Dynamics of multiphase plumes in sheared stratified crossflows: implications for managing the environmental impacts of volcanic eruptions (Ref: 4659)

Volcanic ash and gas clouds pose significant hazards to human life, infrastructure, and aircraft. Understanding the relationship between the height of a volcanic plume, the intensity of an eruption (i.e. its mass flux) and atmospheric conditions (e.g. wind speed) at the volcano is key to managing eruptive crises, reconstructing past eruption dynamics, and preparing for future eruptions.

However, estimates of eruption intensity can be uncertain by over an order of magnitude which undermines our understanding of volcanic plume dynamics.

An alternative approach is to use small-scale laboratory experiments analogue to volcanic plumes in which measurement uncertainties are small, but an intrinsic limitation is the simplification of conditions occurring in real-world plumes. For example, only a handful of analogue experiments have accounted for the strong influences of wind on plume dynamics, and all of them used a uniform crossflow which critically undermines their analogy with wind profiles which are commonly strongly sheared vertically.

Beyond volcanology, very little experimental work has been carried out in fundamental fluid dynamics to investigate the dynamics of multiphase plumes in sheared stratified crossflow, despite such plumes being common in many environmental and industrial problems.

To make a breakthrough in our understanding of the dynamics of volcanic plumes, this doctoral project will aim to combine three approaches:

i) Using satellite observations, a database of eruption intensity derived from the growth rate of volcanic umbrella cloud will be built. Combined with the novel Independent Volcanic Eruption Source Parameter Archive (IVESPA) database that contains eruption intensity derived from field deposit, this will result in an unprecedented dataset with large number of well-observed volcanic events with two independent constraints on intensity.

ii) A novel laboratory experiment on multiphase buoyant plumes rising in a stratified crossflow will be designed and, for the first time, include vertically sheared crossflow. A coloured saltwater plume with silicate sand particles will be injected into a water tank with a salinity gradient to reproduce atmospheric stratification. A non-uniform crossflow, created via an array of pumps, to reproduce realistic atmospheric wind profiles.

Key regime parameters will be scaled to match the dynamical regimes in which volcanic plumes occur. The macroscopic properties of the plume (e.g., top height and plume width) will be monitored using video cameras.

iii) The observations from natural eruptions (i) and laboratory experiments (ii) will be used to evaluate and develop numerical volcanic plume models of various complexity, ranging from one-dimensional (1D) plume models with parameterized turbulent entrainment to 3D volcanic plume models based on the OpenFOAM computational fluid dynamics software.