Silicate melts are complex fluids whose physical properties (e.g., viscosity) change with time due to cooling, shearing, and crystallization (to name just a few changes). The rheologic shifts will in turn influence volcanic eruption mechanisms. Often times, key processes are manifested as structural elements formed within the volcanic vent over length scales of mm’s to tens of meters. For example, flow bands, buckle folds, and preferred crystal alignments have been shown to be good records of viscous flow in conduits and in lava domes. We have begun to analyze ubiquitous brittle failure structures such as breccias and welding fabrics in obsidian from Chaitén and Krafla volcanoes. These features may yield information about shallow level degassing and flow/fracture processes in shallow volcanic conduits and lava domes. We are conducting these analyses in collaboration with Dr. Hugh Tuffen of Lancaster University.