AVALANCHE RELEASE AND SNOW CHARACTERISTICS .fA. ~~~,i~::ft~~.-.. ~ . t~:;,~···~·~·· .:: . UNITED STATES PROGRAM Richard L. Armstrong ON MAN AND THE and Jack D. Ives, Editors BIOSPHERE Unesco MAB Project 6 Occasional Paper No. 19, 1976 Report to the Bureau of Reclamation INSTITUTE OF ARCTIC AND ALPINE RESEARCH• UNIVERSITY OF COLORADO MS•280 (2·72) Bureau or Reclamation 1. REPORT NO. INSTAAR-14-06-D-71 4. TITLE AND SUBTITLE 5. REPORT DATE Avalanche Release and Snow Characteristics, May 1976 San Juan Mountains, Colorado 6. PERFORMING ORGANIZATION CODE 7 . AUTHOR($) 8. PERFORMING ORGANIZATION REPORT NO. Richard L. Armstrong and Jack D. Ives (Eds.) NSTAAR-14-06-D-7155-4 9 . PERFORMING ORGANIZATION NAME AND ADDRESS 10. WORK UNIT NO . Institute of Arctic and Alpine Research University of Colorado 11. CONTRACT OR GRANT NO. Boulder, Colorado 80309 14-06-D-7155 13. TYPE OF REPORT AND PER I OD COVERED 12. SPONSORING AGENCY NAME AND ADDRESS Final Report Division of Atmospheric Water Resources Mgt. April 1971-Sept. 1975 Bureau of Reclamation 14. SPONSORING AGENCY CODE Denver Federal Center, Denver, Colorado 80225 15. SUPPLEMENTARY NOTES 16. ABSTRACT A methodology for the accurate prediction of snow avalanche occurrence has been developed through investigation of quantitative relationships among terrain, climate, snowcover properties and avalanche formation. An instrumentation network was established to measure air and snowpack temperatures, wind speed and direction, precipitation rate and amount, snow settlement rate, net all-wave radiation, and stratigraphic snow density values. Avalanche events were monitored by direct observation of, 214 avalanche paths. Detailed investigations into the physical properties of the snow within the study area were carried out by stratigraphic studies at standard, level snow study sites, test slopes representative of avalanche release zones and actual avalanche fracture lines. Such studies allowed definition of a local snow climate. An "in-house" stability evaluation and avalanche forecast were prepared at daily intervals during three winters. Each forecast was evaluated the following day in terms of actual events subsequent to the initial forecast. A statistical forecast model based on discriminant function analysis of four years of data was developed. 17. KEY WORDS AND DOCUMENT ANAL YSIS a . DESCR /PTORS-- avalanche, Colorado, snow, weather modification b . IDENTIFIERS-- c . COSATI Field/Group 18. DISTRIBUTION STATEMENT 19 . SECURITY CLASS 21. NO. OF PAGE (THIS REPORT) Available from the National Technical Informat i on Operations Service. UNCLASSIFIED 256 Division , Springfield , Virginia 2215/ . 20. SECURITY CLASS 22 . PRICE (T HIS PAGE) No limitations UNCLASSIFIED AVALANCHE RELEASE AND SNOW CHARACTERISTICS, SAN JUAN MOUNTAINS, COLORADO Final Report 1971 - 1975 May 1976 Richard L. Armstrong and Jack D. Ives (Eds.) San Juan Avalanche Project Institute of Arctic and Alpine Research University of Colorado Boulder, Colorado 80309 Prepared for: Division of Atmospheric Water Resources Management U.S. Bureau of Reclamation Department of the Interior Denver, Colorado 80225 Contract No. 14-06-D-7155 A contribution to the United States Unesco Man and the Biosphere (MAB) Program Project 6: Study of the impact of human activities on mountain and tundra ecosystems University of Colorado Institute of Arctic and Alpine Research Occasional Paper 19 ISSN 0069-6145 ii © Copyright 1976, The Regents of the University of Colora do All rights reserved. Looking across Red Mountain Pass onto the Red Mountain Group. INSTAAR's 12,325 weather station is situated along the skyline to the right. V PREFACE This INSTAAR Occasional Paper represents the final report to the Division of Atmospheric Water Resources Management of the Bureau of Reclamation, United States Department of the Interior. An original three-year contract was signed in May 1971 that was subsequently extended to permit data collection during a fourth winter season (1974-75) and to facilitate data analysis and write-up during the current winter (1975-76). The report has also been designated as a contribution to the United States Unesco Man and the Biosphere (MAB) Program, especially since its objectives fall so naturally within the scope of US MAB Directorate 6A: study of the impact of human activities on mountain ecosystems. During the course of the previous five years, the Silverton avalanche research project, as originally conceived, has evolved extensively and has undergone many changes. Personnel have changed, methods of study have been refined, and some of the original areas of investigation, especially those concerning seismic and infrasonic signals from avalanches, carried out under the direction of J. C. Harrison, were completed earlier. Nevertheless, this report has been prepared so as to ensure that the user has as complete an understanding as possible of the overall avalanche project. This has necessitated some duplication of data presentation and discussion. However, the report is intended to supersede all earlier interim publications and to stand as the final statement on work ema­ nating directly from Bureau of Reclamation Contract No. 14-06-D-7155. A few words about project organization and personnel should be of assistance to the reader. The initial contract, awarded to INSTAAR, designated Jack D. Ives, J. Christopher Harrison and Donald L. Alford as principal investigators, with Edward R. Lachapelle, Malcolm Mellor (snow mechanics) and Wilford Weeks (statistical analysis) as principal consultants. Christopher Harrison was responsible for the seismic and infrasonic studies. Donald Alford played a vital role in the setting up of the operational framework and by serving as Silverton Field Director during the first winter (1971-72). Subsequently, Richard Armstrong succeeded to the position of Field Director and became a principal investigator, and indeed carried the main burden of the project through to its completion such that he rightly deserves the first author position indicated here. The three consultants proved invaluable throughout and INSTAAR has been highly privileged to have such support. Edward Lachapelle, in particular, has de facto played the role of a principal investigator and, as a Research Associate of INSTAAR, has been a pivotal member of the research team throughout, making readily available his wealth of personal experience in snow and avalanche research. Second only to the contributions of the principals have been those of the field team. These included Betsy Armstrong, Don Bachman, Juris Krisjansons, Gail Davidson, Bill Isherwood, Fred Johnson, Phillip Laird, Bill McClelland, Len Miller, Rod Newcomb and Imants Virsnieks. All played a vital role, often under exacting physical and mental conditions. It need not be stressed that four full winter seasons between 3,000 and 4,000 meters elevation in avalanche terrain is not entirely devoid of personal risk. That no accident was incurred is a tribute to each individual and to the team as a unit. Administrative and clerical back-up has also been extensive. Claudia Van Wie acted as scientific assistant for the first three years and helped extensively vi with editing, preparation of interim reports and statistical analysis in particular, and in all other phases of the project. Her enthusiasm and cri­ tical faculty are especially acknowledged. Laura Osborn provided budgetary assistance and Marilyn Joel undertook all the drafting. Ann Stites, as admin­ istrative assistant to the INSTAAR Director, helped extensively, including organization of this report. John Clark, INSTAAR climatologist, assisted with the meteorological instrument site selection, calibration and maintenance, and, our remarkably good climatological data collection is largely due to his per­ sistence and dedication. Michael J. Bovis entered the project in a special capacity and at a relatively late stage, and made a major contribution by breaking through the mass of data and developing the statistical approach to avalanche forecasting. This is reflected in Chapter 5 of this report and Michael's separate publications which constitute a significant advance in the field of avalanche forecasting. In this he was assisted by Nel Caine of the INSTAAR faculty and consultant Wilford Weeks. Our contacts with and assistance from persons outside of INSTAAR have been ex­ tensive. These are acknowledged separately innnediately following this preface, although the special supportive role of Olin Foehner, contract monitor, Bureau of Reclamation, must be emphasized above all. The backbone of the project, however, was Richard and Betsy Armstrong and daughter Johanna, who entered this world as an avalanche baby. For some years Betsy and Richard had their second name substituted by "Avalanche" and people in Silverton came to regard them as decidedly odd since they were not like the other visitors to Silverton who came in the sunnner and departed with the first snows of autumn; they came with the bad weather and stayed through summer also. Projects of this nature invariably induce scientific excursions in parallel and divergent directions. The intimately related projects include studies of snow temperature-gradient metamorphism, supported by US Army Research Office (Durham), Grant No. DARCO 4-75-G-0028, assessment of alternate methods for artificial avalanche release, supported by grants from the Highway Departments of the states of Colorado and Washington, and the Federal Department of Trans­ portation (University of Washington Subcontract