Final Hazard Profile – Avalanche
Washington State Hazard Mitigation Plan June 2013
Tab 5.2 – Avalanche Profile - Page 1
Avalanche
Risk Level
Frequency – Avalanches occur annually in Washington.
People – National and international statistics show that there is the potential for
significant loss of life from an avalanche.
Economy – An incident is unlikely to cause the loss of 1% of the State GDP.
Environment – An incident is unlikely to cause the loss of 10% of a single species or
habitat.
Property – An incident is unlikely to cause $100 million in damage.
Summary
o The hazard – An avalanche occurs when a layer of snow loses its grip on a slope and
slides downhill. Avalanches typically occur from November until early summer in all
mountain areas, but year-round in high alpine areas. They primarily pose danger to
people in areas where there is no avalanche control, and to continued movement of
people and freight over the state’s mountain highway passes.
o Previous occurrences – Avalanches occur frequently each year and kill one to two
people annually in the Northwest (about 25-35 deaths annually in the U.S.). Avalanches
have killed more people in Washington than any other hazard during the past century.
In 90 percent of avalanche fatalities, the weight of the victim or someone in the victim’s
party triggers the slide.
o Probability of future events – Avalanches occur regularly every year in mountain areas.
Many weather and terrain factors determine actual avalanche danger. Avalanches
along two key mountain highway passes are limited due to ongoing mitigation to control
slides during winter months.
o Jurisdictions at greatest risk – Twelve counties in which the Cascade, Olympic, Blue or
Selkirk Mountains are found.
o Special note – This profile will not attempt to estimate potential losses to state facilities
due to avalanche. Very few are in avalanche hazard zones, and other hazards pose a
greater threat to people and the built environment than avalanches and thus, are more
important to address. However, this hazard profile will identify a number of state
highways that experience closure due to avalanches during the winter months.
Avalanche
Frequency
50+ yrs
10-50 yrs
1-10 yrs
Annually
People
<1,000
1,000-10,000
10,000-50,000
50,000+
Economy
1% GDP
1-2% GDP
2-3% GDP
3%+ GDP
Environment
<10%
10-15%
15%-20%
20%+
Property
<$100M
$100M-$500M
$500M-$1B
$1B+
Hazard scale
< Low to High >
Final Hazard Profile – Avalanche
Washington State Hazard Mitigation Plan June 2013
Tab 5.2 – Avalanche Profile - Page 2
Washington State Avalanche Hazard Areas: White areas on the map indicate that those areas are at least 2,000 feet in elevation and most
likely to be prone to avalanches. Avalanches can and do occur outside of these areas during unusual conditions.
Final Hazard Profile – Avalanche
Washington State Hazard Mitigation Plan June 2013
Tab 5.2 – Avalanche Profile - Page 3
The Hazard
1,2,3,4, 5
An avalanche is an often-rapid downhill motion of the snow pack or portion of the snow pack.
Some wet snow or slush-flow avalanches may travel quite slowly. This motion may be natural
or artificially induced, and controlled or uncontrolled in terms of time, place, and severity. An
avalanche occurs when a layer of snow loses its grip on a slope and slides downhill. Avalanches
have killed more than 190 people in the past century in Washington State, exceeding deaths
from any other natural hazard. The nation’s worst avalanche disasters occurred in 1910 when
massive avalanches hit two trains stopped on the west side of Stevens Pass; at least 96 people
were killed. Avalanches kill one to two people, on average, every year in Washington, although
many more are involved in avalanche accidents that do not result in fatalities. Since 1985,
avalanches have killed 56 people in Washington State (through March 14, 2012).
Most current avalanche victims are participating in recreational activities in the backcountry
where there is no avalanche control. Only one-tenth of one percent of avalanche fatalities
occurs on open runs at ski areas or on highways.
Source: USDA Forest Service Utah Avalanche Center. (Accessed August 10, 2009)
Available at: http://utahavalanchecenter.org/education/faq
Avalanches occur in four mountain ranges in the state – the Cascade Range, which divides the
state east and west, the Olympic Mountains in northwest Washington, the Blue Mountains in
southeast Washington, and the Selkirk Mountains in northeast Washington. The avalanche
season begins in November and continues until early summer for all mountain areas of the
state. In the high alpine areas of the Cascades and Olympics, the avalanche season continues
year-round.
Final Hazard Profile – Avalanche
Washington State Hazard Mitigation Plan June 2013
Tab 5.2 – Avalanche Profile - Page 4
There are two types of avalanches, loose and slab, and two types of slab avalanches, soft and
hard. Avalanches can be either dry or wet. Although the most dangerous avalanche is the slab
avalanche, loose slides can and do produce injury and death.
Loose avalanches occur when grains of snow cannot hold onto a slope and begin sliding
downhill, picking up more snow and fanning out in an inverted V. Slab avalanches occur when a
cohesive mass of snow breaks away from the slope all at once. Most slides in the Northwest
are slab avalanches.
Avalanches occur for one of two basic reasons:
1) Either the load on a slope increases faster than snow strength; or
2) Snow strength decreases.
Slab avalanches occur when the stresses on a slab overcome the slab’s attachment strength to
the snow layer below. A decrease in strength is produced through warming, melting snow, or
rain. Decreased strength within the existing snowpack may also result from strong temperature
gradients and associated vapor transfer that produces
recrystallization within the existing snow matrix. An
increase in stress may be produced by the weight of
additional snowfall, or a skier or a snowmobile. Dry slab
avalanches can travel 60 to 80 miles per hour or more,
reaching these speeds within five seconds after the
fracture; they account for most avalanche fatalities. Wet
slab avalanches occur when warming temperatures or rain
increase the creep rate of the surface snow, putting
additional forces on the slab’s attachment to the layer
below. When water percolating through the top slab
weakens the layer and dissolves its bond with a lower
layer, it decreases the ability of the weaker, lower layer to
hold on to the top slab, as well as decreases the slab’s
strength. In 90 percent of avalanche fatalities, the weight of the victim or someone in the
victim’s party triggers the slide. An avalanche is like a dinner plate sliding off a table; a slab of
snow shatters like a pane of glass with the victim in the middle.
Factors That Affect Avalanche Danger
6
A number of weather, terrain and snowpack factors determine avalanche danger:
Weather:
Storms – A large percentage of all snow avalanches occur during and shortly after
storms.
Rate of snowfall – Snow falling at a rate of one inch or more per hour rapidly increases
avalanche danger.
Error! Reference source not found.
Ingredients for a Slab Avalanche
Final Hazard Profile – Avalanche
Washington State Hazard Mitigation Plan June 2013
Tab 5.2 – Avalanche Profile - Page 5
Temperature – Storms starting with low temperatures and dry snow, followed by rising
temperatures and wetter snow, are more likely to cause avalanches than storms that
start warm and then cool with snowfall.
Wet snow – Rainstorms or spring weather with warm, moist winds and cloudy nights
can warm the snow cover resulting in wet snow avalanches. Wet snow avalanches are
more likely on sun-exposed terrain (south-facing slopes) and under exposed rocks or
cliffs.
Wind is the most common cause of avalanches. Wind can deposit snow 10 times faster
than snow falling from storms. Wind erodes snow from the upwind side of obstacles
and deposits snow on the downwind (lee) side. This is called "wind loading".
Terrain:
Ground cover – Large rocks, trees and heavy shrubs help anchor snow, but also create
stress concentrations between anchored and unanchored snow.
Slope profile – Dangerous slab avalanches are more likely to occur on convex slopes that
produce stress concentrations within surface snow due to varying creep rates.
Slope aspect – Leeward slopes are dangerous because windblown snow adds depth and
creates dense slabs. South facing slopes are more dangerous in the springtime due to
increasing solar effects.
Slope steepness – Snow avalanches are most common on slopes of 30 to 45 degrees.
Snowpack:
Snow texture—the feel, appearance, or consistency of the snow determined by the
shape, size and attachment of snow grains that comprise the particular snow layer. Also
the inter-granular relationship— the overall feel of a snow layer, specifically the relative
quantities of the different types and sizes of snow particles in a particular layer, and the
size, shape and arrangement of grains as seen with a hand lens. A layer of small grained
moist snow has a distinctly different texture—much more cohesive and able to make
snowballs—than well faceted snow that falls apart in one’s hands and exhibits very little
internal cohesion.
Snow layering – The snowpack is composed of ground-parallel layers that accumulate
over the winter. Each layer contains ice grains that are representative of the distinct
meteorological conditions during which the snow formed and was deposited. Once
deposited, a snow layer continues to evolve under the influence of the meteorological
conditions that prevail after deposition.
Snow bonding—in the absence of strong temperature gradients within a dry snowpack,
this is the normally stabilizing or “rounding” process whereby individual snow grains or
layers come into contact and gradually strengthen the ice skeleton or snow layer(s)
through sintering or the formation of ice “necks” between the grains. This sintering
process results from shape or size driven vapor pressure differences between or within
grains or layers and involves preferential transfer of water vapor and subsequent vapor
deposition. The associated redistribution of water vapor results in inter-granular
attachments or bonds between grains through an expanding ice matrix, and typically
Final Hazard Profile – Avalanche
Washington State Hazard Mitigation Plan June 2013
Tab 5.2 – Avalanche Profile - Page 6
results in gradual strengthening of the surrounding snowpack structure. However, it
must be noted that in the presence of strong temperature gradients within or between
snow layers, a different metamorphic process in the snow cover can occur which is
known as faceting—a process that results in new crystal growth and/or recrystallization
of existing snow grains, often producing general weakening of the snow structure.
Faceting is characterized by strong (often local) temperature gradients in the snow pack
and resulting strong vapor pressure gradients that move mass from warmer grains
(higher vapor pressure) to colder grains (lower vapor pressure). As the process evolves
and more mass is transferred, faceting snow loses existing grain bonds, forms new
grains, and in general becomes more disaggregated and sugary (hence the related term
“sugar snow”). In observations and tests, the hardness of a faceting snow layer
decreases with time and it becomes easier to penetrate and pull individual faceted
grains out of a snow pit wall.
Avalanche forecasting and control is a regular winter expense. The Washington State
Department of Transportation’s annual budget for removing snow and ice and for avalanche
control for the highways that cross the Cascade Mountains is about $38 million. Additionally,
the transportation department, ski areas, State Parks and Recreation Commission, US Forest
Service, National Weather Service, National Park Service, and other agencies, help fund the
Northwest Weather and Avalanche Center, which provides daily forecasts throughout the
avalanche season for those involved with highway avalanche control and for recreationalists. In
FY 2011 the avalanche center received approximately $603,984 in direct funding and in-kind
contributions for its operations.
7
During the avalanche season, the Northwest Weather and Avalanche Center issues twice daily
mountain weather forecasts and daily (or more often) avalanche forecasts as well as special
statements and avalanche warnings during times of significantly increased avalanche danger.
Additionally, the NWAC maintains and manages a comprehensive network of remote mountain
weather stations (see www.nwac.us/weatherdata/map/) that provide hourly weather data to
users and cooperators alike.
The informational chart below details the current 2010 version of the US Danger Scale utilized
by the NWAC when issuing their warnings.
Final Hazard Profile – Avalanche
Washington State Hazard Mitigation Plan June 2013
Tab 5.2 – Avalanche Profile - Page 7
Final Hazard Profile – Avalanche
Washington State Hazard Mitigation Plan June 2013
Tab 5.2 – Avalanche Profile - Page 8
Avalanche Mitigation
The Washington State Department of Transportation conducts active winter time avalanche
control or mitigation on two of the state’s mountain highway passes: Stevens Pass on U.S.
Route 2 and Snoqualmie Pass on Interstate 90. This means avalanches are triggered
intentionally on slopes above the roadways in a
controlled environment to minimize traffic disruption
and promote public safety. It also conducts passive
avalanche control through elevated roadways so
avalanches can pass under highways, over snow sheds
over highways, into catchment basins to stop avalanche
flow, and into diversion dams and berms to keep snow
off highways. In addition to these controls the WSDOT
closes three passes in winter because avalanches are so
prevalent that control measures would be too costly and
hazardous.
8
These passes are Chinook Pass (elevation
5,430’) that connects Enumclaw and Yakima, Cayuse
Pass (elevation 4,675’) that connects Chinook and White
Pass along the east slope of the Cascades, and
Rainy/Washington Passes (elevations 4,855’ and 5,500’) along the North Cascades Highway,
which connects the Skagit Valley to eastern Washington. This portion of the North Cascades
Highway holds the distinction of being among the top areas in the United States for most
avalanche chutes per mile of highway. Some areas of this highway have five avalanche paths in
a mile of roadway.
9
Specific times of the winter when these passes close vary from year to year
and are based on snow accumulation, personnel, avalanche risk, and a variety of other factors.
Opening for the passes varies as well, although the target date for their opening is May 1 to
coincide with the beginning of fishing season.
Avalanche control is a winter-long task on the two
primary travel corridors in Washington that must
remain open all year long. The more heavily impacted
corridors are Interstate 90 -Snoqualmie Pass (elevation
3,022’); the primary East-West corridor serving the
Seattle-Tacoma-Olympia area and US Highway 2 -
Stevens Pass (elevation 4,061’) connecting Everett and
Wenatchee. Snoqualmie Pass is the only interstate
highway link in Washington through the Cascades. It
averages 450 inches of snowfall each winter and has
traffic volumes of over 32,000 vehicles a day, including
8,000 trucks. Interstate 90 is closed an average of eighty hours per year due to avalanches.
10
It
is estimated that a two-hour closure of Snoqualmie pass costs the state’s economy over $1
million.10
Intermittent winter time avalanche control is also used by WSDOT along US-12 (White Pass)
Use of explosives to prematurely trigger avalanche on
Chinook Pass
Snow shed over Interstate 90 Westbound
Final Hazard Profile – Avalanche
Washington State Hazard Mitigation Plan June 2013
Tab 5.2 – Avalanche Profile - Page 9
when conditions warrant, however, an avalanche control program for US 12 does not exist at
this time. Occasional closures due to avalanche danger have occurred. Avalanche control is
also done during spring time re-opening of SR 410 (Chinook and Cayuse Passes) and SR 20
(Washington Pass).
Transportation Corridor Avalanche Control
11
12
Snow slides are a fact of life in the Cascade Mountains. WSDOT avalanche control technicians
work to reduce the potential hazard using all available experience and tools. This means
operating a comprehensive program to control when and how to bring down unstable snow.
Each winter, WSDOT stations specially trained avalanche control teams at Hyak, near the I-90
Snoqualmie Pass summit and at Berne Camp, near the US 2 Stevens Pass summit. The teams
work to reduce the avalanche hazard as well as the number and duration of highway closures.
Active avalanche control is when crews intentionally trigger an avalanche. To do this, WSDOT
stops traffic and triggers the avalanche. Avalanche control must be done during heavy
snowfall. However, to be most effective, active control work is done just as the snow is
becoming unstable; but before it slides. Whenever possible, the control work is scheduled
outside of peak traffic hours.
When an avalanche hazard develops, WSDOT uses artillery or explosives to trigger the
avalanche. These are various methods of delivery depending on the topography and
accessibility to the avalanche path. Explosives are placed by hand, cable-pulley bomb trams, or
with surplus military weapons. In addition to active avalanche control, WSDOT also uses
passive control methods to control snow slides. These include snow sheds over the highway;
elevated roadways so avalanches pass under them, or with catchment basins to stop the
avalanche before snow reaches the highway. WSDOT also uses diversion dams and snow
berms to keep the snow off the highway.
WSDOT avalanche control activity affects more than travelers. Backcountry recreation has
become very popular. From the US 2/Stevens Pass Ski Area, skiers and snowboarders can
access backcountry areas and potentially venture into the highway avalanche zones. WSDOT
posts warning signs at the top of the ski area and in key locations, but are sometimes ignored.
Besides risking injury, skiers and snowboarders sometimes trigger avalanches. They also create
a hazard for themselves and others by hitchhiking back to the summit. When vehicles stop to
give hitchhikers a ride, it creates a traffic hazard. The Washington State Patrol petitioned
WSDOT to post the avalanche zones from milepost 58 to 66 to prohibit hitchhiking and WSP
troopers vigorously enforce this ban. Skiers and snowboarders face similar personal hazards at
two Snoqualmie Pass ski areas when they ignore signs and venture outside ski area boundaries.
Recreational Activity Avalanche Control
Avalanches don't happen by accident and most human involvement is a matter of choice, not
chance. Most avalanche accidents are caused by slab avalanches which are triggered by the
victim or a member of the victim's party. However, any avalanche may cause injury or death
and even small slides may be dangerous. Hence, always practice safe route finding skills, be
aware of changing conditions, and carry avalanche rescue gear. Learn and apply avalanche
Final Hazard Profile – Avalanche
Washington State Hazard Mitigation Plan June 2013
Tab 5.2 – Avalanche Profile - Page 10
terrain analysis and snow stability evaluation techniques to help minimize your risk. Remember
that avalanche danger rating levels are only general guidelines. Distinctions between
geographic areas, elevations, slope aspect, and slope angle are approximate, and transition
zones between dangers exist. No matter what the current avalanche danger, there are
avalanche-safe areas in the mountains.
The Avalanche Danger Rose represents the highest danger level(s) expected for the indicated
area (by elevation and aspect) for the daylight hours. The danger trend arrow (lower left part
of rose graphic) indicates the most significant (highest impact) avalanche danger change
expected for the daylight hours, ranging from strongly increasing (arrow pointing up) to strongly
decreasing (arrow pointing down). Although the danger rose figures only indicate the greatest
danger for the particular region for the daylight hours, danger trends for overnight hours are
discussed in the text product. The danger rose can be visualized as a conical mountain within
the forecast area that is divided into elevation rings and aspect slices as shown in the example.
The first sample rose shown below with the mountain indicates an avalanche warning along
with a strongly increasing danger trend and high danger above 4000 feet.
The second sample rose shown below indicates two danger levels between 3000 ft (the
outermost ring) and 7000 ft (the innermost ring). The danger is moderate in yellow and
considerable in orange and indicates the following danger description: Considerable avalanche
danger on northwest through northeast exposures above 4000 feet, otherwise moderate
avalanche danger below 7000 feet. The slightly upward angled arrow in the left lower part of
the figure indicates the most significant danger trend is for a slight danger increase during the
day.
Final Hazard Profile – Avalanche
Washington State Hazard Mitigation Plan June 2013
Tab 5.2 – Avalanche Profile - Page 11
Previous Occurrences
As shown, Washington ranks second behind Colorado in fatalities from avalanches with 187
from 1950 to 2006.
13
In the United States since the year 2000, there have been an average 200
people reported caught in avalanches each winter: 90 were partly buried or buried, 32 were
injured, and 28 were fatalities. United States property losses due to avalanches in this same
period ranged from a low of $30,000 to a high of $2 million. The largest accident in Washington
involving an avalanche, known as the Wellington Disaster, occurred in 1910 when two trains
near Stevens Pass were swept off the tracks killing 96 passengers on board. Although there is
not any recorded history of a catastrophic
disaster in this state from an avalanche, the
potential for this hazard to cause massive
destruction exists. A recent disaster from an
avalanche took 50,000 lives in Iran in 1990
burying many villages in its path. The
inhabitants of Yungay, Peru experienced a
similar fate in 1970 when an earthquake
triggered an avalanche on the slopes of
Nevado de Huascarán sending millions of tons
of snow into the valley below (Figure 1-4). The city and its 20,000 inhabitants were buried
under 100 million cubic yards of snow, mud and rubble. Only 92 people survived.
14
Thousands of avalanches occur in the mountains of Washington every winter. Hundreds of
these incidents can affect travel over the mountain pass highways, and all present the potential
for accidents, delays, and fatalities to the citizens of the State. Current mitigation strategies in
place lessen the potential for impact by this hazard. However, the possibility still exists for
avalanches to affect the people, economy, environment, and property of Washington.
Aerial Photo of 1970 Yungay, Peru
Avalanche
Peru Avalanche
Avalanche Fatalities by State 1950-2006
Final Hazard Profile – Avalanche
Washington State Hazard Mitigation Plan June 2013
Tab 5.2 – Avalanche Profile - Page 12
Selected Avalanches in Washington State – 1910 to Present
15
Date
Location
Casualties
1910
Stevens Pass
Two trains swept off their tracks, 96 dead
1939
Mount Baker
6 dead
1958
Silver Creek
4 buried
1962
Granite Mountain
2 dead
1962
Stevens Pass
2 buried
1971
Yodelin
4 dead, several buried
1974
Source Lake
2 dead
1975
Mount St. Helens
5 dead
1981
Mount Rainier
19 dead, 18 injured
1988
Mount Rainier
3 dead
1992
Mount Rainier
2 dead
1994
Mission Ridge
1 dead
1996
Index
3 dead
1996-
1997
Snoqualmie Pass
Hundreds of travelers stranded after repeated avalanches closed Interstate
90 during the holidays
1998
Drop Creek
Snowmobile buried, 1 dead
1998
Mount Rainier
1 climber dead, several climbers injured
1998
Mount Baker
1 dead
1999
Mount Baker
1 snow boarder and 1 skier dead
2000
Crystal Mountain
1 dead
2001
Twin Lakes
2 dead
2001
Mount Baker
1 dead
2001
Lake Ann
1 dead
2002
Crystal Mountain
1 dead
2003
Snoqualmie Pass
1 snowshoer dead
2003
Mount Baker
1 snowshoer dead, 2 snowshoers injured
2003
Navajo Peak
1 snowmobiler dead
2004
Mount Baker
1 snowboarder dead
2004
Mount Rainier
2 climbers dead
2005
Snoqualmie Pass
1 skier dead
2005
Mount Baker
2 snowboarders buried – found alive by beacon (2 separate incidents/days)
2006
Mount Baker
1 skier dead
2006
Tiffany Mountain
1 snowmobiler dead
Final Hazard Profile – Avalanche
Washington State Hazard Mitigation Plan June 2013
Tab 5.2 – Avalanche Profile - Page 13
2006
Mount Hood
3 skiers buried
2007
Edit Ck Basin, Mt Rainier
National Park, WA
2 snowshoers totally buried, found by probing under ~6-10 ft of snow
2007
Union Creek, south-central
WA Cascades, northeast of
Crystal Mt, WA
3 snowboarders dead. Group departed on weekend trip on 11/30/2007.
Reported missing on 12/2/07. Subsequent searches on ground and air
found no evidence of any of the group. Official search abandoned 12/8/07.
Final Search and Recovery effort concluded late June, 2008 when the three
missing snowboarders were found buried in avalanche debris in Union
Creek.
2007
Northway at Crystal Mt
Resort, WA
Two ski patrollers caught, 1 totally buried, 1 mostly buried and able to self
extricate--found and rescued partner; south-central Washington Cascades
at Crystal Mountain Resort, WA
2007
Snoqualmie Pass
2 hikers killed; 1 additional buried, injured & self rescued
2007
Mount Rainier
1 skier dead
2008
Rockford, WA
1 resident caught, buried and killed by roof avalanche while shoveling walk
and clearing roof
2008
Tatie Peak, near Harts
Pass, northern WA
Cascades
1 snowmobiler dead
2008
Kahler Glen, north-central
WA Cascades near Lake
Wenatchee
A large natural avalanche released during the late afternoon of February 7,
impacting and mostly destroying a home in the Kahler Glen development
just above and west of the Kahler Glen Golf Course
2008
Lake Twenty-two trail near
Mt. Pilchuck, north-central
WA Cascades
8 hikers descending Lake Twenty-Two Trail; 4 in party were caught by
avalanche. Slide partially buried one; totally buried three. Three were
found by spot probing and survived; 1 not recovered until later by rescue
team died.
2008
Excelsior Pass below
Church Mtn, northern WA
Cascades
5 snowmobilers high marking in the Excelsior Pass area triggered a large 5-7
ft deep slab. The avalanche caught five, partly burying one, totally burying
and killing two. Victims reportedly found by beacon and probing under
three and six feet of snow.
2009
Hogsback Mtn, south-
central WA Cascades
One skier caught and completely buried under ~2.5 ft of snow. Found by
partner's beacon and recovered within about 10 minutes.
2010
Morning Star Peak, north-
central WA Cascades
One hiker/climber caught, partially buried and killed; dog recovered alive
2011
Hooky Bowl on Trout Ck
drainage, near Mt
Cashmere, east slopes
central WA Cascades
1 BC skier in a group of 5 triggered and caught by slide, carried through
trees and fatally injured. Found deceased on the surface by party
members.
2011
Backside of Cowboy Mtn
toward Tunnel Ck, west of
Stevens Pass Ski Area,
north central WA Cascades
Snowboarder triggered and caught by wet loose slide, swept into tree band
and fatally injured. Found quickly by party members but failed to respond
to CPR
2012
Tunnel Creek draining
west of Stevens Pass
Mountain Resort, north-
central WA Cascades
Four skiers triggered and caught by 2-3 foot slab while skiing the Tunnel
Creek back country off Cowboy Mountain to the SSW of the ski area. Three
buried and killed (combination of trauma and suffocation), one survived
with air bag deployed.
Final Hazard Profile – Avalanche
Washington State Hazard Mitigation Plan June 2013
Tab 5.2 – Avalanche Profile - Page 14
2012
WAC Bluff area, east of
Alpental Ski Area, central
WA Cascades, WA
Three snowboarders entered the 80s chute in the back country to the east
of Alpental Ski Area, triggering a slide. The slide caught two, one of whom
was able to self arrest. The other boarder was carried over a steep cliff
chute and died from trauma.
Probability of Future Events
Avalanches occur regularly every year in mountain areas. Many weather, snowpack and terrain
factors determine actual avalanche danger. Avalanches along two key mountain highway
passes are limited due to ongoing mitigation to control slides during winter months.
Nonetheless, those highways do get closed regularly for control work and cleanup. Recreation
activity in backcountry areas results in countless avalanches and a few deaths each year.
Jurisdictions Most Vulnerable to Avalanches
Based on the location of key transportation routes and recreational areas threatened by
avalanche, parts of the following counties are most vulnerable to avalanche:
Asotin
Chelan
Ferry
Garfield
King
Kittitas
Klickitat
Lewis
Okanogan
Pend Oreille
Pierce
Skagit
Skamania
Snohomish
Whatcom
Yakima
Final Hazard Profile – Avalanche
Washington State Hazard Mitigation Plan June 2013
Tab 5.2 – Avalanche Profile - Page 15
Transportation routes threatened by avalanche
16,17,18.
Highway closures due to avalanche can have a significant economic impact on the state.
Economists estimate that closing Interstate 90 over Snoqualmie Pass has an economic cost to
the state of between $500-750,000 per hour for stalled shipping, lost perishables, and
rerouting. During the winter of 1996-97, there were 276 hours of closure of I-90 over
Snoqualmie Pass, 70 percent related to avalanche control and avalanche safety closures; these
closures were more than in any other year in recent times. The closures cost the state’s
economy an estimated $144 million (in 2002 dollars).
The Washington Department of Transportation spends considerable effort each winter keeping
the following mountain passes open and free from avalanches:
King County – Snoqualmie Pass I-90, Stevens Pass US 2.
Kittitas County – Snoqualmie Pass I-90, Blewett Pass US 97.
Chelan County – Stevens Pass and Tumwater Canyon US 2.
Passes closed all winter with spring openings that have residual avalanche hazard after they are
open are:
Pierce, Yakima Counties – Chinook Pass SR 410, Cayuse Pass SR 123.
Skagit, Okanogan Counties – North Cascades Highway SR 20.
Mountain passes and highways that pose avalanche problems or that have the potential for
problems in the worst conditions are:
Lewis and Yakima Counties – White Pass US 12.
Skagit County – Diablo Canyon SR 20.
Skamania County – Johnston Ridge, SR 504.
Asotin County – SR 129 south of Anatone.
Whatcom County – SR 542 to the Mount Baker Ski Area.
Recreation areas threatened by avalanche
19
With better equipment allowing more people to explore further into the wilderness, areas
threatened by avalanche are those accessible by skiers, snowshoers, snowboarders, climbers,
hikers and snowmobilers outside developed ski resorts in the mountains of Washington. This
includes the areas that people can reach via Sno-Parks (parking lots cleared of snow) in Asotin,
Chelan, Ferry, Garfield, King, Kittitas, Klickitat, Lewis, Okanogan, Pend Oreille, Pierce, Skagit,
Skamania, Snohomish, Whatcom, and Yakima counties; Hurricane Ride in Olympic National Park
(Clallam County) is another area providing easy access to avalanche-prone terrain (see map
generally depicting areas at-risk to avalanche below).
Final Hazard Profile – Avalanche
Washington State Hazard Mitigation Plan June 2013
Tab 5.2 – Avalanche Profile - Page 16
State Agency Structures at Risk
State Agency Structures At Risk
Number and Function
of Buildings
No. of Affected Staff / Visitors
/ Residents
Approx. Value of Owned
Structures
Approx. Value of
Contents
Total at-risk buildings:
0
0
0
0
However, WSDOT has identified a number of state highways as being at risk to avalanche:
1. Asotin County – SR 129 south of Anatone.
2. Chelan County – Stevens Pass and Tumwater Canyon US 2.
3. King County – Snoqualmie Pass I-90, Stevens Pass US 2.
4. Kittitas County – Snoqualmie Pass I-90, Blewett Pass US 97.
5. Lewis and Yakima Counties – White Pass US 12 and SR 410.
6. Pierce County – Chinook Pass SR 410, Cayuse Pass SR 123.
7. Skagit County – North Cascades Highway SR 20.
8. Skamania County – Johnston Ridge, SR 504.
9. Whatcom County – SR 542 to the Mount Baker Ski Area.
Total at-risk critical
facilities: 0
0
0
0
Four state highways considered emphasis corridors because of their importance to movement of people and
freight have been identified as being at risk to avalanche:
1. U.S. Highway 2
2. U.S. Highway 12
3. Interstate 90
4. U.S. Highway 97
Potential Climate Change Impacts
20,21,22,23
With the advent of climate change coming into worldwide focus; it is necessary to take into
account the potential effects this emerging climate crisis may have on the dangers associated
with avalanches. The research done so far indicates the potential for avalanches to become
more frequent and deadly, as global warming effects the melting of permafrost, the permanent
frozen layer of snow that gives our mountains and peaks their distinctive look. Already, the
melting of permafrost can be blamed on several recent Alpine disasters, including the
avalanches which killed more than 50 people at the Austrian resort of Galtur in 1999.
24
According to a 2005 Governor’s report prepared by the Climate Impacts Group titled Uncertain
Future: Climate Change and its Effects on Puget Sound, from “paleoclimatological evidence, we
know that over the history of the earth high levels of greenhouse gas concentrations have
Final Hazard Profile – Avalanche
Washington State Hazard Mitigation Plan June 2013
Tab 5.2 – Avalanche Profile - Page 17
correlated with, and to a large extent caused, significant warming to occur, with impacts
generated on a global scale.” While the report also indicates that the “ultimate impact of
climate change on any individual species or ecosystem cannot be predicted with precision,”
there is no doubt that Washington's climate has demonstrated change.
In July 2007, the Climate Impacts Group launched an unprecedented assessment of climate
change impacts on Washington State. The Washington Climate Change Impacts Assessment
(WACCIA) involved developing updated climate change scenarios for Washington State and
using these scenarios to assess the impacts of climate change on the following sectors:
agriculture, coasts, energy, forests, human health, hydrology and water resources, salmon, and
urban stormwater infrastructure. The assessment was funded by the Washington State
Legislature through House Bill 1303.
In 2009, the Washington State Legislature approved the State Agency Climate Leadership Act
Senate Bill 5560. The Act committed state agencies to lead by example in reducing their
greenhouse gas (GHG) emissions to: 15 percent below 2005 levels by 2020; 36 percent below
2005 by 2035; and 57.5 percent below 2005 levels (or 70 percent below the expected state
government emissions that year, whichever amount is greater.). The Act, codified in RCW
70.235.050-070, directed agencies to annually measure their greenhouse gas emissions,
estimate future emissions, track actions taken to reduce emissions, and develop a strategy to
meet the reduction targets. Starting in 2012 and every two years thereafter, each state agency
is required to report to Washington State Department of Ecology the actions taken to meet the
emission reduction targets under the strategy for the preceding biennium.
Recognizing Washington’s vulnerability to climate impacts, the Legislature and Governor Chris
Gregoire directed state agencies to develop an integrated climate change response strategy to
help state, tribal and local governments, public and private organizations, businesses and
individuals prepare. The state Departments of Agriculture, Commerce, Ecology, Fish and
Wildlife, Health, Natural Resources and Transportation worked with a broad range of interested
parties to develop recommendations that form the basis for a report by the Department of
Ecology: Preparing for a Changing Climate: Washington State’s Integrated Climate Change
Response Strategy.
Over the next 50 - 100 years, the potential exists for significant climate change impacts on
Washington's coastal communities, forests, fisheries, agriculture, human health, and natural
disasters. These impacts could potentially include increased annual temperatures, rising sea
level, increased sea surface temperatures, more intense storms, and changes in precipitation
patterns. Therefore, climate change has the potential to impact the occurrence and intensity of
natural disasters, potentially leading to additional loss of life and significant economic losses.
Recognizing the global, regional, and local implications of climate change, Washington State has
shown great leadership in addressing mitigation through the reduction of greenhouse gases.
Final Hazard Profile – Avalanche
Washington State Hazard Mitigation Plan June 2013
Tab 5.2 – Avalanche Profile - Page 18
References
1
Washington State 2001 Hazard Identification and Vulnerability Assessment, Washington State Military Department,
Emergency Management Division, April 2001.
2
Bruce Tremper. Frequently Asked Questions about Avalanches, USDA Forest Service Utah Avalanche Center. (Undated)
Accessed: Aug. 10, 2009. Available at: http://utahavalanchecenter.org/education/faq.
3
United States Avalanche Fatalities by State, 1985-86 to 2009/10(Feb 1, 2010), Northwest Weather and Avalanche Center,
http://www.nwac.us/media/uploads/pdfs/US%20Annual%20Avalanche%20Statistics%20by%20State--1985-20XX.pdf (Feb 1,
2010).
4
Written communication from avalanche forecaster Mark Moore, Northwest Weather and Avalanche Center, U.S. Department
of Agriculture, May 9, 2003.
5
Ron Judd, Northwest mountains have the right ingredients for avalanches, Seattle Times, February 22, 2004.
6
Avalanche Danger, Mount Rainier National Park, online fact sheet,
http://www.nps.gov/mora/planyourvisit/upload/avalanche.pdf, (Undated).
7
Northwest Weather and Avalanche Center 2007-2008 Annual Report, United States Department of Agriculture, U.S. Forest
Service Pacific Northwest Region, May 2008.
8
“Avalanche Control,” Washington State Department of Transportation, n.d., <http://www.wsdot.wa.gov/
maintenance/avalanche/> (October 5, 2007).
9
As per maintenance staff member, Washington State Dept. of Transportation – North Central Office, October 9, 2007.
10
“I-90 Snoqualmie Pass East – Hyak to Keechelus Dam,” Washington State Department of Transportation, n.d.,
<http://www.wsdot.wa.gov/projects/i90/snoqualmiepasseast/hyaktokeechelusdam/> (October 3, 2008).
11
Washington State Department of Transportation: Avalanche Control. Accessed August 6, 2009. Available at:
http://www.wsdot.wa.gov/maintenance/avalanche/.
12
Northwest Weather and Avalanche Center. Recent Northwest Avalanche Accident Summaries, 1998-2009. Accessed Feb.
19, 2009. Available at: http://www.nwac.us/accidents/.
13
“Avalanche Accident Statistics,” Colorado Avalanche Information Center, n.d., <http://avalanche.state.co.us/
Accidents/Statistics/> (October 4, 2007).
14
“Avalanches: Case Studies,” Forces of Nature, n.d., <http://library.thinkquest.org/C003603/english/index.shtml> (October 9,
2007).
15
Northwest Weather and Avalanche Center. The Avalanche Danger Rose Summary. Accessed August 6, 2012. Available at:
http://www.nwac.us/.
16
Written communication from Terry Simmonds, Washington State Department of Transportation, March 27, 2003.
17
Tom Paulson, In Avalanche County, Thinnest of Defenses Hangs Tough, Seattle Post-Intelligencer, December 27, 2001.
18
Written communication from Terry Simmonds, Washington State Department of Transportation, March 27, 2003.
19
Oral communication with avalanche forecaster Mark Moore, Northwest Weather and Avalanche Center, U.S. Department of
Agriculture, April 8, 2003.
20
Snover, A.K., P.W. Mote, L. Whitely Binder, A.F. Hamlet, and N.J. Mantua. (2005) Uncertain Future: Climate Change and its
Effects on Puget Sound. A report for the Puget Sound Action Team by the Climate Impacts Group (Center for Science in the
Earth System, Joint Institute for the Study of Atmosphere and Oceans, University of Washington, Seattle).
Final Hazard Profile – Avalanche
Washington State Hazard Mitigation Plan June 2013
Tab 5.2 – Avalanche Profile - Page 19
21
Climate Impacts Group, Washington State Department of Ecology, The Washington Climate Change Impacts Assessment, April
2012. Accessed 10 September 2012. Available at http://cses.washington.edu/cig/res/ia/waccia.shtml#report
22
Washington State Department of Ecology, Washington State’s Integrated Climate Response Strategy, April 2012. Accessed 10
September 2012. Available at http://www.ecy.wa.gov/climatechange/ipa_responsestrategy.htm
23
Walsh, Tim. Department of Natural Resources, Geology and Earth Sciences, Washington Geological Survey. Conversation 31
August 2012.
24
Robin McKie, “Decades of Devastation Ahead as Global Warming Melts the Alps,” People and Planet, July 23, 2003,
<http://www.peopleandplanet.net/doc.php?id=2026> (October 9, 2007).
