Micro-Textural Controls on Magma Rheology and Vulcanian Explosion Cyclicity

Understanding the relationship between degassing, crystallization processes and eruption style is a central goal in volcanology, particular how these modulate magnitude timing of cyclical Vulcanian explosions intermediate magmas. To investigate influence variations crystal micro-textures on magma rheology dynamics, we conducted high-temperature (940°C) uniaxial compression experiments at conditions simulating shallow volcanic conduit setting eight samples high-crystallinity andesite with variable plagioclase microlite populations from 2004 to 2010 Galeras volcano, Colombia. Experiments were different strain rates measure rate-dependence apparent viscosities assess dominant deformation associated shear. Variations are spanning over one order for given rate. Samples low numbers large prismatic microlites behaved consistently published rheological laws crystalline dome samples, displayed extensive micro-cracking. high small tabular showed lower viscosity less shear-thinning. The data suggest spectrum behavior controlled by concurrent number, size shape. We use previously micro-textural time-constrained model erupted during 2004–2010 sequence compare results observed SO 2 fluxes. propose that decompression rate, which known produce systematic textural differences cargo, govern conduit. These likely affect rate densifies as result outgassing, leading magmatic plugs range porosities permeabilities. existence physical properties has important implications development critical overpressure driving explosions, thus hazard assessment crises. new conceptual explain andesitic volcanoes based “plug-forming” “dome-forming” magma. advance existing describing rocks inappropriate modeling ( ? 10 6 m 3 ), involved eruptions lacks characteristics required form exogenous lava domes.