Intellectual merit. Explosive silicic volcanism poses a major societal threat, yet the underlying causes for large Plinian eruptions remain unclear. Several contributing factors include [1] the relative contributions of different processes (e.g., fractional crystallization, recharge by new magma, interaction of magma and wall rocks) that control volumes and compositions of magma reservoirs, [2] the role of volatile components (e.g., H2O, CO2, S, Cl, F) in controlling magma properties and exsolution of a separate fluid phase, and [3] temporal variations in the geometry of magma plumbing systems. A detailed study of Popocatepetl volcano, located on the fringe of Mexico City, is proposed to evaluate temporal variations and how these factors correlate with eruptive style over the past 23,000 years of activity (as deciphered from tephrochronology records). During this period, at least seven significant Plinian eruptions of dramatically different volumes have occurred. The eruptive products will be characterized to unravel magma evolution and volatile contents, primarily via detailed study of individual phenocrysts and trapped melt inclusions therein using multiple quantitative analytical methods (electron microprobe, laser ablation ICPMS, FTIR) and experimental simulations.
Broader impacts. The project will support two Ph.D. students, one of whom is a Mexican national, and several undergraduate students. The project will also benefit from direct collaboration with Dr. Claus Siebe (UNAM, Mexico city), who has documented the eruptive history of the volcano via detailed tephrochronology work in the region. This collaboration will result in significant technology transfer between the US and Mexico, and will undoubtedly contribute to understanding of volcanic hazards in the area.
