This (brief!) post spawned from a series of recent video and photo discoveries from Twitter and YouTube. The first time I observed a dust devil was at Vulcano only a few months ago. Although, I suppose it should really be called a gas devil as it was the condensed volcanic gases which made the phenomenon visible! The photo on the right of Vulcano illustrates this and the video at the very bottom shows the formation and development of the "gas devil". Interestingly enough a "gas devil" was seen emanting from almost exactly the same location several times over the course of the few days we spent at the summit.

This leads us to the question, what forms them? I am by no means an atmospheric expert but here goes... The key component is the heating of the ground which creates a large enough temperature difference between the air near to the ground and the air above it (i.e. creating a density difference). This then starts a process of convection (not an unfamiliar topic in volcanology, a similar process likely occurs within volcanic conduits). Following this all that is needed are appropriate wind conditions to push the dust devil into a vertical position and viola! This process probably occurs a lot more often than we observe, as it is with the entertainment of particles that dust devils become visible! A couple of good explanations (which helped a lot!) are included here and here (along with a good graphic in the latter one).

So taking this new found knowledge and applying it to a couple of volcanic situations... In the case of Vulcano the heat comes from both the incoming solar radiation and potentially the heat of the fumarole(s) with a nice side wind over the edge of the crater. In the case of Sinabung (video below) it is entirely possible that the ground (and air) is super-heated by the pyroclastic density currents which have just rolled by, leading to some fantastic examples!

Many thanks are due to Oliver Lamb and Rudiger Escobar Wolf for links to photos of Colima (click on on Oliver Lambs name) and Sanitaguito (photo to the left). Also to Luca D'Auria for the initial post in a Facebook group. Dust devils have also been observed at volcanoes such as Mt. St. Helens and some fantastic examples at Sinabung, which are so good I had to included the YouTube video below. Of course dust devils such as this don't just occur at volcanoes and have also been observed on Mars!

I love a disaster movie, even cheesy ones with volcanoes and bad science in them...In fact one of my favourite volcano related disaster movies (there aren't that many to choose from I know!) is Dante's Peak. What isn't there to enjoy about a volcanologist who nonchalantly waltzes and swaggers his way round or over volcanic obstacles and phenomena (even though plausibility is certainly questionable!). I suppose it also helps that this particular volcanologist is associated with roles such as James Bond, which all aids to "sex and glammer up" what the vast majority of volcanologists really do! Long story short, it was no surprise that I went to this particular movie. Being A Game Of Thrones (GoT) fan too (the lead character "Milo" is also "John Snow" in GoT) it wasn't much of a hard decision. 

The film, of course, revolves around the eruption of Vesuvius in AD 79. Volcanologically and historically this eruption was important for a number of reasons, including it's complete engulfment of Pompeii and other nearby settlements (e.g. Herculaneum) and the unprecedented account of the eruption by a nearby observer - Pliny the Younger. Having never read the accounts of Pliny this was one of the first things I did. Pliny recounts the eruptions in two letters to Tacitus, a prominent historian in his own right. Pliny at the tender age of 18, witnesses parts of the eruption himself and recounts other parts from sources at the time. In these letters, Pliny remarks on significant Earth tremors leading up to the eruption, which certainly were present in the film. He also makes references to the receding of the sea and a significant amount of ashfall - which eventually kills Pliny the Elder. On a side note he also gives a fantastic description of the rising of a buoyant plume. 

So, scientifically, what was questionable in the film or didn't occur at the time? Pliny the Younger does mention a slight recession of the sea, which certainly suggests that a Tsunami did occur, although, I have found/heard no mention of the gargantuan waves depicted in the films. Trawling the internet I tried to find whether there was a consultant volcanologist employed on the film but was unfortunately unsuccessful. As always I am a little behind trend and you can find another summary of the movie here on live science. In this overview, they also mention the volcanic bombs, their absence in any evidence and also the size of any Tsunami.

It was slightly disappointing that the film didn't incorporate more of Pliny, oh well! I would certainly recommend reading the letters of Pliny in their entirety, whilst the majority are related to his doings in the senate, they really are a fantastic insight into the Roman world - there is even a Ghost story thrown in!

I had a bit of spare time in the field recently and decided to do a spur of the moment impression of Sir David Attenborough...(with the greatest respect to the man himself of course!)

Vulcano is one of the most fantastic destinations I have had the chance to do fieldwork so far. Combine an easily accessible summit (on the right), persistently active fumaroles and amazing summit views, with great food and the result is a most enjoyable and productive field session. Another great thing about Vulcano as a target for remote sensors like me is that it is relatively accessible all year round (subject to somewhat erratic boat timetables) and it is less subject to inclement weather conditions. This is something that nearby volcanoes Etna and Stromboli suffer from greatly especially during winter months. However, this is certainly not to say that Vulcano doesn't have its challenges when making measurements because it certainly does! For this particular session we were taking a variety of spectroscopic measurements of the summit fumaroles (first photo on the right) using ultra-violet cameras (see Tamburello et al. 2011 for previous measurements at Vulcano) and transecting the fumaroles using a MultiGAS unit (see Aiuppa et al. 2005; Shinohara, 2005). A MultiGAS unit sucks in surrounding air through a tube and analyses for the concentration of a number of volcanic species (e.g. sulphur dioxide, carbon dioxide etc), it can do this at  an extremely high resolution of approximately every 2 seconds.

To continue with my previous thought, what are these challenges when making measurements? Well first and foremost when using ultra-violet and other spectroscopic systems, for the most accurate of measurements a number of conditions need to be met:

• a clear sky background,
• appropriate light conditions, 
• a non-condensed plume (as in first photo on the right),
• a vertical plume or a plume which is clearly in front of a uniform background.

As you can see the prerequisites for good data are already beginning to climb and I havn't even started to talk about calibration! That is a significantly longer and drier topic for another day and blog post. 

To the left is the merged plume of a number of the fumaroles early on one of the mornings. As you can probably observe, the plume is a little too condensed at this stage...but a few hours of waiting and conditions improved to become almost perfect (as above). In the centre of the image you can just about make out a solitary figure clad all in white. This figure is just about to enter the plume and perform a transect of the upper crater terrace fumaroles using a MultiGAS unit. When transecting the plume it is necessary to where goggles and a gas mask to protect against the high concentrations of toxic gases. The first thing you notice when you reach the vicinity of the plume is a faint rotten egg smell (hydrogen sulphide). Anyone who has stood in the vicinity of such gases will know that one of the first noticeable effects, even at relatively low concentrations, is the irritation of respiratory tracts. This can often result in quite a bit of coughing!

Of course Vulcano is a great place for more than just the summit fumaroles, previous historical eruptions (e.g. the eruption of 1888) have thrown up some quite spectacularly sized bombs with a large number of them the appropriately named bread-crust bombs which are scattered around the place. After stumbling across a book: Vulcano, Tre Secoli Di Mineralogia (Three centuries of minerals). in a little restaurant called Maurizios (which I highly recommend!), I learnt that there were in fact minute amounts of gold found in the fumaroles of Vulcano. However, don't pack your bags, and shovels yet, the amounts present would certainly not be enough to make you rich very quickly! In the photos at the bottom of the post you can see the plume of Stromboli, taken with a canon 300 mm zoom lens and a couple of the surrounding Aeolian Islands. You can find a few more photos in this section on my website! 

Thanks to Tom for inviting me to contribute this blog-post. I should start by telling you a little about me and how I know Tom, so here goes. I am a PhD student at Royal Holloway, University of London, researching volcano-tectonics and specifically the mechanics of caldera collapses. Like Tom I also studied for a Master’s degree in Volcanology and Geological Hazards at Lancaster University, although we did not meet at Lancaster. I first met Tom in May 2013 for a NEMOH organised field school at Stromboli volcano; where we jointly experienced an unfortunately unforgettable, and particularly rough boat back to the mainland of Sicily. I can highly recommend that if the captain of a sketchy looking boat offers to get you off an island when none of the main companies are willing to, think again! 

So, Tom asked me to write this post as he heard that I was working at a really fascinating and important volcano in Greece. The volcano in question is Santorini, which is a particularly famous stratovolcano in the Aegean ocean. The volcano is famous partly because around 3500 years ago the island experienced a huge caldera forming eruption, which is believed to be associated with the demise of the Minoan civilisation. Deposits from the various phases of the eruption can be seen straddling almost the entire circumference of a north-south elongated caldera, which measures approximately 10 km in maximum diameter, several hundred metres in depth and is centrally filled by ocean. In fact, at least three huge eruptions, ~100 thousand years, ~21 thousand and ~3500 years ago contributed to the shape and size of the current caldera. The global impacts of the Minoan eruption have often been overestimated (see the article of Pyle, 1995), however in terms of volume this eruption is up there with the biggest of the past 10,000 years. Active volcanism in Santorini is now constrained to a small island named Nea Kameni, located almost in the centre of the caldera. This resurgent volcano has been the site of several predominantly effusive eruptions, the latest of which occurred in 1950. Importantly, the island of Santorini lies on top of two north-east to south-west trending faults, one in the north of the island is called the Colombo fault and the other which is believed to be associated with the current phase of volcanism lies directly under Nea Kameni, and is named the Kameni fault.

OK, so what was I doing in Santorini? The answer is looking for and studying dykes in the caldera walls. Just so you’re up to speed, a dyke is a magma-driven fracture through which all volcanic eruptions must be fed. As such, it is really important to know the conditions for dyke propagation in a volcanic edifice. Luckily there are many fantastic geological locations (e.g. Iceland/Tenerife) around the world where geologists can see deep inside ancient volcanoes. In doing so it is possible to observe that many dykes (if not most) never reach the surface, and therefore never contribute to a volcanic eruption. They become arrested. 

Santorini is a stratovolcano made up of many layers of contrasting mechanical properties; for example, stiff lava flows and comparatively compliant layers such as ash, volcanic tuffs and breccia’s. So it offers a great opportunity to try to understand how dykes pass through these individual layers. Specifically, I went into the field to take measurements on the thicknesses, directions and compositions of individual dykes. The walls of the caldera are very steep and largely inaccessible, so most of my work was conducted from a boat, which was a really cool experience. The data is important for me because I am trying to understand how calderas form in different volcanoes. I am using the propagation of dykes as a proxy for the propagation of caldera fractures, because presumably the fracture which created the current caldera must have passed through the same materials with which these dykes also passed. 

In 2011, Santorini experienced an unrest period characterised by elevated levels of seismicity and uplift (see Parks, 2012 for details). Such signals are most likely associated with magma being transported as dyke from great depths, to recharge a shallow magma chamber. When and why a magma chamber ruptures and sends a dyke to the surface is still a reasonably poorly understood phenomenon. So the important question at most caldera volcanoes is: when does a period of unrest lead to a volcanic eruption? It is a difficult one to answer!     

As well as gathering data for my PhD I also took the time to help out at the run-off erosion intensive field-course organised by the University of Athens. Sandy Drymoni  and I ran the course’s final day visit to Nea Kameni, where we introduced some basic volcanological concepts and described some of the islands features. This was a very rewarding and enjoyable experience. The previous day I also had the opportunity to meet the mayor of Santorini at a visit to the Minoan ruins at Akrotiri. Although I wasn’t able to question him about the island’s volcanic preparedness, this was partly out of courtesy, but mainly because we didn’t speak any of the same languages.

I will now use the data collected from this fieldwork as an input for numerical models using the structural mechanics module of a program called COMSOL. In doing so, I will try to understand the stress conditions required for dyke propagation; caldera formation and magma chamber rupture in different types of volcanic edifice.

The receival of a last minute NERC Impaft Fund has meant a mad dash to be ready for a sampling session at Vulcano. The volcano which all others take their name! I am quite excited about adding another volcano to my growing list.

So....what do I do to prepare for fieldwork. One of the first things you do is check all the main equipment is working! In this case, I am developing a new technique which means a brand new Matlab Application finished the Friday before I leave! Hopefully its suitably free of bugs! Next I list the equipment I need, check I know how to use it and I have plenty of spare batteries.

As always, last minute clothes packing and as always I forget one thing...this time it was deodrant...

Vulcano is one of the Aeolian Islands (which includes Stromboli, Lipari) and is fantastic for remote sensing for the majority of the year because of generally good measurement conditions and persistent fumaroles at the La Fossa Crater! Its easily accesible by boat from Milazzo.

So, here I am writing this blog on the pier in Milazzo after surviving two days of driving in Palermo (one Italian told me if you can drive in Palermo you can drive anywhere) and the North coast of Sicily! I am going to try and do a little bit of tweeting/blogging from the field if I have time!

Its certainly a great feeling to get that first publication (with colleagues of course!) under my belt on the creation of a technique for capturing high time resolution fluctuations in CO2 at a 1 s interval, published in the Journal of Volcanology and Geothermal Research. To the right is the location of the study, the NEC of Mt Etna, one of the more frequently used pictures on my blog! The picture is taken from the Pizzi Deneri Observatory. So, how did we produce the dataset, and why is it important? 

Firstly, the ability to directly measure CO2 with traditional remote sensing techniques is difficult, primarily because of the very high atmospheric background levels of the gas! We therefore combined the use of ultra-violet cameras (for more info see Mori and Burton, 2006) to measure SO2 and an instrument called a Multi-GAS analyser (for more info see Aiuppa et al. 2005) which has the ability to measure CO2/SO2 ratios. We can then combine the two sources of data to produce a CO2 flux series.

So, why is the ability to view CO2 at 1 Hz important? Simply put, CO2 exsolves from magmas at greater depths than the other common volatiles H2O and SO2. We can therefore get a better idea of any fresh injection of magma into storage systems if we have detailed records of CO2 emissions. Prior to this point (to my knowledge anyway!), it hasn't been possible to directly compare CO2 emissions at this high rate (of 1 Hz) with other volcanic information, such as seismic and infrasonic data. As a result we reveal interesting trends that may be shared between CO2, SO2 and seismicity. For more information see the paper!

Below is the "AudioSlides" presentation created for the paper, which is great by the way, it has to be less than 5 minutes long and certainly condenses any paper into an easily digestible format, I would certainly encourage others to do something similar! 

In a fantastic end to the first day of VMSG a "Rubbish Bin Volcano" was exploded, using liquid nitrogen similar to this previous example from the University of East Anglia. On the right I am ashamed to say is my poor poor attempt at painting the University of Sheffield name onto my duck. Needless to say, art, or hand-writing of any sort is not my strong point! Although I did manage to get some great glow-in-the-dark paint from Hobbycraft... Anyhow, below is the video of the volcano below, if you were there, you can relive the 'eruption', if you weren't here it is for the first time! It's certainly a great example and analogue for the rapid expansion of gas, ash (and ducks) at the beginning of an explosive eruption. You can also see the 'eruption' in thermal infrared here.

The rest of the day was devoted to posters/talks on intra-plate volcanism and rifting, with tributes to the late Barry Dawson. A broad mixture of talks today on topics ranging from Kimberlites, Feripicrites and the fantastic carbonatite lavas of Oldoinyo Lengai. It was great to hear Mike Widdowson talk about the recent 2013 Nature Geoscience paper on the Shatsky Rise Oceanic Plateau and the discovery that the Tamu Massif could be the largest shield volcano on Earth.

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).

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.