that I worked on with Nicola involved developing a historical geography prototype Android app under the aegis of REACT, http://www.react-hub.org.uk/ It covered many themes but foremost among them were issues of gender, biography, race and status in the Indian Raj, using the life, celebrity and experiences of Mary Curzon, the former Vicereine of India, as something of a prism with which to interrogate these themes; here’s a blog I wrote that highlights how fashion became enrolled in such discourses: http://www.react-hub.org.uk/books-and-print-sandbox/projects/2013/digitising-the-dollar-princess/journal/delhi-durbar-dress-in-derbyshire/ The second AHRC project involved me initiating a timeline for the 80^th anniversary of the Gloucestershire Guild of Craftsmen. Like the Curzon one, this was largely archival in nature and involved extensive research into the Guild's history, most of which was undertaken at The British Library, the Gloucestershire County archives and the Crafts Study Centre in Farnham.

And then finally, in 2013, to Hull. To that place with the distinctive and likeable “end of the line sense of freedom”, as Philip Larkin so accurately put it. An end of the lineness that is even more appropriate in this context given that mobility is one of the geographical themes that I’m most interested in and because my arrival in Hull is where this blog kisses the buffers.

Vintage LNER Hull and London poster

It turns out that I never did get round in this blog to saying what it is that I do all day. I suspect I prevaricate for the most part, hence not getting around here to saying what it is that I do... But I do know what it is that excites me about being a cultural/music geographer: it is coming across all those seemingly random but actually not random at all connections, that sense of “oh look, this links to that, and that informs this.” That’s what keeps me interested, that exploration of those endlessly rich links between, for example, Kerouac and Sinatra (artists both at their prime in 1950s America), between London and Tokyo (Olympic cities), New York and Glasgow (creative connections), Liverpool and Hull (Cities of Culture) and many more besides. And the geography department at Hull is an excellent place in which to feed one’s wonder and intrigue about such things. 

Should you want a or a more straightforward account of my teaching and research there’s always my Hull webpage: http://www2.hull.ac.uk/science/gees/staff/milburn.aspx Additionally, on my blog, www.sonicgeographies.com, I write about music and geography; I also tweet (@kevmilburn), sometimes about the former, and occasionally about the latter #butiamstillcluelessaboutoxbowlakes.