Subtitle: HRXCT Analysis of White Dacite Pumice from Popocatépetl Volcano, Mexico

Samantha Abbott

Vesicle textures in pumice have been used to interpret eruption intensity and conduit processes such as vesiculation, shear, and fragmentation, although the relationships linking pumice textures to vesiculation and fragmentation processes are not well understood. My project was a three-dimensional examination of large vesicle textures of pumice from the White Pumice plinian eruption of Popocatépetl Volcano, Mexico, in an attempt to discern what processes produce heterogeneous vesicularities and textures from homogeneous pre-eruptive conditions. Four samples of the white pumice from Popocatépetl, Mexico, were scanned in the high-resolution X-ray computed tomography (HRXCT) facility at UT. Vesicle sizes, shapes, and distributions were quantified using the software package Quant3D, and the relative orientations of vesicles and phenocrysts in the pumice were analyzed using Quant3D.
We found a bimodal vesicle size distribution in all of the pumice samples. Vesicles become increasingly deformed with increasing bulk vesicularity. The volume percent of large vesicles and their bubble number densities increase with increasing vesicularity. The vesicles and phenocrysts in all of the samples show preferred unidirectional or planar orientations, which are attributed to pre-fragmentation shear within the conduit during an eruption. The strongest vesicle and crystal orientations are seen in the highest vesicularity pumice. The presence of welded textures in two pumice samples is evidence for post-fragmentation evolution.

Advisor: James Gardner, Rich Ketcham