Rheological Evolution of Basaltic Lava Flows During Cooling and Crystallization

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Basaltic lavas cover large portions of the surface of the Earth and several other planets and moons. The morphology of lava flows and other structures such as cones and domes is related to the physical properties of the lava, the effusion rate, and environmental factors such as surface medium (submarine vs subaerial) and slope. Important physical properties of lavas include viscosity, yield strength, thermal diffusivity and heat capacity, all of which vary with temperature (T) and crystal fraction (φ, which itself varies with T). Melt viscosity can vary by many orders of magnitude within a single eruptive event, and despite recent advances the rheology of crystallizing basaltic magma is still relatively poorly constrained. The PI and graduate students will measure the rheological and thermal properties of basaltic lavas from various tectonic settings at conditions appropriate to basaltic volcanism, and model variations in these properties as a function of T, composition (X) and φ. The aim is to provide a better understanding of how these properties can vary across a flow at a particular instant in time, and within a single quantum of magma from vent to final emplacement. By combining information on rheological and thermal properties of magma, we seek to explore potentially complex feedback relationships between crystallization, latent heat release, melt viscosity and yield strength that control the overall rheology and flow morphology. The lava samples to be studied will come from Kilauea (Hawaii), Laki (Iceland), Etna (Italy), Fuego and Pacaya (Guatemala), and Arenal (Costa Rica). Experimental measurements will include: determination of melt viscosity from 1 to 1012 Pa.s as a function of temperature, using parallel-plate and concentric-cylinder viscometers. Yield strength will be determined at low stresses relevant to lava flows by measuring strain rate as a function of stress, for carefully selected time series experiments to obtain samples with different crystal contents. Liquid heat capacity and the enthalpy of fusion will be determined by drop calorimetry. Heat capacity of glasses and supercooled liquids, and enthalpy of crystallization under supercooled conditions, will be determined by differential scanning calorimetry. Melt viscosity and multiphase magma rheology (effective viscosity and apparent yield strength) will be parameterized as a function of T, X and φ. The research program will be divided into smaller projects that will provide many opportunities for integrated graduate and undergraduate training and education. The project will provide data and models with applications extending to natural hazards, planetary geology and materials science.