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.

First of all, happy new year! It is set to be a busy one for myself, no doubt involving various volcanic visits which you will all here about.

Today, in my why is gas important series, a brief look at 'Passive Degassing'. This is gas which is released at all times from a volcano, even when there is no eruption occuring. This can also be termed as quiescent. The major gases emitted include Water Vapour, Carbon Dioxide and Sulphur Dioxide (amongst others) and are usually in that order for amounts released.

Monitoring emissions of gas is important as it can inform volcanologists of amounts that are being released and whether these are in a normal range. An increase in emissions could indicate that an eruption is imminent, but a decrease could also indicate the same! It can vary greatly on a volcano basis. For example, an increase in emissions could indicate that a fresh batch of magma has entered the plumbing system with lots of entrained gas (the major driver of volcanic eruptions) and the increased emissions at the surface is showing this. Or there could be a large decrease in emissions, which could indicate that either there is a shortfall in gas supply from depth or that the gas cannot escape. This could indicate a build up in pressure and that a volcanic eruption is more likely. Of course, to make such assessments accurately a detailed history of amounts of gas released is needed to determine the normal behaviour for a given volcano. As with all volcanic situations, a large and unusual change in emissions doesn't necessarily mean an eruption will occur!

How do we measure these emissions? There are a variety of technqiues, those which involve collecting gas from fumaroles or a plume or remote sensing techniques be it via a satellite or more mobile ground-based cameras. Most monitoring is of Sulphur Dioxide due to its ease of measurement. Of course emission of other gases are also important. The eruption of Laki, Iceland released a large amount of Fluorine which is thought to have caused a large amount of disease throughout Europe.