Strength and permeability recovery of tuffisite-bearing andesite
- 1Volcanology and Petrology Laboratory, Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, V6T 2B4 Vancouver, BC, Canada
- 2Laboratoire de Déformation des Roches, Institut de Physique de Globe de Strasbourg (UMR 7516 CNRS, Université de Strasbourg/EOST), 5 rue René Descartes, 67084 Strasbourg cedex, France
- 3Earth and Environment, LMU – University of Munich, Theresienstr. 41/III, 80333 Munich, Germany
- 4Rock and Ice Physics Laboratory, University College London, Gower Street WC1E 6BT London, UK
Abstract. Tuffisites, the products of subsurface fragmentation, transport and deposition, are common in explosive volcanic environments. Their study provides direct insight to the mechanical processes operating within volcanic conduits. Here we document the influence of the presence of coherent tuffisite veins on the physical properties of andesitic rocks. We find that (1) compressive strength is unaffected by the presence and/or orientation of tuffisites, (2) permeability doubles when tuffisites are oriented favorably (at 45° to the fluid flow direction), and (3) ultrasonic wave velocities show a continuous increase with depth, independent of vein presence and orientation. Although the influence of tuffisites on andesitic rock properties determined here is modest, we emphasize that the material tested represents the post-eruptive state of tuffisite. Thus, these results likely delineate the upper and lower boundaries of strength vs. permeability and porosity, respectively. Our evidence suggests that, via compaction and lithification, tuffisites may restore the strength of the volcanic host-rocks to that of their pre-tuffisite values.