EXPLORATION AND STUDY OF THE GLACIER FUMAROLE CAVES IN THE SUMMIT CRATER OF MOUNT RAINIER, WASHINGTON STATE, U.S.A

A multi-national research effort on Mount Rainier initiated in 2015 aims to better understand glacial plug dynamics in the summit crater and the interaction of glacial melt with the magmatic source. The glacier fumarole cave system in the summit craters of Mount Rainier will serve as a focal point of that work. Expeditions mounted in 2015 through 2017 have mapped more than 3 km of cave passages in the east crater that circumnavigate the crater rim. These caves have developed primarily along the contact between the ice and the crater floor and spanning more than 100 m of vertical relief. Earlier mapping efforts and historical documentation indicates that these glacier caves have persisted since 1870. Mapping efforts in the comparably smaller caves of the west crater have been significantly impeded by toxic levels of CO₂ gas. High levels of CO₂ in the east crater cave is limited to passages that penetrate deepest into the crater and away from significant convective airflow.

Survey data will allow for the calculation of ablation of glacial ice by using detailed inter-annual measurements of the volume of referenced cave passage segments. Complementing these data are thermal images of fumaroles and data from an array of temperature-humidity dataloggers to model convective heat flux and moisture advection. Initial results suggest that deeper cave passages are in near equilibrium with heat flux from fumaroles; higher level passages near the crater rim change annually in response to the annual accumulation of snow. Reference stations in the cave wall provides a preliminary estimate of downward ice motion of almost 8 meters. Supplementing the mapping effort are measurements of water level, temperature, and specific conductivity within in-cave meltwater pools, as well as sample collections for meltwater and fumarole chemistry expanding upon earlier USGS and NPS datasets. Ultimately, this project provides a blueprint for thermal and chemical monitoring of volcano activity which could integrate into hazard monitoring and rescue pre-planning.