This is an EarthCache, meaning there is no cache at the posted coordinates.
Instead, to claim a find, read the description and submit answers to the questions below.
Liquefaction takes place when loosely packed, water-logged sediments at or near the ground surface lose their strength in response to strong ground shaking. Liquefaction occurring beneath buildings and other structures can cause major damage during earthquakes. For example, the 1964 Niigata earthquake caused widespread liquefaction in Niigata, Japan which destroyed many buildings. Also, during the 1989 Loma Prieta, California earthquake, liquefaction of the soils and debris used to fill in a lagoon caused major subsidence, fracturing, and horizontal sliding of the ground surface in the Marina district in San Francisco.
You can experience a liquefaction for yourself in the water-soaked sand near the edge of a beach. It feels pretty solid if you stand still, but if you wiggle your feet, the movement causes the sand to liquefy beneath you and you start sinking.
During a liquefaction event (e.g. earthquake) soil particles, in combination with the water located in the pore spaces between them, tend to behave like quicksand.
This is because loose soil has the tendency to compress when sheared, generating large excess porewater pressure as load is transferred from the soil skeleton to adjacent pore water during undrained loading. As pore water pressure rises, a progressive loss of strength of the soil occurs as effective stress is reduced. Liquefaction is more likely to occur in sandy or non-plastic silty soils but may in rare cases occur in gravels and clays.
You are standing (black circle) at the tip of a "finger" of Quartenary Alluvium soil that reaches into Fairwood area of Renton as seen on this map from the Washington Geologic Information Portal (https://geologyportal.dnr.wa.gov/2d-view#wigm?-13601672,-13595940,6015213,6017958?Surface_Geology,500k_Surface_Geology,Map_Units)
Quarternary alluvium (Qa) is unconsolidated or semiconsolidated alluvial clay, silt, sand, gravel, and (or) cobble deposits. In this area of Washington this can include:
a. peat, muck, and diatomite;
b. beach, dune, lacustrine, estuarine, marsh, landslide, lahar, glacial, or colluvial deposits;
c. volcaniclastic or tephra deposits;
d. modified land and artificial fill.
Though the coordinates are over 400 ft above sea level, the type of soil and flow of wetlands and rivers from the Cascade Mountain range make this area prone to liquefaction as seen in King County Liquification Potential Map below (you are standing at green circle).
The most common way of preventing the occurrence of liquefaction are foundation soil improvement methods, including:
1. Replace the susceptible soil with the appropriate amount of gravel.
2. Vertical gravel drains are often used for faster water drainage due to their permeability, since saturation with water is one of the main factors affecting the occurrence of liquefaction
3. Stone columns are one of the best methods of reducing the liquefaction potential. Because they are performed by vibration, they increase the compactness of the foundation soil on one side, and because of their water permeability, they also allow faster water drainage.
4. There are also chemical soil stabilization methods using cement, but they are not used as much because they are not as profitable.
Questions:
1) Look at the settled soils in the depression at the coordinates. Describe the mix of soil are you seeing here? (see Quartenary Alluvion (Qa) a-d above)? Why do you think that is?
2) What type of soil improvements (see 1-4 above) do you see in the area to prevent liquefaction.
3) Take a photo of yourself (or a personal item) near the coordinates.
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