The rheology of particle-liquid suspensions, the shape and connectivity of vesicles in pyroclasts and implications for the Plinian eruption of basaltic magma

Abstract

This thesis consists of three projects based on magma ascent dynamics during volcanic eruptions. In the first project, I quantified vesicle shapes in pyroclasts, from different styles of volcanic eruptions, using a dimensionless shape factor. I found that this shape factor can be related to a dimensionless Capillary number, estimated from coupled bubble growth and magma ascent modeling and thus, to the eruption styles. My second project dealt with understanding the effect of crystals on the rheological properties of magma from dynamically similar analog laboratory experiments. I found that the rheological properties of particulate suspensions depend on the applied shear rate and maximum packing fraction of a particulate system, which is a function of particle size- and shape-modality. Using empirical formulations, I showed that non-Newtonian rheology of crystalline magma may cause large changes in magma discharge rates for small changes in driving pressure gradient and/or crystal shape- and size-modality. In the third project, I measured permeability of pyroclasts from the Plinian style eruptions of basaltic magma at Mt. Etna (122 BCE) and Mt. Tarawera (1886) and found that the permeability of these pyroclasts are 1-2 orders of magnitude larger than that of the pyroclasts from Plinian style eruptions of silicic magmas. Using numerical modeling I found that the permeability thresholds are approximately at 35% of magma porosity and formulated the porosity-permeability relationships for pyroclasts from both the studied eruptions.