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.
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).
Why this post? Well, it is related to my own work which focuses on the passive degassing (see previous post for info) of basaltic magma, such as that at Stromboli and who doesn't love to talk about their own work! To the right is a still of the summit area and below is a video of this passive degassing in process. The visible part of the plume is mostly water vapour but also mixed with other such as sulphur dioxide and carbon dioxide. If you look closely at one of the smaller vents in the centre of the video below you can see a regular, but small, puffing, which is likely some form of atmospheric transport effect created by the small vent itself. This can also occur on a larger scale, and largely invisible to the naked eye. The summit of Stromboli is consistently throwing out these gases at a varying rate, it is part of my work to try and understand why and how this emission rate varies at volcanoes such as Stromboli and Etna.
Strombolian explosions, Stromboli
Stromboli and its activity is some of the most charismatic and beautiful you will ever see, especially at night (my next post)! What visit to Stromboli would be without multiple attempts at trying to capture that perfect explosion (which many many tourists do during the day and night). During the day, explosions were ash-rich and the day-light prevents from seeing the majority of that amazing incandescence. The photo on the right shows a typical explosion from one of the summit vents, note how the ash and larger blocks are falling down the flanks and onto the Sciara del Fuoco. The Sciara del Fuoco is a large collapse feature on the island and presents one of the major hazards for tourists and locals alike. Inset (right) is another explosion from the same crater where you can see the hints of incandescence and the hot nature of the rock. Below is a real time video of an explosion from the same crater. In it you can see the initial thrust of the explosion and convective rise of ash into the atmosphere which eventually disperses as inertia is lost and mixing with cooler air occurs. The activity is fairly frequent, every 5-15 mins or so dependent on activity levels, so it is quite easy to get snap-happy if you have a lot of time on the summit!