On the sunny morning of March 22nd, 2014 at 10:36 a.m. the community of Steelhead Ha-ven was totally buried in debris from a landslide that would forever be referred to as the ‘Oso Landslide’ or “SR 530” in most publications of the event. Oso, Washington is only a few miles from the event and was impacted as well by covering a well-traveled highway for nearly a mile in debris and mud. Although there were people saying that this event was unexpected, the locals always knew that it was an untrustworthy slope, referring to it as ‘Slide Hill’ because of land-slide events that have been seen as far back as the 1900s.
While many smaller, less damaging landslides had happened here before, this particular one was one of the deadliest in Washington’s history and would forever change the future building plans of the town as well as it’s mitigation strategies for the future.
Landslides are very common in wetter climates and places with fairly steep slopes.
Although steep slopes aren’t always part of the reason they fail, sometimes it is multiple factors that cause a slope to fail. These factors include vegetation, time, climate, and the one that is most important in this disaster; water, in this case it is an extended period of heavy precipita-tion. Slopes move and deform over time as the earth moves and changes. There are about 6 different types of landslides. The Oso landslide would be referred to as a Complex Slide because “there are two or more types of sliding.
” The two that I am referring are fallen, where there are free-falling rocks from a cliff that collect dirt and debris and may even form a talus at the bottom of a slope if it doesn’t start to flow like Oso did. When there is flowing you get a combination of wet dirt and soil, as well as rock. It tends to be closer to a mud consistency. In terms of Oso there was liquefaction which highly increases a landslide’s mobility. When this process happens it can also increase how destructive a landslide can be for humans and structures in its path.
There were many indications that there was to be a landslide in this particular area in Washington for years. In fact there had been many landslides before this one on 2014, just not nearly as destructive as Oso. In 2009 there was a mitigation plan put in place for Snohomish County, and in the plan they identify ‘Slide Hill’ as a landslide hazard zone(Gowen). As well as a geomorphologist named Dan Miller who in 2006 made a predictions slideshow of the possible mobility of this slope that if failed, would reach the Steelhead Haven neighborhood(“Building Toward Disaster”). Dan Miller is someone who consistently mentions the instability of the slope and how it could cause a serious loss of life and property if not addressed properly. The straw that broke the camels was the 20 days prior through to March 24th, it rained a record amount, over 200% more than average in this particular season Fully saturating the slope.
This extreme amount of moisture and already built up soil and rock from previous smaller land-slides from the Whitman Bench slump from which the Hazel landslide originated, caused the slope to fail. In many reports of the event they state that if the soil had been denser or drier it wouldn’t have had such mobility, to travel about mile in both directions in one minute(Iverson). First washing over Stillaguamish River and gaining more water to increase flow, to burying a mile of State Route 530 in large pieces of earth and mud. Lastly, the landslide ended after com-pletely destroying the Steelhead Haven neighborhood as predicted by Miller. Covering it with 25 feet of deep thick debris. This landslide wasn’t understood fully at the beginning so it took the Governor of Washington ten days to call a state of emergency. If they had better calculated the risk of such a disaster it wouldn’t have been so deadly.
In this particular landslide there was a enormous loss of life and property. There were forty- three tragic deaths and four injuries that were not fatal. As well as more than fifty properties that were completely demolished and countless livestock(“Building Toward Disaster”). In a publication “Revisiting the Oso Landslide” is it stated that the landslide was moving at about 40 miles per hour, if not faster and that “it moved about 18 tons of sand, till, and clay.” Since there was a lack of preparation and planning involved there was a $60 million dollar settlement to the family’s and victims of the disaster. Landslides can be linked to almost any other natural hazard on our planet. Such as earthquakes, volcanic eruptions, fires, and flooding. In the United Sates an average of 25 people a year are killed from landslides. In this particular landslide we know that a large amount of mud and debris flowed across the North Fork of the Stillaguamish River and caused it to form a dam that caused serious flooding upstream from the disaster that took two or more weeks to subside.
A few months after Oso there were a lot of recommendations by the Governor Inslee on how they as a community and a governing body would help to avoid another disaster like Oso. A few things were suggested such as laser-mapping of these landslide-prone areas and ariel mapping to keep a closer eye on the movements of these areas but this would require more funding, same goes for their disaster relief and recovery systems(Gowen). Since you can not keep a landslide from happening, all you can do is be better prepared for them when it does. Gov. Inslee proposed a $36 million dollar mitigation plan that included landslide relief in pri-oritized areas of the state. Another thing that needed to be adjusted was the emergency rescue, during Oso their rescue team had to fly over in helicopters to try and save anyone they found in the disaster since there was no other way to reach them.
This was a problem when they couldn’t properly analyze the extent of the disaster to ask for the assistance they needed. So in response to this the Governor updated their mobilization laws when it came to large disasters. Another mitigation strategy was regulating land use in these potentially hazardous areas. This landslide in Oso, Washington was one of the largest in United States history and can still teach us a lot about preparation and readiness for a disaster of such magnitude. This tragic disaster was foreseeable if we had been looking at all the clues that came before it. Allowing a proper assessment of risk and a better mitigation plan when these natural disasters do happen. As well as a far less greater loss of life. All of that combined with a disaster relief plan and better monitoring of landslide-prone areas we can have an upper hand on the natural functions of Earth and plan accordingly with the proposed mitigation.