Dynamics and global relevance of fumarolic ice caves on Erebus Volcano, Antarctica by Aaron Curtis DISSERTATION Submitted in Partial Fulfillment of the Requirements for Doctorate of Philosophy in Earth & Environmental Science with Dissertation in Geochemistry New Mexico Institute of Mining and Technology Department of Earth & Environmental Science Socorro, New Mexico May, 2016 To my family, who gave me the world, and the Cambridge University Caving Club, who showed me what lies beneath it. Aaron Curtis New Mexico Institute of Mining and Technology ABSTRACT This dissertation seeks to characterize the cave atmospheres and dynamics of fumarolic ice caves. The introduction presents a broad framework for understanding the caves and describes the historical and conservation context into which the work fits. This framework provides the motivation for five investigations which are presented as Chapters 2 through 6. Chapter 2 details a fiber-optic distributed temperature sensing (FODTS) experiment in which 438m of fiber-optic cable was deployed along the main passages of Warren Cave on Erebus Volcano, Antarctica. Point sources of warm gas flowing into the cave manifested as multi-degree C temperature anomalies and persisted throughout the week- long experiment. Observed temperatures were anti-correlated with local atmospheric pressure, indicating barometric pumping of the gas vents. Chapter 3 extends the FODTS technique used in Chapter 2 to three dimensions for volumetric imaging of the temperature field inside a fumarolic ice cave chamber. Using terrestrial laser scanning (TLS) and automatic pointcloud classification techniques, I precisely located each virtual temperature sensor along the fiber optic cable. Interpolation and analysis of spatial patterns revealed a strong, upward-positive temperature gradient which averaged 0.265C m-1 over the 7 day experiment. I used satellite data and a permafrost model to assess potential Holocene volcano-ice interaction globally, finding that 19.8% of known Holocene volcanic centers host glaciers or areas of permanent snow. The results, presented in Chapter 4, suggest that fumarolic ice caves are globally widespread and largely undiscovered. Fumarolic ice caves are expected to form when degassing begins beneath any volcano with moderate ice overburden. In Chapter 5, I present six years of morphological observations using TLS, structure from motion (SfM), and traditional cave survey, revealing that fumarolic ice caves change on the scale of tens of centimeters annually, and that the topography above the caves responds to enlargement of chambers through melting. I find that the cave wall ice has passed the pore-closeoff density, and conclude that densification is accelerated by heat from the cave. The rapid passage enlargement observed means that fresh rock substrate regularly becomes available to the cave microbial communities. For theoretical context, I developed two “toy” models. A computational fluid dynamics (CFD) simulation of cave melt is presented which represents a cave during initiation of growth. A simple flow model based on Glen's flow law, gives a first estimate of expected passage closure rates due to ice creep. Chapter 6 represents a collaborative effort to characterize the isotopic and chemical composition (δ2H and δ18O) of Erebus' snow and ice mantle which hosts the fumarolic ice caves. We found that snow samples from the entire summit caldera area, including ice cores collected through fumarolic ice tower walls, fall far outside an Antarctic Meteoric Water Field which encompasses all other available Antarctic snow isotope data. This suggests a magmatic component in the snow, which may be supplied by the plume emanating from Erebus' main crater. Several cross-cutting themes are addressed in multiple chapters. I discuss how fumarolic ice caves provide important indicators of volcanic unrest, analogues of extraterrestrial systems, and critical habitats for microbes. Going forward, this dissertation should be a foundation on which to plan the further exploration of fumarolic ice caves on Earth and elsewhere in the solar system. Keywords: distributed temperature sensing, LiDAR, isotopes, glaciovolcanism, flank degassing, Erebus, Antarctica ACKNOWLEDGEMENTS Harry Keys, Bill McIntosh, and Nelia Dunbar introduced me to the caves, sharing decades worth of accumulated wisdom and coordinates. My trusty mapping partner Nial Peters volunteered hundreds of hours underground during the early years of this work, and continued to support the cave project despite the demands of his own Erebus fieldwork. Drea Killingsworth, Jed Frechette, Laura Jones, Marianne Okal, and Brendan Hodge assisted with TLS collection. The Center for Transformative Environmental Monitoring Programs (CTEMPS) provided FODTS equipment and training. Sune Tamm, Tim Burton, and the mountaineers of the USAP Field Safety and Training Program assisted with cave access and safety. Committee members Penny Boston, Oleg Makhnin, and John Wilson provided invaluable technical advice. Clive Oppenheimer first told me of the caves and recommended New Mexico Tech. He is the most famous kind of fish. My advisor, Phil Kyle, worked tirelessly to establish and maintain the Mount Erebus Volcano Observatory which provides the theoretical framework and logistical infrastructure that enabled this project. ii TABLE OF CONTENTS LIST OF TABLES.........................................................................................................vi LIST OF FIGURES......................................................................................................vii 1. INTRODUCTION...........................................................................................................1 1.1 References.............................................................................................................7 1.2 Appendix A: Cave surveys..................................................................................11 1.3 Appendix B: Temperatures recorded in Erebus FICs..........................................14 1.4 Appendix C: Gas concentrations.........................................................................21 2. GEOTHERMAL POINT SOURCES IDENTIFIED IN A FUMAROLIC ICE CAVE ON EREBUS VOLCANO, ANTARCTICA USING FIBER OPTIC DISTRIBUTED TEMPERATURE SENSING........................................................................................23 2.1 Abstract................................................................................................................24 2.2 Introduction.........................................................................................................24 2.3 Fiber-Optic Distributed Temperature Sensing (DTS)..........................................24 2.4 Methods...............................................................................................................25 2.5 Results.................................................................................................................25 2.6 Analysis...............................................................................................................25 2.7 Conclusions.........................................................................................................29 2.8 References...........................................................................................................29 3. VOLUMETRIC TEMPERATURE FIELD MEASURED IN A FUMAROLIC ICE CAVE ON EREBUS VOLCANO, ANTARCTICA BY COMBINING FIBER OPTIC TEMPERATURE SENSING WITH LASER SCANS.................................................31 3.1 Abstract................................................................................................................31 3.2 Introduction.........................................................................................................31 3.3 Research setting...................................................................................................33 3.4 Methods...............................................................................................................34 3.4.1 FODTS.......................................................................................................34 3.4.2 TLS............................................................................................................35 3.4.3 Spatial registration of FODTS data............................................................35 3.4.4 Spatial interpolation (kriging)....................................................................37 3.5 Results.................................................................................................................37 3.6 Discussion............................................................................................................42 iii 3.7 Conclusions.........................................................................................................45 3.8 References...........................................................................................................46 4. DETERMINING THE GLOBAL DISTRIBUTION OF VOLCANO-ICE INTERACTION............................................................................................................49 4.1 Abstract................................................................................................................49 4.2 Introduction.........................................................................................................50 4.3 Background..........................................................................................................51