Rising Taylor bubble in a vertical tube simulated using Ansys
The fantastic thing about modelling volcanic activity is that we can take our current understanding of the physics surrounding a volcanic problem and apply it safely at a desk. It may not be as exciting as being 'out in the field' but is certainly as valuable as we always need real world data to validate and verify models! Modelling activity takes many forms from investigating the dispersal of ash in the atmosphere for aviation, certainly a very prominent and current problem, to analysing potential lava flow paths, vital for determining potential construction sites. The other arguably most valuable thing about modelling is that it often enables us to see things that we otherwise wouldn't be able to view. For example sub-surface processes such as the motion of magma and gas beneath the surface, which just happens to be my modelling area.When involved with computational modelling, we try to constantly balance between levels of accuracy, an appropriate representation of the physics involved, computational power, solution time and storage space.
- Accuracy - when running a model you first have to define your area (or geometry), in my case its usually just a simple elongated rectangle. Great! I hear you say. Then we have to mesh the domain, that is define a grid which snaps onto our defined geometry. This is where it starts to get more complex, what kind of mesh do we use, do we make it adaptive (i.e. alters during model run), and the key thing what resolution do we use - too small and solution time may take an eon (and also produce unmanageable amounts of data), too large and we may not be able to represent the physics of the problem sufficiently!
- Appropriate representation of the physics - what equations are we going to use? Are they appropriate for the situation? How long do they take to solve?
- Computational Power - I can guarantee that this is often the major problem for modellers. I am lucky, in that I have access to the University of Sheffield supercomputer Iceberg (don't ask me why its called that but it sounds cool!) to run applications off and hence a large amount of RAM to draw off. During my MSc I was on the other end of the spectrum, using a desktop computer with 2GB of RAM, waiting 3/4 days to perform 30 s of a model run (probably an under-exaggeration actually). From this you can certainly start to see the challenges mounting up!
- Solution Time - As mentioned above, solution time is certainly key, some climate models can take months to run, which if you are doing a 3 year PhD doesn't leave much room for error! It is therefore inherently important to plan model runs for available time and with available resources.
- Storage Space - In a world where data is easy to create but costly to store this is another key issue. Some of my recent model runs have produced >20 GB of data for just 10 s of model run (and took over 10 hours), when preforming multiple model runs it is obvious that cumulative data production will get larger and quickly run into the terabytes. Some ways of getting around this include only exporting/saving the data you actually need, if your only interested in temperature outputs only save this!
There are many excellent fluid dynamics software applications in existence, however, they are usually costly (running into the tens of thousands, notable exception here is OpenFoam
). It is lucky therefore that the University of Sheffield has access to one of the leading applications Ansys
and the dynamic Ansys Fluent package. Below is an example of Ansys Fluent model run, simulating the rise of a volcanic slug, generally believed to be the cause of strombolian eruptions at the such volcanoes as the archetypal Stromboli. Cheaper applications such as Matlab, certainly offer the ability to perform, less complex physics problems but lack the user-friendly interfaces such as Ansys and necessitate an in-depth knowledge of the maths and physics behind the problem!
I am sure I have missed many considerations off here, but these are just a few tasters!
It is vitally important that models are not just used on their own, as there is nothing to calibrate or validate the model against. The best way of modelling is by comparing observations in the field, in my case gas emissions, with laboratory proxies, and models. Anyhow, when weighing all of these points against the benefits, a clear and greater understanding of environmental processes is essential and is something which can only occur with significant modelling of processes.
Below is an example simulation of a taylor bubble (or slug) rising through a tube as a proxy for the root cause of a strombolian eruption (the type seen at stromboli).
The plume of the NEC in September 2012.
Recent research published in Geophysical Research Letters
by Tamburello et al. (2013)
has demonstrated that Sulphur Dioxide emissions can vary rapidly over very short timescales during passive degassing (see previous post for info on passive degassing
). The study also demonstrates that there are links between the emission of Sulphur Dioxide and Seismicity over certain periods. This is achieved by taking high resolution readings of Sulphur Dioxide using UV cameras every second or so, which allows the comparison of the Sulphur Dioxide and Seimsic datasets at this high resolution.
Great! But what does this mean? In short it means that the two process are potentially linked over these timescales, which could implicate that gas emissions are driving seismicity (I am sure there are other possibilities though...). It confirms that volcanoes such as Etna are very dynamic and that sub-surface processes (which almost inevitably cause these fluctuations) rapidly alter the gas emissions that are recorded at the surface (or vice-versa). This is where my PhD research kicks in, why are we seeing these changes over these timescales? What is causing these very periodic structures? Of course this trend in emissions is not just seen at Etna but at other volcanoes worldwide. It could therefore be important for understanding the state of shallow magma pathways and storage areas in basaltic systems generally.
The US government shutdown a few days ago and it has already begun to have a severe impact on people's lives and potentially the stability of the US economy if it continues much longer. This is not a political blog (although I am interested in such things sometimes) so I thought I would take a brief look at how it will effect volcanology. First things first, potentially one of the most obvious effects, the Smithsonian institution is closed which means no more volcanic updates. This also includes the weekly volcanic update which I am sure most agree is an invaluable source of reliable information on present eruptions, something which will not occur until this shutdown ends.
What about national parks? Log on to the National Park Service website and the message on the right appears - all national parks are closed, this includes valuable tourist destinations such as Yellowstone National Park (to my knowledge anyway!). The wonderful natural attractions which support so many jobs and attract many tourists will not be able to be visited. I am certainly glad that I got my visit in earlier in the summer! It is not also the national parks which are affected but the Volcanic Observatory's as well. The following is taken from the USGS Hawaiian Volcano Observatory website:
The U.S. Volcano Observatories will remain operational during the lapse of federal government appropriations. Basic volcano monitoring will continue, as will forecasts and regular updates of volcanic activity. However, because of reduced staff, instrument network maintenance will cease, meaning that our monitoring capability will degrade over time. This website will remain functional, but only those pages containing information about current volcano hazards will be maintained.
Reading between the lines, what does this statement mean? Well first things first, volcano monitoring will continue so air traffic updates will continue keeping aircraft safe and people in case of an event or a change in hazard status (no need to worry on that point then!). An increased workload for employees will likely however be an undesired effect. Volcanic monitoring instruments often need frequent calibration, checking or repair to keep them sending reliable information to observatory's, as such the shorter the shutdown the better. However, the longer it continues the number of instruments in operation will decline but also the reliability of the data which will not only be bad for science (i.e. less science will be done with a reduction in instruments and quality of data) but bad for volcano monitoring. Of course after the shutdown ends, whenever that might be, it will take longer to repair or check equipment and generally get up and running again. I certainly detect a bitter undertone in the statement directed at the US government as it will likely create a large backlog of work.
Here's to hoping the shutdown ends soon for more reasons than just volcanological!
Another year, and another return to the Pizzi Deneri observatory for more Sulphur Dioxide gas measurements. One of the things which never ceases to amaze me whilst around the summit of Mt. Etna is the large numbers of ladybirds (ladybugs/cocchinella?) that are littered across the landscape. This particular group (photo on right) was found on the bottom of a rock, quite incredible!
This time the weather was a little better overall than last year
. However, when remote sensing things are a little bit more complex when looking for the 'perfect' measurement weather. This year, we were lucky, not too many optically thick clouds which cover the summit and in general a good plume location and direction. Below is a photo taken from La Montagnola of the South East Craters. Unfortunately Etna decided not to wake up fully during my visit, oh well, that just means I may get to go back sooner! Must keep an eye on those webcams
Left - the lens with IR filter. Right - webcam.
A little side project of mine over the past few weeks has been experimenting with the optical properties of very cheap web cameras, this one in particular costing around £6, roughly $10. The average web camera has what is called a CMOS sensor installed which allows detection of light in the wavelengths roughly between 400 and 1000 nm. In practice this means the 'Visible Spectrum' between roughly 400-700 nm and part of the near-infrared spectrum as well. However, installed in most of these cameras is an infrared filter (the slight reddish tint on the picture of the lens). It is relatively simple to remove this filter, unfortunately on this particular camera it is not possible to remove it intact but I didn't want it leftover anyway!
After removing this filter, I reassembled the webcam and went to the park just by the geography department. Here I took a 'Full Spectrum' image (left below) and one with a visible light filter (in one specific wavelength - right below). I am sure you can agree the results are very cool! There are a number of things you can use for cheap visible light filters, you may even have one of them lying around the house or in a dusty cupboard somewhere. A very simple option is to use a black bin liner or an exposed camera negative which is as dark as possible.
Why not try it yourself, it is very easy to do and takes no time at all. There are many applications of this sort of photography including night vision (generally using a separate infrared light source), looking at absorption of greenhouse gases and general coolness!
Left - an image taken with no visible light filter showing a full spectrum image possible with the webcam. Right - an image taken with a specific wavelength filter in the near infrared.
For all the eagle eyed people who read my blog you may have noticed that I have recently added a page to my blog called "Codes
". I have now started adding files to this page and also to vhub - which, for those of you who don't know is short for the Volcano Hub (I assume so anyway!). It is an insanely awesome resource for an immensely broad array of random and useful volcanic material.
All of the code currently listed is described fully in the two separate areas, so I won't bore you with details here!
Here are the links to my files on vhub:Stokes Rise calculations Normalising datasets in MatlabMagma Density Magma Viscosity
Any questions/comments on these please don't hesitate to contact me.
Blogging from Tokyo Narita International Airport. So, with IAVCEI finished, people are dispersing back home, on holidays, post conference field-trips or field-work. Myself I am travelling home. The last few days of the conference were certainly valuable with some great talks on Open Vent volcanoes such as Erebus and some fantastic posters to discuss. It was certainly good to hear all about others using Ultra-Violet cameras and what they are up to.
On the last day, I had a few hours before my flight, so, back to Sakurajima...why not! On the way, some dolphin activity in a little canal leading from the aquarium. Hiking up a hill just outside the ferry port on Sakurajima side to a dinosaur park to look at the view of Kagoshima and of course the dinosaur! I do love a good submarine movie so when I see one I have to get as close as possible to get a picture (this happened to by first!) and when you zoom in on the photo apparently a submariner is trying to enjoy the view of the volcano. I am quite sure that is the direction he was looking, but it was quite cloudy so I'm not sure he saw a lot!
Final reflections, a well organised conference, very valuable, I hope to see many of you again on future travels!
Left - lava near the Sakurajima visitor centre. Middle - a submarine in the harbour. Right - a submariner enjoying the (rather cloudy) view of the volcano!
At a conference with many volcanologists, what's the best thing that could happen, free beer on a boat? Well yes that happened. Fireworks just for our enjoyment? Well, yes, that happened too. So what you ask...well, an eruption of Sakurajima would suffice I suppose, and WOW it was timed well (for me and others). The activity lasted for more than an hour an consisted of quite a few (around 10ish) individual explosions, the largest of which reached approximately 3 km in height (verified by someone from the Sakurajima observatory). Not only that, there was at least 3 occurrences of visible volcanic lightning. The photo on the right shows the beginning of the eruption, when I eventually trawl through my photos, I hope to find the lightning activity present, fingers crossed! I do have many many photos/videos that I will sort through and post when I can. Weirdly, the very start of the eruption was caught in a photo of me and the volcano (below right), you can just see it as a bump on the right hand slope (just) - thanks Michelle - Vancouver University IAVCEI participant! Small, bump on right of centre, the eruption start!
However, the day did not just consist of an eruption of Sakurajima, although that was certainly a very important part! A visit to an archaeological dig showed the inhabitants of the area around 9000 years ago, whilst a visit to the shrine was most illuminating. Although I (and I am sure others) were worried about getting the order of actions wrong - approach the entrance, throw a coin in, bow twice, clap twice, then bow again. I think that;s correct...I have to say how excellently organised the whole event was, well done Kagoshima and IAVCEI.
All in all an excellent day topped off with my first experience of Japanese karaoke...great fun but very different. Now back in the hotel room (after getting a little lost on the way back - don't know how it happened). Good night all.
Replica ancient village on left and shrine on the right.
Japanese volcano entertainment!
Day 2, another good day started off by a look at the occurrence and possible reasons for volcanic lightning, a look at cyclic activity at Santiaguito and the recent Taupo 2008 unrest.
Heading in to my own section, some great discussions were had on my poster, so thanks all for comments. It is fantastic coming to events such as these when you come from such a small volcanology department (there are certainly benefits to this as well though!). Controversy in the CO2 section, what is the true value of global volcanic CO2 emissions? What is the error? Apparently estimations keep growing, now there are very significant variations in peoples estimates. It was also good to hear from experiences of others at the IAVCEI Early Career meeting - major lesson learnt - sometimes success is just luck!
Visiting the back streets of Kagoshima with two friendly Americans, one from Cambridge Uni and the other from New Mexico Tech. We found a great restaurant on the 2nd floor with the below menu (all in Japanese - we're in trouble you say! Wrong! As luck would have it, New Mexico Tech used to live in Japan and new some of the writing. So after a lot of deliberation we decided on what we thought were Satsumas, Soba noodles and something called "children of the trees with bacon". We ended up with fried sweet potatoes, a bacon salad, soba noodles and some chicken thing. It was the best meal I have had so far, and I received free postcards for my trouble, people here are so friendly.
That's it for today, field trip tomorrow around Aira caldera (I think!), time to get some rest.
Left - Ordering food at a Japanese restaurant with no English menu - interesting! Right - A snapshot of my poster.
What an amazing first day, kicked off by an excellent talk by Barry Voight and representation in 2D and 3D of the 1980 Mt. St. Helens eruption. Followed by interesting talks on numerical and lab (well a quarry!) experiments by Ed Llewellin and a further high-speed imagery look at slug dynamics prior and during burst by Jacopo Taddeucci. To finish off the scientific session for the day, philosophical thoughts on simplicity in modelling and interesting overviews of Campi Flegrei (Italy) and White Island (New Zealand).
Then, courtesy of IAVCEI
two free boat tickets to get to Sakura-jima for the festival. Incredibly good fun, sitting on the grass watching some large drums played by somewhat smaller drummers and local dancing, whilst eating some amazing food (I wasn't brave enough to try fried Octopus). A great firework display which seemed to last for more than 30 minutes, with a superb sequence to finish with fireworks exploding above a firework volcano! My attempt at phone photography on the right, the town hall below and Sakurajima also below - a little bit hazy, and no explosion this time...I managed to see an aftermath of an explosion yesterday (drifting ashy plume), fingers crossed for a complete look at one. Oh and another experience, bouncing cars...I have certainly never seen that one before!
For me this is my first big conference and what an excellent experience it has been so far. Everyone is very friendly and it is great to meet amazing new people, listen to others work and of course talk about my own (poster tomorrow by the way session 3J)! Anyway must get to sleep, early start tomorrow.