Dufek, JosefKemmerlin, Sage2021-11-232021-11-232021-11-23https://hdl.handle.net/1794/26852The Miocene Grey’s Landing ignimbrite is a large (≥ 23,000 cubic km), intensely welded, highly rheomorphic extremely high-grade ignimbrite. The cause of rheomorphism can be attributed to syn-depositional strain heating and post-depositional gravitational flow of the deposit, but the relative contributions of both are not fully constrained. We model the Grey’s Landing pyroclastic density current as a dilute current under the assumption that the particles do agglutinate. The model informs a one-dimension thermal diffusion model that allows for progressive aggradation of the pyroclastic density current with strain heating. Three different methods to calculate viscosity in the shear zone were used: two from measurements of the Grey’s Landing ignimbrite and inferences of magmatic viscosity, and one from the granular viscosity calculated from the multiphase model. The results from the granular viscosity model were the only physically realistic results but generated virtually no strain heating, implying that post-depositional flow is primarily responsible for rheomorphism.en-USAll Rights Reserved.Electronic Thesis or Dissertation