Wednesday, August 22, 2018

Magma Plumbing Systems: A Geophysical Perspective


- Guest blog! Craig Magee


Volcanic systems are complicated. Nearly as complicated, it turns out, as figuring out how to introduce your first blogpost. I’ve finally decided on...

This is me trying to be artistic with a 
jaunty selfie in front of Lake Taupo
Hello! I’m Craig.

Usually I introduce myself as a volcanologist. It’s much easier and sounds more exciting than saying ‘I’m a structural igneous geologist’, which then requires deciphering. Unfortunately, given the expertise of the usual reporters for this most excellent blog, I cannot really pass myself off as a volcanologist. The only active volcanoes I’ve been to are on Lanzarote, which I can’t even remember the name of, and Taupo in New Zealand. I’ve never even seen a volcano erupt! Instead, I specialise in mapping ancient magma plumbing systems in 3D and reconstructing their formation.

To circle back to my opening remark, we have learned a lot about volcanoes but it seems the more we learn the more complicated they become. One problem that I’m sure we’re all aware of and that becomes immediately apparent whenever you stand on an active volcano is how do we actually know what is going on inside and below active volcanoes?


There are two main ways we explore what is going on within volcanoes: (1) we can examine the structure and distribution of ancient intrusions now exposed at the surface that may be analogous to the plumbing systems beneath active volcanoes; or (2) we can use geophysical (and geodetic) techniques to image and/or piece together what is actually happening beneath the surface. However, a new problem arises in how to integrate observations, whether they are from ancient and active systems and/or obtained by geophysical or more classical (e.g. petrological and geochemical) techniques.

Top: Complex network of exposed dyke, sill, and inclined sheet intrusions cross-cutting volcaniclastic deposits on Madeira (photo by Craig Magee). Bottom: 3D view of the -600 kg m3 density contrast isosurface beneath the Laguna del Maule, derived from gravity data, which is interpreted to define a magma reservoir (>50% melt) within a larger region of a crystal mush system hosted by volcanic and sedimentary rocks; the 2D planes show slices through the dataset (redrawn from Miller et al., 2017).

I personally get a bit annoyed when I read or see work on a volcano or ‘magma chamber’, which may incorporate extensive quantitative textural analyses or detailed isotope work, and it is all summarised by a cartoon showing a volcano underlain by ‘blobs’ of magma. I say this not to disparage any such diagrams as I completely understand the need to simplify and summarise information. But out of all the sub-volcanic systems I’ve looked at from around the world, I would confidently say such simple systems rarely exist.

What has taken me awhile to learn is that the opposite of my view is just as true. I produce diagrams detailing the structure of plumbing systems, incorporating information on host rock deformation, and then hurriedly throw in some geochemical or petrological data to briefly support my interpretation. I can now imagine that my flippant use of such data, which is borne more out of my ignorance for the power and subtleties of the techniques involved, must annoy volcanologists.

We are all aware that we need to integrate data and techniques, whether it’s to get work published or a grant funded, but I would argue that such integration is usually limited. Of course, there are many cases where this is not true, particularly where a multitude of scientists with very different expertise have got together to solve a problem. Limited integration is a failing I have recognised in my own research and one that I have come to realise is not necessarily easy to rectify. It’s quite obvious that integration is easier when you find and work with a colleague who is an expert in something you are not, but that integration will always be limited if you yourself cannot get a grasp of the technique you want to synthesise your work with.

Hopefully having explained my viewpoint, I can (finally!) get to the main reason for this blog. In 2016 I was offered an opportunity to help satisfy my relatively new desire to promote integration and collaboration. Through Carl Stevenson, my former PhD supervisor, I was asked by Marian Holness to put together a review article on how geophysical techniques could be used to study magma plumbing systems for the Journal of Petrology’s (JPet) exciting new ‘Perspectives in Petrology’ initiative. The end result was our recently published review ‘Magma Plumbing Systems: A Geophysical Perspective’. Here’ I want to provide a brief explanation of what we did and why.

Marian’s vision for the article was to provide fundamental information for readers of JPet on how geophysical techniques could be integrated with petrological and chemical approaches to study igneous systems, all in the hope of promoting collaboration between the two overarching disciplines. Whilst I jumped at the opportunity, I soon remembered I’m not a geophysicist. I’m a field geologist at heart and whilst I use some geophysical techniques, I don’t necessarily understand all about their underlying physical principals. There’s also many geophysical techniques with which I am totally unfamiliar. It was therefore necessary to assemble a team of experts to write what I could not; I am entirely grateful to all 16 co-authors who volunteered their time to help out and would like to think they had as much fun as I in building the review.

For the first part of the review, the assembled team of experts included Susi Ebmeier, Derek Keir, James Hammond, Jo Gottsmann, and Kathy Whaler, who helped collate sections on how geophysical techniques are used to examine active volcanoes. For example, in the review we discuss: (1) Interferometric Synthetic Aperture Radar (InSAR) and other geodetic techniques can relate ground deformation to the geometry and location of moving magma in the subsurface; (2) seismicity (earthquakes) can track magma intrusion and link to petrological indicators of changes in magma dynamics; (3) various seismological techniques (e.g. P-wave travel-time tomography) allow us to map locations and volumes of melt and/or crystallised intrusions beneath active volcanoes; (4) gravimetry can be used, particularly in conjunction with geodetic techniques, to identify regions of magma accumulation; and (5) electromagnetic techniques (e.g. magnetotellurics) provides unique insights into the distribution of fluids, including magma, in the subsurface. These techniques mentioned above are primarily used to study active volcanic systems and, although they all have limitations, their integration is critical to understanding active magma plumbing systems. As we highlight in the review, there is incredible potential, as evidenced by a few studies, in further integrating these techniques with petrological, geochemical, and geochronological information.


Top: Schematic showing how InSAR is collected and how ground deformation patterns may correspond to different intrusion types (Magee et al., 2018). Bottom: Correlation between seismicity, SO2 flux and number of calculated crystal ages over the 1980-1986 Mt St Helens eruption period (from Saunders et al., 2012).
Putting the sections mentioned above together emphasised to me the further importance of integrating such studies with geophysical analyses of ancient intrusions. To shed some light on how this could be achieved and the benefits, I worked together with Chris Jackson, Nick Schofield, Carl Stevenson, Brian O’Driscoll, and Mike Petronis, to discuss how: (1) seismic reflection data, which provides ultrasound-like images of Earth’s subsurface, reveals lateral magma transport in networks of sills and inclined sheets (i.e. sill-complexes) can transport magma over significant lateral (>4000 km!!!) and vertical (>12 km) distances; and (2) rock magnetic techniques, principally anisotropy of magnetic susceptibility (AMS), allows fabrics related to magma flow, layering, textural modification, and/or deformation to be identified and interpreted. These techniques reveal how magma plumbing systems are structured and constructed, providing an important framework in which geophysical data from active plumbing systems can be interpreted.

Uninterpreted and interpreted seismic reflection images from the Rockall Basin, offshore Ireland showing an interconnected network of sills and inclined sheets extending >20 km laterally (modified from Magee et al., 2014).

Beyond a review of what geophysical techniques are already used to study igneous systems, we also highlight the future role that Full Wave-form Inversion (FWI) (Jo Morgan), Unmanned Aerial Vehicles (UAVs) (Sandy Cruden, Steve Micklethwaite, Stefan Vollgger, Greg Dering), and numerical modelling (Matt Jackson) may play in developing our understanding of magma plumbing systems. FWI offers amazing potential in imaging the 3D structure of plumbing systems beneath active volcanoes, allowing insights from the worlds of seismology and seismic reflection data to be combined. UAVs provide an unprecedented resource for mapping and photographing outcrops in detail, but with the potential addition of geophysical sensors to drones, they can help integrate field and geophysical studies. Numerical modelling similarly allows data from different techniques to be integrated and hypotheses tested.

To wrap up, it is important to emphasise that this review is by no means exhaustive and there are so many other techniques and examples that we would have liked to have included and explored: apologies to all those works we were just unable to incorporate and acknowledge.

Hopefully the review will form a foundation for anyone wanting to develop their understanding of how different geophysical techniques can be used to investigate different aspects of active and ancient magma plumbing systems and, in particular, how those techniques could be integrated with each other as well as more classical methodologies (e.g. petrology, geochemistry, geochronology, etc...).

If anything, I had a great time putting this review together and with all that I learnt from the experience I can see an exciting and integrative future within igneous geology. I would thus like to finish by once again thanking all my co-authors for their time and effort in helping put together the review article. I also extend my gratitude to Juliet Biggs, Martyn Unsworth, John Bartley, and Magnús Gudmundsson who dedicated the time and effort to provide four excellent reviews. Lastly, I would thank Marian Holness for the invitation to put together what has certainly been a very rewarding piece of work.

If you are interested in learning more about the techniques discussed in the review or wish to collaborate and integrate one or several of those discussed, please feel free to contact me and I can direct you to the relevant co-authors. I would also particularly love to hear any stories where this review has sparked off an idea and/or collaboration!



Kind regards,

Craig Magee

(Twitter: @DrCraigMagee)



References:

Magee C., Jackson CL., Schofield N. (2014). Diachronous sub‐volcanic intrusion along deep‐water margins: insights from the Irish Rockall Basin. Basin Research, 26, 85–105.

Magee C., Stevenson CTE., Ebmeier SK., Keir D., Hammond JOS., Gottsmann JH., Whaler KA., Schofield N., Jackson CAL., Petronis MS., O’Driscoll B., Morgan J., Cruden A., Vollgger SA., Dering G., Micklethwaite S., Jackson MD. (2018). Magma Plumbing Systems: A Geophysical Perspective. Journal of Petrology, egy064, https://doi.org/10.1093/petrology/egy064

Miller, C.A., Williams-Jones, G., Fournier, D. and Witter, J. (2017). 3D gravity inversion and thermodynamic modelling reveal properties of shallow silicic magma reservoir beneath Laguna del Maule, Chile. Earth and Planetary Science Letters, 459, 14–27.

Saunders K., Blundy J. D., Dohmen R., Cashman K. (2012). Linking Petrology and Seismology at an active volcano. Science, 336, 1023–1027.























































Tuesday, August 14, 2018

Out in the field, doing experiments, meeting other scientists, and eating LOTS of pizza – a student’s perspective

A guest post:

Hello! We are three of Alison’s students at the University of Missouri – Kansas City. Kadie Bennis is a Master’s student in the Department of Geosciences researching subaqueous volcanism while combining both field observations and experimental techniques to characterize sediment-magma interfaces. Sierra McCollum is a Senior undergraduate Geology major researching morphology and microtextures of ash and glass particles of small scale phreatomagmatic eruptions. Julia Boyd is a Junior undergraduate Physics major researching Martian maars and their quantitative shape relation to Earth maars and simple impact craters. Together, the three of us traveled with Alison to Buffalo, New York with a heightened sense of curiosity – and excitement – surrounding large-scale experiments performed at the University at Buffalo. #uBLASTworkshop


Travel adventures: Alison, Julia, Kadie and Sierra sleep deprived selfie. Night one was spent in a hotel in Charlotte, NC, circa 3:00 am. We were extremely tired due to multiple flight delays and cancellations and were ready to arrive in Buffalo! 



Day one, we finally arrived in Buffalo. We met up with Arianna Soldati (recently of University of Misouri and soon LMU Munich, Germany) and Kae Tsunematsu (Yamagata University, Japan) who were also there for the workshop and played tourist as we explored the US side of Niagara Falls.
 
The three of us (along with almost 50 others) participated in the Center for GeoHazards Field-Scale Experiment Workshop that involved studying the effects of a volcanic eruption in a controlled environment (videos from past experiments). Some of the data includes measuring the direction in which ejecta (debris from the blast) deposits, the shape of the crater post-blast, using drone technology and photogrammetry, and collecting and weighing the ejecta. We set up 60 sample boxes in two directions with boxes in one-meter increments. Ejecta collection is important at this scale, because it provides information on the direction deposits will travel, which serves as an analogue to natural volcanic eruptions. Ejecta movement is crucial in hazard assessments, since one of the basic questions is 'where is it unsafe to be?'. Some of the other participants used drones to document the size and shape of the crater formed after the detonation. This, in conjunction with multiple ground photographs will be used in Julia’s research to study how an eruption affects the size and shape of the resulting volcanic crater. 

 In the beginning, we didn’t really know what to expect, other than, we were going to use chemical explosives to puncture holes in the ground, which we would then document for photogrammetry (aka take a plethora of photos in order to piece them together to create a model). The first day was a rush of excitement with jumbled up nerves and shy “hellos.” As young, beginning scientists, the three of us knew absolutely no one in the large lecture room filled with high profile scientists. We had to peel ourselves away from our comfort zones in order to walk up to someone new and say, “hello,” which, admittedly, was quite difficult in the beginning; we stuck together in our group throughout the morning, working on a few preparations before the experiments took place. However, one of the first people that we met was a friend and colleague of Alison’s: Kae Tsunematsu. She also stayed in the same hotel as us, so we quickly became more comfortable talking with her. Thanks to her bubbly and inviting personality, we felt at ease after our initial moment of shyness and lack of confidence. Kae actively invited us into her conversations, talking with animated excitement and asking us questions about not only our research, but also about who we were as people, an aspect that we believe is extremely important in the sciences, and sometimes easily forgotten in a swarm of names and research papers.


As the introduction part of the workshop commenced, we all sat together in a line like little ducks, scrambling to take notes while silently acknowledging all the important scientists around us. A few were even geologists that we had cited in our own research and now we finally had a face to the name. Intimidating. Nervous leg-bouncing movements lightly shook the table as fingers drummed in anticipation. We were really going to work with all these scientists? How would this work? What data do they hope to collect? Oh – what as his name again? He just told me! Near the end of the intro presentation, we all broke out into separate data collection groups, based on our primary goals of the workshop. Our small team of four comprised a majority of the post-blast ejecta analysis group, so we slowly introduced ourselves to the few other scientists that joined the group. This moment was our first break in success – a crucial step in the workshop where we learned how to introduce ourselves, present ourselves to other scientists, and engage with them. We spent the rest of the day working on injecting plaster into ping pong balls. We would bury these in the ground near the charge and measure how far they traveled as a result of the blast. Since the ping pong balls were larger, they acted as volcanic bombs (they can range from a few meters to tens of meters or larger) relative to the finer ejecta collected in the sample boxes in this scenario. 

Day one of the workshop. Kae Tsunematsu, Sierra McCollum, and Julia Boyd (clockwise left to right) hard at work filling ping pong balls with plaster in preparation for the large-scale experiments.


Day one of the workshop back at the hotel. Kae Tsunematsu, Sierra McCollum, Julia Boyd, and Alison Graettinger (clockwise left to right) still working on ping pong balls – we made a little less than 50 of them!

The next day was pre-detonation day, and let me tell you, it was incredibly crazy, incredibly busy, and just plain incredible. A reporter for UB News was there with a notebook in hand and a small camera crew; NPR was there with their camera crew; scientists from all across the world were setting up various pieces of equipment at once, laying out cords, cables, microphones, high-speed cameras, 4K cameras, drones – we’ve never seen so much high-tech, fancy (not to mention, quite expensive) equipment before in one setting. There were people on the roof of the building, people on the detonation pads, people running in and out of the small, rectangular building, people peeping out from behind the tall grass, and even a person climbing a tree, hoping to capture a wider perspective of the blast from his camera. Despite the chaos, we all worked together harmoniously. When one person finished setting up their equipment, they would go to another group and ask how they could help and the job completed in half the time. We looked out for each other; we reminded each other to eat and hydrate, as the unbearable sun continuously beat down on our bodies. As we worked on setting up our boxes in which we would collect our ejecta samples, we found that someone, if not multiple someones offered their help to us, of which we were extremely grateful. Sometimes, they were people that we didn’t know at first, but as we worked together on the same project, we grew more and more comfortable talking with them and asking them questions. Eventually, we came to know the names of most of the participants, all thanks to us working together as a single large data collection team. At the end of the extremely long work day, we had never felt prouder or more accomplished. We met up with a majority of the workshoppers behind the hotel in the parking lot near a dumpster – a fantastic place to have a pizza party. As we munched hungrily on pizza and buffalo wings, we had grown accustomed to talking with people we didn’t know, unlike at the beginning of the workshop. We introduced ourselves to the other students participating in the workshop while we worked in an assembly line fashion to conclude our final preparations for the next day.

Detonation Day. It was finally here. The most anticipated day of the week. Our boxes, all labelled and assembled stood in a neat formation, hungry mouths open and ready to catch ejecta. Microphones from the Brigham Young University (BYU) Acoustics group stood tall in the middle of the silent field and cables to various instruments snaked their way through the frosty morning grass. The dense fog was a curtain ready to reveal the final act. We were one of the first groups to arrive at the site so that we could prepare our collection boxes. The field was quiet, the calm before the storm. Everything was in order. We double checked. Triple checked. Our fingers had grown accustomed to duct tape that tore at our skin, plastic trash bags that clung to us like blankets, and yellow lights that made everyone in the room look like green aliens. We were ready, and so was everyone else. A whirlwind of activity blew away the fog as we began to set up our collection boxes, making sure they were perfectly one meter apart. People talked across the field in many languages, Spanish, Italian, and English, but we all breathed a collective sigh of relief as gusts of cool wind blew through our sweaty clothing. It was time.
Day three of the workshop. Early morning fog with microphones and cameras set up in anticipation for the first blast.
We cleared the area, safe from the detonation pads. An air horn sounded and silence settled once again upon the grassy field. A countdown from five. Then. Bam.Bam. Bam. Bam. Bam. Bam. Six times, each half a second apart. It was over as soon as it began. All the scientists stood there and cheered. We stood there, clapping and in absolute awe. And then came the rush for data collection. We had spent the last two days in preparation for this moment. We approached the pads, excited to see the fruits of our labor. There, in every single box, all 60 of them, ejecta ranged from large particles to fine-grained ones. We set to work collecting all the sample bags and running them to the building for weighing. Again, we experienced the power of people – when someone had finished their data collection, they would come over to us and offer their help, thus decreasing the time it would have normally taken the three of us. At the end of the day, we were exhausted from the day full of heat and manual labor, but it was a good exhaustion. The kind that we could be proud of and even feel accomplished. As we stood there, draining the last few drops of water from our bottles we couldn’t wait to shower. But first…ice cream! Ice cream, the best way to celebrate the end of an incredibly long, hot, and exciting day.
Day three of the workshop. Kadie Bennis proudly pushes the detonation button for blast #3.

Day three of the workshop. Sample boxes spread laterally from the blast pad one meter apart.
The last day of the workshop came faster than we could have imagined. Unlike the first day of introductions, we no longer sat in a line like little ducks; we had grown just outside our comfort zone to mix in with some of the other students from BYU. We quietly observed as everyone presented the data that they collected the previous day. It was fascinating, the way that everyone talked about different methods in which to collaborate and share their data. Everyone was amicable, willing to be open and honest about their data sharing. Some even formed groups afterwards to collaborate on AGU abstracts (come meet us there if you plan on going)! Later that night, once a majority of the group had dispersed, a few remaining participants met at Greg Valentine’s house for dinner. It took the three of us a little coaxing again to talk with some of the senior scientists, but once we integrated ourselves into a conversation, the entire evening exploded into stars, our eyes and minds, open. We absorbed information like a well-sorted sandstone. We learned about different ways in which physicists apply their skills to geological problems, what we could do if we wanted to study or do research abroad, and we even discussed some of the paths that people took to get to a certain point in their careers.
Overall, this workshop was a fantastic learning and networking opportunity that we are all grateful to have experienced. We met many students, scientists, and professors who encouraged us to continue in our education and explore multiple research and job-related possibilities post-graduation. Sometimes leaving your comfort zone is difficult, but that shouldn’t stop you from asking questions and learning. There are so many people that we would like to thank for allowing us to partake in this amazing experience. Thank you to our advisor, Alison Graettinger for encouraging us every single day, whether it be in the classroom or in the middle of nowhere. Thank you, Kae Tsunematsu, for your kind and energetic personality, for your patience, and for your massive help with our post-blast preparations. Thank you, Arianna Soldati, for inspiring us to talk with new people and for your invaluable research and educational advice. Thank you to all the BYU students for your intriguing conversations and your physics perspective on the experiments. Finally, a huge thank you to Ingo Sonder and Greg Valentine, for being wonderful hosts, for your patience, and for planning the entire workshop so that students like us are able to branch outside of the classroom and learn how to apply real research techniques to real large-scale experiments.
Day three of the workshop. Kadie Bennis, Julia Boyd, and Sierra McCollum (left to right) watch as blast #4 goes off in the distance. Science really blows their mind.