Fluid analogue experimentation is a critical tool for determining processes and mechanisms within volcanic eruptions and magmatic flow.
Samuel began his research career in analogue experimentation, and is still involved in a number of studies that assess phenomena such as: settling velocities of ash in the atmosphere, how melt lenses are transported through magma storage regions, and how gas pipes form (or secondary eruptions occur) in volcanic deposits.
Secondary hydroeruptions in volcanic deposits
Pyroclastic density currents can cover large areas of land around a volcano including inundating and displacing large bodies of water such as lakes and rivers. The vaporization of water trapped within pyroclastic deposits, or in near sub-surface aquifers, can lead to large pressure build-ups of steam that eventually erupt into the atmosphere as secondary explosions or "hydroeruptions".
Particle-gas analogue experiments in a recent study produced a simplified demonstration of this phenomena by pumping gas through a bed of fine and overlying coarse particles. Gas pockets could be held stably within a deposit until some critical gas flow, at which point, the gas pockets erupted and fine particles were released in a plume.
The ratios and proportions of different grain sizes were found to control the different styles and intensity of hydroeruptions produced. Future research will look at more complex experimental setups analogous to natural conditions in pyroclastic deposits.
Ascent of melt lenses in crystal mushes
The addition of new melt into crystal-rich magma storage regions (crystal mushes) is thought to be one of the primary drivers for triggering volcanic eruptions. Relatively low-density melt can rise through a mush zone as a "Rayleigh-Taylor" instability (RTI). Knowledge of the initiation, development, and growth rate of RTIs as melt lenses is important for understanding possible timescales of eruption triggering.
Previous experimental research by colleagues characterized the initiation of RTIs using a reverse-density setup of fluids with differences in density, viscosity and volume. RTIs were found to grow exponentially until some point where growth became linear. Current research is continuing to assess these changes in growth rates of RTIs as melt lenses.
Other research initiatives are assessing what happens to melt lenses that pass through mush zones with variable viscosities. These experiments also utilise fluids with a range of appropriate differences in viscosity, density and volume. This work will be presented at the upcoming AGU Fall meeting.
Settling of concentrated ash in the atmosphere
Modelling the dispersal and sedimentation of volcanic ash is critical for hazard monitoring and risk mitigation during volcanic eruptions. However, the accuracy of these models is very dependent on our knowledge of ash settling behaviour in the atmosphere.
Current research is assessing how ash settling velocities may vary substantially from modelled velocities in regions proximal to the volcanic vent. This comes as a possible result of localized grain concentrations, turbulence and en-masse sedimentation. This work will be presented at the upcoming AGU Fall meeting.