MORPHODYNAMICS, MORPHOLOGY, AND MICROCLIMATE OF THE GLACIOVOLCANIC CAVE SYSTEM AT THE SUMMIT OF MOUNT RAINIER, WASHINGTON, USA

The longest and deepest known glaciovolcanic caves in the world lie in the summit craters of Mount Rainier, Washington, USA. Formed by volcanogenic gases and atmospheric advection in ice and firn at the glacier-ice margin in the volcanic crater, they are a unique laboratory to study an interplay producing speleogenesis in ice, and the resulting morphodynamics and unique microclimates in glaciovolcanic caves. Previous research in these caves provided a snapshot of a transient environment; we merged these earlier surveys with our recent data collections to understand how the shape and character of glaciovolcanic caves on volcanic edifices change through time.

A comprehensive survey of the cave system 2014-2017 and ice surface transect were combined with time-series data on subglacial fumarole temperature, air pressure and temperature, subglacial lake temperature and depth. We also collected measurements of volcanogenic gas, glacier subsidence, and external climactic conditions. Comparative cartography aligning historical surveys to the updated version provided a window into cave morphodynamics over a 47-year timespan.

A subset of conserved cave passages maintained constant position over 47 years. These passages exhibit low temperature variation. These persistent passages were generally sub-horizontal, followed curvilinear crater contours, and were dependent on perennial fumaroles or distributed heat flux. The subglacial climate data from 2015-2017 combined with comparative cave survey data reveal a dynamic equilibrium in the system over a multi-decadal timescale. Transient dendritic passages that descend from entrance zones to the persistent passages have higher temperature and airflow variability. Complex associations exist between seasonal weather, fumarole activity, and subglacial lake level. Cave entrances seal during rapid snowfall and cause subglacial air temperature and pressures to increase. Meanwhile, persistent subglacial volcanogenic CO₂ traps collect in the lowest areas of the cave, with atmospheric pressure as the main factor influencing CO₂ concentrations. The findings highlight the dynamics in understudied parts of the cryosphere as they intersect with speleology, and have broad implications including crater mass wasting and potential volcanic hazards.