Glacier Cave Explorers

Abstract The fumarole ice caves of Mount Rainier in the Cascade Volcanic Arc in Washington, USA, provide unique insight into the dynamic equilibrium between thermal flux of fumaroles on volcanic edifices and snow accumulation on summit glaciers. More than 3.5 km of surveyed cave passage nearly circumnavigate the East Crater, reaching within 19 m of the 4,392 m summit and extending to 144 m depth along the glacier‐crater boundary. The large circum‐crater passage connects entrances on the crater rim to steep transverse passages, and cave morphology is maintained by fumarole gas convection and advection. A melt‐ and condensate‐formed lake, Lake Adélie, occupies a portion of the circum‐crater passage. Hourly data were collected between August 2016 and August 2017 and included the measured temperatures at three fumaroles, the cave air temperature and pressure, the lake water temperature and depth, and the outside temperature and snow depth at Paradise Visitors Center. Time‐series analyses of these data reveal complex associations between synoptic to seasonal weather, fumarole activity, and lake level. On seasonal and longer scales, fumarole temperatures follow independent pathways connected to spatial and temporal changes in volcanic heat flux and the circulation of glacial melt. Major snowfall seals the cave entrances, increasing cave air temperature and pressure from fumarole output and causing rising lake levels from increased melt until entrances reopen. Repeating freeze‐thaw cycles observed in the cave monitoring data are a primary cause of crater mass wasting. Despite these transient variations, the scale and morphology of the caves is preserved over decadal or longer scales.

Abstract. A new and extensive system of glaciovolcanic caves has developed around the 2004–2008 lava dome in the crater of Mount St. Helens, Washington, USA. These systems offer a rare view into a subglacial environment and lead to a better understanding of how glaciers and active volcanoes interact. Here, we present first results from geodetic and optical surveys done between 2014 and 2019 as well as climatologic studies performed between 2017 and 2019. Our data show that volcanic activity has altered subglacial morphology in numerous ways and formed new cave systems that are strongly affected by heat flux from several subglacial fumaroles. More than 2.3 km of cave passages now form a circumferential pattern around the dome, some several hundred meters long. Air and fumarole temperature measurements were conducted in two specific caves. Whereas air temperatures reveal a strong seasonal dependency, fumarole temperatures are affected to a minor extent and are primarily regulated by changes in volcanic heat flux or the contribution of glacial melt. Related studies from Mount Hood, Oregon, and Mount Rainier, Washington, are used as comparison between glaciovolcanic cave systems. Fumarolic heat and resulting microclimates enable further genesis of this dynamic system. Already one of the largest worldwide, it is very likely that the system will continue to expand. As Mount St. Helens is the Cascade Volcano most likely to erupt again in the near future, these caves represent a unique laboratory to understand glaciovolcanic interactions, monitor indicators of recurring volcanic activity and to predict related hazards.

Crillon-La Perouse stock and vicinity