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South Central Avalanche Photos

Photo Gallery for I-90 Snoqualmie Pass and SR 410 Chinook Pass 

Snoqualmie Pass I-90 

Avalanche Control Towers Interstate 90 (I-90) is the major east-west transportation route between the ports, industry, and population of the Puget Sound region and the northern United States. Only 50 miles from the Puget Sound is a major north-south mountain range, The Cascade Mountains. I-90 crosses these mountains via Snoqualmie Pass. At just over 3000’, Snoqualmie Pass is the lowest pass through the Cascades and therefore a logical site for a major interstate highway.

Even with this low elevation, Snoqualmie Pass averages nearly 450” of snowfall each winter, and over 100” of precipitation a year. These heavy amounts of precipitation, combined with the surrounding mountainous terrain, create areas of avalanche hazard. Add to this a traffic volume in excess of 32,000 vehicles per day and the potential for an avalanche problem becomes apparent.

Weather and Snow pack

Checking for crystals The WSDOT Avalanche Control Crew at Snoqualmie Pass continually monitors weather and snow pack conditions to determine the avalanche hazard to Interstate 90. Information is gathered at the Pass, and from a system of remote weather stations located in the Central Cascade Mountains of Washington State. 

Avalanche Control

Using explosives Avalanche control is the process of keeping people and their property safe from avalanches. Two distinct means, Active Avalanche Control and Passive Avalanche Control achieve this. Active avalanche control involves artificially triggering avalanches by use of artillery, explosives, or skis.

Passive avalanche control uses natural and manufactured features to prevent avalanches from reaching people or their property. In a highway setting, this may include snow sheds, elevating the highway, or creating a catchment basin to stop the flow of avalanches.

Reduce snow that reaches highway Active and passive means are sometimes combined to reduce the frequency of active avalanche control and to reduce the amount of snow that reaches the highway when active control is necessary.



When large volumes of avalanche debris reach the highway it causes extensive delays due to the necessary clean up efforts.

Using trucks Our Avalanche Control Crew not only works to reduce the avalanche threat to the highway, but also to reduce the amount of snow that reaches the road. They work with the maintenance crew to ensure that your travels over Snoqualmie Pass are safe and with as few delays as possible.


Chinook Pass SR 410 

At 5432’, Chinook Pass is the highest point along SR 410 as it crosses the central Cascade Mountains of Washington State. Chinook Pass connects the Seattle-Tacoma area to Yakima and I-82 on the east side of the Cascades. Chinook Pass crosses the Cascade Mountains just to the north of Mount Rainier.

This scenic highway provides access to a variety of recreational opportunities. On the west side of Chinook Pass is Mount Rainier National Park, and to the east lies the Wenatchee National Forest. Because of the recreational nature of the area, commercial vehicles are prohibited in Mount Rainier National Park, which SR 410 travels through between Chinook Pass and Crystal Mountain Blvd.

Numerous avalanche paths affect the Chinook Pass highway. These avalanche paths present a significant hazard to the highway when there is snow present. Because of this threat, the highway closes in the late fall and winter months and reopens in the spring or early summer.

SR 123 Location

State Route 410 extends between Enumclaw, WA and Yakima, WA. Over the course of travel the highway crosses two major passes, Cayuse Pass at the junction of SR 123, and Chinook Pass on the crest of the Cascade Mountains. 

Avalanche Control

Avalanche control is necessary during the spring opening of Chinook Pass due to the highway being located in the middle of many avalanche paths. 

Explosives Avalanche control is conducted primarily for the safety of the maintenance crews who must work in the avalanche paths while clearing the highway. The avalanche control crew attempts to stay ahead of the maintenance crew when releasing very large avalanches, as these may damage the road and guardrails if exposed.

Explosives are used to get the big results, but the process of ski cutting can also get some desirable results. Getting big slides to come down also has a secondary benefit of exposing rocks and vegetation, which helps to melt the snow from an avalanche starting zone and eliminate the threat of snow avalanches. 

Avalanche Sign


It is important for backcountry users to understand that avalanche control work is being conducted in the area of SR 410 throughout the spring. Signs are present at the closure gates both east and west of Chinook Pass, and on the hillside just east of Chinook Pass. Artificially released avalanches can occur above and below the highway.

Avalanche hazards also exist from the clearing of snow from the highway. Please be aware of that Bulldozers, snow blowers and other machinery are capable of triggering avalanches below the highway.

Remote weather station

Weather and Snow pack

Weather and snow pack information is important to determine the local avalanche hazard on any given day. The Avalanche Control Crew utilizes remote weather stations for meteorological information and conducts daily surveys of the snow pack to make these determinations. This information is used to determine when and where avalanche control work will be done.



A naturally triggered avalanche puts snow on the road Maintenance

The maintenance crew removes the winter’s snow to open the highway to travelers each spring. Their hard work, often in harm’s way, is what clears the road of snow. Some sections of the road must be cleared many times, as avalanches put more snow on the road. Most of the avalanches are artificially triggered, for the safety of the maintenance crew, but occasionally a naturally triggered avalanche puts snow on the road.

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