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The Avalanche Phenomenon
AVALANCHES A mE 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 I). This emphasizes the important point that snow avalanches are an
integral part of the U.S. landslide problem (Voight and Ferguson, 19~; Voight, 19784.
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 ~ workers engaged in dam construction were billed by an avalanche released by the
AlIalin glacier (Fraser, 1966; Mellor, 1978; Roethlisberger, 1978~. In the United States,
large ice avalanches are known to happen in Alaska (Slingeriand 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
9
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TABLE 1 Classification of Slope Movements in Snow, Rock, and Soil Based on Kind of Material and Type
of Movement (Modified from Varnes, 1978)
Few Units
TYPE OF MOVEMENT
Falls
Topples
Rotational
Slides
Translational
Lateral Spreads
Flows
Complex
TYPE OF MATERIAL
Engineering Soils
Bedrock Predominantly coarse Predominantly fine
Rock fall D~s fall Earth fall
Rock topple Debris topple Earth topple
Rock slump Debris slump Earth slump
Rock block slide Debris block slide Earth block slide
Rock Slide Debris slide Earth slide
Rock spread Debris spread Earth spread
Rock flow Debris flow Earth flow
(rock creep) l (soil reep)
Combination of two or more principal types of movement
Snow
Snow fall
Snow topple
Snow slump
Snow block slide
Many Units
Snow slide
Snow spread
Snow flow
(snow creep)
leads to breakdown of individual snow slabs and, if sufficient disintegration occurs, to rapici
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 (PerIa, 197Sa, 19SO).
A point release or loose snow avalanche (slum is the result of a small amount of
cohesionIess snow slipping out of place, moving downsIope, and encountering additional
cohesionIess snow, such that the failure progresses and spreads out into a characteristic
inverted V-shaped pattern. Point releases usually occur either within the cohesioniess near-
surface layers of newly fallen snow or within the wet surface snow resulting from melt
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TABLE 2 Morphological Classification of Snow Avalanches (after UNESCO, 1971)
Zone
Criterion Alternative characteristics, Denominations, and Code
Zone of origin A Manner of A1 Starting from a point A2 Starting from a line
starting (loose snow (slab avalanche)
avalanche) A3 Soft A4 Hard
B Position of B1 Within snow cover B4 On the ground
sliding surface (surface layer (full-depth avalanche)
avalanche)
B2 (New snow B3 (Old snow
fracture) fracture)
C2 Present
C Liquid water in C1 Absent (dry snow (wet-snow avalanche)
snow avalanche)
Zone of transition D Form of path D1 Path on open slope D2 Path In gulley or channel
(free and retarded (unconfined avalanche) (channeled avalanche)
How)
E Form of E1 Snow dust cloud
movement (powder avalanche)
E2 Flowing along the ground
(flow avalanche)
Zone of deposition F Surface
F1 Coarse (coarse deposit)
roughness of F2 Angular F3 Rounded
deposit blocks clods
G Liquid water in G1 Absent
snow debris at (dry avalanche deposit)
time of
deposition
F4 Fine
(fine deposit)
G2 Present
(wet avalanche deposit)
H Contamination H1 No apparent contamination H2 Contamination present
of deposit (clean avalanche) (contaminated avalanche)
H3 Rock debris' H4 Branches
soil
HS Debris of structures
trees
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.
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
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TABLE 3 Scale of Snow and Ice Avalanches
ORDER-OF-MAGNITUDE ESTIMATES
Vertical Impact pressure
descent Volume
Size Potential effects (m) (my (Pa) (prim
Stuffs Harmless 10 1-103
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1934) and water-wave damage or flooding due to large avalanches into water bodies and
mine-tailings impoundments (Slingeriand and Voight, 1979; Vila, 1987; NG1, 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 cohesionIess 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 downsIope (McClung, 1987~. When clifferential
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 concentrates!
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, 19~. 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 sIope'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; PerIa and Ommanney, 1985; R. Lo. 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
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passage of skiers through the starting zone, rockfalIs, or elastic waves from blasting or
earthquakes (Hackman, 1965; LaChapelle, 1968; Voight and Pariseau, 1978; Johnson,
197S, 1980; Brown, 1980~. Finally, rain-on-snow events may cause wet snow avalanches
and sTushflows. 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
195~1951 through 1987-19% (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 (McFarIane, 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, 19~), 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 Heming
(1986~. Single avalanche events killed 96 people in Washington in 1910, 70 in Alaska in
IS9S, and 40 in Utah in 1939 (Gallagher, 1967; PerIa, 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 27S
persons are known to have been trapped, injured, or killed If. ~ 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, 19~; 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 Behrencis Avenue
path, contains 40 houses, a motel, a highway, a large boat harbor, and a school in its runout
zone. Since IS90, avalanches released from its 43-acre starting zone have run down this path
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5
12
I:
f ::::::::
i'''
/,.,~,..~.. i,
~ ~~Cj~
FIGURE 2 Qualitative indication of the severing of snow avalanches by state.
..,....
~] no avalanches
23 low severity
moderate severity
high severity
· Regional Forecast Centers
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 At. ~ Fredston, Alaska Mountain Safety Center, personal
communication, 1986~.
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
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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 he avalanches are individuals who live. travel. work. or vacation in
avalanche-prone mountain environments In winter. Lee trend trom luau 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 or office in Denver
show a 15 times increase in winter recreation use on Forest Service lands between 1970 and
198() (Tro~ert. 19811- vet another indication of the increasing hazard.
~ ~ _ _7 ~ ~ ~
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 (~) 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 (~) 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
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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 com-
panies 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 IS, 1987, on U.S. Forest Service (USFS) land just
outside the boundary of the Breckenridge ski area; four people were ~led. 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
USES 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 3l, 1982, resulted in seven deaths and caused extensive damage
to the base area's facilities. Property damage to buildings, vehicles, and equipment was
approximately $~.5 million, not including rescue costs and timber loss. However, the families
of a number of the victims subsequently sued Alpine Meadows, the USES, Placer Count,
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
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jury exonerated Alpine Meadows and rendered a verdict of nonnegligence for standards of
"ordinary care" (Garbolino, 1986; Gerdes, 19~. In addition to undisclosed amounts for
out-of-court settlement from the subsequent appeal and a suit against the USES, 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 At. 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 bv
Olshanskv and Ropers (19871.]
O ~ ~ ~ ~
~ O ~ ~ ~
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 ava-
lanche 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. MilbroUt, city manager of South Lake Tahoe,
which is affected by the periodic closure of U.S. Hi~hwav 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
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suggests that fear of possible closure from avalanche control does discourage visitation. Ibis 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 Placerv~lle, California business activity suffered
declines. Those communities previously were of the opinion that they were not dependent on South
Lake Shoe 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 Shoe, written communication)
Similarly, serious local economic losses due to highway and rail closures have been cited for
the Glacier National Park area in Montana (ButIer, 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 $~.4 million was placed on the costs incurred from Alaskan
avalanches for the period 1977-1986 (D. Fester, 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-doliar 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, 19SS).
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 IS 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.
Representative terms from entire chapter:
snow cover
