Turbidity currents, pretty pictures, and an amazing 3D imaging tool

As well as my work on pyroclastic modelling, my first postdoc was spent investigating submarine turbidity currents. It’s fair to say most of the general population have never heard of the things, which might be considered bizarre considering the fact that a single one of these flows can transport more sediment than the all the worlds rivers put together manage in a year.  To put that into numbers, rivers are estimated to throw out something like 13-15 billion tons. That equates to around 5 x 10^12 L, or 5 cubic km of sediment. For scale, that’s about 5 times the amount of material that Mt St Helens threw out in 1980. However, even a small turbidity current will deposit volumes of 10 cubic kilometers. 100 cubic kilometers is relatively common. There are big ones which have been known to move as much as 3,500 cubic km. (Sidenote, the deposit of a submarine turbidity current is called a turbidite).

How do we know this?  Geology. And interestingly, almost only geology. We can observe the deposits of these flows, but no-one has ever seen one in action. We have not a single measurement from within one of these deep-basin flows. We have some measurements of small scale flows occurring in shallow water which we believe behave in a similar way to the deep basin stuff, but even these experiments have never measured the concentration in the important dense part of the flow. Our only other line of evidence is one which raises the importance of understanding these things; in 1929 an Earthquake triggered a turbidity current on the Grand Banks. That current severed a dozen subsea communications cables, but we can at least use those data to estimate speeds of that current. Turbidity currents have caused plenty of other subsea damage in more recent history as well. With almost all of our international communications traffic delivered by subsea infrastructure, these things have huge potential for damage.

Some months ago I was invited to attend a workshop being held in Italy to address where turbidity current research is, and what future work might focus on. This was being organised by Pete Talling at the National Oceanography Centre in Southampton, who recently put out an excellent review article on the subject. I of course accepted, and a fortnight ago found myself in Bologna trying to look for a ‘brown haired Italian man’ who was going to pick me up.

The workshop was excellent, with 32 attendees from across the world and specialisms. We spent about half the time in discussions, and the other half in the field (still having discussions). I won’t go into too much detail on the work presented as I know a lot of it is still heading for publication, but suffice to say we had a fantastic mixture of modellers, sedimentologists, industry guys (turbidites can form major petroleum reservoirs), and experimentalists. It’s the first workshop I’ve been able to attend, and it blew the socks off every conference I’ve ever been to for enabling dialogue between people, and it was useful dialogue.

There were some awesome presentations from the guys at MBARI and the Canadian Geological Survey looking at flow observations around Monterey Bay, the Fraser Delta and the Black Sea. Some really interesting modelling from Andy Hogg at Bristol demonstrating how important modelling a variety of grainsizes is in getting deposits correct. There were also plenty of presentations on how we model and observe complex 3D architectures from a variety of perspectives.

The fieldwork was focussed on looking at a turbidite sequence in the Apennines, which formed as a pretty much perfect layer-cake of horizontal beds. Did I mention that turbidity currents have no problem propagating for hundreds of kilometres along slopes shallower than that on a  football field?

IMG_1583So what you see in the field are alternating layers of sand (the turbidite) and mud (some of it settling out after the sand deposits, some of it then settling out of the water column as normal hemipelagic mud over the hundreds or thousands of years between flows). Interestingly, you can tell the difference between the turbidite mud and the hemipelagic mud from the colour contrast; The mud deposited by the turbidite is a slightly bluer colour than the paler hemipelagic mud. This photo shows a layer of turbidite mud at the bottom, then a pale hemipelagic mud above that, finally capped by the next turbidite sand, with mud again on top of that.

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The really nice thing about turbidite sequences is that while you get the really clear differential weathering between the hard sand and the softer mud highlighting the broad structure, there is so much amazing fine structure to observe as well. Take, for example, mm-scale horizontal laminations:

IMG_1624And convoluted bedding formed by remobilisation of wet sediment

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And my personal favourite, dewatering features. Favourite because they are really difficult to see unless the sun is just right.

IMG_1640Those dewatering features also seem to be associated with really subtle surface ridges. I got into a very interesting and ultimately inconclusive debate with Esther Sumner and Frank Peel about how you could form these uniform ridges (which appear to be strongly correlated with the original flow direction).

IMG_1646One of the best discoveries of the week, however, was a little something Mike Clare from Fugro introduced me to. Geological community – may I introduce 123D Catch. In summary, take a few dozen photos at different angles around an object, and this free bit of software automatically works out where each is in relation to the other and builds a 3D model, which it then textures and allows you to manipulate as a 3D object.

I’m still very new to it, and the two samples I tried in Italy have not come out brilliantly. however, I present to you the dewatering features in glorious 3D:

A little shonky with a few model gaps because I didn’t take enough pictures. There’s another one of convolutions that I’ll upload for another post, probably describing the app in a bit more detail.

Get to it geofiends – I think this has some real potential.

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#IAVCEI2013 wrap-up & photos

The conference is done, the return flight completed, and the bag of laundry dealt with.

The general consensus amongst those I spoke with after the conference (and a view I agree with) was that it certainly ranks up there with the memorable ones.  There was some excellent science presented, and the city of Kagoshima made a great venue. That was all topped off with some spectacular activity from Sakurajima, and a couple of impressive events put on by the organising committee.

My particular favourites with the science I think go to:

1) Ben Andrews, who presented some really lovely work looking at dilute pyroclastic density currents (PDCs), and some work from his most recent experiments using a laser array to observe the turbulent cloud dynamics.

2) Anne Mangeney, presenting work on PDC erosion, which is desperately understudied at the moment.

3) Robin Matoza, who highlighted that some of the physics being used to monitor eruption jet acoustics is 40 years out of date with regard to the present understanding used in the aerospace industry.

It would be remiss of me not to wax a little more lyrical about the behaviour of Sakurajima while we were there; with an average of 6 eruptions per day we were treated to a lot of picturesque photo opportunities…

This was the view on the first night from Kagoshima harbour

IMG_0959And the second night from the island itself as the sun went down

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On Monday a series of mid-conference field trips were run, and the one I was on spent a couple of hours in the morning at Sakurajima, before heading up to Kirishima later in the day. This was Sakurajima about 2km  from the vent when it was kind enough to spend an hour or so throwing intermittent pulses up for us.

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Of course, what we didn’t expect was what we saw in the mid-afternoon, just as we were returning to Kagoshima…

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The luck of the draw meant that we were just the wrong side of a hill and stuck on a coach. We also knew that then other group were almost certainly at the lookout point the previous photo was taken from.  we eventually got the coach driver to stop after about 10 minutes to see the plume drifting away, having reached a final height of about 3200 m.

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Still trying to get hold of some photos from colleagues on the other trip, and still phenomenally jealous that they got such a good view (including co-eruption lightning within the plume). EDIT – there’s a couple of lovely links in the comments.

The conference was rounded off with an amazing dinner, although made somewhat weird by the rapid ushering-out we received once the meal was over and the coaches were all ready to leave. That in turn was followed by a visit to several bars in Kagoshima, including a tiny reggae bar jammed full with about 200 volcanologists, including 3 or 4 behind the bar helping to serve.

If you’re at all interested, I’ve uploaded my poster presentation here, although the oral will stay offline for the moment as it doesn’t make a lot of sense without a lot of commentary.

I’ll leave you with a final few shots I took on the morning before my flight back, while visiting the Kagoshima aquarium. well worth a visit.

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#IAVCEI2013 – The second best volcanology conference in Kagoshima

It may come as no surprise that Kagoshima – home to the most active volcano in one of the most volcanically active countries in the world – has played host to more than this years IAVCEI meeting when it comes to getting volcanologists into town. You might guess from the spectacular way in which they play host; notices, flags and IAVCEI branded fans and accessories adorn much of the town. The conference goody bag bears not just the usual USB stick, local promotional material and a notebook, but full geological maps and hazard maps of Sakurajima and a variety of other volcanoes in Japan. In fact, one outstanding full map showing Japan in its complete volcanological beauty. Oh, and a 3D plastic map of Sakurajima. And tickets to a festival of music and fireworks. And an invitation to go and watch the ’round volcano yacht race’ and complimentary tour cruise.

The reason I feel IAVCEI may be playing second fiddle to another conference is that both these events – the festival and boat race – are held to commemorate the 1988 Kagoshima International Conference on Volcanoes. I’ve never heard of an event being staged to commemorate the anniversary of a conference before, let alone two. It must have been one hell of a conference. My mind can’t decide whether it should be picturing volcanological luminaries dangling from light fittings, dripping sake from their over-gorged throats, or some kind of terrible boating disaster with fireworks.

Anyway, this evening was the festival, so I took the opportunity to skip out of the conference early (5.30 start time for the event was not handy for the 6.30 finish of seminars – fortunately nothing took my fancy this afternoon anyway). Grabbed the complimentary ferry across to Sakurajima, and went and sat in a field. I will say this for the Japanese – they do events in a unique and special way. After finding a spot that was just about in the shade, and occasionally catching the dregs of a breeze to take the edge off the 34 degree heat, I sat down, and relaxed. Camera in hand, I was determined to get a good sunset shot of Sakurajima if nothing else. She did not disappoint, and photo will be forthcoming just as soon as I have a USB cable.

However, it would be doing the festival a disservice if I didn’t recount some of my favourite moments here. Billed as offering a Hinoshima drum performance, I was looking forward to some tubthumping music. The “6000 vigorous fireworks” also sounded appealing. The build up to these, however, was sublime. First up, we had some kind of stage play featuring what I can only describe as a guy dressed as a Power Ranger, another as a teddy bear, and a couple of guys dressed in form-fitting white lycra bodysuits having sword fights. Not knowing the language I was free to make up my own story in my head, and completely failed to come up with anything coherent. So I assume it was an actual episode of Power Rangers.

Next up, we had the local choir doing their thing. Very choral, but the crowd weren’t interested. After that we had a couple of ladies doing a fan dance, followed by another dance troupe with ribbons or scarves (I was too far away to tell). After that we had a rather bizarre karate act who sang. She would do a few karate moves, sing a song, then smash a bit of wood, another song, smash a brick, etc. With no clear idea of what was going on I decided it was some kind of superhero or videogame character, and she could only do 30 seconds of karate after a 2 minute power-up period of singing.

Next up the drums, which were excellent. However, at this point I was aware that last up were the fireworks, then there were going to be about 10,000 people or more crowding back to the ferries, so I wound my way back down the hill to try and catch the firework display from the water, with Sakurajima in the background. On my way back I took the opportunity to grab some dinner. Japanese festivals it turns out have an impressive array of Things On Sticks. Sweet things on sticks, savoury things on sticks, miscellaneous things on sticks. I treated myself to the squid-on-a-stick, although opted for the body portion rather than the Lovecraftian tentacles-on-a-stick.

And here we are back in the hotel, 9.30 pm, aiming to kill the last of the jet lag in the hope I don’t fall asleep tomorrow, particularly as I’m presenting. 3pm session in A4 for anyone here.

Some great science today – some lovely experiments looking at magma chamber dynamics, and gas-slug growth through conduits. I love me a good experiment, and Ed Llewellin and others at Durham have a 13 m monster conduit they’ve produced some fascinating results in. Also some really interesting work on the effects of melting the roof of magma chambers, although with so few variables investigated it felt a bit like a spherical cow at the moment – clearly more work to be done.

Right – off to wash the volcanic ash from my grubby feet, and rest my weary head. More updates to follow.

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#IAVCEI2013 – The land of the rising sun

Japan is bloody hot and humid. Stepping off the plane was more like walking into a well-prepped sauna.

Just thought I’d get that out of the way.

After three flights, no sleep, and 3 hours in a park twiddling my thumbs before being able to check in to the hotel I’ve finally managed to have a shower, put on some clean clothes and get over here to internet land.  I just thought I would share with you some cool things and observations from the last day or so of travel.

Firstly, Charles De gaulle is a sprawling mess of an airport. I know this is hardly a controversial opinion, but I’ve flown through that place probably 2 dozen times in the last year and I just wanted to take this opportunity to express my loathing.

Secondly, the Paris-Tokyo flight route is fascinating for a number of reasons:

  • You get some great views over Holland and Scandinavia (pics to follow).
  • Your sense of scale also gets a life-changing smack around the face when you spend the best part of 9 hours flying over the completely unpopulated expanse of Northern Russia. I’ve flown over Canada before, but there’s always a few roads or settlements or whatever. There is a wild untamed beauty to the forests and tundra of Northern Russia that is really quite breathtaking.
  • During the summer, if you leave at about mid-day, you experience an interesting phenomenon; the sun never sets, which seems to somewhat steal Japan’s thunder, given what the name literally translates to (see title of post if you’re not sure). I had the sun coming in through my window for 10 of the 12 hours – the only reason I didn’t for the first two hours was that we were pointing in the wrong direction. It was my first experience of an arctic circle night, and it was quite bizarre – particularly as at both the departure and destination locations the sun was high in the sky and blazing a fierce heat.

Japan’s topography is amazing. As well as a great view over Mt Fuji (again, photos to follow once I have access to an appropriate USB cable), the terrain is utterly ‘ruffled’. Everywhere you look the land is carved up into inhabited and farmed floodplains along narrow river valleys (itself broken up into impossibly regular and bizarrely small field systems), fingering between wooded ridges and hills which Slartibartfast himself might have said were going a bit overboard with the detail work. Take this perfectly standard example:


The trip from Kagoshima Airport to the city centre was made vastly more enjoyable by the conversation with the young lady completely astounded that so many Westerners would want to all go to Kagoshima. Her parents run a hotel on nearby Yakoshima (a world heritage site), and she was going back for the weekend. On asking what she would recommend to do on any free days the best she could manage was ‘there’s probably some old buildings? Personally I would go shopping’. Then she recommended that I had to try the local speciality of ‘Black Pork’. She had no idea why it’s black but apparently it’s delicious.

Right, off to rest my weary head and make a vague attempt at avoiding jet lag. Last time I flew out in this direction for a conference was IUGG in Melbourne a couple of years ago. I went straight over to see a friend in Tasmania before the conference, had a lovely first day, then sabotaged the second by somehow falling asleep for 18 hours. For someone who normally lives on 6-7 hours a night it came as a bit of a surprise. Fingers crossed I can make it up in time to get a sunrise shot of Sakurajima out in the bay.

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IAVCEI 2013

Sunday sees the start of the biggest gathering of volcanologists in a specialist conference. The International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI) General Assembly is only held every 4 years, each occasion at a different place.

Last time it was Reykjavik (excellent science, superlative rollmops). I was presenting the analyses coming out of my PhD, and had my first proper opportunity to meet the key players in my field. I was also a broke student, and spent the week camping. My lasting memories of it as my first international conference are ones of being a bit shy, not really knowing anyone, and utterly loving every minute of seeing what was going on at the cutting edge in the field.

This year we’re in Kagoshima, Japan. Now I’m a broke postdoc staying in the cheapest hotel we could find. As well as some top science (and hopefully some top seafood and sushi) I also have a visit to Sakurajima to look forward to. It’s a fascinating volcano, not just in terms of it’s activity but also in terms of the defence engineering that has gone on there. The Japanese have had fantastic success diverting lava using purpose-built culverts. Can’t wait to see it all.

This will also be my first time in a country where I speak not one jot of the language. The Kindle phrasebook will be keeping me company on the flight. I also spent an hour earlier putting bookmarks into a mapping app on my phone so I can find everywhere easily without resorting to gazing at unintelligible signs. Note for others – Google Maps doesn’t work in offline mode in Japan.

I’m presenting twice at the conference – once on the Sunday in the 3pm session in room A4, on the outcomes of my recent experimental work (“Experimental investigation of pyroclastic flows generated by continuous supply of material”). Lots of fluidised granular flows doing cool things as analogues for pyroclastic density currents.  The second is a poster on Tuesday the 23rd which is a project I’ve been putting together in my spare time with a whole bunch of collaborators looking at whether turbidity current models can help explain what happens when a pyroclastic flow enters water (“What happens when a pyroclastic flow enters the water  - numerical modelling of an offshore pyroclastic turbidite”).

Very much looking forward to seeing a few of the GeoTweeps there, and I’ll b e attempting to do some updating both here and on Twitter during the week – the hashtag seems to be #IAVCEI2013. Fingers crossed for a spectacular and safe display from Sakurajima over the next week.

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Centres of mass and another reason to love Photoshop

With the experimental work on this project pretty much wrapped up I’ve been spending a large amount of time playing with spreadsheets, making frame-by-frame measurements from high-speed video files, and plotting data up as I start to draw together a paper. With hundreds of experiments completed the real task is identifying those which demonstrate the results in the best way, without displaying so much data that the whole thing becomes unmanageable.

Part of this process is deciding which types of results show things best. For example, if I am trying to demonstrate the effect of mass flux (how much material is put into the experiments per second), am I best showing the effect on the speed that the flow moves, or  in how far the flow finally reaches? Should I be plotting mass flux at all, or should I actually be plotting things in terms of the concentration of the flow (which varies as a function of mass flux)? Should I describe the deposit rather than the flow?

Because different types of flow form different shaped deposits one of the ways of describing the deposit is by its centre of mass; how far down the flume is the midpoint of the resting mass? A long flat deposit will have a midpoint much further away then a simple wedge, where much of the material as not travelled far at all. This is a really useful way of describing how mobile the flow must have been which formed the deposit, but it’s a non-trivial thing to measure.

Today, I worked out a solution and I’m going to put it up here in case a) anyone else finds it useful, and b) I forget how I did it.

All you need is a copy of Photoshop. I’m guessing GIMP might do it as well, but it’s a long time since I’ve used it.

So, we start off with an image of a deposit.

Deposit 1Next up we simply mask out the face of the deposit on a new layer.

MaskWith that done, we get to the clever bit. You need a simple black-to-white gradient (there’s one as default in the gradient tool), and apply it over the masked shape.

gradientYou’ll notice that in the Histogram tool it gives us a total pixel count in the shape of 31,125 pixels. The histogram demonstrates how many pixels of each shade are in the image.

Now, you move your cursor across the histogram window, looking for the point which represents the 50th percentile (you could equally do this for any other percentile you’re interested in). Note it also gives you the colour level (in this case 76):

50th percentileThis level represents where on the scale of 0 – 255 levels of grey the midpoint lies. So in our case 50% of the pixels have shades between 0-75, and the other 50% of the pixels have shades between 77-255. It’s also worth remembering that level 0 is black (no brightness) while 255 is white (full brightness).

So now we simply open the info panel, and move our cursor over the image itself to identify whereabouts along it we get level 76 (you might have to ensure the image is in RGB). That’s our mid point. The image below shows a selection which divides the left 50% of deposit from the right 50%. We can verify the result by looking at the pixel count in the histogram window which is showing the number of pixels within the selection in the gradient layer (should be half that we started with – in this case 31125 / 15560 = 2).

Complete2So there we go. We now can use the scale on the background image (checkerboard grid at the bottom is 1cm, the lined grid is 2cm) to identify the centre of mass in the deposit at about 25.5 cm.

Hopefully this may be of use to someone somewhere.

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Spaced

Today is the day that Expedition 35 return from the International Space Station. Later tonight they will climb into the docked Soyuz capsule, and perform a re-entry back to Earth, bringing to an end a truly phenomenal period of public engagement with the ISS, driven largely by the incredible content provided by Commander Chris Hadfield via his Twitter stream.

Clouds demonstrating the very British art of queuing over Hull, 12 May 2013. C. Hadfield.

Slinging aside the (often justified) criticism that Twitter is mostly banal we’ve been treated to months of photos and commentary, giving a more humanised view of our planet than could ever be achieved by even the Blue Marble image taken by the Apollo 17 crew. Tonight that stops, and the world is a poorer place for it.

I struggle to think of a single science engagement activity which has had anything like the success that Commander Hadfield achieved on this expedition. The Twitter posts and images caught peoples imagination, and the numerous videos and broadcasts that he has since been involved with draw people into contact with day-to-day life on the ISS like nothing else.

In my free time I help moderate the reddit forum /r/Askscience – a place where experts from across the spheres of science can answer any question that any user cares to ask. As a result of Hadfields work, the subreddit has seen an unprecedented number of questions regarding life in space, space engineering, and similar themes. There’s been loads. He has generated the kind of outreach which rather than just being passive listening, has genuinely peaked peoples curiosity and interest. It’s the kind of outcome that every teacher in every classroom in the world aims and hopes for. It’s the kind of engagement that encourages people to pursue and kindle an interest in science and technology that leads to new scientists, and a wider public understanding of science.

20 years ago I was able to participate in a conference video call with the JASON Project as they explored part of the ocean – we were able to hear directly from the crew and science team, and pose questions to them. It was a fantastic experience, but available to a lucky few – approximately 100 or so of us drawn from dozens of schools in the area, crammed into a small lecture hall at the nearby US Airbase at Mildenhall. That is now an experience which millions have been able to share. The opportunity to directly connect with an individual or team doing something amazing.

The tragedy really is that Hadfield is the first to really take this potential so firmly to hand. That he is personable, funny, and an excellent communicator helps enormously. A guitar-playing photojournalist astronaut I think possibly confounds many of the assumptions the general public can hold about the people, while the content he’s provided has enabled a discussion that communicates the mission far more broadly than has been achieved before.

With this high profile mission coming to a close, there are now a number of opinion pieces appearing – some of which ask the question “but what is it good for“. It’s a question that is always worth asking – my only hope is that the scientific and science-supporting community can step up to the plate and vocally provide the broadside which Hadfield himself is championing: “We’re not going to do it tomorrow and we’re not going to do it because it titillates the nerve endings. We’re going to do it because it’s a natural human progression.”

The ISS suffers the same problem that impacts much of science, and that is one of voice. The real power in democratic systems is held by politicians, and the voices they listen to. The voices they listen to are frequently driven by the journalists and editors prominent in that society. And as Mark Henderson pointed out in his excellent book The Geek Manifesto, the overwhelmingly vast majority of politicians and journalists have absolutely no science training whatsoever. They are simply not trained to grasp the incremental and long term development that cutting edge science so often requires. Couple this with the short-term nature of political career interests, significant sustained projects like space exploration and large scale blue-sky research will find themselves in the same cross-hair.

The solution is simple. Be vocal about how important we think these things are. Get your friends to be vocal about it. Help politicians and journalists, and the rest of the public understand *why* it’s important.

That’s why Expedition 35 has been so brilliant – Hadfield has provided an astonishing role-model in (among many, many other things) how you go about making *everyone* understand how amazing the ISS is, and how important the work there is to pushing forward any kind of future manned space travel. So thank you Commander Hadfield, I will miss being reminded several times a day that a group of human beings are flying at 7.7km a second over our heads, and are enthusiastic in communicating directly with any member of the public about what they do, how they do it, and why we should keep on doing it.

I’ll leave you with the already widely circulated but nonetheless brilliant farewell to the ISS Hadfield posted this morning.

https://www.youtube.com/watch?feature=player_embedded&v=KaOC9danxNo

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