Snow Avalanche Hazards and Mitigation in the United States (1990)

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THE AVALANCHE PHENOMENON 9 2 The Avalanche Phenomenon AVALANCHES—A TYPE OF GROUND FAILURE. The geotechnical community recognizes five ways that slope failure can occur under the force of gravity (Varnes, 1978; Ground Failure, 1985). Material may fall freely (or almost freely) through the air—from a cliff, for example. It may topple or tilt over a pivot point. It may slide downward along an identifiable surface or narrow zone that is curved or spoon shaped (rotational slide or slump) or relatively planar (translation slide). It may spread laterally across a slope or flow as a thick fluid—sometimes very rapidly, sometimes so slowly as to be barely perceptible (creep). Slope movements involving two or more of these types of movements are termed complex. As both the kind of material involved and the motions that occur are of importance in slope failure investigations, these factors are commonly used to classify slope movements. The approach can be extended to include snow and ice, and the resulting classification places the full range of gravitational movements of snow and ice within the logical format familiar to engineers (Table 1). This emphasizes the important point that snow avalanches are an integral part of the U.S. landslide problem (Voight and Ferguson, 1988; Voight, 1978). Ice avalanches usually begin with the slow basal sliding and creep of ice caps and glaciers that overhang cliffs. Instability produces true falling or toppling, followed by partial disintegration and flowage. Ice avalanches can be devastating, as in Switzerland in 1965 when 88 workers engaged in dam construction were killed by an avalanche released by the Allalin glacier (Fraser, 1966; Mellor, 1978; Roethlisberger, 1978). In the United States, large ice avalanches are known to happen in Alaska (Slingerland and Voight, 1979) and in the Cascade Range (Williams and Armstrong, 1984a; Voight, 1980, 1981; Voight et al., 1981; Williams, 1934; Bleuer, 1989). Falls and sometimes topples characterize the failure of snow cornices and the release of snow from building roofs (Paine and Bruch, 1986; Taylor, 1985), but typically the initial failure mechanism of the snow cover is translational sliding, utilizing a sloping surface of weakness within the snow cover or at the ground-snow interface. Continuation of movement 

THE AVALANCHE PHENOMENON 10 leads to breakdown of individual snow slabs and, if sufficient disintegration occurs, to rapid mass flowage. Like rock avalanches, most snow avalanches are complex phenomena involving several basic types of motion in succeeding phases. Use of the standard geotechnical terminology for precisely depicting this complexity can lead to an unwieldy vocabulary (rockfall-rapid rock fragment flow, for example). As a result, other classification schemes have been developed over the years, and these have been widely adopted by snow scientists (e.g., Table 2; UNESCO, 1971). In one such scheme, two basic types of snow avalanches are recognized— point release and slab—based on the conditions at the release zone or place of origin. Each scheme is subdivided according to whether the snow is dry, damp, or wet; whether the movement originates within the snow layers or involves the entire snow cover down to the ground surface; and whether the motion is mainly over ground, through the air, or mixed (Perla, 1978a, 1980). A point release or loose snow avalanche (sluff) is the result of a small amount of cohesionless snow slipping out of place, moving downslope, and encountering additional cohesionless snow, such that the failure progresses and spreads out into a characteristic inverted V-shaped pattern. Point releases usually occur either within the cohesionless near-surface layers of newly fallen snow or within the wet surface snow resulting from melt 

THE AVALANCHE PHENOMENON 11 conditions. Point releases usually involve small volumes of snow and can be predicted without much difficulty, so they generally present only a small degree of hazard. TABLE 2 Morphological Classification of Snow Avalanches (after UNESCO, 1971) Zone Criterion Alternative characteristics, Denominations, and Code Zone of origin A Manner of starting A1 Starting from a point A2 Starting from a line (loose snow avalanche) (slab avalanche) A3 Soft A4 Hard B Position of sliding surface B1 Within snow cover B4 On the ground (full- (surface layer avalanche) depth avalanche) B2 (New snow B3 (Old snow fracture)fracture) C Liquid water in snow C1 Absent (dry snow C2 Present (wet-snow avalanche) avalanche) Zone of transition (free D Form of path D1 Path on open slope D2 Path in gulley or and retarded flow) (unconfined avalanche) channel (channeled avalanche) E Form of movement E1 Snow dust cloud E2 Flowing along the (powder avalanche) ground (flow avalanche) Zone of deposition F Surface roughness of F1 Coarse (coarse deposit) F4 Fine (fine deposit) deposit F2 Angular F3 Rounded blocks clods G Liquid water in snow G1 Absent (dry avalanche G2 Present (wet avalanche debris at time of deposition deposit) deposit) H Contamination of deposit H1 No apparent H2 Contamination present contamination (clean (contaminated avalanche) avalanche) H3 Rock debris, H4 Branches soiltrees H5 Debris of structures In contrast, slab avalanches initiated within cohesive snow cover on slopes steeper than 25 degrees provide most of the avalanche hazards and are the primary focus of defense and control measures. Failures occur when the shear load parallel to the slope exceeds the shear strength of supporting layers. In this case the layer of cohesive snow, poorly anchored underneath, fractures as a continuous single unit. Given relatively homogeneous snow properties, the fracture may propagate for a great distance across a slope and may incorporate a large volume of snow into the moving avalanche. Fractures may extend as much as several meters into the snow cover. Prediction of slab avalanches is difficult 

THE AVALANCHE PHENOMENON 12 because the location of initial failure is frequently well below the surface, within layers that accumulated weeks or months earlier (LaChapelle, 1985; McClung, 1979; Armstrong, 1979; Ferguson, 1984a,b; Perla, 1978a). These layers are hard to locate and monitor prior to actual failure. Slab avalanches present a significant hazard due to this difficulty of prediction, in addition to their potential for release over large areas. Escape from these avalanches can be difficult or impossible (see frontispiece). The hazard to activity and structures in the avalanche runout zone is high due to the large volumes of snow that can be mobilized by a slab release. Table 3 provides a qualitative scale of the destructive potential of snow avalanches and related physical parameters. TABLE 3 Scale of Snow and Ice Avalanches ORDER-OF-MAGNITUDE ESTIMATES Impact pressure Size Potential effects Vertical descent (m) Volume (m3) (Pa) (psi)a Sluffs Harmless 10 1-103 <103 <0.15 Small Could bury, injure, or kill a 10-102 10-102 103 0.15 human Medium Could destroy a wood frame 102 103-104 104 1.5 house or auto Large Could destroy a village or 103 105-106 105 15 forest Extreme Could gouge landscape, 103-5×103 107-108 (includes ice, soil, 105-106 15–150 world's largest avalanches rock, mud) (Himalayas, Andes, Alaska) a Pa is approximately 1.5 × 10-4 psi. SOURCE: After McClung and Schaerer (1981). Wet snow avalanches present additional problems due to their high mobility and erratic style of runout (see frontispiece; Martinelli, 1984). Also important is the rapid mass movement of water-saturated snow known as a slush avalanche or slushflow. Analogous to the mudflows and debris flows of conventional geotechnology, slushflows are major natural hazards in Scandinavia, the U.S.S.R., Canada, Greenland, and Alaska (Hestnes, 1985; Hestnes and Sandersen, 1987; Onesti, 1985, 1987; Nobles, 1965; Nyberg, 1985; Rapp, 1960). The multiple-hazard concept can also be important in relation to avalanches, such as downstream flooding due to breakout of avalanche-dammed rivers (Fraser, 1966; Williams, 

THE AVALANCHE PHENOMENON 13 1934) and water-wave damage or flooding due to large avalanches into water bodies and mine-tailings impoundments (Slingerland and Voight, 1979; Vila, 1987; NGI, 1984, 1986). CAUSES OF AVALANCHE RELEASE Use of the term natural release implies the occurrence of a trigger beyond human control. In a simplified sense, natural releases fall into two end-member categories: in one case the load increases while the strength remains generally unchanged (e.g., rapid loading by snowfall); in the other the load remains approximately constant while the strength decreases (e.g., strength loss due to melting). Of course, hybrid situations also exist in which both load and strength vary over time. Artificial release usually results from the placement of explosives by hand, military weapons, or specialized avalanche control equipment. Skiers, snowmobilers, and climbers crossing an avalanche starting zone may also cause artificial release. Point release avalanches occur when cohesionless snow rests on a slope that is steeper than its natural angle of repose. Failure is localized, and the mechanism is not difficult to understand. In contrast, slab release occurs when a cohesive cover of snow rests above a layer of lesser strength along which the eventual sliding failure occurs, when shear stress exceeds shear resistance. Slab release typically results from a complex series of events, often originating within a snow cover creeping downslope (McClung, 1987). When differential stresses cause localized failure, load is transferred to the adjacent snow structure; if this additional load cannot be sustained, cracks are initiated and propagated by a rapid increase in stress due to stress concentration and the release of stored strain energy. The failure process can also be initiated by a tree or rock acting as the anchor and source of concentrated stress to a slowly sagging snow cover or by additional dynamic loading from a falling object. In terms of predicting slab avalanche occurrence, the average mechanical values are frequently less important than the range of values (Gubler, 1988; Sommerfeld and King, 1979; Ferguson, 1984b; Conway and Abrahamson, 1988). For example, overall conditions can be moderately stable, while localized stress concentrations in an otherwise strong and homogeneous snow cover allow local slab failures to expand and incorporate a major portion of a slope's snow cover. Failure is most common during or soon after a heavy snowstorm, when potentially weak layers cannot strengthen rapidly enough through crystal-to-crystal bond formation (sintering) to support the increasing shear load of new snow. In addition, weakness may originate as the snow recrystallizes by temperature-sensitive metamorphism deep within the snow pack (Colbeck, 1980, 1987; Perla and Ommanney, 1985; R. L. Armstrong, 1977, 1981, 1985; Marbouty, 1980). Metamorphism within snow is a continuous process that begins when snow is deposited and continues until it melts. The processes causing changes in crystallinity are complex, but it is known that important roles are played by mass transfer, water vapor diffusion, and temperature and temperature gradient (Colbeck, 1982, 1987; Sommerfeld, 1983; Gubler, 1985). The susceptibility of the snow cover to rapid changes (over hours or days) in layer and bond strength is a reflection of the proximity of the ambient temperature of the snowpack to the melting temperature of ice. Mechanical and thermal properties and conditions for snow are closely intertwined, and the interplay of geomechanics, thermodynamics, and meteorology contributes to the complexity of stability analysis. Avalanches can also be triggered by direct dynamic loads due to falling cornices, the 

THE AVALANCHE PHENOMENON 14 passage of skiers through the starting zone, rockfalls, or elastic waves from blasting or earthquakes (Hackman, 1965; LaChapelle, 1968; Voight and Pariseau, 1978; Johnson, 1978, 1980; Brown, 1980). Finally, rain-on-snow events may cause wet snow avalanches and slushflows. While rain-induced slides constitute a small proportion of all avalanches, such events can produce substantial damage (Hestnes, 1985; Hestnes and Sandersen, 1987; Kattelmann, 1984, 1987; Moskalev, 1966; Onesti, 1987; Ambach and Howorka, 1965). GEOGRAPHIC DISTRIBUTION OF AVALANCHE HAZARD Figure 2 shows the severity of avalanche hazard in the United States; the assignment of severity classes is qualitative but is based on avalanche fatality data for the winters of 1950–1951 through 1987–1988 (cf. Armstrong and Williams, 1986). These data indicate that avalanche activity occurs in nearly all western states (Washington, Oregon, California, Idaho, Nevada, Montana, Utah, Wyoming, Colorado, New Mexico, and Alaska); in Minnesota; and in the northeastern states of Maine (McFarlane, 1986), New Hampshire, and New York. Thus, about one-third of the 50 states face avalanche hazard during winter months. In at least two states, avalanches kill more people than any other natural hazard. In addition, avalanches can occur in man-made snow (Avalanche Review, 1988), and fatalities, injuries, and damage—as well as litigation—have been produced by avalanches from sloping roofs (Taylor, 1985; Paine and Bruch, 1986; Nakamura et al., 1981). Current annual U.S. mortality due to snow avalanches exceeds the average number of deaths from earthquakes and generally exceeds the combined average number of deaths due to all other forms of landslides [about 12 per year according to Jahns (1978) for the period 1925–1975; accurate statistics are not available for landslides, cf. Schuster and Fleming (1986)]. Single avalanche events killed 96 people in Washington in 1910, 70 in Alaska in 1898, and 40 in Utah in 1939 (Gallagher, 1967; Perla, 1970). U.S. avalanche fatalities were routinely reported to the U.S. Forest Service from about 1960 to 1984 and since then to the Colorado Avalanche Information Center (Gallagher, 1967; Williams, 1975; Williams and Armstrong, 1984a). Alaska leads the nation in the number of reported avalanche accidents per capita; over 3,000 Alaskan avalanche events involving humans have been documented. Between 1980 and 1985, Alaska recorded 441 events affecting people; in those events 278 persons are known to have been trapped, injured, or killed (J. A. Fredston, Alaska Mountain Safety Center, written communication, 1986). However, apart from fatalities, accident data for other states are less complete, and probably fewer than 10 percent of nonfatal avalanche accidents are reported (Armstrong and Williams, 1986). Currently about 140 Americans are reported each year to be caught in avalanches, 65 being buried and 17 killed (Armstrong and Williams, 1986). Enough private property is threatened by avalanches to have prompted the enactment of local avalanche zoning ordinances in California, Colorado, Idaho, Utah, and Washington (Armstrong and Williams, 1986; Clark, 1988; Niemczyk, 1984). Zoning regulations have not yet been adopted elsewhere, although hazards have been recognized. In the last 105 years, for example, over 80 structures within a 10-mile radius of Juneau, Alaska, have been hit or destroyed by avalanches, and several large avalanche paths from Mt. Juneau—which towers above the city—threaten residential housing (Hart, 1972; LaChapelle, 1972, 1981; Hackett and Santeford, 1980). One of these avalanche paths, the North Behrends Avenue path, contains 40 houses, a motel, a highway, a large boat harbor, and a school in its runout zone. Since 1890, avalanches released from its 43-acre starting zone have run down this path 

THE AVALANCHE PHENOMENON 15 almost to tidewater at least five times, and in 1962 an avalanche physically relocated two dozen homes and took roofs off many others. The Behrends Avenue path has a significant potential for a large-scale avalanche disaster, but despite several detailed studies identifying specific hazard areas within city limits (Hart, 1972; LaChapelle, 1972, 1981), construction in known runout zones continues (J. A. Fredston, Alaska Mountain Safety Center, personal communication, 1986). FIGURE 2 Qualitative indication of the severity of snow avalanches by state. Frequent avalanche activity threatens transportation corridors along numerous year-round highways and railroads in such areas as Washington state; the Alaskan coastal region; California's Sierra Nevada; and canyons in Utah, near Jackson Hole, Wyoming, central and western Colorado, and western Montana. For example, in the decade preceding 1986, 205 avalanche events in Alaska blocked highway traffic, with 30 vehicles hit or disabled; 274 events blocked railroad traffic, with 21 cars derailed; and 2 aircraft were damaged (D. Fesler, Alaska Mountain Safety Center, personal communication, 1986). Eleven state and federal highways in Colorado are also susceptible to avalanches, and during the winter of 1983–1984, Colorado highways were closed by natural avalanches on 60 days (Williams and Armstrong, 1984b). One example of a high-risk highway is U.S. Highway 550 in southwestern Colorado, where avalanches threaten a third of the road from Ouray to Coal Bank Pass. Ninety-three 

THE AVALANCHE PHENOMENON 16 individual avalanche paths intersect this highway (Armstrong and Ives, 1976), and during an average winter more than 100 avalanches are observed to reach it. If each of these avalanches covered the highway with its historical maximum quantity of debris during the same storm, nearly 30 percent of the 36-mile-long highway would be covered by avalanche debris. Although such an event is unlikely, this example provides a measure of the high potential risk. In fact, extensive data indicate a 79 percent probability that on this highway at least one vehicle will be hit by an avalanche each winter (B. Armstrong, 1980). Highway travelers have also been killed on Interstate 90 in the Cascade Range in Washington, creating a significant need for avalanche control. Here, dense forest growth provides avalanche protection at some locations, but clear-cut timber harvesting has created new avalanche starting zones and paths and has significantly increased the hazard. State highway personnel want to restrict logging, which is carried out under government permit, but the decisions involve the State Department of Natural Resources, the land-owning railroad company, and the contract logging firm. Communications and decision making are hampered by the lack of established guidelines for timber management in avalanche hazard zones and lack of guidance from state or federal agencies with competence in avalanche mitigation. Those endangered by avalanches are individuals who live, travel, work, or vacation in avalanche-prone mountain environments in winter. The trend from 1940 to the present shows an increase in recreation-related accidents. As a result, the population at risk is, in fact, spread throughout the nation, rather than being restricted to the resident population of avalanche hazard states. Vacationers from Texas, Illinois, New York, Florida, Georgia, and California account for more than half of the tourists in Colorado and Utah and provide 90 percent of the tourist income. Data from the U.S. Forest Service Region II office in Denver show a 15 times increase in winter recreation use on Forest Service lands between 1970 and 1980 (Trogert, 1981)—yet another indication of the increasing hazard. ECONOMIC COSTS OF U.S. AVALANCHES Avalanches damage and destroy public, commercial, and private property and forest lands and result in costs for restoration, maintenance, and post de facto litigation. No comprehensive study has been attempted of the economic impact of snow avalanches in the United States. Direct costs can be defined as the cost of maintenance, restoration, or replacement due to damage of property or structures within the boundaries of a specific avalanche. All other costs from avalanches are indirect and include (1) reduced real estate values in areas threatened by avalanches, (2) loss of productivity of forest lands, (3) loss of industrial productivity as a result of damage to land or facilities or interruption of services, (4) loss of tax revenues on properties devalued as a result of avalanches, (5) cost of measures to mitigate additional land or facility damage, (6) loss of access to recreation lands and facilities, (7) cost of lost human productivity due to injury and death, and (8) the cost of litigation as a consequence of avalanches. Some of these indirect costs are difficult to measure and tend to be ignored. As a result, most estimates of avalanche costs are far too conservative. If rigorously determined, indirect costs probably exceed direct costs. Direct and indirect costs can be further subdivided into ex-anti and ex-post costs (D. S. Brookshire, University of Wyoming, unpublished manuscript, 1986). Ex-anti costs are those incurred prior to an avalanche event for preventative measures such as forecasting 

THE AVALANCHE PHENOMENON 17 and control; added research and design in planning; and the cost of materials, labor, and delay time in the implementation phase. Ex-post costs are incurred following an avalanche event and include the costs of search and rescue personnel and equipment, reconstruction, loss of productivity, property damage, injury, and loss of life. It is useful to further divide direct and indirect costs by categorizing them as either public (government) or private. Direct public costs have traditionally been limited to the ex-anti cost of avalanche forecast and information centers, hazard mitigation in the form of structural and/or active control measures for roads or public work facilities, and the ex-post cost of clearing debris and repairing damage. Historically, the federal government funded ongoing avalanche research, an ex-anti cost, but in 1985 it withdrew all research support. Direct private costs (both ex-anti and ex-post) have been borne primarily by utility companies and the winter recreation industry in the form of structural and/or active mitigation measures, forecasting, and facility repair and maintenance. Private property owners have mainly incurred ex-post costs with a major avalanche potentially resulting in financial ruin for affected individuals because of the unavailability of avalanche insurance or other means of spreading the costs of damage. With the recent implementation of avalanche hazard zoning ordinances by some county and municipal governments, ex-anti costs in the form of mapping and additional planning and construction, as well as indirect economic losses from property devaluation, are also beginning to be incurred by private home and property owners. It should also be noted that for major avalanche events the costs are sustained at all levels of the public and private sectors for emergency services, disaster aid, and reconstruction. EXAMPLES OF ECONOMIC IMPACT The economic impact of snow avalanches can be determined only through accurate and complete cost data, but in most cases such data are either nonexistent or are hidden in the cost data of other programs. In a limited number of instances, accurate and specific cost data are available that illustrate the type and extent of the economic impact of avalanches in the United States. In the following examples, cost figures have not been adjusted to current dollars. The costs associated with rescue depend on the magnitude of an avalanche, but a recent incident adjacent to the Breckenridge ski area in Colorado provides a fairly typical example. The avalanche occurred on February 18, 1987, on U.S. Forest Service (USFS) land just outside the boundary of the Breckenridge ski area; four people were killed. The ski area's rescue costs were $35,000, including helicopter time, salaries, and miscellaneous costs; the cost to the Colorado Search and Rescue Board was approximately $39,250. In addition, the USFS incurred undisclosed losses for in-house and town meetings and for preparation of anticipated litigation. Litigation is a major economic cost. An avalanche at the Alpine Meadows ski area in California on March 31, 1982, resulted in seven deaths and caused extensive damage to the base area's facilities. Property damage to buildings, vehicles, and equipment was approximately $1.5 million, not including rescue costs and timber loss. However, the families of a number of the victims subsequently sued Alpine Meadows, the USFS, Placer County, Southern Pacific Land Company, and the food service company operating the lodge's cafeteria on the day of the accident (Penniman, 1986, 1987). Several suits were settled out of court for undisclosed amounts. In an ensuing court battle involving three plaintiffs, the 

THE AVALANCHE PHENOMENON 18 jury exonerated Alpine Meadows and rendered a verdict of nonnegligence for standards of “ordinary care” (Garbolino, 1986; Gerdes, 1988). In addition to undisclosed amounts for out-of-court settlement from the subsequent appeal and a suit against the USFS, litigation costs for the defense, not including the USFS's defense costs, were approximately $700,000, and litigation costs for the plaintiff were about $800,000. The out-of-court settlement cost potentially could have been $14 million (J. Fagan, University of San Francisco, personal communication, 1986). [The theory of strict liability as it applies to avalanche explosive control is discussed by Fagan and Cortum (1986). Liability of adjoining property owners and liability for failure to maintain unstable land, among other matters, are examined by Olshansky and Rogers (1987).] Other types of losses result from the impact on property values of ordinances enacted by local municipalities in the mountain states. These ordinances either prohibit construction in high and moderate avalanche hazard areas or call for special engineering practices. An example is provided by Placer and Nevada counties, California, where avalanche ordinances were enacted in 1982 as a direct result of the Alpine Meadows avalanche. A real property loss of $712,000 was estimated in this case, reflecting the difference in the value of property sold before and after enactment of the ordinance (R. Penniman, consultant, Tahoe City, California, personal communication, 1986). Here, the restrictions for building in high and moderate avalanche hazard zones are so severe that no lots (out of a total of 52) have been sold there. Thus, by applying the average percentage loss of real property values to these no longer salable properties, an additional loss to property value can be estimated at $7,100,000. Yet the loss extends beyond the potential sale of property: when property values decrease, tax revenues also are affected. The potential yearly tax loss in this case is $72,000, based on percentages of 1.0103 and 1.1003 quoted by the Placer County Assessor's Office for Squaw Valley and Alpine Meadows, respectively. Hundreds of mountain communities in the United States have the potential for avalanche incidents similar to those experienced at Breckenridge and Alpine Meadows. An incident could involve large numbers of people within or near ski areas and on roads and residential and commercial areas in surrounding communities. A single avalanche disaster at any one of these areas is likely to trigger action by litigants and communities similar to those listed above and have similar far-reaching economic effects. The overall costs associated with avalanche control, mitigation, and damage are difficult to estimate. Annual loss figures from the Washington State Department of Transportation, for example, amount to approximately $330,000 (M. Moore, Northwest Avalanche Center, Seattle, Washington, personal communication, 1986). However, this figure does not include salary costs for personnel employed directly in avalanche control nor the costs of plowing, snow removal, or avalanche control on Cayuse Pass, Chinook Pass, and Washington Pass, which are normally closed during the winter season but require considerable labor and equipment to clear avalanche debris prior to closing and upon reopening (Wilbour, 1986; cf. Sherretz and Loehr, 1983). Similarly, the state's annual loss figure does not account for adverse impacts on ski resorts, restaurants, lodging, or other businesses in the area. That these impacts are extensive can be inferred from a report by R. Milbrodt, city manager of South Lake Tahoe, which is affected by the periodic closure of U.S. Highway 50 for avalanche control: If an avalanche results in road closure (U.S. 50) there is an immediate impact if full closure occurs from lost visitor days. Should the closure only be temporary (less than a day) it is unlikely that economic impact will be noticed in the short-term. In the long-term, however, our market research 

THE AVALANCHE PHENOMENON 19 suggests that fear of possible closure from avalanche control does discourage visitation. This indirect impact is not measurable, but can be significant. There are also impacts beyond the scope of our immediate community. For example, during the 1983 event we found that Carson City, Nevada and Placerville, California business activity suffered declines. Those communities previously were of the opinion that they were not dependent on South Lake Tahoe for economic activity and much surprise arose from the losses during U.S. 50 closure. However, we simply do not have any measurements for all of these economic impacts. (R. Milbrodt, city manager, South Lake Tahoe, written communication) Similarly, serious local economic losses due to highway and rail closures have been cited for the Glacier National Park area in Montana (Butler, 1986). It is clear from such examples that economic losses from avalanches, though usually unspecified as to amount, are of considerable local significance. A conservative estimate of $11.4 million was placed on the costs incurred from Alaskan avalanches for the period 1977–1986 (D. Fesler, Alaska Mountain Safety Center, Anchorage, personal communication, 1986). This estimate reflects the actual costs of known damage resulting from known avalanche events affecting bridges, buildings, vehicles, power lines, railroads, highways, and miscellaneous structures. Again, however, it does not account for snow removal from highways and railroads or for the cost of avalanche rescues or commercial losses due to delays. This small sample of losses incurred as a result of avalanches in the United States clearly illustrates that costs recur each winter and will continue to recur year after year. With high media visibility, avalanches have some potential to influence the multibillion-dollar tourism industry that sustains the local economies of many mountain regions. In Colorado, for example, the ski industry accounts for 25 percent of employment, 21 percent of personal income, and 45 percent of housing construction in the western slope region (Frick, 1985). Yet public and private policies in the United States have focused on short-term solutions to the avalanche problem, using relatively inexpensive mitigation measures. Inevitably this effort is subject to local failure, with resulting loss of life and property and a lingering economic impact. Other nations have learned that such losses cost far more in the long term than do structural mitigation measures that can render avalanches harmless. In Canada, for example, the cost of avalanche research is about 10 to 15 percent of the profits to management, a figure that fully justifies research expenditures (D. M. McClung, National Research Council of Canada, written communication, 1989). An international perspective on hazard management thus is important and is provided in succeeding chapters. First, however, the U.S. policy toward avalanche management is outlined.