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 Over Two Years: Reflecting on the Oso, Washington Landslide

For a majority of people hearing the news, they were awaken to the impact of what landslides actually do ..

10-05-16

It has been two-and-one-half years passed since a devastating landslide took place near Oso, Washington carrying 18 million tons of sand, till, and clay broken away from a portion of unstable hill onto the community of Steelhead Haven.  Over 40 homes and structures were covered along with one mile of State Route 530.  The Oso slide is considered the deadliest single landslide event in United States history claiming 43 lives and covering one-half square mile depositing debris 30 to 70 feet deep. The killer landslide has been a subject of a NOVA documentary which aired on PBS September 21, 2016.
 


Aftermath of Oso Landslide on March 22, 2014

Most often it is precipitation or earthquakes that trigger landslides.

After one year since the disaster occurred on March 22, 2014, insights were acquired which estimated the speed of the slide at an average of 40 miles per hour and the amount of the material equivalent to covering 600 football fields 10 feet deep.  For a majority of people hearing the news, they were awaken to the impact of what landslides actually do since prior news of landslides reaching the average citizen only involved minor cases of rivers damming up from nearby hills under heavy rains, which are considered inconvenient - but not nearly extreme as the fatal Oso slide.

The landslide is said to have involved a complex sequence of events, including rotation, translation, and flow mechanisms referred to as a debris-avalanche flow. The slope failure occurred in two stages over about one minute, the second stage of movement greatly accelerating crossing the North Fork Stillaguamish River.  The leading edge of the wet-debris avalanche most likely acquired additional water as it crossed the North Fork Stillaguamish River transforming into a water-saturated debris flow.  Debris flows are defined as liquefied slurries of rock, water, and mud that travel great distances at high speeds carrying with it nearly all objects in its path. 

After two years since the incident, further insights indicate that weak saturated ground made the Oso hillside highly susceptible to landslide.  A study of the rainstorm that triggered the landslide found that the precipitation during the weeks leading up to the event were only moderately intense, although considered unusual timing during the normally drier Spring season.

Landslide basics involve the downslope movement of rock or soil which are the natural geologic processes that form and shape landscapes.  A slide occurs when the downward forces of gravity exceed the strength of soil or rock within the slope.  The most precarious settings are steep terrain, although landslides can affect a wide range of slopes.  Most often it is precipitation or earthquakes that trigger landslides.

There are several types of landslides with the most dangerous being flows which happen when saturated ground changes into a liquid-like state swamping downslope areas within minutes.  When they spill into communities, such as the one at Oso, it leaves people virtually no time to escape.  However, eight persons were rescued on the day of the slide, four in serious condition of which two were admitted to intensive care.

One was a 59-year-old military veteran, Tim Ward, and his dog, a German shorthaired pointer, who after a year from the incident were walking one day stopping short when seeing daffodils blooming in a neighbor’s yard.  The flowers reminded Mr. Ward of a garden kept by his wife, Brandy, who died along with 42 others in the massive landslide.

Mr. Ward was flung 700 yards through trees and blackberry bushes into a muddy pile of debris.  His pelvis crushed, he had to learn to walk again and lived at a rehab center and his daughter’s home before finding his own place.  He still has scars on his torso.  Mr. Ward goes three times per week to physical therapy, once to a psychologist, and once to a survivors group.

Robin Youngblood, 64, who escaped from the slide bruised and battered, said she still struggles with PTSD (post traumatic stress disorder) a type of condition military veterans often have, also referred to as “shell-shocked”.   She was in her home when she heard a loud crack, “like thunder,” and wondered, “Is a 747 crash-landing in the valley?”  Then she saw a wall of mud: “I yelled, ‘Oh, my God!’ and at that moment it hit us and we were flying across the valley.”

Gary “Mac” McPherson survived by clawing his way out of the muddy debris but also lost his wife, Linda.  Afterwards, he decided to move 220 miles east and live with his daughter in Bridgeport, Washington.  “[Bridgeport] is really nice.  It’s a small town—very, very dry.”

Tim Ward’s dog, named Blue, was pinned under a fallen cedar tree for three days.  It was the second time during its life that the dog almost died.  The first time was because Blue was stillborn (dying at birth) and Tim’s wife Brandy saved him by giving him resuscitation.  “The only reason Blue is here is because Brandy’s breath was put back into his body,” he said. “So, as he’s with me lying in the bed every night, as I hold him, I am holding a little bit of my bride.”

The 43 Victims

Stories of survivors from The Wall Street Journal, Zusha Elinson, March 20, 2015.