Microclimates in Fumarole Ice Caves on Volcanic Edifices—Mount Rainier, Washington, USA

Abstract

Classic ice cave literature is oriented toward bedrock caves that include perennial ice (Persoiu & Lauritzen, 2017, and references therein). In the literature on ice caves formed within glaciers, conduit development results mainly from flowing water, either through moulins or along the glacier base (Gulley et al., 2009). While air flow in ice caves and resulting ice melt has been investigated through the lens of "cold-air traps" or the "chimney effect" (Bertozzi et al., 2019; Luetscher & Jeannin, 2004; Meyer et al., 2016; Williams & McKay, 2015), these processes do not adequately describe systems that are formed entirely within ice and solely from advective air flow driven by temperature and pressure gradients at the ice-bedrock interface. Strictly speaking, this last category is glacio-thermo karst and is amplified in regions with increased geothermal gradient and, therefore, high heat flux. These high heat flux regions are often volcanic settings, glaciovolcanic caves. The speleogenesis of glaciovolcanic caves is one of thermal equilibrium. Heat flux creates melt, and on active volcanic edifices, this glacial melt percolates into the bedrock and undergoes a phase change to steam. Heat flux may be by conduction where the heated bedrock and ice are in contact (Giggenbach, 1976), but heat transfer by radiation and convection dominate where melt-formed voids that separate bedrock and ice. Discrete fumaroles of steam and volcanic gas, as well as thermal springs, enhance cave formation; the size and shape of the "fumarole ice cave" (Curtis & Kyle, 2011; Pflitch et al., 2017) is guided by the magnitude and locus of heat flux, larger cross sections form near concentrated fumarole and spring activity and localized heat transfer by convection (Kiver & Steele, 1975). The positive pressure gradient from fumarole activity causes lateral and vertical advection of steam and volcanic gas toward the glacial margins or moulins, which can enlarge and connect voids into conduits for moisture, volcanic gas, and heat transfer, such as on Mount Erebus in Antarctica (Wardell et al., 2003). Thermal equilibrium and, therefore, advection through conduits in fumarole ice caves is modulated by short-and long-term changes in volcanic activity and external climate. Certainly, volcanism may rapidly

Implications of the study of subglacial volcanism and glaciovolcanic cave systems

“…To fully explain speleogenesis and to assess morphological changes, factors such as geothermal heat fluxes, their combination with cave microclimates, and external weather also need to be considered. One feature that distinguishes glaciovolcanic caves from non-volcanic glacier caves is that cave air temperatures and air pressures increase in winter, initiating cave expansion (Florea et al 2021a;Sobolewski et al 2022). In volcanic settings, seasonal snowfall and the resulting closure of cave entrances prevent warm air, heated by fumarolic activity, from escaping (Pflitsch et al 2017;Florea et al 2021a).…”

“…One feature that distinguishes glaciovolcanic caves from non-volcanic glacier caves is that cave air temperatures and air pressures increase in winter, initiating cave expansion (Florea et al 2021a;Sobolewski et al 2022). In volcanic settings, seasonal snowfall and the resulting closure of cave entrances prevent warm air, heated by fumarolic activity, from escaping (Pflitsch et al 2017;Florea et al 2021a). Thus, melting processes inside the caves increase periodically, which could accelerate hydrothermal alteration of the edifice (Florea et al 2021a).…”

“…In volcanic settings, seasonal snowfall and the resulting closure of cave entrances prevent warm air, heated by fumarolic activity, from escaping (Pflitsch et al 2017;Florea et al 2021a). Thus, melting processes inside the caves increase periodically, which could accelerate hydrothermal alteration of the edifice (Florea et al 2021a). It is not yet clear, however, whether changes in glaciovolcanic cave temperatures and pressures can be associated with, and used to track, changes in volcanic activity, or are a result of seasonal rainfall and snowmelt affecting both the hydrothermal and cave system.…”

“…2). Mount Rainier (USA), for example, hosts a melt-and condensate-formed subglacial lake that is located within the East Crater Cave (Florea et al 2021a) (Fig. 2a).…”

“…Because glaciovolcanic cave formation starts as a subglacial process, detection difficulties have limited research. Recent work on glaciovolcanic cave systems, however, has considered their relevance to hydrothermal cycles and the unique microclimates within the caves themselves (Florea et al 2021a;Pflitsch et al 2017); has investigated them as analogs for understanding life on other solar system bodies (e.g. Tebo et al 2015;Curtis 2020;Davis et al 2020); and has used them for testing robotic technologies for the exploration of similar planetary environments (Cushing 2012;Duncombe 2018).…”