Problems in physical volcanology: Analytic and computational models of buoyant diapir ascent, variable viscosity volcanic dome emplacement, and temperature dependent non-Newtonian lava tube flow.

摘要

This work examines the processes of heat transfer and fluid flow in three volcanic contexts: (1) Buoyant ascent and cooling of magma diapirs in the thermal lithospheres of Venus and the Earth. (2) The emplacement and cooling of pancake-shaped venusian volcanic domes as cooling viscous radial gravity currents. (3) The characterization of basaltic rheology with non-Newtonian temperature dependent curve fits to empirical data, and the effects of and Non-Newtonian rheologies on the thermal and velocity fields in terrestrial lava tube flow. These studies suggest that a careful look at the heat and fluid flow within and from lava using a combined analytical and computational approach will allow significant insights into lava behavior not obtainable from traditional empirical and non-computational studies.;The second study demonstrates the importance of cooling-induced rheological changes in the spreading of volcanic domes. It is shown that including an increase in viscosity due to cooling in the dome spreading analysis results in a wide range of allowable compositions for a final dome morphology, and concludes that composition cannot be inferred from final morphology alone. It is thus suggested that the venusian pancake domes could be basaltic rather than silicic, as assumed from previous studies.;The third study characterizes tube flow in terms of nondimensional fluid mechanics parameters, and fits rheologic flow curves to empirical data for basaltic lava in Bingham, Power Law and Newtonian temperature dependent forms for temperatures ranging from crystal free liquid to solid behavior. The results from a constant properties forced convection laminar thermal entry tube model are consistent with field measurements a few degrees temperature drop over many kilometers for lava tube flows.;It is found in the first study that the differences in planetary surface temperature between Venus and Earth helps to explain the spatially widespread volcanism on Venus relative to Earth. The higher surface temperature on Venus results in a higher thermal gradient for Venus if the planetary interiors of Venus and Earth are similar. This allows a reduced venusian cooling rate, and a greater likelihood of any given diapir reaching the surface before solidification.