Ash Sintering in the Presence of a CO2-H2O Vapor

• Main Author: Hoxsie, Erin
• Other Authors: Reed, Mark
• Language: en_US
• Published: University of Oregon 2018
• Online Access: http://hdl.handle.net/1794/23715

We carried out rhyolite ash sintering experiments in the presence of a mixed CO2-H2O vapor using both fine and coarse ash. Fine ash is barely sintered after 7 minutes and fully densified after about 30 minutes. Coarse ash is barely sintered after 45 minutes and fully densified after a few hours. Vesicle relaxation from initially angular shapes to spherical shapes takes longer than estimated from scaling relations. The experimental sintering and vesicle relaxation timescales substantiate the hypothesis that natural obsidian pyroclasts from Mono Craters, California (USA) form by ash sintering. Two observations are interpreted as the most direct evidence yet that CO2 flushing from a deeper magmatic was involved in the eruption: (1) the preservation of sharp-tipped vesicles in domains of clasts that have high dissolved CO2 concentrations, and (2) the anticorrelation between H2O and CO2 observed in multiple clasts. This thesis includes previously unpublished co-authored material.