A VALIDATION OF GROUND PENETRATING RADAR FOR RECONSTRUCTING THE INTERNAL STRUCTURE OF A ROCK GLACIER: MOUNT MESTAS, COLORADO, USA A Thesis by WILLIAM REVIS JORGENSEN Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE May 2007 Major Subject: Geology A VALIDATION OF GROUND PENETRATING RADAR FOR RECONSTRUCTING THE INTERNAL STRUCTURE OF A ROCK GLACIER: MOUNT MESTAS, COLORADO, USA A Thesis by WILLIAM REVIS JORGENSEN Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Approved by: Co-Chairs of Committee, John R. Giardino Mark Everett Committee Member, Vatche P. Tchakerian Head of Department, John H. Spang May 2007 Major Subject: Geology iii ABSTRACT A Validation of Ground Penetrating Radar for Reconstructing the Internal Structure of a Rock Glacier: Mount Mestas, Colorado, USA. (May 2007) William Revis Jorgensen, B.S.; B.S., Texas A&M University Co-Chairs of Advisory Committee: Dr. John R. Giardino Dr. Mark Everett Rock glaciers are dynamic landforms and, as such, exhibit interesting and well- developed structural features, which translate to surface morphology in the form of ridges and furrows. These distinguishing features have led researchers to study the physics behind the movement and internal deformation of rock glaciers. For years researchers had no access to the internal makeup of rock glaciers. Thus, proposed models and discussion have been based on theoretical concepts of electromagnetic (EM) wave propogation. With the application of ground penetrating radar (GPR) to provide a view of the interior structure of a rock glacier, researchers had “real” data to verify their models. However, no comparison has been made between a GPR profile and an actual cross-section of a rock glacier. The purpose of this thesis is to validate the fidelity of GPR in showing the actual structure of a rock glacier. A trench that was excavated through the toe of a rock glacier on Mount Mestas in south central Colorado provided a view of the actual structure of the landform. The structure in the trench was compared with GPR and EM data. The GPR study was conducted using a PulsEKKO TM 100A subsurface imaging radar with 25, 50, and 100 iv MHz antennas, to detect dielectric contrasts within the rock glacier. A frequency domain EM34 by Geonics Ltd TM was also used to supplement the GPR data by measuring the rock glacier’s conductivity at various depths. This thesis proved, by utilizing statistics, that GPR is a useful tool in visualizing the interior structure of rock glaciers. The 100 MHz antennas clearly show small scale reflection horizons caused by changes in clast orientation and subsurface material composition. These events coincide with structures seen in the trench. Individual clasts greater than 0.375 m were also recognized as point sources in the GPR profiles. Large continuous bedding layers were observed with the 25 and 50 MHz antennas, which reflect the structure seen in the trench. A large scale thrust fault was also located with the GPR. However, this was not visible in the panoramic photograph because the fault occurs below the base of the trench. v DEDICATION To my parents, Martha and Bill, for always being there. Thank you for everything. vi ACKNOWLEDGMENTS I thank my advisor John R. Giardino for providing me with the opportunity of studying and learning with him. I am very grateful for his patience and understanding in the midst of his hectic schedule. I also to thank Mark Everett for the time he spent with me and for sharing his knowledge of geophysics. I especially thank Andrew Nigrini for his willingness to allow me access his property at the rock glacier for the advancement of science. In addition, I thank my friends and field assistants John Degenhardt, Allison Potscavage, Netra Regmi, Douglas Rodriguez, and Rebecca Stokes for their hard work. And lastly, to my mother, Martha, as well as my Aunt Bonnie, who waded through rough draft after rough draft of my manuscript in helping me polish my research communications. Your help was invaluable. vii TABLE OF CONTENTS Page ABSTRACT............................................................................................................... iii DEDICATION........................................................................................................... v ACKNOWLEDGMENTS ......................................................................................... vi TABLE OF CONTENTS........................................................................................... vii LIST OF FIGURES ................................................................................................... ix LIST OF TABLES..................................................................................................... xi INTRODUCTION AND PROBLEM STATEMENT............................................... 1 Objectives ...................................................................................................... 3 MOUNT MESTAS SITE LOCATION AND GEOLOGY ....................................... 4 LITERATURE REVIEW .......................................................................................... 6 ROCK GLACIER MECHANICS.............................................................................. 12 METHODS ................................................................................................................ 18 Surface Morphology Mapping....................................................................... 20 Construction of Visual Image of Trench ....................................................... 22 Electromagnetic Survey................................................................................. 22 Ground Penetrating Radar.............................................................................. 24 Ground-Truth the Use of GPR....................................................................... 30 RESULTS AND ANALYSIS.................................................................................... 32 Surface Morphology Mapping....................................................................... 32 Construction of Visual Image of Trench ....................................................... 34 Electromagnetic Survey................................................................................. 35 Ground Penetrating Radar.............................................................................. 37 Ground-Truth the Use of GPR....................................................................... 46 Rock Glacier Morphology ............................................................................. 49 Statistical T-Test ............................................................................................ 53 viii Page CONCLUSION.......................................................................................................... 62 RECOMMENDATIONS FOR FUTURE STUDY ................................................... 65 REFERENCES .......................................................................................................... 66 VITA.......................................................................................................................... 70 ix LIST OF FIGURES FIGURE Page 1 Location map of Mount Mestas....................................................................... 5 2 Ridge and furrow development through fault-propogation folding ................................................................................ 15 3 Ridge and furrow development through fault-bend folding............................................................................................ 15 4 Fault-bend folding diagram............................................................................. 16 5 Fault-propogation folding diagram ................................................................. 17 6 Panoramic photograph of Mount Mestas trench ............................................. 19 7 Aerial photograph showing the different parts of the rock glacier along with a geographical outline of the rock glacier showing locations of GPR profiles.............................................. 21 8 Electromagnetic induction prospecting system............................................... 24 9 PulseEKKO TM 100A radar system from Sensors & Software, INC ................................................................................ 25 10 Diagram of the GPR process showing ray paths of transmitted, reflected, and refracted energy................................................ 25 11 Common midpoint survey showing ray paths of reflections from the Transmitter (Tx) to the Receiver (Rx) ............................ 29 12 Common offset reflection technique showing ray paths of reflections from the Transmitter (Tx) to the Receiver (Rx) .............. 29 13 Profile layout ................................................................................................... 29 14 Local geomorphology map of the area............................................................ 33 15 Panoramic photograph of the trench with the interpreted image .................... 34 x FIGURE Page 16 Location and amplitude of EM conductivity readings perpendicular to trench.................................................................................... 35 17 CMP analysis of Mount Mestas rock glacier showing average velocity at 0.15 meters per nanosecond [m/ns] ..............................................