RAPID DEVELOPMENT OF FUMAROLIC ICE CAVES AND ASSOCIATED SUBSIDENCE TOPOGRAPHY ON EREBUS VOLCANO

Erebus Volcano hosts between one and two hundred fumarolic ice caves: voids melted into the interface between the solidified lava edifice of the volcano and the overlying ice. These phase change caves are useful for comparison and contrast with dissolutional karst, of interest for what they reveal about volcano geothermal systems, and of astrobiological relevance. We conducted a six-year program mapping the locations of all known Erebus caves, monitoring microclimates in many caves, and producing detailed annual 3D models of the several caves using a variety of techniques including laser scanning and multiview photogrammetry.

We observed a relationship between cave entrance locations and underlying geology, and then studied the speleogenetic mechanisms in detail. We noted significant annual morphological change in Warren Cave including upward enlargement of one chamber at a rate of about 1m yr^-1, with a corresponding subsidence of 5cm yr^-1 in the ground (ice) surface about the chamber. Using fiber-optic distributed temperature sensing, we demonstrated that this rapid speleogenesis results from emission of warm volcanic gas from discrete vents in the cave floor. Volumetric temperature measurements in Mammoth Cave revealed a strong positive-upward temperature gradient in the cave atmosphere of 0.26ºC m^-1.

Our observations shed light on the question of process equivalence between this ice-hosted system and dissolutional karst. Resulting morphologies are similar from the landform scale (caves, subsidence) to the decoration scale (scallops, stalactites, stalagmites). Due to shorter rate constants and extreme temperature gradients, these morphologies develop and change orders of magnitude more quickly in the Erebus ice than in typical limestone karst environments.