THE INFLUENCE OF TERRAIN PARAMETERS ON THE SPATIAL VARIABILITY OF POTENTIAL AVALANCHE TRIGGER LOCATIONS IN COMPLEX AVALANCHE TERRAIN by Zachary Mark Guy A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Earth Sciences MONTANA STATE UNIVERSITY Bozeman, Montana November, 2011 ©COPYRIGHT by Zachary Mark Guy 2011 All Rights Reserved ii APPROVAL of a thesis submitted by Zachary Mark Guy This thesis has been read by each member of the thesis committee and has been found to be satisfactory regarding content, English usage, format, citation, bibliographic style, and consistency and is ready for submission to the Division of Graduate Education. Dr. Stephan G. Custer (Co-Chair) Dr. Karl W. Birkeland (Co-Chair) Approved for the Department of Earth Sciences Dr. Stephan G. Custer Approved for The Graduate School Dr. Carl A. Fox iii STATEMENT OF PERMISSION TO USE In presenting this thesis in partial fulfillment of the requirements for a master‟s degree at Montana State University, I agree that the Library shall make it available to borrowers under rules of the Library. If I have indicated my intention to copyright this thesis by including a copyright notice page, copying is allowable only for scholarly purposes, consistent with “fair use” as prescribed in the U.S. Copyright Law. Requests for permission for extended quotation from or reproduction of this thesis in whole or in parts may be granted only by the copyright holder. Zachary Mark Guy November, 2011 iv ACKNOWLEDGEMENTS This research would not have been possible without all of the support that I received along the way. I would like to thank my advisor, Karl Birkeland, for his wisdom and assistance through the entire research process. I‟d also like to thank my other committee members, Stuart Challendar and Steve Custer and also Jordy Hendrikx for their involvement in my research. Moonlight Basin, Big Sky, and Jackson Hole Ski Patrols were incredibly supportive in allowing access to their terrain, their weather data, and for looking out for the safety of sampling teams. I‟d especially like to thank Brad Carpenter, Nick Armitage, Chelan Babineau-Z, and Bob Comey. I am grateful for research grants from the American Avalanche Association, Mazamas, the American Alpine Club, and the Association of American Geographers. LiDAR data was provided by Brian McGlynn and the MSU Watershed Hydrology Laboratory with support from the U.S. National Science Foundation (BCS #0518429) and from the Bridger Teton National Forest Avalanche Center. I‟d like to thank all of my field assistants for putting up with cold, windy, and long days on exposed terrain, especially Jordan Mancey, who was always far too eager to help out. I‟d also like to thank Lucy Marshall and Jim Robison-Cox for their statistical counsel, Diana Cooksey for her assistance with the GPS units, Alex Marienthal and Leila Sterman for peer reviews, and everyone else who offered advice along the way. Lastly, I am most grateful to my close friends and family for supporting me through my graduate studies. v TABLE OF CONTENTS 1. INTRODUCTION......................................................................................................................1 2. LITERATURE REVIEW ........................................................................................................ 4 Weak Layers..................................................................................................................4 Spatial Variability.........................................................................................................7 Terrain Influences.......................................................................................................11 Summary.....................................................................................................................16 3. METHODS .............................................................................................................................. 17 Study Sites...................................................................................................................17 Big Sky Study Area .............................................................................................18 Teton Study Area.................................................................................................25 Weather History ..................................................................................................28 Field Methods.............................................................................................................30 Mapping Points with GPS...........................................................................................37 Terrain Parameters......................................................................................................39 Exploratory Analysis...................................................................................................50 Designing the Response Variable........................................................................50 Mapping PTLs .....................................................................................................54 Correlation Analysis ............................................................................................55 Terrain Parameter distribution comparisons .......................................................55 Modeling Potential Trigger Locations........................................................................56 Classification Tree Modeling ..............................................................................57 Logistic Regression Modeling.............................................................................61 Groupwise Modeling ...........................................................................................70 4. RESULTS AND DISCUSSION .......................................................................................... 73 vi TABLE OF CONTENTS - CONTINUED Case Study: Upper AZ1 Depth Hoar Layer................................................................73 Depth Hoar Results and Discussion............................................................................93 Individual Couloirs ..............................................................................................93 Geographic Groups............................................................................................103 Facet Results and Discussion....................................................................................123 Individual Couloirs ............................................................................................123 Geographic Groups............................................................................................130 Surface Hoar Results and Discussion........................................................................136 General Discussion....................................................................................................146 Summary ...........................................................................................................146 Terrain Parameter Influences ............................................................................149 Modeling Success ..............................................................................................156 Uncertainty ........................................................................................................162 Scope of Inference .............................................................................................165 5. CONCLUSION ..................................................................................................................... 167 Summary ..................................................................................................................167 Future Work .............................................................................................................169 REFERENCES CITED ............................................................................................................ 171 APPENDICES..................................................................................................................180 APPENDIX A: PTLs Mapped on Shaded Relief..............................................181 APPENDIX B: Groupwise Modeling Statistical Outputs.................................191 APPENDIX C: Supplementary 3D Maps......................................................... 230 vii LIST OF FIGURES Figure Page 1. Regional study site map .................................................................................. 17 2. Lone Mountain study sites. ............................................................................. 19 3. The Gullies ..................................................................................................... 21 4. Upper A to Z chutes. ...................................................................................... 22 5. Headwaters. .................................................................................................... 23 6. North Summit. ................................................................................................ 24 7. Lone Lake Cirque. .......................................................................................... 25 8. Southern Tetons study sites. ........................................................................... 26 9. Seven Dwarves. .............................................................................................