The summit of Popocatépetl. Photo credit: Jakub Hejtmánek
Around the Pacific Ring of Fire over 200 million people live near active volcanoes. The largest population at risk in the world from a single volcano is that near Popocatépetl in the Trans-Mexican Volcanic Belt. Located 70 km southeast of Mexico City and 40 km west of Puebla, Popocatépetl threatens >30 million people living on or near its flanks. In its lifetime there have been at least two cone collapses and accompanying debris avalanches, as well as 7 large Plinian eruptions that have distributed ash across hundreds of km2, including the ground upon which Mexico City is built. After ~65 years of quiescence, Popocatépetl reawakened in December 1994. This proposal aims to constrain the geochronology of past cycles of eruptive output and destruction and develop an historical context in which Popocatépetl's current eruptive tempo will be better understood.
The mechanism(s) and kinetics of noble gas diffusion in the crust and mantle are critical to many topics in the Earth and planetary sciences. Thermochronometry by the 40Ar/39Ar, 4He/3He, and (U-Th)/He techniques provides insights into geologic processes that span immense time and temperature regimes, from rapid and high temperature asteroid impact events to mountain uplift occurring over plate tectonic timescales at near surface temperatures. Despite the breadth of applications, our understanding of the mechanisms and pathways of noble gas diffusion within many minerals remains fragmentary. Each day noble gas isotopes contained within different solid matrices are analyzed in the Livermore Noble Gas Lab, and detailed temperature-dependent gas release curves are generated. Synthesis of these data has potential to lead to a better atomistic understanding of noble gas diffusion in minerals, metals, and glasses.