Volcanic eruptions pose hazards to life and insfrastructure, and contribute to the resurfacing of earth and other planetary bodies. Lavas and magmas are multi-phase suspensions of silicate melts (liquids), solid crystals, and vapor bubbles, and solidify into glass and rock upon cooling. The interactions between phases place important controls on the dynamics and timescales of magma and lava transport and emplacement. The purpose of this thesis is to explore the role of multiphase interactions in controlling eruption dynamics and inform conceptual and numerical models for hazard prediction. In Chapters 1 and 2, centimeter to meter scale analog experiments are used to explore the multi-phase rheological properties and flow behaviors of bubble- and particle-bearing suspensions. Optical imaging of dam-break experiments presented in Chapter 1 expand existing experimental parameter ranges for lava analogs to higher bubble concentrations than existing datasets (up to 82% by volume bubbles and 37% by volume particles). I develop a constitutive relationship for threephase relative viscosity, and demonstrate that at the low strain-rate conditions relevant to many natural lava flows, accounting for the rheological effect of bubbles can result in the prediction of slower runout speeds. Chapter 2 expands upon the work of Chapter 1 using different analog materials observed using nuclear magnetic resonance imaging (MRI) phase-contrast velocimetry (PCV) to measure velocity in the flow interior of three-phase dam-break experiments. I find that for high-aspect ratio particles (sesame seeds), phase segregation into shear bands readily occurs, even at low particle fraction (20%) and results in strain localization. I suggest that the presence of shear bands can lead to faster flow runout than predicted using assumptions of bulk rheology. Chapter 3 analyzes thermal infrared (IR) time-lapse photography and videography of Hawaiian to Strombolian explosive activity during the 2021 eruption of Cumbre Vieja volcano, La Palma, Canary Islands, Spain. Images are analyzed to find time series of apparent plume radius, velocity, and apparent volume flux of high-temperature gas and lava. I compare with other measures of eruptive activity, including remote observations of plume height, SO₂ flux, effusive flux, tremor, and events at the volcano edifice including edifice collapses and the opening of new vents. I find correlations between tremor and explosive flux, but no correlation with SO2 flux or effusive flux, which I interpret as evidence of bubble segregation, highlighting the role of phase segregation and temporal variability in material properties in natural systems. Finally, in Chapter 4, I develop a novel finite element model to explore the interaction between a viscous flow with a solidified crust, and the effect of these interactions on lava flow and lava dome emplacement. I develop a model that couples a temperature-dependent viscous interior with an elastic shell flowing into air, water, or dense atmospheres. The model expands upon existing numerical simulations used in volcanology to have direct applications to lava flows and domes on the sea floor, which accounts for a large portion of the volcanism on Earth, and volcanism on other planetary bodies. Additionally, the formation of levees or solidified flow fronts that fracture and lead to a restart of flow. These lava flow breakouts pose a significant hazard, but there are currently no volcanological community codes capable of using a physics-based approach to predict the timing or location of breakouts. The model in Chapter 4 is the first to allow for assessment of the likelihood of failure at the scale of a flow lobe. Chapter 4 describes the model formulation and verification, and validation against centimeter-scale molten basalt experiments. The dissertation as a whole integrates work using a variety of methods including analog experiments, observations of natural eruptions, and numerical simulations to contribute to our understanding of the effects of multi-phase interactions on volcanic eruptions.

D. Tech. Mechanical Engineering. / Investigates and/or rank the performance of locally available materials (i.e. limestone, dolomite, or calcrete) as sorbents in the capture of SO2 emissions from coal-fired power plants. Two experimental procedures were adopted in this work: the pH-stat method was used to simulate conditions encountered in wet flue gas desulphurisation (WFGD); and the fixed-bed reactor was used to simulate conditions encountered in the dry in-duct flue gas desulphurisation (DFGD) process. It is important to note that most studies of using calcium-based materials as sorbents for SO2 removal have been carried out in overseas countries. These studies were carried out using materials and research conditions prevailing in the particular countries. Furthermore, all South African coal-fired power stations burn low grade coal allowing the high grade coal to be exported. As a result, coal-fired power stations in South Africa emit higher emissions than the overseas power stations which are operated on high grade coals. Thus the results achieved internationally may not be directly translated to the South African conditions.

M. Tech. Mechanical engineering. / Acid deposition is caused by the emission of acidic gases, for example, nitrogen oxides and sulfur dioxide. Nitrogen oxide emissions can be controlled by the proper selection of equipment and operating conditions. Sulfur dioxide on the other hand, can be cleaned by means of procombustion, combustion or post-combustion techniques; the latter being the most effective. The objective of this study is to find suitable additives which will augment the reactivity of lime towards FGD (flue gas desulfurization), while at the same time being easily available at a low price. Zeolite based sorbents yielded the highest reactivity, and all additives, except iron waste, had pozzolanic materials as their main reactive compounds.

M.Sc. / Please refer to full text to view abstract