Pontificia Universidad Católica de Chile Pontificia Universidad Católica de Chile
Browning J., Tuffen H., James M.R., Owen J., Castro J.M., Halliwell S., Wehbe K. (2020)

Post-fragmentation vesiculation timescales in hydrous rhyolitic bombs from Chaitén volcano

Revista : Journal of South American Earth Sciences
Volumen : 104
Páginas : 102807
Tipo de publicación : ISI Ir a publicación


Bubble nucleation and growth dynamics exert a primary control on the explosivity of volcanic eruptions. Numerous theoretical and experimental studies aim to capture the complex process of melt vesiculation, whereas textural studies use vesicle populations to reconstruct magma behaviour. However, post-fragmentation vesiculation in rhyolitic bombs can create final quenched bubble (vesicle) textures that are not representative of the nature of fragmenting magma within the conduit. To examine bubble growth in hydrous rhyolitic bombs, we have used heated stage microscopy to directly observe vesiculation of a Chaitén rhyolite melt (with an initial dissolved water content of ~0.95 wt %) at atmospheric pressure and magmatic temperatures upon reheating. Thin wafers of obsidian were held from 5 min up to two days in the heated stage at temperatures between 575 °C and 875 °C. We found that bubble growth rates, measured through changes in bubble diameter, increased with both temperature and bubble size. The average growth rate at the highest temperature of 875 °C is ~1.27 ?m s?1, which is substantially faster than the lowest detected growth rate of ~0.02 ?m s?1 at 725 °C; below this temperature no growth was observed. Average growth rate Vr follows an exponential relationship with temperature, T and inferred melt viscosity ?, where Vr = 5.57