RECENT PROGRESS IN NORTH AMERICAN AVALANCHE
By E. R. LACHAPELLE
(United States Forest Service)
It is surprising that the disastrous avalanche winter of 1909-10 (Beals 3) did not create wider interest in avalanche defense measures. Public attention was especially directed to the problem by the Wellington tragedy near Stevens Pass, Washington, where 101 persons were killed by an avalanche which swept three trains off their tracks and into a canyon below (Hubbard 4). The passage of time quickly relegated avalanche problems to a few isolated mountain communities, and little active concern was found except at certain railroad passes, where snowsheds were the only common countermeasures. Eventually, two major trans-continental railroads, at Rogers Pass, British Columbia and Stevens Pass, resorted to tunnels to avoid the most serious dangers.
The modern development of avalanche control in the United States originated with the advent of skiing as a popular winter sport. Beginning in the winter of 1937-38, the U.S. Forest Service5 assigned men to full-time duty on snow safety problems in ski areas on National Forest lands. Such work was mostly administrative until 1946, when a study pro gram for the development of instruments and techniques for avalanche forecasting and control was established at Alta, Utah. This period coincided with the post-war dissemination
of information concerning the more fully developed European avalanche techniques, particularly those from Switzerland. Surveys of snow and avalanche problems in the U.S. and Canada were made at this time by de Quervain6 in 1948-49 and by Roch7 in 1949. The latter assisted in organizing the avalanche program of the Forest Service. More recently, Fuchs8 working with the U.S. Army Corps of Engineers, has assessed the state of avalanche control work in the United States.
In the past decade progress has been rapid, reflecting an increasing
interest by State and Federal agencies as well as by private corporations in active
methods of preventing or con trolling avalanches. The success of these techniques in the
ski areas served to illuminate the practicality of avalanche control on highways and
railroads where snow dangers had for years been regarded as an inescapable force of
nature. In 1950 the U.S. Forest Service was the only organization in North
America engaged in full-time work on avalanche problems each winter. The National Ski
Patrol System, a volunteer organization, cooperated on a part-time basis in certain
localities. Today the number of organizations so concerned is large and growing each year.
This present activity is summarized below in Part II, wherein are listed the agencies and
locations known to be engaged in or planning avalanche fore casting and/or control.
PART II-ORGANIZATIONS ENGAGED IN AVALANCHE WORK
An intensive training program has been in operation since 1949,designed primarily for Service personnel, but it is also utilized widely by the National Ski Patrol System and other Government and private agencies.
(2) The ski patrols are in many areas active participants in avalanche work. The National Ski Patrol System requires rescue training of all its fully qualified patrolmen, which has served to form a nucleus of competent avalanche rescue personnel in the United States. In some localities NSPS men conduct such active control work as artificial release by blasting.
Professional patrols at certain major ski resorts where avalanche hazard exists, such as Aspen, Colorado and Sun Valley, Idaho, undertake routine avalanche control. Training of both these and the volunteer patrols is coordinated closely with the Forest Service.
(3) The Colorado Highway Department has used artillery fire to reduce highway avalanche dangers for the past decade. A 75 mm. mountain howitzer is stationed in the Loveland Berthoud Passes area (Front Range), and a second similar weapon is used in the Silverton Durango-Ouray region of the San Juan Mountains. Artificial avalanche release to reduce hazard is a routine task, but blind firing as a preventive measure has not yet been undertaken.
Experimental installations of avalanche defense structures have been made by this Department near Loveland Pass. Wind baffles (Kolktafeln) and snow fences for deposition control have been in place for several years. More recently a diversion barrier has been installed on the outrun of the Bethel Mountain Slide. A snow and weather observation station to aid in hazard forecasting has been operated intermittently near Loveland Pass.
(4) The Washington State Highway Department has experimented with artificial avalanche release by blasting at Stevens Pass, but this has not yet become fully established as a routine measure. Two large snowsheds have been constructed near Snoqualmie Pass to provide avalanche protection for a major four-lane highway.
(5) The United States Bureau of Public Roads organized a program of avalanche investigation and control in 1957 for certain dangerous areas in Alaska. The principal site for this work has been Girdwood, Alaska, where both an important highway and a railroad are threatened by a series of avalanche tracks. An observation station with a full schedule of snow, weather and avalanche records is in operation at Girdwood. A number of successful installations of avalanche breaker mounds have been made here and at other sites near Anchorage, Alaska. Some use has been made of artillery fire in cooperation with the U.S. Army. Weather and avalanche occurrence records have been initiated in areas where future highway construction is proposed.
(6) The Government of Canada has begun the first large-scale study of avalanches in that country while planning for construction of the new Trans-Canada Highway through the Selkirk Mountains of British Columbia. Collection of snow, weather and avalanche records began at Rogers Pass in 1955,and has continued to date. Tests have been made of defense installations and artillery fire in preparation for the opening of the new highway scheduled by 1961.The most dangerous sections of this highway will be protected by snowsheds. Rogers Pass probably is the most difficult highway avalanche problem in North America at the present time, and a full range of protective measures from defense structures to routine artillery fire is planned.
(7) On 26 January 1955 an avalanche near Kildala Pass, British Columbia, destroyed three towers of the Kitimat-Kemano power transmission line serving the Aluminum Company of Canada's major aluminum smelter at Kitimat, B.C., and interrupted service for nine days. The protective measures designed for this power line to prevent repetition of such a costly interruption probably represent one of the largest expenditures to date on completed avalanche defenses in North America. Largely utilizing helicopters, a cross-valley suspension system was installed, supporting the transmission line completely free of the avalanche paths (White9). Towers on other sections of this line also receive protection from diversion barriers and V-shaped deflectors constructed of heavy rubble. Experience over several winters has proven these barriers to be very effective.
(8) The United States Army Corps of Engineers has sponsored a continuing series of investigations on snow stratigraphy in relation to avalanche formation at Berthoud Pass, Colorado (Borland10). In the winter of 1955-56 this agency engaged in a cooperative investigation of explosives in snow with the United States Forest Service.
(9) The National Park Service is confronted with avalanche hazard during the annual spring snow-clearing operations to re-open a highway over Logan Pass in Glacier National Park, Montana. Experiments are currently under way to reduce or control the occurrence of wet spring slides which endanger the highway crews. A test of artillery fire is scheduled for May 1960 and a new technique has been tested to encourage winter avalanching to relieve the snow burden on the mountain sides. (See Part III below.)
(10) The California Highway Department is planning the use of artillery to reduce avalanche hazard on U.S. Highway 50 across the Sierra Nevada Range. Such work is presently done by cooperative agreement with the U.S. Forest Service on Highway 40 in this same region.
(11) The Nevada Highway Department is planning an avalanche control program for an endangered section of highway on Mt. Rose, Nevada.
(12) A system of avalanche fences to protect the Southern
Pacific Railroad main line near Donna Summit, California, is in the design stage.
PART III-PROGRESS IN TECHNIQUES
Portable weapons are used in a number of areas for highway protection, as mentioned above in Part II. Recently permanent, fixed, installations of recoilless rifles have been made at Squaw Valley, California and at Alta. The gun tower for a 105 mm. rifle at Alta is illustrated in Figure I, p. 685. Such fixed gun mounts permit establishment of accurate blind firing data and consequent improvement in control and preventive measures.
Alta and, more recently, Squaw Valley, are the only locations where blind firing has become an established routine. By thus preventing avalanche build-up during storms, and by routine firing at avalanche slopes after every major snowfall whether a serious hazard exists or not, a very marked gain in safety through avalanche prevention has been achieved. Slopes at Alta which formerly yielded frequent large avalanches are now only rarely active as a result of routine and regular artillery fire.
(2) Defense Structures
Systems of earthen mounds designed to arrest the fall of avalanches have been successfully used in Alaska, following the style of construction developed in Austria. Of particular interest is one such installation near Girdwood, Alaska, which is on a slope steeper than usually considered suitable for mounds. This has proved quite effective in arresting wet slides common to this area. An experimental installation of mounds has also been made near Rogers Pass, British Columbia (Schaerer11), and Red Mountain Pass, Colorado. See Figure 2.
A large diversion barrier near Loveland Pass, Colorado has recently accomplished its designed purpose by deflecting a large avalanche away from an important transcontinental highway.
A series of experiments has been conducted at Berthoud Pass and Loveland Pass by the Colorado Highway Department and the U.S. Forest Service to test the effectiveness of wind baffles (Kolktafeln). To date these have proven to have only limited value in this area, where wind action is especially intense. Fences for drift control have also been installed in connection with the experiments.
Reforestation measures, either separately or in association with defense structures, have not yet been introduced, though there exists wide scope for such measures.
(3) Avalanche Signal Installation
(4) Weather Telemetering
(5) Hazard Forecasting
Forecasting techniques in use by U.S. agencies are based primarily on the empirical methods outlined by Atwater (see U.S. Forest Service5), strongly reinforced by personal experience of the various forecasters in different areas. The analysis of contributory factors has proved a sound means of evaluating slide hazard, particularly for slab avalanches which fall during or immediately after heavy snowfalls. Such evaluations constitute a forecast when they are projected into the future on the basis of mountain weather forecasts. Difficulty in obtaining accurate mountain weather predictions over the widely scattered ranges of the West has been one of the principal obstacles to accurate hazard forecasting.
The basis for advances in the use of explosives in snow was laid by a cooperative investigation initiated jointly by the Forest Service and the Snow, Ice and Permafrost Research Establishment. Results of these studies, dealing mainly with the fracturing and disruptive effects of different blasting agents, have been reported by LaChapelle14 and Fuchs.l5
An interesting practical test in avalanche release was begun in the winter of 1959-60 by the National Park Service in Montana in connection with the highway problem described in Part II. An effort is being made to reduce the spring slide activity by encouraging winter avalanching to relieve some of the snow burden on the slopes. Trigger mechanism used is the sonic boom from low-flying jet aircraft. Through cooperation with the U.S. Air Force, low level winter flights over this area have been made by F-106 Delta Dart aircraft at speeds up to Mach 1.2. These aircraft have made aimed supersonic dives at selected target areas in order to concentrate the effects of the shock wave. Ground observers have witnessed a number of slab avalanche releases on these occasions which indicate that the sonic boom is a powerful triggering force (Edgar16).
The U.S. Army Corps of Engineers has supported investigations of snow
stratigraphy in relation to slab avalanche formation, mentioned above in Part II. These
have yielded a large body of information of ram profiles typical for slab avalanches as
well as a detailed record of weather conditions contributing to the stratigraphic
evolution (Borland, op. cit.).
The Snow, Ice, and Permafrost Research Establishment has translated a number of important technical works on snow, avalanches and avalanche defense construction which are available in limited circulation to Government agencies. The National Research Council of Canada also made available some reports and translations in this field.
MS. received 31 March 1960
2. Muckleston, H. B. A short description of the Canadian Pacific Railway through the Selkirks. (In Wheeler, A.O. The Selkirk Range. Vol. 1. Ottawa, Canadian Government Printing Office, 1905.)
3. Beals, E. A. Avalanches in the Cascades and northern Rocky Mountains during winter of 1909-1910. U.S Weather Bureau. District No. 12. Climatological Summary, June 1910, p. 4-10.
4. Hubbard, F. Avalanche. Argosy, March 1959, p. 60-61, 96-l00.
5. U.S. Forest Service. Avalanche handbook. Washington, D.C., U.S. Government Printing Office, 1952.
6. Quervain, M. R. de. Snow and ice problems in Canada and the U.S.A. Canada. National Research Council. Division of Building Research. Technical Report No. 5, 1950.
7. Roch, A. Report on snow and avalanche conditions in the U.S.A. Western ski resorts from the 26th of January to the 24th of April 1949. Swiss Federal Institute for Snow and Avalanche Research. Report No. 174, 1949.
8. Fuchs, A. Avalanche conditions and avalanche research in the United States. U.S. Snow, Ice and Permafrost Research Estab1ishment. Report 29, 1955.
9. White, H. B. Cross suspension system Kemano-Kitimat transmission line. Engineering Journal, Vol. 39, No. 7, 1956, p. 901-11, 926.
10. Borland, W. M. Investigation of snow conditions causing avalanches. U.S. Army. Corps of Engineers. Interim Reports 1-7, 1953-59.
11. Schaerer, P. The planning of the avalanche defense for the Trans-Canada Highway at Rogers Pass. Proceedings. Western Snow Conference, . . . Santa Fe, N. M., April 1960. [In press.]
12. Atwater, M.M. The relationship of precipitation intensity to avalanche occurrence. Proceedings. Western Snow Conference, 20th annual meeting, 21 and 22 April 1952, . . ., p. 1l-l9.
13. Atwater, M.M., and others. Avalanche research: a progress report. Parts 1-2. By M. M. Atwater, E. (R.) LaChapelle, R. M. Stillman and F. M. Foto. Appalachia, N.S., Vol. 20, No. 12, 1954, p. 209-20; N.S., Vol. 21, No. 7, 1955, p. 368-80.
14. LaChapelle, E. (R.) Some effects of high explosives on snow: a report on preliminary investigations. U S. Forest Service. Internal Report, May 1956.
15. Fuchs, A. Effects of explosives on snow. U.S. Snow, Ice and Permafrost Research Establishment. Special Report 23, 1957.
16. Edgar, M. Personal communication, 1960.