Natural Disasters

The Oso Slide

March 22, 2014, was a dreadful day in Washington state history. A tragic landslide occurred 4 miles east of Oso, Washington, a small, rural community 60 miles northeast of Seattle, nestled in a beautiful valley of the North Cascades. A hillside collapsed, sending mud and debris rushing south across the North Fork of the Stillaguamish River.

In the left image above, State Route 530 is the winding thin vertical line on the far left. The adjacent vertical line, more or less parallel to the highway and to the right of the road, is the Whitehorse Trail, laid over the road bed of the historic Northern Pacific Railway, known as the Whitehorse Express. Arlington would be above the top of the image, Darrington would be below the image. Steelhead Drive is a faint, thin line that runs between the highway and trail on the left and the Stillaguamish River that winds through the center of the image. In the image on the right, the entire neighborhood is covered by deep piles of detritus from the slide.

Oblique aerial photograph of the 2014 landslide in northwest Washington. This image shows the entire extent of the landslide source area and path. This event is commonly named the “Oso Landslide” in many official reports. It is also referred to as the “SR530 Landslide,” as named by Snohomish County and Washington State. Credit: Mark Reid, USGS (public domain)

The Steelhead Drive neighborhood was destroyed, buried by a fast moving wall of mud roughly 1 mile square and 30 to 70 feet deep. Forty-three children, women, and men lost their lives, and 49 homes and other structures were destroyed. Excluding landslides caused by volcanic eruptions, earthquakes, and dam failures, the Oso slide is the deadliest single landslide in US history. This set of posts is a memorial to the lives lost in the Oso Slide, and a commendation of the rescuers and re-builders following the slide.

The Oso Slide, known more formally as the Hazel Slide for geologic purposes, was much more than a geological event. It was also a human tragedy, involving death and serious injury, and the complete destruction of almost 50 homes. The story is more than geologic disaster and human loss. Rescue and recovery efforts by communities near and far were also vital elements of this story.

The Rain

The image below is a Google Earth view of the Oso slide.

These images shows the slide from the valley floor in 2020.

Oso Slide and Memorial Sign

The autumn and early winter of 2013 and January of 2014 were unusually dry in northwest Washington state. Concerns about the severe drought conditions caused the Washington State Department of Ecology to convene the Water Supply Availability Committee in early February, 2014, for the first time in four years. Snowpack in the Cascades and Olympic Peninsula was a fraction of normal, 33% of normal in the Olympic Mountains, and 49% of normal on the western slopes of the North Cascades.

The weather changed dramatically in February. Heavy rain and mountain snow began falling in Washington, alleviating fears for summer drought. The rain and snow continued for days and weeks on end, and in just two weeks, the ground became saturated, and fears of substantial flooding grew. Between February 1 and March 1, snowpack in the Olympic Mountains grew from 32″ to 64″. Snohomish County, Washington, north of Seattle, was one of 20 counties included by Governor Inslee in a disaster declaration because of severe, life threatening local flooding in February.

The Washington State Department of Natural Resources states on its website, “Washington is one of the most landslide-prone states in the country, with hundreds to thousands of events each year. The direct cost of landslide damage includes the repair of roads and property and the loss of life.” The winter of 2014 was tragic demonstration of the dangers of slides in Washington.

Gravity, friction, and the addition of water affects the potential for slides. The addition of water makes a slope more slippery by reducing friction between upper and lower layers of soil. Water also reduces cohesion of soil particles, decreasing the internal strength of soil material, and water increases the weight of soil. Water is heavy. If an acre of land soaks up just one inch of rain, that acre gains as much as 234,000 pounds.

The top of the Oso Slide, aka the Hazel Slide above the location of the historic small community of Hazel, is at the southeast end of the Whitman Bench, a ridge some 800 feet above the river valley floor, that is west and southwest of Mt Higgins, and about four miles east, up the Stillaguamish River Valley, from the community of Oso.

Environmental Factors Affecting the Hazel Landslide Shaded relief image of U.S.G.S. Oso and Mt. Higgins 7½-minute topographic quadrangles illustrating regional topography for the Hazel landslide.

History of Flooding and Slides

Despite the tragedy and devastation of the Oso Slide there were reasons that a mudslide of this magnitude, in this general location, could have been anticipated. The Whitehorse Express, the Northern Pacific Railway spur line from Arlington to Darrington, was completed in 1901 to transport lumber and logs from the mills and timber companies in the Sauk Prairie. The spur line was abandoned in 1991, in part due to severe damage to infrastructure caused by flooding along the Stillaguamish River.

Flooding and slides are closely entwined with the history and development of the Stillaguamish River Valley. Various sources, including contemporaneous accounts, described the long series of floods and mudslides, dating back as far as the beginning of the 20th century.

A 1904 landslide described as 180 feet long and 10 feet thick cut the NP tracks between Darrington and Oso. A one-room school in Hazel was damaged by flooding in 1924 and the road and railroad tracks were blocked for several days until they could be cleared. Hazel Holm, a young resident at the time, recalled, “There was a bad flood in 1924 that washed away two homes, the school, Seattle City Light building and the big water tank for the train.  A big slide made the railroad tracks and road impassable for several days.

Heavy rains in 1932, during the Great Depression, resulted in serious flooding of the Sauk and Stillaguamish Rivers. Bridges and buildings at Darrington, Hazel, and Mansford, including the sawmill and homes at Hazel. The small school at Hazel-Higgins was forced to close permanently and students were sent to the larger school at Whitehorse. Darrington lost four bridges. The Hazel sawmill could not recover and was taken over by the bank.

Severe flooding in 1937 caused an extensive mudslide on the north bank of the Stillaguamish River at Hazel, resulting in upriver flooding and forcing the river to cut a new channel to the south. Aerial photos at the time revealed multiple active slides. The Stillaguamish was again blocked briefly by mudflow in 1951. The following year, aerial photos showed that large blocks of soil and rock had been moved by flowing mud, leaving escarpments 70 feet high.

In January, 1967, mud flows and large moving blocks of rock and debris forced the river channel 700 feet south at the Hazel site. A November, 1988 slide pushed river channel even farther south. On January 25, 2006, a new channel was cut to ease flooding caused another large slide.

One survivor of the 2014 Oso slide, Robin Youngblood, told CNN at the time that she had no idea about the flood and slide risks despite the then-recent 2006 flood. Others were fatalistic, crediting Mother Nature. Another survivor, living in a barn temporarily after the slide, promised to return, saying, ““People say those people should have known and shouldn’t have bought there. Nobody could have known,”

Despite the residents’ lack of prior knowledge, a century of flooding, mudslides, and destruction could have reasonably informed the residents’ of the potential, the likelihood, of danger.

The next post in this series will describe the slide itself, the loss of life, the rescue efforts, and the living memorial to the victims.

Images and text are copyrighted by Tom Cochran Vagabond Photography, except as noted above. My gallery of images that I took of the Oso slide and nearby areas along SR 530 are available for purchase at Oso Washington. My blog about State Route 530 describes the highway from Arlington to Darrington to Rockport in a series of posts.

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