Effect of rigid crystals on the experimental sintering of rhyolitic ash under shallow conduit conditions
We present an experimental investigation of surface tension-driven sintering and associated densification of crystal-bearing rhyolitic ash under shallow volcanic conduit conditions. Suites of isobaric (40 MPa) experiments were held at a constant temperature of 675 to 850 °C for durations of 30 minutes to 9 hours. A 50/50 mixture of rhyolitic glass powder (<45 μm) and quartz crystals, in three distinct size distributions, were used: 250 - 500 µm, 90 - 125 µm, and 45 - 76 μm. All samples evolved similarly, from loose, cohesion-less particles to sintered particles forming a friable, agglutinated framework with an interconnected network of pores of ≥20 vol.%. All mixtures took longer to sinter and remained at a higher final porosity than crystal-free experiments performed by Gardner et al. (2018) under the same conditions. Samples sintered more slowly and remained more porous with cooler temperatures and finer crystals. Estimates for permeability indicate that these crystal-rich mixtures are as permeable as natural samples of equivalent porosity. Our experimental results suggest that solid particles inhibit the sintering process by holding porous networks open, allowing for sustained degassing. Therefore, solid particles may have important consequences for outgassing in the shallow conduit if the material is sintered together.
Sintering, Welding, Volcanism, Silicic, Volcanology, Geology, Microscopy, Petrography, Ash, Bubbles
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