Spatial Variations in Snow Stability on Uniform Slopes
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SPATIAL VARIATIONS IN SNOW STABILITY ON UNIFORM SLOPES: IMPLICATIONS FOR EXTRAPOLATION TO SURROUNDING TERRAIN by Christopher Cameron Landry A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Earth Sciences MONTANA STATE UNIVERSITY Bozeman, Montana April 2002 COPYRIGHT by Christopher Cameron Landry 2002 All Rights Reserved ERRATA The author, Christopher C. Landry, wishes to inform readers of the Master of Science thesis titled "Spatial variations in snow stability on uniform slopes: implications for extrapolation to surrounding terrain", published April 2002, of an error in the statistical analyses of project results. T-statistic tests were mistakenly performed at p < 0.10 rather than at p < 0.05. Nonetheless, re-performing the T-statistic analyses at p < 0.05 altered the results only marginally, and the conclusions of the research remain unchanged. Subsequent to the publication of the thesis, and the discovery of this error, a peer- reviewed article was submitted, using an alternative statistical approach, and published in Cold Regions Science and Technology. Readers of the original these are referred to the following article: Landry, C., K. Birkeland, K. Hansen, J. Borkowski, R. Brown and R. Aspinall. 2004. Variations in snow strength and stability on uniform slopes. Cold Regions Science & Technology, Vol. 39, p. 205-218. APPROVAL of a thesis submitted by Christopher Cameron Landry This thesis has been read by each member of the thesis committee and has been found to be satisfactory regarding content, English usage, format, citations, bibliographic style, and consistency, and is ready for submission to the College of Graduate Studies. STATEMENT OF PERMISSION TO USE In presenting this thesis in partial fulfillment of the requirements for a master’s degree at Montana State University – Bozeman, 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. ACKNOWLEDGEMENTS It has been my good fortune to have enjoyed the guidance and encouragement of my esteemed graduate committee, Katherine Hansen, Karl Birkeland, John Borkowski, Robert Brown, and Richard Aspinall. Each was indispensable to this research I wish to gratefully acknowledge support of my research by the Department of Earth Sciences, the Barry C. Bishop Scholarship for Mountain Research, and EPSCoR MONTS. Contributions by the American Avalanche Association and the Canadian Avalanche Association were particularly meaningful. The Mazamas, the American Alpine Club, and the Geological Society of America Foundation’s John Montagne Fund all provided vital resources. And, Bridger Bowl Ski Area, the Parks Canada avalanche control program at Glacier National Park, Life Link International, and Snowmetrics each contributed access to research sites, in-kind products, and services. For his moral support, thanks to Hal Hartman. For technical support, thanks to Karin Kirk. Finally, and especially, my thanks go to Jeff Deems, Ron Johnson, and Karl Birkeland for leading data collection teams, and to assistants Chuck Lindsay, Doug Chabot, Stuart Dominick, Lance Riek, Chas Day, Aleph Johnston-Bloom, Zach Matthews, Mark Schaffer, Jim Rasmussen, John Kelly, Johann Schleiss, Dan Miller, Michael Cooperstein, Jeanette Romig, Blase Reardon, and Reid Sanders for their undaunted enthusiasm for snow science, despite sometimes miserable conditions. It was my pleasure to work with you all. v TABLE OF CONTENTS Page 1. INTRODUCTION . 1 2. RESEARCH HYPOTHESES . 6 3. LITERATURE REVIEW . 8 Avalanche Forecasting Principles and Data Collection . 8 Snowpack Stability Testing and Indices . 10 Spatial Variation of Snowpack Properties . 13 Modeling Snowpack Stability . 15 Modeling Snowpack Accumulation . 17 4. STUDY AREA . 22 5. METHODS . 25 Selection of Study Plot Sites . 25 Avalanche Cycle Capture . 31 Quantified Loaded Column Stability Test . 33 Study Plot Stability Sampling Design . 35 Study Plot Stability Sampling Sessions . 37 Winter of 1999/2000 . 37 Winters of 2000/2001 and 2001/2002 . 38 Avalanche Starting Zones Atlas . 40 Avalanche Observations . 44 GIS “BASEDAT” Preparation . 45 Stability Modeling . 50 Storm Weather Data Collection . 59 vi TABLE OF CONTENTS – CONTINUED Page 5. METHODS continued ……….. Data Analysis . 60 Inter-Study-Plot Variability . 60 Coefficients of Variation . 60 Z Score of Strength . 61 Stability Ratio SQLCT . 61 Z Score of Stability SQLCT . 62 Two-Sample t-Tests . 62 Intra-Study-Plot Stability Variability . 64 Stability Model Evaluation . 65 6. RESULTS AND DISCUSSION . 66 Winter of 2000/2001 . 66 Weather and Snowpack . 66 Inter-Study-Plot Variability . 70 Bacon Rind Study Plot Trials – 1/3/01 . 70 Bradley Meadow Study Plot Trials – 1/27/01 . 77 Round Hill Trials – 2/4/01 . 85 Baldy Mountain Study Plot Trials – 2/18/01 . 91 Saddle Peak Study Plot Trials – 2/18/01 . 98 Bradley Meadow Study Plot Trials – 2/18/01. 107 Bradley Meadow Study Plot Trials – 3/17/01. 112 Intra-Study-Plot Variability . 119 Bridger Range Study Plot Trials – 2/18/01 . 119 Summary . 123 Winter of 2001/2002 . 125 Weather and Snowpack . 125 Inter-Study-Plot Variability . 127 Middle Basin Trials – 12/7/01 . 127 Lionhead Mountain Plot Trials – 1/9/02 . 139 Lionhead Mountain Plot Trials – 1/15/02 . 147 Lionhead Mountain Plot Trials – 1/26/02 . 156 Bridger Range Stability Model . 164 vii TABLE OF CONTENTS – CONTINUED Page 7. CONCLUSIONS . 168 Sampling Method . 168 Study Plot Stability and Hypothesis #1 . 171 Extrapolation of Study Plot Stability and Stability Modeling . 182 Implications for Conventional Avalanche Forecasting . 184 Scales of Spatial Variation in Stability and Suggestions for Future Research . 186 8. REFERENCES CITED . 189 9. APPENDICES . 195 Appendix A: Southern Bridger Range SWE Transect . 196 Appendix B: 2000/2001 Study Plot Trials QLCT Results . 198 Bacon Rind Study Plot 1/3/01 Trials . 199 Bradley Meadow Study Plot 1/27/01 Trials . 200 Round Hill 2/4/01 Trials . 201 Baldy Mountain Study Plot 2/18/01 Trials . 202 Saddle Peak Study Plot 2/18/01 Trials . 203 Bradley Meadow Study Plot 2/18/01 Trials . 204 Bradley Meadow Study Plot 3/17/01 Trials . 205 Appendix C: 2001/2002 Study Plot Trials QLCT Results . 206 Middle Basin Plot 12/7/01 Trials . 207 Lionhead Mountain Plot 1/09/02 Trials . 208 Lionhead Mountain Plot 1/15/02 Trials . 209 Lionhead Mountain Plot 1/26/02 Trials . 210 Appendix D: t-Tests of Strength 2000/2001 Trials . 211 Bacon Rind Study Plot 1/3/01 Trials . 212 Bradley Meadow Study Plot 1/27/01 Trials . 212 Round Hill 2/4/01 Trials . 213 Baldy Mountain Study Plot 2/18/01 Trials . 213 Saddle Peak Study Plot 2/18/01 Trials . 214 Bradley Meadow Study Plot 2/18/01 Trials . 214 Bradley Meadow Study Plot 3/17/01 Trials . 215 Plot-to-Plot 2/18/01 Trials . 215 viii TABLE OF CONTENTS – CONTINUED Page Appendix E: t-Tests of Strength 2001/2002 Trials . 216 Middle Basin Plot 12/7/01 Trials, Pooled Weak Layers A & B (no “NR” results) . 217 Middle Basin Plot 12/7/01 Trials, Pooled Weak Layers A & B (inc. est. “NR” results) . 217 Lionhead Mountain Plot 1/9/02 Trials . 218 Lionhead Mountain Plot 1/15/02 Trials . 218 Lionhead Mountain Plot 1/26/02 Trials . 219 Appendix F: t-Tests of Stability 2000/2001 Trials . 220 Bacon Rind Study Plot 1/3/01 Trials . 221 Bradley Meadow Study Plot 1/27/01 Trials . 221 Round Hill 2/4/01 Trials . 222 Baldy Mountain Study Plot 2/18/01 Trials . 222 Saddle Peak Study Plot 2/18/01 Trials . 223 Bradley Meadow Study Plot 2/18/01 Trials . 223 Bradley Meadow Study Plot 3/17/01 Trials . 224 Plot-to-Plot 2/18/01 Trials . 224 Appendix G: t-Tests of Stability 2001/2002 Trials . 225 Middle Basin Plot 12/7/01Trials, Pooled Weak Layers A & B (no “NR” results) . 226 Middle Basin Plot 12/7/01 Trials, Pooled Weak Layers A & B (inc. est. “NR” results) . 226 Lionhead Mountain Plot 1/9/02 Trials . 227 Lionhead Mountain Plot 1/15/02 Trials . 227 Lionhead Mountain Plot 1/26/02 Trials . 228 ix TABLE OF CONTENTS – CONTINUED Page Appendix H: 2000/2001 Snow Profiles . 229 Profile #1 . 230 Profile #2 . 231 Profile #4 . 232 Profile #7 . 233 Profile #9 . 234 Profile #12 . 235 Profile #14 . 236 Profile #15 . 237 Profile #16 . 238 Profile #17 . 239 Profile #18 . 240 Profile #19 . 241 Appendix I: 2001/2002 Snow Profiles . 242 Profile #2 . 243 Profile #7 . 244 Profile #9 . 245 Profile #10 . 246 Profile #11 . 247 Profile #12 . 248 x LIST OF TABLES Table Page 1. Avalanche Forecasting “Contributory Factor” Data Classification . 9 2. Bridger Bowl Ski Area Climate Data . 24 3. Study Plot Stability-Sampling Trials Summary . 39 4. Canadian Snow Avalanche Size Classification System . 41 5. GIS “BASEDAT” Theme Variables . 50 6. Stability Model Data and Variables . 51 7. Bacon Rind Study Plot (BRSP) 1/3/01 Trials: QLCT Results . 71 8. Bacon Rind Study Plot (BRSP) 1/3/01 Trials: Shear Stress . 74 9. Bacon Rind Study Plot (BRSP) 1/3/01 Trials: Stability . 74 10. Bacon Rind Study Plot (BRSP) 1/3/01 Trials: t-Tests of Strength . 75 11. Bacon Rind Study Plot (BRSP) 1/3/01 Trials: t-Tests of Stability . 76 12. Bradley Meadow Study Plot (BMSP) 1/27/01 Trials: QLCT Results . 78 xi LIST OF TABLES - CONTINUED Table Page 13. Bradley Meadow Study Plot (BMSP) 1/27/01 Trials: Shear Stress . 80 14. Bradley Meadow Study Plot (BMSP) 1/27/01 Trials: Stability . 81 15. Bradley Meadow Study Plot (BMSP) 1/27/01 Trials: t-Tests of Strength .