Presentation on theme: "“And the Landslide Brought me Down: a look into the hazards and joys of living in Tacoma’s Salmon Beach Community.” By: Kyle Sleeper."— Presentation transcript:
“And the Landslide Brought me Down: a look into the hazards and joys of living in Tacoma’s Salmon Beach Community.” By: Kyle Sleeper
My area of study is the residential community known as Salmon Beach located on Puget Sound in Tacoma, Washington. Quite literally. Its proximity to the ocean exposes the community to both land and sea hazards. On land it is prone to landslides, and has had multiple large-scale slides causing damage and even death. In the event of a large magnitude earthquake, the saturated ground which Salmon Beach rests upon is prone to liquefaction. From the ocean residents can also expect both tsunamis and seiches.
Term Definitions A feeder bluff is an eroding landmass that provides fresh sediment to replenish beaches and provide nourishment for water based ecosystems. An earthquake is the rapid release of stored energy from motion along a fault. A landslide is the gravity-driven down-slope movement of a slide mass composed of rock, soil, and vegetation. Liquefaction is the process of loosely packed, water-logged sediment, coming loose from intense vibrations, like the shaking of an earthquake. Seiches are water waves generated in enclosed or partly enclosed bodies of water such as reservoirs, lakes, bays and rivers by the passage of seismic waves caused by earthquakes. A tsunami is a large and fast wave generated from the displacement of a large volume of water beneath the surface.
The cliff is made up of layers meant to move: silt and clay at its base, followed by a layer of sand and gravel, followed by more silt, sand and glacial till. Interwoven through it all is a series of springs, some of which gush into small waterfalls at the base of the bluff.
A history of destruction! A landslide at Salmon Beach occurred in 1949 three days after a surface-wave magnitude 7.1 Olympia earthquake. Estimated 6- to 8-foot tsunami waves were generated in The Narrows, damaging piers and boats in Gig Harbor and Salmon Beach. In 1996 heavy rains caused a landslide destroying 3 homes. In February 2001 the Nisqually Earthquake severing municipal services and damaging 8 houses. Another sliding event occurred just in the past 2 years. And the bluff is thought to move downward up to two inches every year.
Julie Newcombe’s Photo
April 13, 1949 Puget Sound Tsunami - Salmon Beach Lander, et al. (1993): “An eleven million cubic yard landslide occurred on Point Defiance, at the Tacoma Narrows when a 400 foot high cliff gave way and slid into the water.” – “The water receded feet from its normal tide line with an ominous sucking sound. Then an eight foot tidal wave rushed back against the beach smashing small boats, dock areas, a wooden boardwalk and other waterfront installations.” (Tacoma News-Tribune, April 18, 1949, p.1) =
Nisqually Federal Disaster #1361 From the President: “I have determined that the damage in certain areas of the State of Washington, resulting from an earthquake on February 28, 2001 and continuing, is of sufficient severity and magnitude to warrant a major disaster declaration under the Robert T. Stafford Disaster Relief and Emergency Assistance Act, 42 USC 5121(Stafford Act). I, therefore, declare that such a major disaster exists in the State of Washington. “
From the GOVERNMENT “The landslide with the highest hazard to date is a rock/soil slide from the bluffs above the community of Salmon Beach north of the Tacoma Narrows bridge near Tacoma, Washington. A rock/soil slide of about 1000 cubic meters has demolished two houses located at the base of the steep bluff along the shores of Puget Sound. A larger slide of about 10,000-20,000 cubic meters of material remains poised on the slopes above the houses and threatens 5 to 6 additional dwellings. This larger slide has already slid 20 to 25 feet and has a scarp near the top of the bluff extending for about 60 meters below the top of the bluff. We have alerted Pierce County officials, they have dispatched a geotechnical engineer to evaluate the situation. She called back yesterday and reported that eight houses have been red tagged as a result of the inspection.” (USGS) POST NISQUALLY
“Two homeowners associations that manage Salmon Beach and the city of Tacoma Public Utilities department (D. Koberstein, oral commun., 2001) have estimated total losses for the 2001 Salmon Beach landslide activity at $1,505,428.” (L. Highland, 2001)
Sue Martin Sue Martin, an engineer with the City of Tacoma doesn’t believe in issuing permits for building in Salmon Beach, "That's an eroding bluff," Martin said. "That's not a natural use to put houses there. The city feels there is some danger. It continues to slide (some) every day.“ The state Department of Ecology believes such eroding cliffs are an important part of the Puget Sound environment. Called "feeder bluffs," the sand and gravel constantly washing down onto the beach is picked up by the water and deposited onto other beaches, nourishing the shoreline and providing habitat for plants and animals, she said. Environmental concerns aside, it would take a multimillion-dollar project to shore up the bluff enough to prevent major slides. And because that's a cost that would have to be borne by the residents of Salmon Beach, it probably will never happen, Martin said.
Pierce County Hazard Mitigation Team Quote “The Planning Team determined the probability of recurrence for the landslide hazard in Pierce County to be “100 years or less occurrence.” This is based on information from past landslide occurrences, information from local hazard experts, and in conjunction with Mitigation 20/20 tools.”
Tsunamis in the Sound A project is underway to assess the tsunami hazards within Puget Sound communities and to provide information for tsunami planning and mitigation. “Using a finite difference model based on nonlinear shallow water wave theory and high-resolution digital elevation model, we simulate the generation, propagation, and inundation of tsunamis in Puget Sound. The tsunamis are generated as a result of possible earthquake scenarios for the Seattle Fault.”
Atwater and Moore “Water surged from Puget Sound sometime between 1000 and 1100 years ago, overrunning tidal marshes and mantling them with centimeters of sand. One overrun site is 10 kilometers northwest of downtown Seattle; another is on Whidbey Island, some 30 kilometers farther north. Neither site has been widely mantled with sand at any other time in the past 2000 years. Deposition of the sand coincided—to the year or less—with abrupt, probably tectonic subsidence at the Seattle site and with landsliding into nearby Lake Washington. These findings show that a tsunami was generated in Puget Sound, and they tend to confirm that a large shallow earthquake occurred in the Seattle area about 1000 years ago.”
Why would someone want to live THERE? The city already requires residents to sign a waiver agreeing to hold the city blameless for any slides that damage their community. Beauty Community Seclusion
References An Account of Preliminary Landslide Damage and Losses Resulting from the February 28, 2001,Nisqually, Washington, EarthquakeBy Lynn M. Highland USGS Lander, J.F., P.A. Lockridge, and M.J. Kozuch (1993). Tsunamis Affecting the West Coast of the United States , NGDC Key to Geophysical Record Documentation No. 29, NOAA, NESDIS, NGDC, 242 pp. Pierce County Landslide Hazard PDF: NOAA Technical Memorandum OAR PMEL-132: TACOMA, WASHINGTON, TSUNAMI HAZARD MAPPING PROJECT:MODELING TSUNAMI INUNDATION FROM TACOMA, Arcas, Mofjeld, Titov, Chamberlin, Gonzalez, Venturato B Atwater and A Moore, “A Tsunami About 1000 Years Ago in Puget Sound, Washington,” Science. December 4 th,