Topics in planetary geology. Ph.D. thesis

This dissertation consists of three parts. Part I describes the global color and albedo variations on the surface of Jupiter's moon Io. The temporal variability of Io's surface over short time scales is marked, yet the long-term hemispherical patterns have been remarkably constant. Part II is an analysis of the global distribution, abundance, and stability of sulfur dioxide on Io. Mixing models with three end-members indicate ~30% coverage of Io's total optical surface by SO₂. Part III is a computer modeling study of the kinetics of sediment gravity flows and application to the lahars, avalanche, pyroclastic flows, and blast surge of Mount St. Helens, Washington. The best models for the lahars and avalanche result from the use of a Bingham model, whereas the pyroclastic flows require the addition of turbulent resistance mechanisms. Decompression of the blast surge must have contributed, along with the force of gravity, to driving the 20-30 km travel distance of the cloud against the resistance from turbulence against the ground and air drag. -from Author