SURFACE HOAR OBSERVATIONS AT THE SCALE OF A HELICOPTER SKIING OPERATION by Matthew John Borish 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 2014 © COPYRIGHT By Matthew John Borish 2014 All Rights Reserved ii ACKNOWLDEGEMENTS This study certainly would not have been possible without the support I received from my primary advisor, Karl W. Birkeland. His tutelage and patience were unwavering. Additional assistance from the rest of my graduate committee, Steve Custer, Jordy Hendrikx, and Stuart Challendar was also greatly valued. Melanie Baldwin and Gail Weidenaar of the Earth Sciences Department certainly deserve an honorable mention. Their clerical assistance and institutional expertise were imperative. I would also like to thank the American Avalanche Association, Mazamas, Montana State University Milton J. Edie Memorial Scholarship, and Montana Association of Geographic Information Professionals for their generous funding contributions, as well as Montana State University and the Department of Earth Sciences for financial support via a graduate teaching assistantantship. The USDA Forest Service National Avalanche Center graciously loaned weather station equipment during the duration of this study which was greatly appreciated. Alaska Heliskiing also provided transportation and several hardy guides during the weather station instrument installation process at the beginning of the 2011 season. Finally, I would like to thank the owners of SEABA, Nick Trimble, Scott Sundberg, Shawn Macnamara, and Ben Anderson for the opportunity of a lifetime, financial support, and usage of helicopters, snow machines, and tools. The steadfast dedication of the guide team which included Bill Buchbauer, Christian Cabanilla, Kent McBride, Tom Wayes, David Sundnas, Reggie Crist, and William Spilo also made this research a reality. iii TABLE OF CONTENTS 1. INTRODUCTION ............................................................................................................... 1 Objectives ........................................................................................................................ 4 Thesis Organization ......................................................................................................... 4 2. LITERATURE REVIEW ....................................................................................................... 6 Snowpack Properties and Slab Avalanche Formation .................................................... 6 Surface Hoar Formation .................................................................................................. 7 Near-Surface Facets ........................................................................................................ 9 Surface Hoar and Snow Surface Spatial Variability ....................................................... 10 Surface Hoar Modeling .................................................................................................. 15 3. METHODS ...................................................................................................................... 18 Study Area ..................................................................................................................... 18 Weather Stations ........................................................................................................... 24 Data Collection .............................................................................................................. 26 Data Management......................................................................................................... 31 Data Analysis ................................................................................................................. 32 The Spatial Distribution of Surface Hoar Presence or Absence ............................ 32 The Effect of Elevation on Surface Hoar Crystal Size ............................................ 36 4. RESULTS ......................................................................................................................... 41 Event 1 ........................................................................................................................... 45 Event 1 Background and Weather ........................................................................ 45 Event 1 Spatial Distribution of Surface Hoar Presence ......................................... 48 Event 1 Effect of Elevation on Surface Hoar Crystal Size ...................................... 51 Event 2 ........................................................................................................................... 55 Event 2 Background and Weather ........................................................................ 55 Event 2 Spatial Distribution of Surface Hoar Presence ......................................... 58 Event 2 Effect of Elevation on Surface Hoar Crystal Size ...................................... 60 Event 3 ........................................................................................................................... 63 Event 3 Background and Weather ........................................................................ 63 Event 3 Spatial Distribution of Surface Hoar Presence ......................................... 67 Event 3 Effect of Elevation on Surface Hoar Crystal Size ...................................... 69 Event 4 ........................................................................................................................... 72 Event 4 Background and Weather… ..................................................................... 72 iv TABLE OF CONTENTS – CONTINUED Event 4 Spatial Distribution of Surface Hoar Presence ......................................... 76 Event 4 Effect of Elevation on Surface Hoar Crystal Size ...................................... 79 Results Summary ........................................................................................................... 82 5. DISCUSSION ................................................................................................................... 87 Event 1 ........................................................................................................................... 88 Event 1 Background and Weather ........................................................................ 88 Event 1 Spatial Distribution of Surface Hoar Presence ......................................... 89 Event 1 Effect of Elevation on Surface Hoar Crystal Size ...................................... 90 Event 2 ........................................................................................................................... 91 Event 2 Background and Weather ........................................................................ 91 Event 2 Spatial Distribution of Surface Hoar Presence ......................................... 92 Event 2 Effect of Elevation on Surface Hoar Crystal Size ...................................... 93 Event 3 ........................................................................................................................... 94 Event 3 Background and Weather ........................................................................ 94 Event 3 Spatial Distribution of Surface Hoar Presence ......................................... 94 Event 3 Effect of Elevation on Surface Hoar Crystal Size ...................................... 96 Event 4 ........................................................................................................................... 97 Event 4 Background and Weather ....................................................................... 97 Event 4 Spatial Distribution of Surface Hoar Presence ........................................ 99 Event 4 Effect of Elevation on Surface Hoar Crystal Size ..................................... 99 General Discussion ....................................................................................................... 100 Spatial Distribution of Surface Hoar Presence ................................................... 100 Surface Hoar Kriging Interpolation ..................................................................... 104 The Effect of Elevation on Surface Hoar Crystal Size .......................................... 106 Uncertainty .................................................................................................................. 110 6. CONCLUSIONS ............................................................................................................. 112 Research Findings ........................................................................................................ 112 Future Work ................................................................................................................ 114 REFERENCES CITED .......................................................................................................... 116 APPENDIX ........................................................................................................................ 125 APPEDNIX A: Field Data .............................................................................................. 125 v LIST OF TABLES Table Page 1. Table 2.1 Snow Process Scales ........................................................................... 6 2. Table 2.2 Factors Affecting Surface Hoar Spatial Variability ........................... 12 3. Table 3.1 Haines, Alaska