Fragmentation behavior of eruptive products of Popocatépetl volcano: An experimental contribution

Abstract

The fragmentation behavior of eruptive products from Popocatépetl has been investigated experimentally in a shock-tube apparatus. Rapid decompression experiments have been performed that mimic Vulcanian explosions that have occurred at Popocatépetl since its reawakening in 1994. We detail the behavior of several fragmentation parameters including the fragmentation threshold, fragmentation speed, ejection velocity and fragmentation efficiency. Our results confirm that the connected porosity of the rock and the applied pressure are strong influences on the fragmentation process. The values of the fragmentation threshold presented here provide quantitative constraints on the overpressure required to generate an explosion at Popocatépetl. We also present the first experimental estimates of the fragmentation speed at magmatic temperatures. We have further applied fractal fragmentation theory to the experimentally-generated pyroclasts to evaluate fragmentation efficiency and we observe thereby that groundmass texture and composition may play an important role in the grain-size distribution. The grainsize distributions of ash fall deposits from several explosive events of Popocatépetl exhibit a fractal dimension higher than the experimentally-generated particles, consistent with the occurrence of secondary fragmentation processes at Popocatépetl. Finally, we analyzed and discussed the information extracted from elasto-acoustic signals associated with the dynamic behavior of the fragmentation process triggered by rapid decompression. The analysis of the experimental results provided in this work are useful for the calibration of eruptive models, the interpretation of the data obtained from monitoring techniques of intermediate composition volcanoes that produce Vulcanian eruptions and may thereby contribute to the improvement of hazard assessment at high risk volcanoes.