From shrinking to fragmentation: new findings from 1 atm - high temperature experiments with rhyolitic glasses.

PABLO FORTE; JONATHAN CASTRO

Mainz

Conferencia; Physics of Volcanoes 2016; 2016

Johannes Gutenberg Universität

Rhyolitic systems are responsible for the most explosive volcanic activity in our planet. Due to the extensive environmental and social consequences that these events could cause, effort was invested to understand how these complex systems work. Since the pioneer study of Murase and McBirney (1973), a number of experimental studies were carried out using natural rhyolitic glasses with the goal of understanding the physical and chemical processes related to gas exsolution and vesiculation in rhyolitic systems (e.g. Bagdassarov and Dingwell (1993), Bagdassarov et al. (1996), Stevenson et al. (1997) and Ryan et al. (2015)). Notwithstanding the importance of these existing studies, our knowledge about these systems is still incomplete to fully explain their dynamics, and in particular, how explosive fragmentation occurs.  In this study, 80 experiments were performed in the laboratories of the Johannes Gutenberg University with the aim of investigating an unexplored field of H2O - temperature conditions. Experiments were carried out at 0.1 MPa, temperatures between 740°- 1030°C and H2O contents ranging from 0.62 to 1.3 wt.%. The materials used for the experiments were cylindrical obsidian cores obtained from bombs of 2008 Chaitén volcano (Chile) eruption. Taking advantage of new technologies, an experimental design that allowed us to observe and monitor the evolution of the experiments was used. It includes a Nabertherm® LT24/12  furnace with a sapphire window and the use of a high speed camera and an IR thermometer laser.  Three types of behaviors were identified that appear to be linked to different H2O - T experimental combinations: a) expansion + equilibrium, b) expansion + shrinking and c) expansion + fragmentation. This presentation will present a detailed description of the phenomenological traits of each of these behavioral categories.