Copyright by Eric Ivan Petersen 2018 The Dissertation Committee for Eric Ivan Petersen Certifies that this is the approved version of the following Dissertation: The Ice Content and Internal Structure of Candidate Debris-Covered Glaciers on Mars and Earth: Insights from Radar Sounding Committee: John W. Holt, Supervisor Joseph S. Levy, Co-Supervisor Ginny Catania Cyril Grima David Mohrig The Ice Content and Internal Structure of Candidate Debris-Covered Glaciers on Mars and Earth: Insights from Radar Sounding by Eric Ivan Petersen Dissertation Presented to the Faculty of the Graduate School of The University of Texas at Austin in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy The University of Texas at Austin August 2018 Acknowledgements This dissertation work was made possible by the NASA Earth and Space Science Fellowship (NESSF) awarded to the Author. Fieldwork at Galena Creek Rock Glacier was made possible by a Jackson School Seed Grant awarded to Cassie Stuurman. I would like to thank Stefano Nerozzi, Dan Lalich, and Cassie Stuurman for technical help, productive and amusing office conversations, and for being excellent fieldwork partners. I thank Philip Petersen and Janice Peltier, my father and mother, for instilling in me the dedication to see this dissertation through. I thank Rebecca Tarvin for her support and Manchego for being my late night writing buddy. I thank Ben Cardenas for his field assistance and friendship. I would like to thank the Planetary Geophysics Field Classes of 2013 and 2015, including Dan Aylward, Jim Pharr, Parvathy Prem, William Hoey, YeJin Lim, Logan Schmidt, Jackie Rambo, Kian Maharaj, Tina Andry, Lizzy McKinnon, and others aforementioned. This class was my first experience with the Mars Research Group as well as field geology; it set me on the road to the completion of this PhD and helped produce some of the data used in my research. I would like to thank Jeff Paine for the loan of his TerraTEM system for several rock glacier field excursions. The SHARAD instrument was provided to NASA’s MRO mission by the Italian Space Agency (ASI), and its operations are led by the DIET Department, University of Rome ‘‘La Sapienza” under an ASI contract. iv Abstract The Ice Content and Internal Structure of Candidate Debris-Covered Glaciers on Mars and Earth: Insights from Radar Sounding Eric Ivan Petersen, PhD The University of Texas at Austin, 2018 Supervisor: John W. Holt Co-Supervisor: Joseph S. Levy Martian lobate debris aprons are enigmatic mid-latitude landforms known to contain a significant fraction of water ice preserved at depth beneath a surface debris layer. They are thought to be important records of climate history and potential water resources for manned missions to Mars. However, their internal structure remains poorly constrained and regional variability in their ice purity is unknown. In this dissertation we report on a regional orbital radar sounding survey of lobate debris aprons in Deuteronilus Mensae – the region of highest concentration of lobate debris aprons on Mars – to constrain trends in lobate debris apron composition and possible internal structure. We also present a geophysical survey of Galena Creek Rock Glacier to constrain its internal structure as an analog to Martian lobate debris aprons. v We found that the majority of radar observations imaged a basal reflector, from which we determined that the apron body is composed of material with dielectric properties consistent with relatively pure water ice and that there is no evidence for region-wide variability. Combining our compositional results with apron volumes constrained by Levy et al. (2014) sets the regional ice budget at 0.9-1.0 x 105 km3, the equivalent of roughly 4x the combined volume of water in the Great Lakes. We additionally showed that non-detection of basal reflectors in 13% of the observations may be attributed to high apron thickness and surface roughness-induced signal loss. In our analog work on Galena Creek Rock Glacier, we imaged its internal structure consisting of a network of englacial debris layers. This internal structure is indicative of intermittent debris and ice accumulation, with debris fall potentially playing a role in enhancing and facilitating ice accumulation. Similar englacial debris layers may exist in Martian lobate debris aprons, but are not imaged by the available orbital radar dataset due to their dip and thickness. vi Table of Contents List of Tables ...................................................................................................................... ix List of Figures ...................................................................................................................... x Chapter 1: Introduction ........................................................................................................ 1 Chapter 2: Literature Review of Candidate Debris-Covered Glaciers ................................ 5 Terrestrial Rock Glaciers ............................................................................................ 5 Martian Lobate Debris Aprons ................................................................................... 8 A RADAR SURVEY OF MARTIAN LOBATE DEBRIS APRONS ............................................... 17 Chapter 3: All Lobate Debris Aprons Penetrated by SHARAD are Debris-covered Glaciers: Evidence From an Orbital Radar Sounding Survey ..................................... 17 Abstract ..................................................................................................................... 17 Introduction .............................................................................................................. 17 Study Region ............................................................................................................ 19 Methods .................................................................................................................... 19 Results ...................................................................................................................... 23 Discussion ................................................................................................................. 25 Conclusions .............................................................................................................. 36 Chapter 4: Surface Roughness Prevents Radar Penetration of Some Lobate Debris Aprons ......................................................................................................................... 38 Introduction .............................................................................................................. 38 Study Sites ................................................................................................................ 44 Methods .................................................................................................................... 44 Results ...................................................................................................................... 53 vii Discussion ................................................................................................................. 61 Conclusions .............................................................................................................. 63 A RADAR SURVEY OF A TERRESTRIAL ROCK GLACIER ................................................... 65 Chapter 5: New Insights Into Ice Accumulation at Galena Creek Rock Glacier from Radar Imaging of its Internal Structure ....................................................................... 65 Introduction .............................................................................................................. 65 Site ............................................................................................................................ 66 Methods .................................................................................................................... 68 Results ...................................................................................................................... 70 Discussion ................................................................................................................. 79 Conclusions .............................................................................................................. 84 Chapter 6: Discussion and Conclusions ............................................................................ 85 Bibliography ...................................................................................................................... 90 viii List of Tables Table 1: List of SHARAD observations used in Surface Roughness Analysis. ............. 47 ix List of Figures Figure 1: MOLA-derived map of Deuteronilus/Protonilus Mensae summarizing radar survey .................................................................................................. 23 Figure 2: Sample SHARAD Data for Lines 755102000 and 806502000 ...................... 25 Figure 3: Sample SHARAD Data for Lines 722102000 and 266602000 ...................... 27 Figure 4: Example of a radar observation for which echoes from off-nadir sources clutter the data, obscuring and/or masquerading as subsurface signal ......... 29 Figure 5: Distribution of determined bulk dielectric constant values ............................ 30 Figure 6: Distributions of calculated loss tangent with two-layer model applied .......... 34 Figure 7: An illustration of the effect