Avalanche Hazard Evaluation and Prediction at Rogers Pass Schaerer, P

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Avalanche hazard evaluation and prediction at Rogers Pass Schaerer, P.

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CANADA DIVISION OF BUILDING RESEARCH

THE AVALANCHE HAZARD EVALUATION AND PREDICTION AT ROGERS FASS

P. Schaerer This is a joint report of. the Department of Public Works and the National Research Council

Internal Report No. 227 of the Division of Building Research

Ottawa December 1961 The Trans-Canada Highway through Glacier National Park, British Columbia, was designed and constructed by the Federal Department of Public Works, Because the highway would have to cross numerous avalanche paths, the Department began, as early as 1953, preliminary observations on the snow cover, weather and avalanche conditions that would be encountered and in the winter of 1955-1956, established a regular observation program to provide the information required for the specification of the avalanche defences. In 1956, the National Research Council, in response to a request from the Department of Public Works, supplied some of the special instruments required for the observations. About that time, the Division of Building Research of the Council re- cruited to its staff a civil engineer trained in Switzerland. in road construction. The services of this engineer, Mr. Schaerer, were offered to the Department of Public Works. In 1357 he was seconded to that department and given the task of recommending to them the avalanche defence for the highway. Through Mr. Schaerer and valuable contacts with Dr. M. R. de Quervain, Director of the Swiss Federal Institute for Snow and Avalanche Research, the valuable experience of the Swiss was applied to the problem at Glacier. !Phe development of the avalanche defence for the Trans-Canada Highway through the park area, and the associated snow cover, weather and avalanche observations required for the specification of that defence, was the first project of its kind to be undertaken in Canada. It is probable that this project will serve as a model if similar projects should be undertaken in the future. A11 too often, the experience obtained in such work is not recorded in a form that will make it readily available. The National Research Council welcomed the chance to assist in the program at Glacier and to have the opportunity to prepare such a record. One very important part of avalanche defence is the evaluation and prediction of the avalanche hazard. Although it was the responsibility of the Parks Branch of the Department of Northern Affairs and National Resources, to organize and operate this service after the Highvlray was completed, it was necessary to predict the character of this service in designing the over-all defence system. Furthermore, such a service had to be available during the period when the observations required for specifying the defence system were made, and while the defences and Highway were constructed. The experience obtained in avalanche hazard evaluation and prediction during that period, and the role that it plays in the over-all defence system, is recorded in this report. 'This report is one of a series reporting the work at Glacier. It represents singularly close co-operation between the Department of Public Works and the Division of Building Research, co-operation which it is a pleasure to acknowledge in this way.

Ottawa Robert P. Legget December 1961 Director. TABLE OF CONTENTS

TERRAIN

1. Climate Zone. 2. Snowfall. 3. Temperature. 4. Wind. AVALANCHES AT ROGERS PASS Periods of Avalanche Activity

SOME FUNDUIENTAL CONSIDERATIONS TO THE AVALANCHE HAZARD EVALUATION AND PREDICTION The Testing Method The Analytic Method ORGANIZATIOII OF THE OBSERVATIONS Snow and Weather Observations Observations at Rogers Pass Summit and at Glacier State of the Weather Observations at Flat Creek and Stoney Credk Observations on Mount Abbott Special Observations Records Survey of the Avalanches Personnel CAUSES OF THE AVALANCHES Rupture Zones Climate Areas The Snow Cover The Snowfall Wind Temperature Spring Thaw Avalanches Special Avalanches AVALANCHE \ITARNING The Avalanche Hazard Forecast Highway Closures ANTICIPATED ORGANIZATION AND RESPONSIBILITIES OF THE AVALANCHE WARNING SERVICE Responsibilities of the Avalanche Warning Service Personnel Snow Cover and Weather Observations Effec-t of Avalanche Warning on Highway Traffic Avalanche Warning for Skiers Table of Contents (Contld)

ACKNOWLEDGMENTS REFERENCES APPENDIX I: Selection of the Mountain Observatory APPENDIX 11: Equipment and Methods of Observations APPENDIX 111: The Weather Forecast

APPENDIX IV: Mount Green Avalanche

APPENDIX V: Crossover Avalanche THE AVAUNCHZ HAZARD EVALUATION AND PREDICT1 ON

AT ROGERS PASS

2. Schaerer

In the early 1950fs, consideration was given to the use of Rogers Pass as a possible route through the Selkirk Range for the Trans-Canada Higl~tvay. The pass, the lowest and shortest route through the Selkirlcs, is located between the towns of Golden and Revelstolce in British Columbia. The summit of the Bss is near the town of Glacier in Glacier National Park (pigs, 1 and 2).

The discovery of the Pass by Major A. B. Rogers during his survey for the Canadian Pacific Railway enabled that company to complete the first railway link between Eas-tern Canada and the West Coast in 1885. The line through the 'Pass was used. until 1916 when it was abandoned on the completion of the Connaught Tunnel. The valleys associated with the Pass are narrow and have steep sides. Because of heavy snowfall in the area winter and spring avalanches are a common occurrence, In 1953, the Department of Pu3lic Ihiorlcs, responsible for the construction of tbe highway in Glacier National Park, began a study of the location of each avalanche site and the conditions under which the avalanches occur, Mr. N. C. Gardner was in charge of these observations, In 1956, when the decision was made to construct the higllv~aythroug-11 the Pass, the Department of Public 1,filorks established an avalanche observation station at Glacier. The observation program was enlarged to obtain the information required for the specification and design of the defence system. An avalanche hazard forecast routine was established for the protection of the avalanche observers, surveyors and construction crew, The National Research Council, through its Divisioil of Building Research, co-operated in the organization of the avalanche observation station. Initially, the National Research Council contributed information and apparatus for taking the necessary weather and snow cover observations; when the author joined the Snow and Ice Section of the Division of Building Research, the follv~vingresponsibilities were assumed: 1. To make recommendations on the type, location and design of the defence for each avalanche site, To assist in the organization and taking of the observations required for the recommendations, In April of 1957, the author was seconded to the Department of Public !Vorks and joined the avalanche observation station at Glacier on a full-time basis. During the winters 1957-1958 and 1958-1959 he was responsible for the snow cover, weather and avalanche observations that were made. Based on these observations and others taken prior to 1957, a defence plan was drawn up and reconmendations made for the defence at each avalanche site. This information is published in a separate report (1). The recommended defence plan included highway closure and control of avalanches with explosives. The evaluation and prediction of the avalanche hazard is therefore a necessary and integral part of the avalanche defence. The National Research Council had no responsibility for the organization of the avalanche hazard prediction and warning service required for the highway but it was necessary to anticipate the nature of this future service when establishing the defence for each avalanche site. It was considered that a record of the nature of the future warning service that had been in mind when the recommendations were prepared for the avalanche defence works, and a record of the experience gained in avalanche hazard evaluation and forecasting for the Rogers Pass area would be valuable to the people responsible for the avalanche warning service for the completed highway. This report contains this record. In it are presented: (a) a description of the weather and snow cover observations -taken,

(b ) a summary of experience gained in making the avalanche hazard evaluation and forecast during the period when the NRC was directly associated with the field observations, (c) an outline of the organization and duties of the future avalanche warning service which had been in mind when planning the complete defence system. Responsibilities for snow and weather observations and for avalanche hazard evaluation and forecast were trans- f erred from the Department of Public Works and the National Research Council to the National Parks Branch of the Department of Northern Affairs and National Resources on 2 October 1959.

TERRAIN The valleys (Table I) ad joining Rogers Pass run in a general east-west direction. The mountains, mainly of quartzite rock, with steep sides and bands of bold cliffs, rise between 8,000 and 10,000 ft above sea level. Water has carved numerous gullies into the mountain sides and has deposited decomposed rock in alluvial fans in the valley below. Timber covers most of the mountain sides below 6500 ft except for the gullies and many areas where frequent avalanches hinder the growth of trees (Figs. 3, 4, 5).

TABLE I

VALLEYS AND ELEVATIONS AT ROGERS PASS-

Elevation Valley Location above Distance, Sea level, miles ft

Columbia River Golden to Beaver 2600 and Beaver River junction 2800 40 River Bear Creek Beaver River 2800 junction to Rogers 4 350 7 Pass Summit

Illecillewaet Revelstoke to 1500 River Albert Canyon to 2200 20 Glacier -to 3800 18 Rogers Pass Sumrnit 4350 1.6

The average width of the valleys is 800 ft at the bottom. At some places the mountain sides approach one another to form a narrow V-shaped valley with the river flowing between the steep talus slopes and sharply rising roclcfaces. One of these narrow defiles lies between Mount Tupper and Mount MacDonald on the east side of Rogers Pass (Fig. 3) and another important one is formed by the sides of Fidelity and Fortitude Mountains at the west boundary of Glacier National Park. Apart from two short sections, each 2 miles long, the highway was constructed on the north side of the valleys.

1. Climate Zone. - A. Roch (2) has divided the mountain area of the western United States into three different climatic zones. The Selkirk Mountains are in the northern extension of the middle zone. This zone is characterized by heavy snowfalls with moist to dry snow, medium temperatures which are only occasionally below O°F and strong winds on the mountains. 2. Snowfall. - Rogers Pass is in one of the highest snov~fallareas in Canada. The average total snowfall for the winter, measured at Glacier over a 30-year period between 1321 and 1950, is 342 in. The maximum total snowfall observed was 680 in. measured in the winter of 1953-54. At the 4000-ft level of the valley snowfall usually begins at the end of October and ceases at the end of April. Summer snowfalls may occur on the mountains at 7000 ft, but this soon melts. At this altitude, for an average year, snow covers the ground from the end of September until the end of June. There are no yearly recurring periods of maximum snowfall intensity. Snowfalls have been recorded daily for one month and periods of two weeks duration have passed without snowfall. Storms with heavy snowfalls are infrequent. During winters of light snovifall two storms may occur yielding 12 in. of snow in a 24-hr period. Winters of heavy snowfall produce 8 to 10 such storms. A snowfall of more than 20 in. in 24 hr is a rare occurrence. The magnitude and the frequency of the 24-hr snowfalls at Glacier during the winters between 1953 and 1960 are shown in Table 11.

TABLE I1

FREQUENCY OF SNO\VPALLS AT GILACIER

Number of Days with Snowfalls Total Snowfall Winter Less than 4 to 12 12 to 20 More than of the Winter 4 in. in. in. 20 in. in.

1953/54 56 44 7 2 680 1954/55 35" 17* - - 310 1955/56 42 30 - - 336 1956/57 47 17 3 1 341 1957/58 74 26 1 - 321 1958/59 85 41 3 - 442 1359/60 84 29 1 - 368 o Records of the winter 1954-55 include only snowfalls after 1 January 1955. Storms with a high snowfall rate are usually of short duration. A day with heavy snov~fallis normally followed by a period of light snowfall. Records from 1930 to 1960 show that the maximum total snowfall at Glacier for a 5-day period was just under 70 in. It is possible that once in 20 years a winter with very heavy sno~~fallcould occur when the above-mentioned snowfall amounts are exceeded. On 21 January 1935, 35 in. of snow were recorded in a 24-hr period, but this extreme rate has not been observed since. 3. Temperature. - The mean monthly winter temperatures at Glacier for the 30-yr period 1921 to 1950 are given in Table 111.

TABLE I11

MEAN TEPIIPERATURES OF THE WINTER MONTHS

Nov. Dec. Jan. Peb. March April

MeanTemperature, 25,2 17.5 13.6 18.6 26.8 35.8 OP

The temperature is below OOP only a few times during the winter and this cold weather usually does not continue for more than a week. The lowest temperature ever measured at Glacier was -33OP. The temperature during a snowstorm normally ranges between 20 and 32OF. After a stom has ended it is usual for the cloudy weather to continue and the temperature to change relatively slowly, The temperature frequently rises during a snowstorm and the snowfall in the valleys changes to rain. 4. Wind. - Most snorrfalls are accompanied by southerly and westez:minds of variable speed. Large amounts of snow can drift over the mountain ridges and be deposited on the lee side. Heavy snov~fallsmay occur with no significant wind,

AVALANCHES AT ROGERS PASS First studies revealed that the avalanche hazard to the highviay through Rogers Pass would be high and would equal the worst conditions encountered on highways and railroads kept open during the winter in the mountainous areas of Switzerland, Austria and Western United States, The highway would have to cross the following number of avalanche paths: 9 sites where avalanches of dangerous size occur more than once each winter. 21 sites where avalanches of minor size occur once or more than once each winter. Large avalanches occur occasionallg, but not every winter. 13 sites where avalanches occur only under severe conditions and not every winter. The avalanches would be large in most cases. 31 sites where avalanches occur only occasionally under severe conditions. The snow that would reach the highway would usually be airborne and little would be deposited on the highway.

TOTAL 74 avalanche sites, In this report, the location of the avalanche site is given by the highway mileage from the east boundary of Glacier National Park. Most of the sites have a name and have been fully described (1)- The avalanche hazard is very high at the two defiles where the valley has a narrow V-shape and the highway is located at the bottom of the long, s%eep mountain side. These two most active avalanche areas are located: (a) Below Mount Tupper between Mile 10 and Mile 13 (Figs. 3 and 4). (b) On the south side of Fidelity Mountain immediately west .of Glacier National Park. Avalanches may reach the highway at both sections during and after every significant snowfall, particularly after snowfalls of more than 10 in. accompanied by wind, Between and outside the two areas, the avalanche sites are more scattered and the valley floor is wider (Figs. 2 and 5). Avalanches reach the highway only under bad conditions. Dangerous ones usually occur after snowfalls of more than 24 in. and during the snow melting period. Periods of Avalanche Activity There are two avalanche periods each year, In the first period, between early November and late February, avalanches are caused mainly by snoivfalls , wind action, and rain in association with snoi8ifalls. In the second period, between late Idarch and mid-May, avalanches are caused mainly by warm weather and melting of the snow, Records of the avalanches affecting the railway line between the years 1910 and 1952 were studied in the office of the Division Engineer of the Canadian Pacific Railway at Revelstoke, The study revealed a cycle of some years of heavy activity followed by years of few avalanches, Avalanches affecting the railway line between Stoney Creek and the east portal of Connaught hel, and between the west portal of the tunnel and Illecillewaet siding during the period 1910-1960 are plotted in Fig, 6, The graph shows periods of high avalanche activity with maxima 1920, 1935 and 1952, The observations required for the defence planning of the highway appear to have been made during a period of low avalanche activity,

SOME FUNDAMENTAL CONSIDERATIONS TO THE AVALANCHE HAZARD EVALUATION AND PREDICTION The technique of observing different snow and weather factors and evaluating from them the likelihood of avalanche occurrences is called "avalanche hazard forecastingw by the U,S, Forest Service, An avalanche is caused by different factors which are interrelated closely. Certain rules have been established through experience concerning the dependence of the avalanche hazard on these factors, but the forecasting of avalanches is still an arl-, rather than a science. It requires a certain skill which includes a thorough understanding of the behaviour of snow on the ground, the terrain, the weather in the mountains, and their inter- relationship. -) The hazard can be evaluated quite accurately for the time of observation, but the prediction of the future hazard is only as good as the weather forecast, In practice, the avalanche hazard forecaster has to assume that the weather will follow a certain pattern and his prediction is based on this. The author, familiar with the Swiss method of avalanche hazard forecasting, was pleased to have the opportunity to co-operate with people who received their training in avalanche hazard forecasting from the United States Forest service, During frequent disc~ssionsit became evident that the evaluation of the avalanche hazard can be approached by two different methods, the testing method and the analytic method.

The Testing Method The testing method is the basis of technique used by the Swiss Snow and Avalanche Research Institute, and is widely used for avalanche warning in other countries (3). The avalanche hazard forecast is based on snow cover observations. These observations, usually called the snow profile, show if there are unstable layers which raigJbt collapse and cause avalanches. The stability of the snow cover can be tested at any time when the conditions warrant it. Weather factors such as snowfall, wind and tenperature are used to determine its stability between observations. Experience and tests have sho-m which factors may lead to a fracture and which conditions contribute to stabilization. The sim2lest application of the testing method is the direct testing of the stability of a slope. This testing method has the following advantages: (a) The actual material, the snow on the ground, is studied. This material can be observed by anyone and its conditions are clearly visible.

(b) It is universal and can be applied to any avalanche area. llountain climbers and slciers who usually have a feeling for snow need only little training to recognize whether the snow on a given slope is likely to slide. The disadvantages of the testing method are: (a) Inaccurate deterinination of the avalanche hazard if the stability of the slopes is not tested continuously. (b) A basic understanding of snow behaviour under different weather conditions and terrain is required.

The Analytic Method The analytic method has been developed mainly by the U.S. Porest Service (4, 5). It was found that most avalanches are caused by snowfalls and occur either during or immediately after storms. A method was developed, therefore, by which the occurrence of these direct action avalanches could be forecasted accurately. A number of different contributing factors have to be observed and the avalanche hazard is evaluated from the magnitude of each factor. The stability of the original snon cover is only one of these, The influence of each factor is found by analyzing Lhc avalanche conditions over a few winters. The ?orecasting [email protected] tliis repo?.d fo,- spring thaw avalanches, and also for Mount Green and Crossovar avalanches are examples of the analytic method (Appendices IV, V). This method is similar to that used in forecasting the forest fire hazard.

The analytic method has the following advantages : (a) Good results are obtained for the forecast of direct action avalanches. The chances of whether or not a direct action avalanche will occur can be predicted more accurately than by the testing method, (b) After many years of experience rules can be found to evaluate the hazard for a given avalanche area, These rules can often be applied by an observer with a little training. Rules for the time when avalanches should be controlled by explosives can also be established and be applied by the people in charge of this defence . (c) The method is suitable for predicting the avalanche hazard when an accurate weather forecast is available. The method has the following disadvantages:

(a ) Many weather observations are required, Numerous instruments and frequent observations may make avalanche hazard forecasting appear to be a special science. Amateurs, such as skiers, may be dis- couraged from obtaining the knowledge on avalanche occurrences necessary for their orm safety,

(b) The method cannot predict some delayed action avalanches caused by changes in the snow cover, unless the observers consider very carefully the stability of the snow cover. (c) There is a danger that avalanche forecasting will become a mechanical process and human good sense will be lost. The factors that cause avalanches are related in such a complex way that it is impossible to accurately express this relationship analytically, as there are always odd conditions to which the rules cannot be applied. (d) The value of factors causing the avalanches in one area may not be the same in another area. Experience gained through observations over a few winters is usually required before this method can be applied to any site. I,!Iost avalanche warning services use both methods. The avalanche hazard is basically evaluated with the testing method, and supplemented by the analytic method to improve the accuracy. During the survey, the avalanche hazard on Rogers Pass was evaluated and predicted mainly by the testing method, vri-bh good results. Rules could be established at some sites which allowed a more accurate evaluation of the avalanche hazard. The experience obtained in evaluating the avalanche hazard and the rules established are recorded in this report. It is hoped that this record will assist the Rogers Pass Avalanche Hazard Evaluation and Forecasting Group in developing a working combination of the testing and analytic methods.

ORGANIZLlTIOIT OP THE OBSERVATIONS Snow 2nd Weather Observations The headquarters for the avalanche observation station was at Glacier in the camp of the Department of 32u'olic Worlrs. This st;ation made the required observations on the snow cover and weather, surveyed the avalanches that occurred, and prepared the avalanche hazard forecast. The first problem vras to select the sites for snow and weather observations. The ideal observatory should be located near the rupture zone of the avalanches v~herzthe observations are representative of the avalanche area. Staff accommodation should be near the observation area so that observations can be carried ou-b continuously and special measurements made at any required time, This ideal site would be on the mountains between GOO0 and 7000 ft above sea level and 3000 ft higher than -the valley, with a building for the staff and access by road or aerial tramay, Because time and funds were not available for tlie construction of such a major project, and the su-rvey of the avalanches along the future highway was the inore import-ant task, it was decided to establish the avalanche observation station in the valley. Sites aere chosen for daily observations and two additional sites were choser at the altitude of the avalanche rupture zone at which regular weekly observations or daily could be made, when conditions vrananted it. The principle of keeping the number of ~Sservationswithin the capacity of the observation group i*Jas applied at all -Limes, Experience shoiired that daily observsL'io;zs should be kept to a rriinimum but that they should be reliable and complete. A description of each observation site follows. -Rogers Fass Summit. - The summit of Rogers Pass was chosen as the central observatory where all basic observations were made. It was located at an altitude of 4300 ft in the middle of the 1200-ft wide valley runs from south to north (Fig. 2). Prom this location the weather conditions on both sides of the pass could be observed. It was assumed that the future headquarters of the highway maintelzance staff and the avalanche warning service would be located at the summit of the pass, and it would be an advantage to have the observatory close at hand. A test plot 100 by 150 ft with a small shelter and instrunent stand was established- in October 1957 and observations began in the winter of 1957-1958 (Fig. 7). Daily observations were made between 8 and 10 a.m. by patrols from Glacier. Rogers Pass Summit is moderately exposed to wind; observations on the depth of new snow had to be made in a sheltered area behind the cabin. A protective fence was erected around the area where the snow cover was studied, but it was still disturbed by animals, particularly bears. Glacier. - The survey camp at Glacier on the west side of Rogers Pass, 3800 ft above sea level, was the headquarters of the staff making the avalanche observations (Fig. 8). It was logic61 that continuous weather and snow observations should be made near the camp, particularly when temperature and ~reci~itationobservations have been made at Glabier for the past 40 years. Twice daily observations taken at Glacier indicated the weather conditions on the west side of Rogers- Fass. Plat Creek. - Plat Creek is a park warden station on the west -side of Rogers Bss, 9 miles from the summit at an altitude of 3100 ft. Daily observations were taken there by the warden on a plot close to his house. The purpose of these observations was to determine any difference between the conditions in the Illecillewaet Valley and those observed at Glacier and at the summit.

-Stone7 Creek. - Stoney Creek is a park warden station on the east side of Rogers Pass, 6 miles from the summit and 3650 ft above sea level. Daily observations were taken there by the warden on a plot close to his house. The purpose of these observations was to determine any significant difference between the conditions observed on the summit and on the east side of the pass. 1101;mt Abbott. - Possible sites for a rnountain observatory are 7.- - discussed in Appendix I. Nount Abbott, 6800 ft above sea level, was chosen because it was avalanche safe, a summer trail was available, and access in winter was short (Pig. 2). A cabin was built there in September 1956 (Fig. g), and a test plot was established on a terrace 200 ft below the cabin. A radio telephone connected the observatory with the headquarters at Glacier. me observatory was occupied continuously during the winter of 1956-57, but only during storms and the snow-melt period in the following two winters. Weekly inspections were made when no observer lived there. The observations taken at Mount Abbott indicated the snow cover and the weather conditions at the altitude of the rupture zone for the avalanches. Balu Pass. - A second mountain observatory was established at Balu Pass, 6600 ft above sea level (Fig. 10). Test plots were staked out on both sides of the pass where the snow profile was surveyed monthly during the winter 1957-1958. A cabin was built at the summit of the pass in September 1958. This observatory served primarily for wind observations as Mount Abbott was an unsatisfactory site for such measurements. The wind speed and direction were measured with a standard anemovane and recorded on an Esterline Angus recorder in December 1958 and January 1959. Special wind telemetering equipment was developed for this observatory by the Radio and Electrical Engineering Division, NRC, and installed in September 1959 (6). Information on the wind speed and direction was thus transmitted to Glacier by radio. The station performed well in the following winter, and needed only occasional inspection. The absence of icing on the anemovane offered some encouragement that the wind equipment might be installed on a more exposed and remote mountain with difficult access, e.g., on the ridge of Mount Abbott. An extensive study on the conditions causing spring thaw avalanches was conducted at Balu Pass in May 1959.

Observations at Rogers Pass Summit and at Glacier The description of the equipment and rnetliods used for the snow cover and weather observations are given in Appendix 11. The following daily observations were taken at the two observatories:

Air temperature : - daily maximum temperature - daily minimum temperature - temperature at the time of observation Precipitation: - depth of new snow - density or specific gravity of new snow - total snowfall from the beginning of a storm (storm stake) - settlement of new snow - rainfall Snow cover: - total snow depth - settlement of the snow cover - snow temperature - surface of the snow (e.g. soft, crust ) - depth of penetration of a footprint or depth of penetration of the first section of the ramsonde - a shallow snowpit was dug and the hardness and shear strength of the different snow layers were tested whenever such observations were required

Wind : - windspeed - wind direction - observations on the direction and the magnitude of snow movements on mountain ridges (snow flags) and in the valley whenever visibility permitted.

State of the Weather Daily observations on precipitation and air temperature were continued during the summer. The complete profile of the snow cover was surveyed twice a month on Rogers Pass Summit.

Observations at Flat Creek and Stoney Creek The following daily observations were taken at the two park warden stations: - maximum temperature - minimun temperature - depth of new snow - total snowfall from beginning of a storm - rainfall - total snow depth Observations were not made on some days during the winter and measurements were discontinued during the summer. Observations on Mount Abbott The same daily observations made at Rogers Pass Summit and at Glacier were made, on llount Abbott when the observatory was occupied. At other times, precipitation and temperature were measured with recording instruuents. The snow profile was surveyed weekly.

Special Observations The rupture zones of avalanches were visited whenever the avalanche hazard made such visits feasible. The profiles of the snow cover in these areas were studied and compared with the profiles taken at Rogers ?ass Summit and Mount Abbott .

Records All observations were recorded on special forms (is11, 12, 13). The observations on the snow cover and the weather were plotted against time. All records were stored at the avalanche observation station at Glacier and were transferred to the Department of Northern Affairs and National Resources on 2 October 1959.

Survey of the avalanches Recording all avalanches along the proposed highway was the primary work of the avalanche observation station. These avalanches were surveyed frequently by patrols and recorded in a special book. Those depositing snow near or on the highway right-of-way were traced on location plans. The location of the fracture zone and the path of some important avalanches were traced on photographs (Pig, 14). It was important to know not only the date but the hour when the avalanches had occurred. The time could be obtained fairly accurately by daily and often twice daily patrols between Mile 11.5 and 17, and patrols through other areas when avalanches could be expected.

Personnel The staff of the avalanche observation station averaged six men during the winter and three during the summer. These numbers were required for safety reasons. Fatrols through avalanche areas should be done by at least two or more men. At least two should be at the mountain observatory when occupied during storm periods. It was foimd that half of the staff should have a good knowlkdge of skiing and be experienced in mountain travel. The others need only a fair knowledge in skiing but must be physically fit for the work.

CAUSES OP THE AVALANCHES Observations showed that avalanches are caused by the same factors as in other countries so that experience gained by other organizations in the forecasting of avalanches can be applied to Rogers Pass. In this section, the factors which contribute to the development of avalanches are summarized and those of particular importance for the avalanche hazard forecast at Rogers Pass are emphasized, This summary is not meant to be a general handbook on avalanche hazard forecasting; it is addressed to those who require an introduction to the conditions at the pass. The rules that are given here are based on all available observations and can probably be improved with more experience.

Rupture Zones Rogers Fass has an upper and lower zone from which avalanches can start to slide. A terrace with a slight incline, located between 5500 and 6500 ft divides these two zones on many of the mountain slopes (Pigs. 15, 16). &lost avalanches starting to slide in the lower zone rupture on the cliffs or at the toe of cliffs. The upper zone contains steep slopes rising from 6500 ft to the mountain ridges. Many small avalanches that originate in the upper zone stop on the terrace between the two zones. A knowledge of the two different rupture zones is important to predict avalanches caused by high temperatures. It was observed frequently that the temperature in the lower zone was high enough to cause avalanches, whereas in the upper zone the temperature was so low that the snow was still stable,

Climate Areas

At Rogers Pass there are two major climate areas, and the avalanche hazard for each should be evaluated separately. The two areas are: - the Tupper area on the east side of the Pass, - the Illecillewaet Valley on the west side of the Pass. Most snowstorms approach the Pass from the west and southwest and deposit a greater amount of new snow in the Illecillewaet Valley than in the Tupper area. Observations during the two winters between 1957 and 1959 showed that the average total snowfall in the Tupper area was 80 per cent of 3 the snowfall measured in the Illecillewaet- Valley. As less snowfall is required to cause avalanches on Mount Tupper, the avalanche hazard is usually about equal in both areas. Occasional storms from the north and east deposit more snow in the Tupper area than on the west side of Rogers Pass. Observations at the summit give a good ind.ication of weather conditions on the east side of Rogers Pass. A special observatory in Stoney Creek is not essential, but additional observations on the east side of Mount Tupper would be useful for a control. Generally higher precipitation on the west side of Rogers Pass than that measured at the summit; indicates a need for additional weather observations on the west side, either at Glacier or at Flat Creek. The difference in precipitation at Glacier and at Flat Creek is not significant. Since Flat Creek is a little warmer, rain sonetimes falls here when there is snowfall at Glacier. Glacier is, therefore, a more suitable station for weather observations with the additional advantage of having been a climatological station for over 40 years.

The Snow Cover Frequent snowfalls with fairly constant temperatures during and after each snowfall usually produce a stable snow cover. The typical snow profile has layers with increasing strength toviard the ground (Fig. 13). Snow with a high degree of metamorphism (depth hoar, sugar snow) forming layers with low strength are not often observed. Unstable layers causing avalanches may develop from the foj~owin~conditions: (a) Snow covers the mountains in September and early October, and cold weather with little snowfall persists during October and November. The snow in the avalanche rupture zones changes into depth hoar thus creating an unstable base for future snov~falls. This situation is typical for the Rocky Mountain area but appears only occasionally in the Selkirks. It was observed in the Rogers Pass area in the winter of 1957-58, but the unstable snow covered small areas only. (b) Cold weather in January and February with a period of no snowfall for two or more weeks may cause considerable me-tamorphism of the snow at the surface. This snow layer has low cohesion and may fracture later under the weight of new snow or during the snow-melt period. Such a condition was observed in February 1957 and was the cause of numerous spring thaw avalanches in ?flay of that year. (c) A period of rain or sunshine occurs resulting in a crust which forms a sliding surface for winter and spring avalanches, particularly in the lower rupture zone. Although unstable loose layers are infrequently observed in the Rogers Pass area, the snow profile proved to be important as the basis for the daily avalanche hazard forecast. The ram resistance of the whole snow cover and the profile of the upper 5 ft (150 cm) was surveyed once per week. Since the properties of snow deeper than 5 ft from the su-face do not change very rapidly, it was found necessary to observe the complete profile only once per month. Influenced by rain and sun, the profile at the summit observatory did not always represent the conditions in the rupture zone of the avalanches. Snow profiles from the test plot on nlount Abbott and from slopes of different exposure in the rupture zone proved more useful. Experience showed that when the snow c6ver was more than 4 ft deep, observations on the settlement were not necessary for the avalanche hazard forecasting. The ground had to be covered with a certain depth of snow before avalanches could increase and attain the speed necessary to reach the valley and the highway. The observed depths for the period 1957 to 1959 are given in Table IV. These observations indicate that Mount Abbott requires a snow depth of about 28 in. (70 cm) before avalanches from the upper zones reach the valley. A similar depth observed at the summit appears to be necessary before avalanches from the lower rupture zone can reach the highway, It must be noted that avalanches from the upper zone may reach the highway even when there is no snow in the valley.

The Snowfall The majority of avalanches are caused by snowfalls. It was observed that under "normal" conditions, avalanches may occur at Rogers Pass if the amounts cf new snow listed in Table V are deposited during a snowstorm. "Normal" conditions SNOW DEPTHS WHEN THE FIRST AVALANCHES REACHED THE VALLEY

First Avalanches from Snow Depth on the Upper Rupture Zone l~lountAbbott

26 November 1357 90 cm = 35 in. 8 November 1958 70 cm =L 28 in. 18 November 1958 70 cm = 28 in. 24 October 1959 28 in., estimated from observations made on Fidelity Mountsin. First Avalanches from Snow Depth on the Lower Rupture Zone Rogers Pass Summit;

12 December 1957 73 cm = 29 in. 20 November 1958 70 cm = 28 in. 23 November 1959 73 crn = 29 in.

exist when the snow cover is stable and the temperature is below 32°F and almost constant. The figures given in the table are based on the experiences of three winters only. Lack of information on the wind made it difficult to analyze observations fron winters previous to 1957. Comparisons between observations from Glacier and Mount Abbott on the amount of snow that fell during a stom show only a slight difference between the amount measured on the mountain and in the valley below. In soine storms more snow falls on Mount Abbo-t;t than at Glacier and vice versa. The difference is not large enough to influence the avalanche hazard forecast as it can be assumed that the same amount of new snow falls in the upper and lower avalanche rupture zones as in the valley. When rain is measured in the valley and snow is falling on the mountain it can be assumed that 1 in. of rain corresponds to 12 in. of snow. Rain following a snowfall in the avalanche rupture zones can start avalanches within one or two hours of its beginning. If the snowfall is not more than 12 in. the avalanches will probably be small and will not reach the highway. Most big avalanches $hat blocked railway traffic in previous years resulted from heavy snowfalls followed by rain (e.g. on 1'7 February 1930, 9 to 10 January 1933 and 24 to 26 January 1935). TABLE V AMOUNTS OF SNOWFALL CAUSING AVALANCHES

Total Snowfall Wind Measurement Total for Influence Avalanche Hazard on storm- 12 stake hours

8'l (20cm) 10" (25cm) Strong wind Hazard 2: Small avalanches at sites where avalanches occur frequently, e. g. at Mount Tupper. 10" (25cm) 14" (35cm) No wind Hazard for mountain skiing.

10" (25cm) 16" (40cm) Strong wind Hazard 3: Minor avalanches may occur at all known sites. 16" (40cm) 20" (50cm) No wind Smaller avalanches may reach the highway at unprotected sites.

16" (40cm) 20" (fjOcm) Strong wind Hazard 4: Major avalanches may occur at all known sites 22" (55cm) 28" (70cn) No wind and may reach the highway.

32" (80cm) 40" (100cm) Mostly Hazard 5: Avalanches without of unusual size may wind reach the highway at all lmo~vnand also at new sites.

The specific gravity of the new snow ranges between 0.07 and 0.10. The average specific gravity of the new snow was 0.083 in the winter of 1957-58 and 0.084 in the winter of 1958-59. New snow with specific gravities lower than 0.07 and higher than 0.10 are more likely to cause avalanches. Snow with a low specific gravity will result in avalanches before the amounts of snow indicated in Table VI are reached. Wind Wind is a dominant factor in the build-up of an avalanche situation. The direction of the prevailing wind in the rupture zone determined in most cases whether a certain avalanche would start to slide after a snowfall. Observations at Rogers Pass Summit showed the wind at this site to be influenced by the mountains and direction of the valley and not necessarily related to the direction and speed of the wind in the rupture zone of the avalanches. Therefore, observations at an exposed site on the mountains are required. During the winter of 1958-59, insufficient observations were made on Balu Pass to allow an adequate correlation at all sites between the wind speed and direction and avalanche occurrences.

Observations at Rogers Pass Summit indicated that a wind of speed greater than 8 mph will influence the avalanche hazard. The information collected during the avalanche survey on the influence of wind on the avalanche hazard at some sites is sulnmarized in Tables VI and VII. This information was obtained from observations on the drifting of snow on mountain ridges and associated cornice formation and from the wind observations taken at the Balu Pass site.

TABLE VI AVALANCHES AFFECTED BY WIND

Highway Wind Direction Favourable Avalanche Site Mile to Avalanche Occurrence

Gullies at Mount MacDonald 10.2-11.7 South Tupper - Timber 10.4-10.6 West, f ollov~ingthe valley of Bear Creek Tupper 1 11.3 TI 11 Pioneer 11.4 1 I II Tupper-Minor 11.6 II II Benches 12.0-12.2 11 11 IIounds 12.4 !I ?I Crossover 12*3 Southwest to south Tractor shed 12.7-13.0 tt 1t P,TacDonald-West shoulder 14.5-15.0 South to southeast Avalanche Crest 16.3 East Abbott No. 3 17.8 Southwrest to south nlount Green 20.3 ';Jest to southwest Fidelity 26.0 West Lanarlc - l?/est TABLE VII AVALANCHES FROBABLY INFLUENCED BY WIND (but not enough observations to confirm this)

Avalanche Site Hi&way hlile Favourable Wind Direction

Grizzly 13.4 Southwest to south Cheops 14.5-15.2 11 11 Abbott No. 4 17.85 It 11 Junction 18.7 West Twins - West, following the valley

Temperature

It was found that special.. attention is required& when the temperature during a snowfall is near 32OF, as any rise in temperature could change the snowfall into rain, and create a serious avalanche hazard. A snowfall with temperatures below 20°F produced slow stabilization of the snow cover. The influence of temperature on spring thaw avalanches is discussed in a special chapter. High temperatures in the spring cause the ice to melt and fall from the cliffs. Falling ice which reached the highway was observed in the Tupper-Timber Avalanche area, hlile 10-4 to Mile 10-8, Most of the time the temperature on the mountains is lower than t'ne temperature in the valley. During some important snowfalls and sometimes in spring temperatures were higher on the mountains. Experiences have shotm that a continuous record of temperatures at high altitude is a great asset in avalanche forecasting. During the avalanche survey it was necessary to occupy the observatory on Mount Abbott at critical periods to report tne temperature and other infornla- tion to the headquarters in the valley. It would be useful if the air temperature at a mountain observatory could be telemetered.

Spring Thaw Avala'nches The term spring thaw avalanches is applied to those avalanches that occur in the spring due to loss of cohesion of the snow when it melts. Spring thaw avalanches can be active on Rogers Pass and are more difficult to forecast than direct action winter avalanches. The factors contributing to the start of spring thaw avalanches in 1957, 1358 and 1959 were investigated by J. C. Garland, a member of the avalanche observation station, and the following inf omation was obtained : Spring thaw avalanches occur in two groups. The first group comes from the lower avalanche rupture zone below 5500 ft and the second from the upper rupture zone between 6500 and 8000 ft. The time between the occurrences of the two groups depends on the weather. The second group or late spring thaw avalanches followed the first group or early spring avalanches after 6 days in 1957, 20 in 1958 and 27 in 1953. 2. Spring thaw avalanches may start to slfde as a snow-slab on unstable snow layers, on the ground or as loose snow avalanches. Large spring thaw avalanches can be expected when the snow profile shows layers with low strength. The temperature was 32OP throughout the snow cover in the rupture zone when the spring thaw avalanches occurred. This snovr tempera ture was measured at Rogers Pass Sixmmit when the cycle of the early spring thaw avalanches began and on Mount Abbott when the late spring thaw avalanches began. Local slides on south-exposed sunny slopes canSoccur earlier. 4. When the early avalanches started, the daily maximum air temperature at Rogers Pass Summit was in -the forties and had been continuously above 32OF for the previous 5 days in 1959 and 25 days in 1958. 5. The mean daily air temperature was always above 32OF at Bogers Pass Summit on days when the early spring thaw avalanclles ran, and on Moult Abbott when the late spring thaw avalanches occurred. 6. Humidity observations did not appear to have any bearing on the avalanches. The mean humidity of the air in daylight was relatively high when the avalanches began, 71 per cent in 1957 and 89 per cent in 19 8 but in the following days when avalanches were Ling, the mean humidity was neither constant nor high. 7. The general state of the weather appeared to have no influence on the start of avalanches. In 1957 the weather was cloudy; in 1958 there was rain and snow, in 1959 it was sunny, 8. Rain, unless particularly warnl, did not appear to influence the star* of spring thaw avalanches. 9. In spring 1959 snow compaction tests were made with the compact-ion method recomnended by G. P. Williams (7). It was found that the compacted density of the snow in the fracture plane of the avalanche was as high as 0.904 compared with 0.4 for non-compacted snow. The compacted densi*y in other layers was between 0.7 and 0.8 with a non-compacted density of about 0.4. This would indicate a high free water content in the snow layer *hat collapses and in that upon which the avalanche starts to slide. As it is impractical to test the compacted density in potential sliding layers, the compaction test is not a useful observation in evaluating the avalanche hazard. 10. When spring thaw avalanches are released under the influence of the sun on clear days, they start to slide between 9 and 10 a.m. on east-exposed slopes, at noon on south, and between 3 and 6 p,m. on west- exposed slopes. The folloTrringrules of thumb were established from the above observations: Before spring thaw avalanches occur the snow temperature must be 32OF in all layers between the ground and the snow surface. After this temperature is reached, avalanches will occur on the first or second day when the mean air temperature is above 32OF. The air temperature measured at Rogers Pass indicates early spring thaw avalanches from the lower rupture zone, while that measured on Dlount Abbott indicates late spring thavr avalanches from -the upper ruptu. 2 zone.

The conditions that caused avalanches at the Mount Green and the Crossover avalanche sites were investigated. Conclusions obtained are given in Appendices IV and V. It was recommended that avalanches at these sites be controlled by artillery fire and, therefore, the avalanche hazard forecast for these areas is particularly important. It was not possible to make a special study of more avalanche sites because of insufficient observations. It would be useful if such studies could be made on the following avalanches : Connaught Grizzly Cl~eops1 MacDonald West-shoulder Avalanche Crest Junct iozl Fidelity

AVALANCHE WARNING The Avalanche Hazard Forecast During the winters of 195'7-58 and 1958-59 the avalanche hazard was evaluated twice every day and more frequently at critical times. The f ollo~vingclassification of the avalanche hazard was used:

Degree 0: No avalanche hazard Degree 2: Very low avalanche hazard. Local avalanches may occur on steep slopes or in areas where drift snovi has accumulated. The sliding snow mass would be small and the slide path short. Degree 2: Low avalanche hazard. Avalanches may occur from steep, rocky rupture zones and may reach the valley at the sites where avalanches occur frequently. Example of avalanches which may occur at hazard 2: Major Tupper avalanches MacDonald gullies Small avalanches in the tractor shed gullies Twins Len's Degree 3: Medium avalanche hazard. Avalanches may occur at all hown avalanche paths and reach the valley at those sites where avalanches occur with an average frequency of more than once per winter. Degree 4: High avalanche hazard. Avalanches of dangerous size that reach the hi@- way may occur at all kno~nrn avalanche sites. Avalanches with an average frequency of occurrence of once in 3 to 5 years may occur. Degree 5: Very high avalanche hazard. Avalanches of dangerous size may occur at all howrl avalanche sites and may reach unusual size. Avalanched may also occur at new sites. This classification' of the avalanche hazard proved satisfactory for the two winters during which it was used. The avalanche hazard had to be evaluated separately for the two climate areas, Mount Tupper and the Illecillewaet Valley. Sometimes it was necessary to establish a special avalanche hazard for single avalanche paths, e. g. , when wind action had created a higher hazard for some avalanche sites. me different degrees of avalanche hazard had the following effect on activities in the Rogers Pass area: Degree 1: Skiing in the mountains and travelling - through the avalanche areas was generally safe. Dangerous slopes had to be crossed with special care. There was no restriction on construction work. Survey work at the avalanche paths on Mount Tupper was stopped. De ree 2: Skiing was restricted to safe routes. Si-tes +w ere avalanches could be expected were crossed only when necessar:i and then very quickly. Consti-uction and survey work at those avalanche sites was discontinued. Degree 3: Skiing was possible on hown safe routes only. All traffic by construction and highway survey crews through the Tupper area were stopped. De ree 4.: Travelling was at a minimum. The avalanches &occurred were observed from safe routes. All movement through the avalanche areas was Hazard 5 never occurred during the survey. It was assumed that this avalanche hazard classification would have the following effect on the operation of the completed highway in the first stage of defence: Degrees 1 and 2: No restrictions. De 'ree 3: Snow-clearing crews would have to be ready +to c ear occasional light avalanches or bankslides from the highway. De ree 4: The highway would be closed to public traffic, -8%-now-c earing operations would be continued with special precaution. De ree 5: The highway would be closed to all traffic, -8-TSnow-c earing operations would be discontin.ued.

Highway Closures During the winters of 1957-58 and 1958-59 the avalanche hazard was forecasted as if the highway were in operation and the first stage of defence completed. The estimated closure times, given in Table VIII include the time estimated for the removal of avalanche snow from the highway, If it is assumed that the first stage of the defence was not constructed, it is estimated that for an average winter the highway would. be closed. about 25 times for a total of 75 days between 1 November and 15 May, One closure might last ten days. \Then the highway was not considered closed, minor avalanches did affec-t the highway at Tupper-Timber (Mile 10.4 to 10.6). Table IX gives the date and extent of these avalanches , To give advance warning for the closure of the highway proved difficult because an accurate weather forecast could not be obtained, Experience gained with respect to the weather forecast is given in Appendix 111. Rough estimates, based on available records, were made of how long the highway would. have been closed in the years previous to 1957 if the first stage of defence had been complete. These are given in Table X,

ANTICIPATED ORGANIZATION AND RESPONSIBILITIES OP THE AVALANCHE WARNING SERVICE To specify the complete defence, it was necessary to forecast the organization and responsibilities of the future avalanche warning service. The basis of these predic- tions was the experience gained from the avalanche observations in the Glacier area and discussions held with the staff of avalanche warning services in the United States and Europe, The information contained in this section is not presented as a recommendation but rather as necessary background material for a complete understanding of the basic principles adopted in formulating the active defence system (Fig. 17).

TABLE VIII ESTIMATED CLOSURES OF THE HIGHWAY IN THE WINTERS OF 1957-58 AND 1958-59

Highway Highway Duration Cause of Avalanclie s Closed Opened of High Hazard on Highway Closure, in hr unprotected Date -Time Date -Time areas 1957-58 16 Jan 0400 17 Jan 1800 38 Snowfal1,wind 2 minor 1 major 21 Jan 0800 25 Jan 0800 24 Snowfall, wind none 19 Peb 1000 19 Feb 2000 10 High tempera- 1 minor ture after snowfall 21 Peb 1400 22 Feb 1700 27 High tempera- 3 minor ture and rain 1958-59 20 Nov 1000 20 Nov 1400 4 Heavy sno~vfall, none poor visibility 2 Dec 0600 3 Dec 0800 26 Snowfall, rain none 18 Dec 0600 19 Dec 1000 28 Snowfal1,wind 1 medium and rain . 2 minor 9 Jan 1900 10 Jan 0700 12 Snorvfall ,rain 1 minor 23 Jan 1500 24 Jan 0800 17 Snonfal1,wind 1 medium Unstable snow 2 minor cover 28 Feb 2130 1 Mar 0600 8& Snowfall, rain 1 minor 1 Apr 1800 2 Apr 1400 20 Snorvf all 1 major 1 minor 10 Apr 1030 11 Apr 2330 37 High tempera- 6 major ture 28 Apr 2000 30 Apr 1200 40 Snowfall 1 medium - 28 -

TABLE IX TUPPER-TIMBER AVALANCHES WHEN THE HIGHWAY WAS OPEN

Width Depth Date on Highway, on Highway ft

18 January 1958 50 2 ft 21 December 1958 200 1 ft 19 January 1959 250 4 in. 6 February 1959 160 1 ft

TABLE X

ESTIMATED CLOSURE OP THE HIGHWAY IN THE IZ'INTERS OF 1953-59

Number of ::Total number of Maximum duration Winter Closures days closed of one closure days

1953-54 6 22 6 1954-55 6 6 1 1955-56 6 8 1956-57 4 9 1957-58 4 5 1958-59 9 12

-x The number of days closed and the maximum duration of one closure include the time required to remove the avalanche snow.

Responsibilities of the Avalanche Warning Service It was anticipated that the avalanche warning service would have the following primary responsibilities: (a) To organize and take the snow and weather observations. (b) To evaluate and forecast the avalanche hazard. (c) To order or recoinnend the closure of the highmay. (d) To provide the highway maintenance crew with an accura$e evaluation of the avalanche hazard at any time. (e) To recommend when and where an avalanche should be controlled by explosives. In addition, it was anticipated that the warning service would have the following secondary responsibilities: (a) To issue a public avalanche warning bulletin for skiers and mountain climbers. (b) To make the avalanche hazard forecast available to the Canadian Pacific Railway. (c) To record the location and size of every avalanche near the highway. This information will be required when preparing the recommendations for future improvements in the active avalanche defence. (d) To investigate and record avalanche accidents in the Glacier area. The planned defence requires that the 'highway be closed when the avalanche hazard is such that there is danger to traffic on the highvlay. It was anticipated that there would be close co-operation between the warning service and the individual with the authority -to close the highway.

Personnel To fulfill the responsibilities it was considered that the avalanche hazard forecasting service would be composed approximately of the folloviing nucleus of staff: One avalanche hazard forecaster in charge One assistant avalanche hazard forecaster One patrolman. The avalanche hazard forecaster in charge would head the avalanche hazard forecastina service and be resDon- sible for organizing the observations and evaluating theA avalanche hazard. He should have at least three year's training and experience with snosr observations and the forecasting of avalanches, as a ski-mountaineer, park warden, etc., and he would have to do actual avalanche forecasting in the Rogers Pass area for two more winters to become familiar with the area and develop confidence in forecasting the avalanche hazard. The assistant avalanche hazard forecaster would assist -the liead of the avalanche hazard l'orccas'cing service and issue the avalanche hazard forecast in his absence. The assistant should have had. a-t least two years of experience in work related with snow and avalanche f orccasting. It would be advantageous if the avalanche hazard forecaster in charge or the assistant were trained in meteorology. At least one of the avalanche hazard forecasters would be on duty each day during the avalanching period. The patrolman would be required for field work, such as studies at the mountain observatory, and the recording of avalanches. He should be able to take routine snow and weather observations.

All Lhree staff members would have to be experienced in mountain climbing and ski mountaineering and be interested in making observations on the snolri cover and weather required to evaluate the avalanche hazard.

Snow Cover and Weather Observations- It was assumed that the avalanche warning service would have an observatory at the summit of Rogers Pass, at Glacier or at an equivalent site on the west side of *Rogers Fass, and on one of the mountains. The headquarters would be at Rogers Pass Summit, the anticipated base of operations for the highway maintenance staff. There would be a test plot for weather and snow cover observations near the office of the avalanche warning service. Observations near the residence of the park warden at Glacier would be satisfactory to determine conditions on the west side of the Pass, Developments in Glacier National Park, e. g. , the construction of forest roads or trails. forest observatories. tourist roads, radio relay stations, etc., would be determining factors in the choice of a site for a high altitude observatory. The observatory chosen mould contain equipment to measure the wind speed and direction, and air temperature. If the observatory is retained on Mount Abbott, the anemovane should be located on the mountah ridge above the present cabin. It was anticipated that t11e avalanche hazard forecasters would evaluate the avalanche hazard twice daily and more frequently during critical times. The avalanche hazard would be evaluated and forecasted based on the following observations: 1. The regular detailed snow cover studies that are composed of the snow profiles surveyed near the mountain observatory and at Rogers Pass Summit at least once per week; the snow profiles taken on occasional patrols through the avalanche rupture zones; and the history of avalanche occurrences during the winter. 2. The twice daily v~eatherand snonl cover observations at the two valley observatories and the continuous wind and temperature observations from the mountain observatory. It was expected that the daily observations at Rogers Pass Summit viould be similar to those made during the period 1958-59. Experience has shown that the observations in the Illecillewaet Valley need only include: Maximum temperature Minimum temperature ?re sent temperature Depth of new snom Total snowfall from beginning of a storm Ra inf a 11 Total snow depth 3. Observations made by highway patrols on avalanches that terminate near the highway. 4. The weather forecast for the area. Temperature and precipitation observations would be continued during the summer at Rogers Pass Summit and at Glacier.

Effect of Avalanche Warning on Highway Traffic If travelling on the highway were hazardous, the highway would be closed at the east boundary of Glacier National Parlc and at the west boundary of Mount Revelstoke National Park. Conditions at Rogers Pass have shum that local traffic between Revelstoke and Albert Canyon or even between Revelstoke and Glacier could continue at times when the avalanche hazard is high in the imnediate pass area, but medium in the Illecillewaet Valley. To a.7.10~ traffic en route to pass dangerous areas before the hazard becomes too great, notification of highway closure at least two hours in advance should be given at Golden and at Revelstoke. Such warnings should also be posted at Clagary, Salmon Arm and Khmloops. The majority of vehicle operators do not realize that severe winter conditions may prevail on the mountain roads when roads in the 1orve:r valleys are ice free. Their cars which are not equipped with chains or snow tires slide on the icy mountain road and block the traffic. In Sviitzerland where such problems were encouiltered, vehicles not properly equipped can legally be banned from using mountain roads; chain rental services were also organizzd.

Avalanche Warning for Skiers limy skiers and mountain climbers will visit the area when the Trans-Canada Highway is completed and should be warned abou--he avalanche hazard. It is recommended that a special avalanche naming bulletin be issued for this purpose which vrould be posted at- parking arcas, lodges, motels etc. The bulletin should include the following information:

(a) A review of snow conditions and the weather (b) The actual warning. The bulletin might read as follows: "15 in. of new snow was recorded on Monday and Tuesday. PAamong winds from south and sout-hwest caused deep accumulations of drift snow. There is high hazard for snow slabs, particu1arl.y on north- and east-exposed slopes. Sliiing should be con- fined to safe routes", or "The snow cover has stabilized under the influence of low temperatures. There is a low hazard of local slab avalanches at altitudes above 6500 ftl'. A new bulletin should be issued at least once a day or when conditions change.

The author wishes to aclmonled~cthe contribution of E. J. Smith, R. R. Srigley, J. ??.:Friollaud, J. C. Garland, J. Tasko, R. E. Graham, oerqbers of the avalanche observation station vdio mcle 2nd mal~rzed%he snow and rvcather observations, of B. C. Gardner nl~oorganized the first observations in the Rogers r'ass area and 2. Engler crho took the photographs and e;u .ded avalanche pa-krols. He also r~ishes to express his thanks to ?ark Superintendent B. R. S-tylcs, Chief ';l'arden B. Pitta~~~ay,the %rlr Ylnrd-ens 0. Thomas, L. Faggetter, V!. Laurilla for their co-operation in ts.king neather observations, Division Engin~crA. F. Joplin for rnnlcing possi-ble -the study of the avalanclies on the Cr:nad-izn l'acii'ic Rail.cq:ay and L. 'iT. Gold for his critical revieu of -b'ni.s rcpor-t. REFERENCES

1. Schaerer, P. A. The avalanche defence on the Trans-Canada Highway at Rogers Pass. National Research Council, DBR Internal Report, (in preparation). 2. Roch, A. Avalanches in the USA 1949. Federal InstituCe for Research on Snow and Avalanches, Weissfluhjoch/ Davos, Int. Report No. 174. 3. Bucher, E., R. Haefeli, E. Hess, C. Jost, and Re U. Winterhalter. Lawinen, die Gefahr fbden Skifahrer. Geotechnische Kommission der Schweizerischen Naturforschenden Gesellschaft, 1940, Aschmann and Scheller, Zurich. (Out of print) 4. Atwater M. and F. Koziol. Avalanche handbook. Forest Service, US Department of Agriculture, 1953. 5. Snow avalanches. Forest Service, US Department of Agriculture, Handbook No. 194, January 1961. 6 Beaulieu, R. and G. Neal. Wind velocity telemetering system. Electronics, Vol. 33, p. 68-70, July 1960. 7. Williams, G. I?. A field determination of free water content in wet snow. Proceedings of the Western Snow Conference 1956, DBR Research Paper No. 26, NRC 4110.

8. Bader, H., R. Haefel.i, E. Bucher, 0. Eckel, and Ch. Thams. The snow and its metamorphism. Bern 1939, S.I.P.R.E. Translation 14. 9. Klein, G. J., D. C. Pearce and L. W. Go1.d. Method of measuring the significant characteristics of a snow cover. National Research Council, Associate Committee on Soil and Snow Mechanics, Technical Memorandum No. 18,' November 1950. 10. The International Classification for Snow. Published as Technical Memorandum No. 31 by the National Research Council, Associate Committee on Soil and Snow Mechanics, Ottawa, August 1954. APPENDIX I

SELZCTION OF TKE MOUNTAIN OBSERVATORY

The site for the mountain observatory, where snow and weather conditions at the rupture zone of the avalanches can be studied should satisfy the following conditions: (a) It should be located in the centre part of the avalanche area, at an altitude where most avalanches originate . (b) It must be avalanche safe under any circumstances. (c) The access must be avalanche safe and relatively short, particularly in the winter, so that the observatory can be visited at any time when observations are required. (d) Access must be easy in summer. A truck road or at least a horse trail should lead from the valley to the observatory. An aerial tramway would be very useful.

(e) Radio transmission between the observatory and the valley must be satisfactory.

(f) There should be located near the observatory a level test plot about 50 by 100 ft sheltered from the wind, on which the snow can accumulate without being disturbed. (g) Slopes of different exposure should be available near the observatory upon which snow conditions may be studied. (h) It should be possible to locate the anemometer so that a true indication of the wind speed and direction in the rupture zone can be obtained.

(i) The observatory should be large enough to store equipment and provide several days' accommodation for at least tv~oobservers. It was impossible to find a location for the early avalanche investigations which satisfied all the above listed conditions. The different locatiolls that were considered are discussed below:

Mount Abbott (Fig. 2) Location: On the grassy bench on the east side of hlount Abbott, alt. 6800 ft. Advantages: Easy and short access in summer by horse trail, safe and short zccess from Glacier in winter. Good site for wind observations on the ridge of BIount Abbott. Good radio transmission to Rogers Pass Summit for telemeter equipment. Disadvantages: Sheltered from west wind by the mountain ridge. The ridge where wind observations could be taken is 400 ft higher than the observatory and is not always accessible during the winter. Test plot and study slopes are $ mile from the observatory.

Balu Pass (Pig. 10) Location: At the summit of Balu Pass, 3 miles west of Rogers Pass Summit. Advantages: Short access by horse trail in summer, easy access in winter. Exposed to the important south, west and north winds. Many avalanche slopes with different exposure in the neighbourhood of the observatory. Disadvantages: Access is threatened by avalanches in winter. Sites for suitable test plots are too far away from the observatory. Wind from the east cannot be observed accurately. Observations made in the winters 1957-58 and 1958-59 have shovm that snow conditions at Balu Pass and Mount Abbott are the same. The west side of Balu Pass would be more suitable for the location of a snow test plot because the snow cover on the east side is influenced considerably by wind and sun.

Fidelity Mountain (Pia. 18) Location: The east shoulder at the south peak of Fidelity Mountain, alt. 6500 ft. Advantages: Safe access in winter, good access on old horse trail in summer. Good sites for snow observations. Avalanche slopes readily available for observations. Good location for wind observations at the south peak of Fidelity Mountain. Disadvantages: The mountain is not centrally located. Before construction of the highway access from Glacier to Flat Creek was difficult and lone; in winter. The peak where wind observations must be taken is one mile from the observatory and 1000 ft higher. The access to this peak is not always easy. Hermit (Fig. 19) Location: On the terrace above the Hermit Hut of the Canadian Alpine Club at 6700 ft. Advantaees: Satisfactory site for all observations. Access safefrom avalanches. Disadvantages: Not centrally located in the avalanche areas. Only a foot trail is available for access in summer.

Mount Cheops (Fig. 20) Location: The terrace of the east side of Mount Cheops below, Napoleon, al-t. 5900 ft. Advantages:- Closely located to Rogers Pass Summit. Short and easy access in winter. Suitable locations for snow observations. Disadvantages: No access trail in the summer. Low altitude. Wind observations cannot be made.

Selected Observatory Accessibility in summer and winter governed the choice of the observatory site. As time and funds did not permit the construction of a special access road, the observatory had to be built at a location where a trail was already available. A short and avalanche-safe access was also essential for the winter. For these reasons, Mount Abbott was chosen. The Mount Abbott site may not be ideal for snow and avalanche studies, but it was found that between 1957 and 1959, observations from this site were satisfactory for the avalanche hazard forecast in the Rogers Pass area. APPENDIX 11

EQUIPfdENT AND METHODS OF OBSERVATIONS

Observations of snow depth, density of snow and ram resistance of snow cover were recorded in the metric system. It is recommended that this system be applied in the future. Many special instruments for snow cover observations are available commercially, graduated in the metric system only. Daily weather observations were recorded on the special forin shown in Fig. 11. Satisfactory methods for snow and weather observations used during the avalanche studies at Rogers Pass are given below.

Air Temperatures Air temperatures were read with the maximum and minimum thermometers used and supplied by the Meteorological Service of Canada. The thermometers were housed in a stand.ard MSC Stevenson screen. On Mount Abbott the air temperature was recorded with a thermograph "Negretti and Zambra, - 40 to +12O0F". The cloclc of this instrument did not operate properly when the temperature dropped belorr O°F.

The snowfa: 1 was measured on a platform stake every 12 hours. The size of the board was approximately 18 in. square and was laid on the snow surface before the snowfall started. The board has a vertical pole at the centre so that it can be found easily when covered with snow (Fig. 21). Experience showed that this platform stake has to be located at a site sheltered from the wind in order to avoid errors due to drifting snow. The &epth of new snow was measured to within 0.5 cm with a ruler at three or four different places on the board. Plastic folding rules, graduated in centimeters, proved the most convenient. The platform stake was cleaned after each observation and laid upon the surface again. A second platform stake that could be read at intervals shorter than 12 hours during heavy snowfalls was found useful. Total Snowfall During a Storm Snowfall was measured from the beginning of a storm on 23 platform stake (storm stake) the same way as the 12-hour snorvfal.1 was measured. The platform was not cleaned until the end of the storm. Rainfall Rainfall was measured with the standard rain gauge used by the Meteorological Service of Canada. Recording Precipitation Gauge A "Bendix Recording Rain and Snow Gauge" Model 775-C was installed at ldount Abbott and during the winter 1957-58 at Rogers Pass Summit. This instrument correctly recorded the precipitation when the wind was not strong. Collection efficiency could be improved by using a properly designed wind screen. The collecting bucket was filled about 6 in. deep with a mixture of one part ethylene glycol and one part water to melt the collected snow. Specific Gravity of the New Snow A sample of new snow was obtained with a sampling tube of known cross-section area. The weight of this sample was measured with a spring scale, graduated in grams. The water equivalent of the new snow in cm water - weight of sample in grams cross-section area of the tube in cm2 The average specific gravity of the new snow - mater equivalent in crn depth of nem snov in cm Two types of sampling tubes were used for avalanche studies at Rogers Pass, one of aluminum with a cross-sectional area of 28.6 cm2 and one of steel with a cross-sectional area of 25 cm2. The aluminum tube proved better as the new snow ,did not freeze on this tube as often as on the steel tube. It was found necessary to store the sampling tubes in cold air shaded from sunlight. A more accurate method of measuring the water equivalent of new snotv?would be to melt a sample of the snow and measure the amount of water obtained with a graduated cylinder. Weighing the sample, however, proved to be much quicker and simpler, and was accurate enough for avalanche hazard evaluation. De~thof Snow Cover The total depth of the snow cover was read on a wooden pole. This pole, graduated in centimeters, was set vertically on level ground. The area surrounding the pole was not disturbed during the winter. It was observed that new snow clings easily to the lower part of the pole. It was removed by using a long slat Prom a position not closer than 4 ft from the pole. Settlement The settlement of the new snow and of the snow cover was computed as follows:

Settlement (inch or cm) = Last reading on the depth pole plus depth of new snow minus present reading on the depth pole. The settlement ratio or percentage, defined as the ratio of the settlement in cm to the present depth reading was also calculated. Experience showed that the settlement in cm proved to be more useful for avalanche hazard forecasting than settlement rati.0. Snow Profile The area for the snow profile observations was staked out in the summer at a site which would probably be left undisturbed all winter. Two poles on each side of the area marked the line where the coloured threads were laid out and where the proTiles were taken, The following equipment was used to obtain the snow profile : Ramsonde wi3h a 1-kg hammer 2 or 3 glass thermometers thin metal plate approximately 12 by 12 in. to cut snom samples snow crystal screen magnifying glass, 6X folding rule snom density sampler and spring scale shear frame 100 cn2 spring scale 0 to 500 gm and 0 to 2500 gm for shear test one large and one small snow shovel forms to record field observations and to plot the profile (Pigs. 12 and 13) blue, green, red, yellow threads. Observations were made and recorded in the following order: 1. ram profile 2. dig the pit 3. air and snow temperatures 4. location of the coloured threads 5. boundaries of the snow layers 6. hardness, grain shape, grain size, free water content and density of each snow layer 7. shear resistance of the snom layer 8. refilling the pit 9. lay a new thread 10. mark the location of the pit with a stake. The next profile was dug 1 or 2 ft from the last profile (Pig. 22). The Ram Profile The ram profile was made with the ramsonde, developed by R. Haefeli (8). The ram resistance is computed by the following formula:

R = Ram resistance in kg P = vveight of the hammer in kg (usually 1 kg) n = number of blows h = height of drop of the hammer in cm d = penetration per n blows in cm q = number of sections of the tube Q = weight of one section - 1 kg for the ramsonde used The ram resistance directly indicates the hardness and indirectly other physical properties of different snow layers. The ram profile is obtained by plotting the ram resistances against depth. Because of the nature of the measurement, thin, weak layers are not usually detected. Neverdcheless, the ram profile does help to assess the general condition of the snom cover, particularly its over-all stability (Pig. 13) . Hardness, Grain Shape, Grain Size, Free Water Content, Density These characteristics of the different snom layers were observed and recorded according to the International Snow Classification (9, 10). Wind The speed and direction of the wind were measured with the standard anemovane and anemograph of the Meteorological Service of Canada. Some difficulties were experienced in the operation of the anemograph if the temperature of the room where it was kept dropped below 10°F. A rise in the humidity of the room when occupied added to the difficulties. Condensation occasionally caused ice on the contacts of the anemovane at Rogers Pass Summit and the contacts usually had to be cleaned twice per winter. No trouble with ice was encountered with the anemovane at the observatory on Balu Pass. A 6-volt wet cell (car battery) charged from time to time proved to be most suitable for the power supply at Rogers Pass Summit. Wind Telemetering Equipment The wind telemetering equipment developed by the Radio and Electrical Engineering Division, National Research Council, was installed for preliminary trials at Balu Pass in September 1959 (6). Temperature Telemetering Equipment The equipment which should be developed for telemetering the temperature from the high altitude observatory should have the following specifications: Thermometer: any suitable and accurate thermometer housed in a Stevenson screen. accuracy: 1°P. Desired temperature range for complete observations during the wl~oleyear: -40 to +90°B. Temperature range required for avalanche forecasting only: 0 to 50°P. Signals should be transmitted once in 30 min. The temperature should be recorded on a chart in the valley station. LIST OF EQUIETdENT USED FOR SNOW AND WEATHER OBSERVATIONS

(0 A -I=' [I] a, i= co 0 % 0 $ k k Q, P m 61i= 0 Q, P (U 7-Ia, .d k Equipment 90 WE *a 0 d @a Q, rdd k3 a bDrn0 +23a 4= d 0 a X ffi rn P-4 z2 IT

Maximum thermometer 1 1 1 1 1 Minimum thermlometer 1 1 1 1 1 Thermograph 1 1 p.t. H y grogra ph 1 1 Sling psychrometer 1 1 1 Stevenson screen 2 2 1 1 2 1 Standard anemovane 1 1 Anemograph 1 1 1 Voltmeter 1 Aneroid barometer 2 Mercury barometer 1 Platform stake 4 3 2 2 Snow rule 4 1 1 1 Standard rain gauge 1 1 1 1 Recording precipitation gauge pot. p*t* Snow density sampler 2 1 Snow cover pole 2 2 1 1 Ramsonde 2 1 Snow thermometer 3 1 Snow crystal screen 2 Magnifying glass 1 Shear frame with 2 spring scales 1 NRC snow kit 1 Mount Rose snow sampler 1 Snow compaction kit 1 p.t. = part-time LIST OF EQUIFMENT THAT WOULD BE REQUIRED FOR THE ANTICIPATED SNOm AND VKEATHER OBSERVATION SITES

0) h k,: kPk E oao a P G G Equipment (II,* k7q '&'E dk -rl3 aa, o-da, crrgco 5: ma:: Gg$ g $

Maximum thermometer 1 1 1 Minimum thermometer 1 1 1 The rmogra ph 1 Temperature telemetering equipment with: Radio transmitter 1 Special thermograph and radio receiver 1 Hygrograph 1 Sling psychrometer 1 Stevenson screen 2 2 Wind telemetering equipment: Anemovane and radio transmitter 1 Anemograph and radio receiver 1 Aneroid barometer 1 1 Platform stake 4 3 Snow rule 3 2 Standard rain gauge 1 Recording precipitation gauge 1 Snow density sampler 2 1 Snow cover poles 2 1 Ramsonde 1 1 Snow thermometer 3 2 Snow crystal screen 2 1 Magnifying glass 2 1 Shear frame with spring scales 1 1 Mount Rose sampler 1 APPENDIX I11

THE WEATHER FORECAST

To be of maximum usefulness, the avalanche hazard forecast should accurately predict the hazard for the next 12 to 24 hours. The forecaster can assess the avalanche hazard at the time of observation from the snom cover and weather observations made in the immediate avalanche area. To forecast accurately for any area he must have a good weather forecast for the area giving the expected snowfall, the direction and speed of the wind, and the temperature for the next 12 hours, or better for the next 24 hours. Discussions were held with officers of the Meteoro- logical Branch of the Department of Transport in Vancouver on how the weather forecast for the avalanche warning could be obtained. Forecasting for the interior of British Columbia is particularly difficult because the weather on one side of a mountain range may be different from that on the other. Furthermore, weather stations in this area are not located close enough together to allow preparation of the accurate forecast required. It was arranged that the daily public weather forecast for 5 a.m. and for 3 p.m. be telegraphed to Glacier during the winter of 1958-59. At critical times, when the avalanche hazard was dangerously high and it was important to know whether the conditions would improve or deteriorate, the public forecaster in Vancouver was telephoned and the weather situation discussed with him. The weather office asked that daily observations on the weather, snowfall, wind and temperature at Rogers Pass be telegraphed to Vancouver. Bperiences gathered from this service during the winter of 1958-59 are as follows: 1. The public weather forecast covering the Kootenay- North Thompson Region shows the general trend of the wea.ther. It proved useful as an indication of whether a storm that might cause an avalanche is approaching. 2. The temperature forecasted for Revelstoke appears to be useful for Glacier. It gives an indication of how the temperature might change at Rogers Pass. 3. Forecasts on snowfall are not reliable. Snowfalls are generally heavier at Rogers Pass than forecasted for the area. Frequently when the forecast indicates "snow flurries" , an ordinary snov~fa 11, which can cause avalanches, may be expected at Glacier. Light snowfall can be expected at Glacier when cloudy weather is forecasted, 4. The public forecast gives the expected wind speed and direction in the main valleys; this wind may differ from the significant wind higher up the mountain, 5. The public forecaster was telephoned four times during the wint;er of 1958-59, and the weather discussed. The information received as to whether the storm would continue or end soon, was found reliable but inforination on the snovffall for the next 24 hours was not accurate enough. No satisfactory solution tc this problem is bown at present. When the responsibility for the avalanche hazard forecast was turned over to the National Parks Branch, the weather forecast was still a problem that required further consideration. The present organization whereby the public forecast is telegraphed to Glacier may be sufficient for the operation of the highway as long as winter traffic remains moderate. When the traffic increases a better forecast would be required so that enough advance warning for the closure and the re- opening of the highway could be given. There are -three possibili-ties to improve the weather forecast in connection with the avalanche warning. They are listed here, in the order considered as being effective:

A trained weat;her forecaster be seconded from the Meteorological Branch of the Department of Transport to the staff of the avalanche warning service. He would organize the weather observations in the area, receive the observations from other weather stations by telegra2h or teletype, plot the weather map and make a weather forecast. It would be essential that this weather forecaster be interested in the work at Rogers Pass and show some interest in the mountains and the work related to them. He could be one of tlie Cdo avalanche hazard forecasters, if he has the necessary training. 2. The weather office in Vancouver take a greater interest in the situation at Rogers Pass, establish a weather station at the pass, and make special forecasts. A weather forecaster might spend one winter or part of a winter at Rogers Pass to get acquainted with the conditions in the area. 3. The avalanche warning service organize special observations. The observatiorm show that the majority of storms %hat cause avalanches, and for which a forecast is required, move from the Pacific coast to the Selkirk Tilountains, taking about 24 hours. If three stations could be set up between the coast and Rogers Pass to take meteorological observations, particularly on precipitation, and report these observations immediately to Rogers Pass, it might be possible to predict how fast the storm is moving and how much snowfall can be expected. The stations reporting the observations could be staffed with personnel from the British Columbia Department of Highways or from the Canadian Pacific Railway, both of whom are interested in the avalanche warning at Rogers Pass. With any of the three above-mentioned possibilities, weather observations would be transmitted to Glacier and Rogers Pass Summit by telegraph, telephone or teletype. There is always a danger that communication lines might be broken by avalanches during a storm just at a time when the weather information is most important. It would be useful if weather observations could be transmitted by radiophone, APPENDIX IV MOUrJT GREEN AVALANCHE

This avalanche is better 'mown as the "Ross Peak ~valanche". H. R. Srigley, a member of the avalanche observation station, investigated the conditions that caused avalanches at this site during the period 1954 to 1959. Descxi~tionof the Avalanche Mount Green, 8870 ft above sea level is located on the south side of the Trans-Canada Highway at Mile 20.3 (Fig. 23). A long ridge runs due north from the peak. The west side of this ridge and the peak itself are bare rock sloping at 30 degrees for a few hundred feet. The east side of the ridge drops sharply for about 200 ft and then continues at a 45- degree slope to a small bench at 8000 ft and then to a steep gully. For most of the winter the flat west side of the mountain is swept bare of snow by the prevailing westerly and southerly winds. This snow develops a huge cornice on the ridge or is deposited on the east side of the mountain. The deep snow on the east side does not melt completely during the summer and forms a small glacier. Avalanches start as slab avalanches below the cornice. Small avalanches stop at the little bench, but larger ones reach the steep gully and follow it to the bottom of the main valley. Analyzed Observations The snow and weather conditions prior to the following occurrences of the Mount Green Avalanche were analyzed on 25 February 1954; 14 February 1955; 11 January 1956; 10 February 1957; 7 December 1957; 16 January 1958; and 3 December 1958. In the winters of 1957-58 and 1958-59 various snowstorms that did not cause an avalanche on Mount Green were also analyzed. The studies of the first four avalanche occurrences are based on the snowfall and temperature observations taken at Glacier and wind information obtained from the 700 mb charts by the Cen-tral Analysis Office of the Meteorologi- cal Branch, Department of Transport. Studies of avalanckes in the winters of 1957-58 and 1958-59 are based on observations at Glacier, Rogers Pass Sumrnit and Mount Abbott. Conclusions The observations indicate the follornring: The majority of avalanches that reached the floor of the main valley were caused by snoivfalls accompanied by strong westerly winds. The total snowfall was more than 12 in. and the new snow had a specific gravity between 0.04 and 0.08. The wind direction at 8000 ft obtained from the 700 mb chart was constantly west or southwest and at a speed greater than 30 mph over a period of three days. South winds did not appear to create an avalanche hazard. During the period 1957-1959 an avalanche occurred when the wind recorded at Rogers Pass Summit had a southwest direction and a speed of more than 13 mph. The size of the avalanche depends on the stability of the snow cover in the avalanche path. When not accompanied by any significant wind, heavy snowfalls of more than 36 in. can cause avalanches. These avalanches may not begin at the usual line below the cornice. CROS SOVEB AVALANCHE

J. P. Priollaud, a member of the avalanche observation station, investigated the conditions that caused the avalanches at this site from 1957 to 1959. Descri~tionof the Avalanche The site of the Crossover Avalanche is in the large cirque on the west side of Mount MacDonald (Fig. 24). The cirque opens northward and is enclosed by ridges with elevations near 8000 ft. The location where major avalanches begin could not be observed. It was assumed that the fracture is on the southwest part of the cirque and close to the ridge. Smaller avalanches have been observed from there and from the west side. Cornices on the west and southwest side of the cirque and slopes bare of snow on the other side of the ridge show that a considerable amount of snow is moved by the wind. Avalanches run through two gullies and enter the valley over a long, wide alluvial fan. Numerous avalanches occur at this site each winter. Major avalanches can cross Bear Creek and reach the highway. Medium-size avalanches stop in Bear Creek but the highway might be affected by the windblast. Minor avalanches stop on the alluvial fan at least 200 ft from Bear Creek. The studies cover only medium-size and major winter avalanches of dry snow which would be a hazard to the highway. They include: 1 avalanche in winter 1957-58 6 avalanches in winter 1958-59 2 avalanches in winter 1959-60 The study is based on snow and weather observatio~lsmade at Rogers Pass Summit, Mount Abbott and occasional special observations in the rupture zone of the avalanche. Conclusions The following could be deduced from the studies: Major avalanches occurred when the snowfall exceeded 16 in. (40 cm) in 24 hours, accompanied by strong southwest to south winds. Medium-size avalanches occurred after a total snowfall of 24 in. (60 cm) to 28 in. in three days and 12 in. (30 cm) during the third day with a strong southwest to south wind. 3. Minor to medium size avalanches were observed to be inconsistent with the above observations. These avalanches occurred after minor snowfalls of about 8 in., when earlier snowfalls did not have the opportunity to stabilize because of cold weather. Summary Major and medium-size danaerous avalanches are caused direcily by snowfalls accompanied by strong southwest to south winds. Cold weather can delay the natural stabilization of new snow and result in dry snow delayed action avalanches. A strong south or southwest wind is one that exceeds 8 mph at the observatory at Rogers Pass Summit. -0 GOLDEN CALGARY LEGEND

---- TRANS-CANADAHIGHWAY

tt+t+ CANADIANPACIFIC RAILWAY U MAINAVALANCHES

SCALE: /'& 2 MILES

MTABBOTT \ TO QEVELSTGZE\ AiVD VAACGUVER

FIGURE I ROGERS PASS WITH MAIN AVALANCHES Figure 2 Rogers Pass Summit, view from north and south, 2 March 1957. (X) Observatories Summit and Mount Abbott. Figure 3 Bear Creek Valley on the east side of Rogers Pass between Mount MacDonald (left) and Mount Tupper (right), 19 May 1957.

Figure 4 Side of Mount Tupper. The highway is located at the bottom of the picture, 14 March 1959. Figure 5 Illecillewaet Valley on the west side of Ro~ersPass. Glacier is in tse foreground, 1 February 1957. SOURCES: YEARS 1910- 1952 REPORTSFROM THE CANADIAN PACIFIC RAILWAY YEARS 1953-1960 AVALANCHE SURVEY DEPT. OF PUBLIC WORKS

FIGURE 6 NUMBER OF AVALANCHES AFFECTING THE RAILWAY LINE BETWEEN STONEY CREEK AND ILLECILLEWAET, 1910- 1960 Figure 7 Observatory Rogers Pass Summit, with test plot, instrument stand and shelter, 18 April 1958.

Figure 8 Upper Illecillewaet Valley with Camp Glacier in the foreground, 13 May 1958. Figure 9 Observatory on Mount Abbott, 29 December 1956.

Figure 10 East side of Balu Pass with observatory site (X), 19 May 1957.

FIGURE 12 FIELD RECORD FOR SNO'JV PROFILE 10 FEB 58

RAM RESISTANCE Kg

TEMPERATURE DEGREES C

SYMBOLS : H: HEIGHT ABOVE GROUND F: GRAIN SHAPE W: FREE WATER CONTENT R: SNOW HARDNESS D : GRAIN SIZE G : DENSITY

FIGURE 13 TYPICAL SNOW PROFILE

UPPER AVALANCHE - RUPTURE ZONE -

LOWER AVALANCHE - -

FIGURE 15 PROFILE OF A TYPICAL MOUNTAIN SLOPE AT ROGERS PASS Upper rupture zone

Lower rupture zone

Figure 16 Site of Cougar Creek Bvalanche showing the two rupture zones. OBSERVATIONSROGERS PASS SUMMIT

OBSERVATIONSILLECILLEWAET VALLEY

WEATHER FORECAST OBSERVATIONSMOUNTAIN OBSERVATORY \\ s OBSERVATIONSFROM PATROLS \\\

AVALANCHEWARNING SERVICE I I EVALUATESTHE AVALANCHEHAZARD I I J

t CONTROL OF ORDERS FOR AVALANCHEWARNING FOR AVALANCHE BULLETIN AVALANCHEWARNING AVALANCHES HIGHWAY HIGHWAY MAINTENANCE STAFF BY EXPLOSIVES CLOSURES FOR SKIERS FOR RAILWAY L

AT GOLDEN EAST GATE THROUGH RADIO WEST GATE AT REVELSTOKE AND EAST NATIONAL PARK STATIONS NATIONALPARK AND WEST

FIGURE17 ANTICIPATED ORGANIZATIONOF THE AVALANCHEWARNING Pigure 18 Illecillewaet Valley with Fidelity Mountain and observatory site (X), 1 February 1957.

Figure 19 Summit of Rogers Pass, view from west to east, with site of observatory Hermit (X), 1 March 1958. Figure 20 Mount Cheops, south side with observatory site (X), 4 February 1957. Figure 21 Platform stake. The vertical pole is graduated in inches for rough snow depth readings. IIlhe observer takes a sample of new snow for the density measurement.

Figure 22 Observations of the grain shape and grain size of the snow profile and recording the observations. The ramsonde is in the centre and the coloured threads can be seen on the right side. ------. - - -- . - . .-- -- .. Figure 23 Mount Green avalanche site, 15 March 1958.

Figure 24 Crossover avalanche site, 8 May 1958.