In response to widespread avalanches that killed 150 people in the European Alps during a three-month period, new programs to mitigate snow hazards were designed and implemented in each country. The Swiss, especially, have been lauded for their programs in land-use control, forecasting and evacuation, artificial triggering of avalanches, and structural techniques.
Snow avalanche disasters in the European Alps occur in reaction to the thickness of snow cover, the prevailing meteorological conditions, and the land use at the base of slopes. Avalanches tend to follow two patterns: Every few years, weather conditions favorable to avalanching last long enough for disasters to occur repeatedly throughout the winter, and single events can cause disasters in years that have a generally lower risk.
During the winter of 1950 and 1951, more than 650 people were killed in France, Switzerland, and Austria, where 2,500 buildings were damaged or destroyed and 6,000 hectares of timber were uprooted by avalanches induced by weather conditions. In 1960, eighty-eight people died when ice from the Swiss Glacier d’Allain collapsed onto a work team constructing a dam. Similarly, in 1965, twenty vacationers were overrun by snow and ice at Garmisch, West Germany, and fourteen people died when a bus was hit by an avalanche near Salzburg, Austria. Such events occur at frequent irregular intervals and do not appear to be related to high-risk weather conditions. For example, several climbers were killed by avalanches on Mont Blanc and Monte Rosa during the summer snow melt of 1993 and 1994.
The year 1970 offers a good example of one of the disaster years, especially as it led to a general reevaluation of avalanche precautions in the Alps. In the second week of February of that year, temperatures varied from –5 degrees Celsius at Zürich to 8 degrees Celsius at Geneva and Locarno, with an overall mean of nearly 2 degrees Celsius. The constant oscillation around freezing point led to widespread instability in snowpacks that had previously been augmented by unusually heavy precipitation.
Disaster first struck on February 10, when forty-two people were killed and about sixty were injured by an avalanche in Val d’Isère
The French authorities recognized immediately, if somewhat belatedly, that there was a very high avalanche risk in Val d’Isère and closed the roads that connect it with nearby towns. A helicopter had been able to land only once to evacuate injured survivors before weather conditions prohibited further flights and Val d’Isère was cut off from the outside world. Within the next forty-eight hours, four new avalanches occurred, one of which swept off the road six of the cars in the first convoy to descend from the scene of the tragedy. Though there were no deaths in this event, two people were buried by an avalanche at Le Châtelard, near Aix-les-Bains. One later died of her injuries. Other avalanches occurred on a practice ski slope and at the site of the youth hostel disaster. In response, as soon as weather conditions permitted, the authorities evacuated five thousand people from hotels and apartment complexes in the area.
Reporting on February 15 from Annecy, Alan McGregor of The Times of London wrote,
It takes an avalanche disaster to turn men’s minds from further expansion of the lucrative winter sports industry to serious consideration of the fact that in places the development of safety precautions is lagging behind.
Much was made of the apparent reluctance of the French to invest in structural methods of avalanche control such as snow fences, jet roofs, and tunnels, and it was pointed out that a recent transfer of the National Snow Research Center from Chambéry to Grenoble had led to the resignation of that institution’s representative in Val d’Isère.
Further avalanches that same year at Val d’Isère damaged two hotels and six houses on February 24, while at Reckingen, in the Upper Rhône Valley, eleven people were killed and nineteen were injured by an avalanche 275 meters (900 feet) wide and more than 10 meters (33 feet) deep. It had been the first such event at the site for at least a century, and it flattened several houses. Five hundred troops and more than a dozen specially trained avalanche dogs searched for survivors, but once they had been rescued it proved difficult to evacuate the survivors to safety, as blizzards prevented helicopters from flying into the area and avalanches kept the roads closed.
On February 25, the village of Lans-le-Villard
On the same day, snow and ice cascaded into the streets of St. Leonhard am Pitztal
On March 6, helicopters were used to drop explosives onto the snowpack above the Swiss village of Unter Engadin
The grand finale occurred late in the season on April 15, when the weather across the Alps had been rather warm, with temperatures of 8 degrees Celsius recorded at Zürich and 17 degrees Celsius at Locarno. At Plateau d’Assy
In the European Alps, the death toll in avalanches tends to vary from season to season. About 2,700 avalanches take place each year in Austria, while an annual mean of 17,480 events and twenty-four deaths has been recorded in Switzerland. Seen in this perspective, the 1970 disasters form part of a pattern of recurrent tragedy, though in the past mortality was often much higher. For example, the spectacular glacier surges of 1595 and 1818 in Switzerland caused about two hundred deaths. Worse yet, the period between 1915 and 1918 saw forty thousand people killed in Alpine avalanches, ten thousand of them in a single day. These avalanches were deliberately released onto enemy troops as they marched along unprotected valleys.
In the twentieth century, progressive depopulation of the Alps has been counteracted in many places by a seasonal influx of vacationers and second-home owners. On one hand, local knowledge of infrequent hazards has diminished, while on the other, high-density ski resorts have grown up, and mountain chalets have been built in nearly every accessible location in the Alps. In fact, during the period between 1945 and 1975, land in some of the fastest-growing resorts appreciated in value from twenty to fifty times. The visiting population is usually not familiar with the risk of avalanche. Moreover, the popularity of winter sports means that the biggest influx into the Alpine valleys often coincides with the time of the greatest avalanche hazard.
In the winter of 1970, the avalanche risks varied with weather conditions. The February events were characterized by large powder avalanches that developed in a cold atmosphere. Such events give rise to air blasts and snow momentum that can generate impact pressures that can seriously damage even reinforced concrete structures. Though the Val d’Isère avalanche probably created an impact pressure less than one-tenth of the maximum force possible, even that may have been two orders of magnitude more than is needed to bury, immobilize, or suffocate a human being. In contrast, the April avalanches were composed of broken-up slabs of old snow, and they generated greater impacts in proportion to their higher bulk density. Whereas the February events were probably induced by storms, thanks to new snow accumulating on slopes, the April disaster involved the relatively uncommon delayed-action avalanches, which result from structural weaknesses that develop in the snow pack as weather conditions improve.
Field reports indicate that it was very difficult to extract bodies and survivors from the February avalanches. Trained dogs were a great help; in fact, Swiss avalanche dogs normally locate about one-half of the people buried in snow. Yet dogs cannot sense victims who are more than a meter beneath the surface of the snow. Deeper snow requires probing, which is a speculative affair, or sophisticated infrared or sonar equipment. Neither search nor rescue is easily accomplished during blizzards and at times when further avalanches could occur, as indeed they did right after the 1970 disasters, injuring several rescuers.
One outcome of the tragedies of 1970 was an improvement in forecasting. The French agency Météorologie Nationale now publishes avalanche-hazard forecast bulletins, which comply with the international avalanche classification. It is difficult to know, however, whether forecasting would have helped significantly in 1970, as forecasting is only effective in saving lives if coupled with long-term mitigation measures and a good civil protection plan that provides for public warning and evacuation. Moreover, avalanches such as those of April, 1970, that are not directly linked to snowfalls are difficult to forecast, as they require detailed knowledge of the strength or weakness of the snowpack.
The situation is more optimistic with respect to the long-term measures. The French, for example, have collected data on avalanches systematically since 1899. During the period between 1970 and 1976, they used stereoscopic aerial photographs to compile scale maps of probable avalanche paths in some 600,000 hectares of the Alps and Pyrénees. At the same time, the Swiss Federal Institute for Avalanche Research recorded the incidence of avalanches at each location. The Italians used an ad hoc approach, which involved the identification of some Alpine hazards that later proved to be very serious.
Because an article of the French town-planning code limits building in areas subject to natural hazards, a ministerial circular of December, 1974, directed the Alpine municipalities to draw up avalanche-zoning plans. By the end of the decade, nearly fifty municipalities had done so. Using the criterion of “avalanches with a mean return period of up to 300 years,” construction is banned in red zones, which suffer a clear risk; limited in blue zones, which have an uncertain avalanche risk; and unrestricted in white zones, where there is no known avalanche hazard. In blue zones, the local prefect can order evacuation at times of major risk, and buildings may be required to have structural protection against impact.
Despite some early confusion about local authority, the Swiss have been praised for their skillful use of both nonstructural methods, such as land-use control, forecasting and evacuation, and artificial triggering of avalanches, among other things, and structural techniques, including snow fences, wind baffles, jet roofs, tunnels, and impact-breaking barriers. The Italians, on the other hand, have relied almost entirely on the structural approach and have made costly investments in the necessary environmental modifications. These, however, have been offset by the scale of deforestation and development on vulnerable slopes.
In sum, disaster aftermaths usually represent a window of opportunity in which public and official sensitivity to the problem enables the introduction of new mitigation methods and the reduction of old vulnerabilities. The progress is often temporary, however, especially if long-term trends suggest increasing risk. Thus, the measures taken in the 1970’s in the Alps have effectively reduced casualties and destruction, but rising standards of living have vastly increased demand for Alpine amenities, especially during the skiing season when avalanches are most common. Hence, there has been little reduction in the frequency of avalanche disasters, though better forecasting and warning appear to have reduced the negative impact of avalanches on human life and property.
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Alexander, David E. Natural Disasters. New York: Chapman & Hall, 1993. Describes avalanches in terms of the processes of snow metamorphosis and instability, hazards, emergencies, and mitigation methods. The account is illustrated with some examples from the European Alps. -
De Crécy, L. “Avalanche Zoning in France: Regulation and Technical Bases.” Journal of Glaciology 26 (1980): 325-330. Describes mountain hazard-mapping programs in France and the use of avalanche path maps and risk maps in conjunction with zoning laws and building codes. -
Frutiger, Hans. “History and Actual State of Legislation on Avalanche Zoning in Switzerland.” Journal of Glaciology 26 (1980): 323-324. Describes the legal and political battle in Switzerland to institute controls on the urbanization of avalanche paths and summarizes progress in the ten years following the 1970 disasters. -
Marboutry, Dominic. “What Triggers an Avalanche?” In Violent Forces of Nature, edited by Robert H. Maybury. Mt. Airy, Md.: Lomond, 1986. Discusses European research on avalanches and their causes. Published in cooperation with United Nations Educational, Scientific, and Cultural Organization. -
Shoumatoff, Nicholas, and Nina Shoumatoff. The Alps: Europe’s Mountain Heart. Ann Arbor: University of Michigan Press, 2001. The authors, who spent more than forty years studying as well as climbing and exploring the European Alps, present a vivid history of not only the Alps as a physical, geographical region but also the Alps as a very human place. Color illustrations, maps, bibliography, index. -
United Nations Educational, Scientific, and Cultural Organization. Avalanche Atlas: Illustrated International Avalanche Classification. Paris: Author, 1981. Multilingual guide to the processes and forms of snow, soil, and rock avalanches.
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