Experimental vesiculation and shearing in conduits of increasing size
Janine Birnbaum1, Jackie E. Kendrick1, Anthony Lamur1, Jonathan M. Castro2, Yan Lavallée1
Affiliations: 1Department of Earth and Environmental Sciences, Ludwig-Maximilians-Universität München, Munich, Germany 2Institute of Geosciences, Johannes Gutenberg-Universität, Mainz, Germany
Presentation type: Poster
Presentation time: Friday 16:30 - 18:00, Room Poster Hall
Poster Board Number: 241
Programme No: 3.17.22
Abstract
Transport in cylindrical conduits is thought to be a common pathway for magma ascent in the near surface. Field observations of lava domes and volcanic vents suggest shearing at the conduit margins promotes localized degassing during ascent and eruption. Despite their ubiquity in interpretations of field observations and the setup of numerical models, experiments that allow for vesiculation and flow of natural materials in open-topped cylindrical geometries remain sparse. We present high-temperature vesiculation experiments of natural obsidians that flow in cylindrical crucibles as a result of their own volume expansion during heating-induced vesiculation. Shear can occur either late in vesiculation, when the sample already contains abundant vesicles, or synchronous with bubble growth. Measurements of permeability on solidified samples show that shear promotes bubble connectivity. But what happens at larger scales when only the margins of the transporting magmas are sheared? We progressively increase the size of samples from 5 mm to 180 mm in diameter to demonstrate the localized effects of shearing and understand the connection between sample interior and margins. Experiments are then used to calibrate numerical models of bubble growth in the sample geometry which improves our ability to predict the dynamics of meter-scale volcanic conduits.