Forever blowing bubbles

Dr Eliza Calder, Professor Stephen Self and Dr Ralf Gertisser.
The Open University.

Dr Jeremy Phillips.
University of Bristol.

Volcanic eruptions are some of the most spectacular phenomena in the natural world, but they can have devastating consequences for the lives of thousands of people. To better determine how, and when, eruptions occur we need to improve our understanding of the internal workings of volcanoes.

So what drives a volcanic eruption? 'Dissolved gases in the Earth's interior have a primary role in driving volcanic activity', says Eliza Calder. 'Some volcanoes can remain dormant for long periods of time and reawaken with large explosive eruptions, while others, usually characterised by a gentler style of activity, remain active for relatively long periods of time.'

Of particular interest to Eliza are volcanoes that display this persistent activity, and how they provide pathways for continuous volcanic degassing over tens to hundreds of years. One such style of activity is termed 'Strombolian' activity, named after the Stromboli volcano in the Tyrrhenian Sea. Stromboli is known as 'the lighthouse of the Mediterranean' because of its intermittent explosions or fountaining of lava, which have been occurring every few minutes or so for several hundred years. Each of these explosions is generated by large gas bubbles in the magma rising up through the volcanic conduit and rupturing explosively at the surface.

To study the wide array of processes involved in volcanic degassing we can follow the journey of the gas from deep inside the Earth until its release into the atmosphere.

As rock crystals grow in the magma chamber deep underground, they trap tiny inclusions of the fluid magma into their crystal structure. The gas content dissolved in these inclusions can be determined using infrared spectroscopy, giving crucial information about the environment the crystals were growing in before degassing occurred.

As the magma flows up the volcano's conduit or vent, the dissolved gases come out of solution, forming bubbles or gas pockets. The fluid dynamics of rising gas pockets is modelled by performing analogue experiments in bubble columns with viscous fluids. In this way a picture of the volcano's 'plumbing' can be constructed. The experiments show that these bubbles can drive turbulent mixing in the magma.