Journal of GladololD'. Vol. 26. No. 94. 1980

CREDIBILITY OF AVALANCHE WARNINGS

By KNOX WILLIAMS

(Rocky Mountain Forest and R ange Experiment Station, 240 West Prospect Street, Fort Collins, Colorado 80526, U.S.A.)

ABSTRACT. Avalanche warnings can provide a valuable public service. To be effective, the warning program must inspire public confidence. Experience gained from the Colorado Avalanche Warning Program is used to develop guidelines for establishing and maintaining credibility. The topics discussed are the requirements for a good forecaster, the working relationship between forecaster and field observers, relations with the news media and the public, and forecast accuracy.

RESUME. CrUibilile des previsians d'avalanches. La prevision d'avalanche peut rend re au public un reel service. Pour et re efficace, la prevision doit inspirer confiance au public. L'experience du programme de prevision d'avalanche du Colorado perm et d'emettre des directives pour conqueri r et garder la credibilite. On discute les qualites d'un bon previsionniste, les relations de travail entre le previsionniste et les observa­teurs sur le terrain, les relations entre les media d'information et le public, et la precision des previsions.

ZUSAMMENFASSUNG. Glaubwiirdigkeit van LawinelZwarnllngen. Lawincnwarnungen konnen von gross em Wert fUr die Offen tlichkeit sein. Urn beachtet zu werden, muss ein Warnprogramm offentliches Vertrauen geniessen. Erfahrungen aus dem Lawinen-Warnprogramm von Colorado werden zur Aufstellung von Richtlinien fur die Begrundung und Aufrechterhaltung van Glaubwurdigkeit herangezogen. Zur Diskussion stehen die Anforderungen an einen guten Vorhersager, die Arbeitsbeziehungen zwischen Vorhersager und Feldbeobachtern, die Verbindung zu den Nachrichtenmedien und die Offentlichkeit sowie die Genauigkeit der Vorhersage.

INTRODUCTION

An effective avalanche warning program can be of benefit to a wide audience, including ski-area operators, backcountry recreationists, motorists, highway maintenance crews, construction crews, and mining companies. The obvious benefit is to minimize injury, loss of life, and property losses . The Colorado Avalanche Warning Program (CA WP) has operated formally for five years and informally for twice that time (] udson, J 976; Williams, 1978). CA WP consists of a central forecast office in Fort Collins and approximately 30 manned observation sites (and several unmanned sites) spread over roughly 100000 km 2 of the Colorado Rockies. It employs the concept of central forecasting also adopted in Switzerland and in the Cascade Range of Washington and Oregon (LaChapelle and Fox, 1974). In these programs, field observers telephone daily reports to the headquarters forecast office where the forecaster analyzes the data and issues warnings when conditions warrant. The other option, that of having each observation site do its own forecasting for its immediate local area (on the order of 100- 1000 km2), has merit but lacks the coordination of central forecasting, a valuable asset. However, there is an upper areal limit of roughly 200000 km2 that can be adequately handled from one office.

The key to successful avalanche forecasting lies in the collection of accurate and timely data from the field coupled with good decision-making by experienced forecasters. A well­coordinated network and decision-making process is a necessary foundation for the establish­ment of a credible warning program. The emphasis in this paper is on those factors that produce credibility (and therefore success) in avalanche warnings.

SKILLS OF THE FORECASTER

A good forecaster must understand avalanches. A background in glaciology, physics, or geology is helpful, but actual experience is essential. Specifically, he should be able to recognize developing stability pa tterns before significant events occur. Experience in synoptic meteorology is also required, whether it is used to make weather forecasts or to obtain them from professional weather forecasters.

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An avalanche forecaster must be articulate, for he speaks regularly with field observers and weather forecasters and frequently to the press, who require telephone-taped interviews for broadcast. The ability to write well is needed for him to compile clear, precisely worded avalanche-warning messages. The job also requires an organized individual who logs and analyzes data faithfully, and who is then firm in his decision-making.

Several field skills also are needed. The forecaster must know his mountains. This enables him to talk more knowledgeably with his field observers and allows him better to define hazard areas. He should also be able to ski reasonably well in all terrain.

FORECAST ACCURACY

A warning program can have all the proper ingredients that would normally ensure success but if weather and avalanche forecasts are not accurate and reliable, credibility will erode. Therefore, the first priority in budgeting should go to equipment and training which will improve forecast ability.

Forecast weather conditions account for about half of the avalanche forecast; the remainder are the snow-pack factors. Heavy precipitation and wind are the weather factors that contri­bute most to avalanche formation in Colorado. In addition to conventional forecast skills, CA WP has the additional benefit of an objective aid for quantitative precipitation forecasts. This numerical model, which was developed specifically for use in the Colorado mountains, predicts amounts of orographic precipitation at specific sites (Rhea, 1978). When applied with good prognostic weather data, this model is exceptionally accurate in its quantitative precipitation forecasts. As a result, the forecaster can more confidently provide a service to his field observers that the National Weather Service cannot provide.

Now, let us consider the avalanche forecast. There are three types of avalanches which are forecast: direction-action avalanches, delayed-action avalanches, and wet avalanches. Direct­action * avalanches occur during or just after a storm and result from loading by falling or blowing snow; they account for roughly 80 % of all avalanches. Delayed-action avalanches occur during non-storm periods and result from stress build-ups within the snow-pack; they account for roughly 5 % of all avalanches. Wet avalanches occur during rapid warm-ups especially in the spring and result from stress due to thaw and free-water percolation; they account for roughly 15 % of the avalanche total. Fortunately for the forecaster, direct-action avalanches are the easiest to forecast, mainly because they involve a prediction of estimable meteorological factors. Delayed-action and wet avalanches are more difficult to forecast mainly because of the inability to calculate snow-pack stresses.

There is a large subjective component in avalanche forecasting which can lead to problems of uneven forecasting over the course of a winter or unequal treatment of a given avalanche situation by two different forecasters. Consistency and credibility would be enhanced if more objectivity could be introduced into the decision-making process. A numerical predictive model would be a valuable aid and research is proceeding on such a model (J udson and others, 1980) . Another step toward objectivity is to define and standardize categories of avalanche hazard. One such scheme employed by CA WP and the Cascades warning program is shown in Table 1. In using this scheme, the normal day-to-day hazard is low to moderate. The avalanche forecaster issues a weekend advisory notice under these conditions. He issues an avalanche warning when the hazard moves into the high or extreme categories. Admittedly, there is still the possibility of subjective interpretation of these categories, but with further experience, their definitions should become better.

• This long-standing terminology may be due for a change to more definite terms. One suggestion is storm­induced (or simply storm) and non-storm for direct-action and delayed-action, respectively.

CREDIBILITY OF AVALANCHE WARNINGS 95

There are other considerations in forecast accuracy that contribute to credibility. Good timing is required for the initiation and termination of warnings. Warnings initiated too late or terminated either too soon or too late will damage credibility. Similarly, the "false-alarm rate", defined as the number of misses (warnings that did not verify) divided by the number of warning episodes, should be low to avoid the "cry wolf" syndrome. Ideally, the false-alarm rate should be zero for a large number of cases. In practice, however, a value slightly greater than zero is desirable, based on the premise that slight overforecasting is a better public service than underforecasting.

TABLE I. AVALANCHE HAZARD CLASSIFICATIONS

Hazard conditioll

Low

Moderate High Extreme

SIlOW

conditioll

Mostly stable

Areas of instability Mostly unstable Widespread instability

RELATIONS WITH FIELD OBSERVERS

Avalanche likelihood on steep snow-covered open slopes and

gulleys

Unlikely except in isolated pockets

Possible Likely Certain; large destructive

avalanches are possible

Backcountry travel

Generally safe

Caution necessary Not recommended Should be avoided

Since CA WP field sites are manned mostly by volunteers, the forecaster must maintain a good working relationship with the observers. He must be available often and respond to the observers' needs. The CA WP operates on a quasi-24 h basis seven days a week (the forecast office is manned 9 to 10 h per day and a recording telephone is used for the remaining hours) so that the observers have ample opportunity to talk directly with the forecaster. The job requires periodic travel into the field so that the forecaster may work directly with the observers. The forecaster must provide training, supplies, and instruments for making observations. The forecaster also provides each observer with a daily weather forecast and resulting snow-stability trends. Obviously, the better the forecasts, the higher the credibility in the program.

RELATIONS WITH THE NEWS MEDIA

A credible warning program spreads the news of dangerous avalanche conditions to the media and the public quickly. ] udson ( 1975) covers the content and dissemination of warning bulletins thoroughly, but a few points of advice bear repetition.

Bulletins must be accurate and timely. Warnings must be issued before serious avalanching has been reported by the press. A warning issued after news releases of several serious accidents damages credibility, since the press and public will correctly realize that the warning should have been issued earlier. Bulletins should be timed so as to receive maximum media coverage. In Colorado, 11.00 and 16.00 h are the optimum release times, just before the noon and evening television- and radio-news broadcasts.

Bulletins should be carefully worded so that there is no misunderstanding in the area or duration of coverage. Bulletins should be believable and interesting; it helps to support generalizations with examples, and this can include the citation of snow-fall amounts, excessive wind speeds, numbers of avalanches, and any avalanche accidents.

It is also helpful to establish personal contact with the media personnel. A general availability and willingness to provide telephone interviews greatly enhances credibility with the press.

96 JOURNAL OF GLACIOLOGY

RELATIONS WITH THE PUBLIC

In Colorado, the public normally learns of dangerous avalanche conditions through news broadcasts. In a few locations, the public can telephone to receive a recorded message of current snow and avalanche conditions or can receive updated information via National Weather Service v.h.f. radio broadcasts. The avalanche forecaster has the responsibility not only for the forecast, but also of making sure that the message reaches the public and is up­dated as frequently as conditions change.

Educating the public in order to increase its avalanche awareness is the most important action that can be taken to reduce avalanche fatalities. This problem is compounded by many mountain users who do not live in the mountains but make occasional trips there mostly for recreational purposes. Too often the avalanche victim never realizes that a danger exists. One way to increase avalanche awareness is to present lectures and slide shows tailored to the needs of the audience. By educating the public, the avalanche forecaster builds credibility and thereby increases the effectiveness of the avalanche-warning program.

SUMMARY

The credibility of an avalanche-warning program depends on several factors. Internally, the field observers must have confidence in the forecaster. The forecaster must supply accurate forecasts, be capable of proper decision making, make himself available often, and respond to the needs of the observers. Failure in any of these responsibilities results in an erosion of credibility within the program, with the emphasis being on forecast accuracy. To be correct often shows that the forecaster has the skills and tools necessary for the job. Thus, his judgment will be respected, his credibility high.

The forecaster needs to establish a working relationship with the press and issue accurate, timely, well-worded, and interesting warning bulletins. Avalanche warnings can provide a valuable public service. The better educated the public, the greater the effectiveness of the warning program. The forecaster can help his own program by presenting avalanche aware­ness lectures to groups involved in winter work or recreation.

REFERENCES

Judson, A. 1975. Avalanche warnings: content and dissemination. V.S. Dept. of Agriculture. Forest Service. Research Note RM-291.

Judson, A. 1976. Colorado's avalanche warning program. Weatherwise, Vol. 29, No. 6, p. 267-77. Judson, A., and others. 1980. A process-oriented model for simulating avalanche danger, by A. Judson, C. F.

Leaf, and G. E. Brink. Journal of Glaciology, Vol. 26, No. 94, p. 53-63. LaChapelle, E. R., and Fox, T. 1974. A real-time data network for avalanche forecasting in the Cascade Moun­

tains of Washington State. (In Santeford, H. S., and Smith, J. L., comp. Aduanced concepts and techniques in the study of snow and ice resources. Washington, D.C., National Academy of Sciences, p. 339-45.)

Rhea, J. O. 1978. Orographic precipitation model for hydrometeorological use. Colorado State Uniuersity. Atmospheric Science Paper No. 287.

Williams, K. 1978. The Colorado avalanche warning program. Canada. National Research Council. Associate Committee on Geotechnical Research. Technical Memorandum No. 120, p. 116--31.

Journal of Gladology, Vol. 26, No. 94, 1980

THE UNIVERSITY COURSE IN SNOW DYNAMICS-A STEPPING-STONE TO CAREER INTERESTS IN AVALANCHE

HAZARDS

By JOHN MONTAGNE

(Department of Earth Sciences, Montana State University, Bozeman, Montana 5971 7, U .S.A.)

ABSTRACT. The principles of snow dynamics, including practical field work, constitute a feasible university-level course where seasonal snowfall and terra ne of varying steepness are accessible. Two to three lectures or discussions per week are combined with one full afternoon in the field to provide a workable course format. We have successfully used the V.S. Departme/lt of Agriculture Forest Service Agriculture Handbook 489 (Avalanche handbook) as a text but also assign readings in diverse world literature.

Field work has centered on standard techniques for snow study in a realistic alpine setting but could easily be adapted to more simple "roadside" conditions if necessary. Student interest during and following the course usually leads to spontaneous and practical research that tends to develop life-long skill and application in the subject.

Our experience indicates that one instructor can manage a maximum of 25 students in the field, con­sidering proper logist ics, safety, and necessary adapt ibi lity of field procedures to changing weather conditions.

REsuME. Les cours universitaires de dynamique de la neige-1II1 marchepied vers les carricres de privision du risque d'avalanche. Les principes de la dynamique de la neige, y compris les travaux pratiques, font I'objet de cours universitaires dans les regions ou se trouvent une chute annuel le de neige d'une certaine importance et un terrain accidente. Un bon format pour un tel cours consisterait en deux ou trois conferences par semaine suivies d'un apres-midi sur le terrain. Comme texte, no us nous sommes servis avec succes Vnited States Department of Agriculture Forest Service Agriculture Handbook 489 (Avalanche handbook) mais nous exigeons aussi des lectures de toutes sortes dans la litterature mondiale.

Les travaux pratiques se basent sur les techniques classiques des etudes de la neige dans un site alpin realiste mais ils pourraient facilement s'adapter a des conditions plus simples "au bord de la route" si necessaire. L'interet des etudiants pendant et apres le cours sou vent les mene a faire des recherches spon­tanees et pratiques, ce qui peut leur donner une habilite et une application dans ce domaine qui dureront toute la vie.

D'apres nos experiences, le nombre maximal d'etudiants ne doit pas depasser vingt-cinq pour des raisons de logistique, de securite et de possibilite de s'adapter a ux changements meteorologiques.

ZUSAMMENFASSUNG. Der Vniversitiitskurs in Sclmeedynamik - eine Stufe ;tur Ausbildung in der Lawinenforschung. Die Grundlagen der Schneedynamik, einschliesslich praktischer Feldarbeit, behandelt ein Kurs auf Universitiitsebene, wobei jahreszeitlicher Schneefall sowie Geliinde verschiedener Steilheit zur Verfugung stehen. Zwei bis drei Vorlesungen oder Diskuss ionen pro Woche sind mit einem Nachmittag im Geliinde kombiniert, urn ein brauchbares Kursprogramm zu bieten. AIs Grundlage wurde das V.S. Department of Agriculture Forest Service Agriculture Handbook 489 (Avalanche handbook) erfolgreich benutzt, ebenso aber verwandte Texte der internationalen Literatur.

Die Feldarbeit hat sich auf bestimmte Techniken des Schneestudiums in naturlicher alpiner Umgebung konzentriert, kann aber, falls notwendig, ebenso einfacheren lokalen Bedingungen angepasst werden. Studentisches Interesse wiihrend des Kurses und danach fuhrt gewohnlich zu spontaner und praktischer Forschungsarbeit, die dahin tendiert, Kenntnisse und Erfahrungcn fur eine lebenslange Tiitigkeit auf diesem Gebiet zu entwickeln.

Die Erfahrung zeigt, dass ein Dozent mit hochstens 25 Studenten im Geliinde arbeiten kann, unter Berucksichtigung angemessener Unterbringung, Sicherheit und notwendiger Anpassung der Feldarbeit an die wechselnden Wetterverhiiltnisse.

INTRODUCTION

For the past 17 years, Montana State University in Bozeman has offered an elementary four-credit course in snow dynamics conducted during the winter university quarter. Its purpose is to provide a thorough background in snow-hazard and management procedures, and to acquaint students with loca l and international scientific snow research. The course received its initial impetus from college students serving on local ski patrols who desired more depth of knowledge than could be gained through voluntary evening and week-end work sessions. Initially, the course was centered on purely scientific aspects of snow but excluded safety, rescue, and snow hazards. More recently, some disaster and safety subjects have been incorporated, improving the practical and applied aspects of the course, and therefore

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sharpening the interest in it. The course meets for 2 hours per week in lecture and discussion, and involves one complete afternoon laboratory per week in on-snow field work.

The course is limited to 25 upper-class students of diverse curricula who can demonstrate that snow dynamics has a practical application in their future and who have the ability to negotiate steep alpine terrane, usually by means of down-hill skis. Lately, the down-hill skills of cross-country skiers have improved and cross-country skis have been allowed. There is usually a waiting list for the course, indicating the general interest in snow dynamics in this part of North America. Although academic preparation in physics, chemistry, and geology is of help, there are no prerequisite courses.

The proximity of the Bridger Range, where excellent avalanche terrane can be experienced 30 km from Bozeman, enhances and expedites the necessary field work.

COURSE MATERIALS AND PROCEDURES

The subject matter for the course more or less follows the sequence of the new U.S. Depart­ment of Agriculture Forest Service Agriculture Handbook 489 (Avalanche handbook) by Perla and Martinelli (1976) . This text serves as an authoritative reference with excellent illustrations. Supplemental readings are assigned from many well-known publications including those of CRREL, U.S. Forest Service, the International Glaciological Society, and standard research works from Switzerland, Austria, France, Canada, and Japan. Of particular interest are those articles published in conjunction with various meetings of the International Association of Scientific Hydrology.

The lecture sequence is developed around the following outline:

World literature on snow. Several approaches to snow analysis: "internal" vs "external" to the snow-pack. Snow crystallography: the influence of weather and other environmental factors on snow

metamorphism. The response of snow to gravitational stress: creep, glide, fracture, avalanche phenomena. Critical factors in stability evaluation; storm case histories. Instruments and measurements. Passive and active methods of control of snow movement and accumulation. Special effects of wind: drifts, slabs, cornices. Avalanche zoning for highways, development, and recreational activities. Snow management for recreational areas and highways; grooming machinery and

procedures. Research in progress: local, national, world-wide. Avalanche safety and rescue.

The field sequence is approximately as follows (note: flexibility is advised for this phase in order to accommodate observation of avalanches, and take advantage of chance visits of visiting scientists. Varying snow-touring conditions should also be co-ordinated with field exercises) :

First week,' terrane analysis in the central Bridger Range area with emphasis on snow accumulation and movements, vegetative scars and patterns, and slope angles.

Second week,' terrane analysis in the northern Bridger Range area; demonstration of ram penetrometer, resistograph, snow-pit techniques; first snow-pit analysis.

Third week,' terra ne analysis in the south Bridger Range area; the study of snow conditions with respect to the directional aspect of slopes.

Fourth week,' the effects of wind on snow; inspection of snow-cornice sites, drifts and changing snow depths, cornice- and drift-control devices.

UNIVERSITY COURSE IN SNOW DYNAMICS 99 Fifth week: snow-management procedures; the problems of machinery; crowd control

under hazardous conditions at large ski areas; trail systems and slope routing for most efficient use of up-hill transportation.

Sixth week: revisit snow-pits and make comparative observations; snow-photography demonstration; snow-safety procedures; rescue beacons; special field experiments.

Seventh week: use of instruments and snow-pit in making stability evaluation for the day; the "snow-column isolation" experiment (see description below).

Eighth week: research in progress; work on individual research projects; special field experiments.

Ninth week: exploration and evaluation of selected avalanche terrane in adjacent mountain areas; the effects of spring weather conditions on snow in general.

SPECIAL FIELD DEMONSTRATIONS AND RESEARCH DEVELOPED DURING COURSE

Snow-column isolation experiment

One of the most useful experiments during the field phase of this course follows a procedure suggested by E. R. LaChapelle and developed by C. C. Bradley for testing the snow resisto­graph (Bradley, 1968). The procedure was designed to gain confidence in obtaining the ratio of snow strength to snow load above the weakest layer in a malure snow-pack as measured by

Fig. I. Isolated snow column ready to be undercut along its weakest strata by saw (shown).

100 JOURNAL OF GLACIOLOGY

the snow resistograph (Bradley and Bowles, 1967). Students can determine the profile for compressive strength of the snow column using either the resistograph or the ram penetro­meter. Following this, the load above the indicated weak layer is determined by means of the Mount Rose snow sampler. The research team then isolates a column of snow I m square using shovels (Fig. 1). The predetermined weak layer is located in the column and undercut by sawing from two sides on the column toward its center. (A crude large-toothed home-made wooden saw is used for this.)

Finally, careful manipulation will nearly always demonstrate that the column will collapse in the weak layer when the weigh t of the column per unit area is somewhat less than twice the indicated strength per unit area. The dynamic nature of this experiment and the clear demonstration that it is possible to measure snow strength quantitatively with instruments contributes a fascination that always attracts students' interest and attention.

In addition to demonstrating the validity of this instrument, the experiment is directed towards the ultimate use of the resistograph as a means for predicting slab avalanches origina­ting from load collapse. In spite of difficulties (Perla, 1977), the shear frame has been suggested as a valid way for determining the most "unstable" layer in the snow-pack (Quervain, 1950; Roch, 1966) and could well be incorporated in this teaching situation.

Cornice dirt-band exercise

Dirt bands and textural changes in the snow can be used to demonstrate the history of snow deformation and cornice accretion (Fig. 2) in transects perpendicular to the long side of a cornice. Dirt bands tend to diverge towards the leading edge of the deformed cornice wedge, indicating that cornice accretion is accompanied by continual down bending, and that hollows can be perpetuated within the leeward areas of cornices as each successive cornice wedge bends downwards. Stakes planted vertically in the growing cornice wedge tend to lean down-hill in time as a result of this distortion.

Jet-roof experiment

Miniature or full-sized jet roofs can be erected up-wind from cormces to deflect and accelerate the wind and thus reduce the cornice.

Roe K

CORNICE

DIRT BANDS

Fig. 2. Typical ridge-top cornice with various generations of deformed wedges. Dirt bands (dashed) diverge towards the leading edge, indicating that deformation was conCllrrent with accretion of wedges.

UNIVERSITY COURSE IN SNOW DYNAMICS 101

Standard snow-pit exercise

Well-known techniques for the study of snow-pit data are always basic to field work. Temperature variations, densities, textural and crystallographic changes, weak and strong layers are among the usual observations. In addition, by isolating a column 0.5 m square and by placing body pressure against this column, the column usually breaks along the bedding of a weak layer. The strength of the weak layer can be quantitatively measured by means of a shear frame as described by the Schleiss brothers in Canada (Schleiss and Schleiss, 1970).

Stability evaluation exercise

Standard instruments for measuring wind speed and wind direction through time, temperature and barometric trends, and snow depth and load are observed by students. Coupled with on-site inspection of snow conditions, a stability evaluation is possible, and practical experience in standard avalanche prediction has proven to be a completely workable and interesting phase Of the field work. An instrument array is usually available at first-class ski areas, and if not, the necessary instruments can be purchased for less than $800.

The number of interesting illustrations of natural snow phenomena in a given area is only limited by the scope of the imagination. In fact, an alpine setting is not absolutely necessary for applicable examples. The creep of snow down an automobile windshield with resultant folds and tensional gaps is a worthwhile simulation of glide on snow slopes. Also, simple stakes or plexiglass tubes planted in sloping snow can demonstrate creep and glide through time. Rills formed in new snow during warm conditions are always interesting and tend to become inverse with time. Complex dune fields develop on local snow-fields, and a variety of forms that simulate mountain-top conditions can be seen in most road "borrow pits". It is not necessary to have a wealth of equipment to design a course around such interesting simple natural occurrences as these.

RESEARCH OUTGROWTH

Interest generated in many diverse phases of snow study during the course has led in some cases to fruitful research either during or following the course experience. In many cases, such activities have stemmed from the imperfections in the state-of-the-art instruments and systems used during the course. One good example may suffice to illustrate that an initial course experience may be the seed that brings about further important scientific accomplishment.

Three students, T. Rayne, A. Satterlee, and G. Findell, found that multiple temperature readings could not be efficiently obtained in deep snow using common methods without digging a snow-pit for each set of readings. While granting the necessity for initial stratigraphic-temperature observations in a local snow-pit, obtaining multiple temperature readings in this way was so slow that it increased the odds for becoming involved with dangerous snow-slides on steep slopes. They, therefore, designed an instrument for rapid determination of snow temperature. With a small grant they built a wood-supported platinum tipped probe and wired it to a Wahl digital meter designed for accuracy to the nearest o. I deg. They have found that a 10 cm interval heat curve can be obtained in 10 ft (3 m) of snow in less than 3 min without digging, and the prototype of the instrument, which is very field portable, is a success. In concept, the temperature probe is not new. Thams (1945) reported using one over 30 years ago. However, the rechargeable digital read-out machine plus the sensitivity of the platinum probe make this latest model worth mentioning.

Other typical student research includes such subjects as a comparison of plant communities and substrates of avalanche and non-avalanche areas in south-central Montana (Eversman,

102 JOURNAL OF GLACIOLOGY

unpublished), a snow-engineering handbook (Burroughs, unpublished), the effects of trees on the snow-temperature profile (personal communication from A. Satterlee, 1978), the use of dyes to bring out the stratigraphy of the snow-pack (personal communication from R. Lang, 1979), or the comparison of effects of compacted snow with non-compacted snow.

The creative activity described here may duplicate lesser known inventions and procedures developed previously in other locations, but the experience of discovery and development of ideas by individuals in a pedagogical situation justifies the activity in this context.

LOGISTICS AND SPECIAL ASPECTS OF TEACHING

Obviously, the dangers inherent in negotiating alpine terrane in winter, coupled with the related physical exertion and sometimes uncomfortable conditions, dictate that an instructor be aware of these particular contingencies when teaching this course. Extensive experience with alpine or sub-alpine conditions and in handling people in those environments are necessary prerequisites for any teacher in this kind of pedagogy. One must build the intuition that dictates whether to "cut the class loose" and let them find their own way to the successive flagged instruction stations, or whether to have the class remain close behind a leader in a controlled mode of ski-ing. The "semi-controlled" traverse is probably the most common approach here.

The hazards involved with providing first-hand experience in avalanche terrane must also be carefully appraised. Conservative safety standards should be employed. This is not always popular with those who do not share the responsibility for the welfare of the group.

Quite aside from safety considerations, the morale and data retention of a class may depend upon many special considerations. For instance, it would make little sense to lecture standing on the crest of a ridge during a high wind if a more sheltered location were available. However, the experience of high wind is valuable. Likewise, to require a class to remain still for hours under very cold conditions is unnecessary and frustrates learning. A teacher needs the intuition to know when to move a class off to allow restoration of body circulation.

One may choose certain projects to fit the particular weather of the day. It would be fitting to schedule long cross-country trips during cold days with unbreakable crusts. Cross-country trips in soft wet snow should be avoided. Snow-pit crystallography is best observed under moderate conditions.

From the equipment standpoint, the few students who come unprepared to stand and work in the snow, in spite of forewarning, may in fact demoralize the entire class. This emphasizes the necessity to insist that cold-weather apparel suitable for sedentary observation be worn or available.

So far, aside from discussing the various aspects of the use of high explosives for control work, it has not been advisable to demonstrate such in the field. It has been policy, however, to recommend that students take week-end time to observe professional snow-testing crews in action. We have likewise made good use of visiting and local scientists in giving lectures on the nature of their work on the forefront of snow science. The past review of work in progress by St Lawrence (seismic and acoustical aspects of snow), Lang (modeling avalanche flow and run-out), Brown (strength dynamics related to snow crystallography and texture), and Bradley (1968) have added authority to the course in general and inspired students to move ahead into the field of snow dynamics. .

At a time when environmental and hazard-impact statements are increasingly required, the avalanche hazard should be included in any geomorphological investigation in which snow-covered slopes are involved. Any university within reasonable commuting distance of hills or terrane with seasonal snow cover could justifiably consider such a course among its science offerings.

UNIVERSITY COURSE IN SNOW DYNAMICS

REFERENCES

Bradley, C. C. 1968. The resistograph and the compressive strength of snow. Journal ofGlaciology, Vo!. 7, No. 51, P·499-506.

Bradley, C. C., and Bowles, D. 1967. Strength-load ratio: an index of deep slab avalanche conditions. (In Oura, H., ed. Physics of snow and ice: international conference on low temperature science. . . . [966. . .. Proceedings, VO!. I, Pt. 2. [Sapporo], Institute of Low Temperature Science, Hokkaido University, p. 1243-53.)

Burroughs, B. J. Unpublished. Snow engineering handbook. [Research project, Montana State University, Bozeman, 1978.]

Eversman, S. T. Unpublished. A comparison of plant communities and substrates of avalanche and non­avalanche areas in south-central Montana. [Ph.D. thesis, Montana State University, Bozeman, 1968.]

Peria, R. I. 1977. Slab avalanche measuremen1S. Canadian Geotechnical Journal, Vo!. 14, No. 2, p. 206-13. Peria, R. 1., and Martinelli, M.,}r. 1976. Avalanche handbook. U.S. Dept. of Agriculture. Forest Service. Agriculture

Handbook 489. Quervain, M . R. de. 1950. Die Festigkeitseigenschaften der Schneedecke und ihre Messung. Geojisica Pura e

Applicata, Vo!. 18, p. 179-9 1. Roch, A. 1966. Les variations de la resistance de la neige. Union de Geodesie et Geophysique Intemationale. Association

Intemationale d' Hydrologie Scientifique. Commission pour la Neige et la Glace. Division Neige Saisonniere et Avalanches. Symposium intemational sur les aspects scientijiques des avalanches de neige, 5-[0 avril [965, Davos, Suisse, p. 86-99. (Publicat ion No. 69 de l'Association Internationale d'Hydrologie Scientifique.)

Schleiss, V. G., and Schleiss, W. E. 1970. Avalanche h azard evaluation and forecast, Rogers Pass, Glacier National Park. Canada. National R esearch Council. Associate Committee on Geotechnical Research. Technical Memorandum No. 98, p. 115-22.

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