Soils Reveal an Ancient Past.

When people think of the Pacific Northwest, they often thing of how lush and green everything is.  Pine trees like Douglas-Fir and conifer trees are just amount the many plants that give Washington State the title, the “Evergreen State.”  The western slope of the Cascade mountain range is home to a very large and dense population of people.  All these people have established themselves on over 1600 different types of soils.  A lot of these soils have been created by historic geographical influences such as volcanic activity and glacial movement.  

Areas where Tokul soils are. (in green))

Tokul Soils

Due to the subduction zone (where the Juan de Fuca plate is pushing under the North American plate) located directly under the western half of Washington State, volcanic activity has over time deposited layer upon layer of ash.  This ash has settled onto the western cascades, along the Puget Trough, from Seattle to the Canadian border.  These soils are called Tokul soils.  Tokul soils are primarily influenced by the ash left by the volcanic activity.
The process of gleization (development of extensive soil organic layer over a layer of chemically reduced clay) and glacial movements helped to create these Tokul soils.  Just as gleization is classified, Tokul soils are somewhat poorly drained of water from the high amounts of precipitation on the western slopes of the Cascades, and glacial influences.  It possesses moderate permeability above the cemented pan, and very slow permeability below the cemented pan.  Permiability is how well the water is able to pass through the soil as it flows downward to the water table.  Tokul is considered to be amorphic, or having no specific shape or structure. The fertile nature and properties of Tokul soils make is some of the most productive soils in the world; making it suitable for the production of crops, forestry (timber), livestock grazing, and even recreation.

Tokul landslide on steep slop due to brittle nature.

 But due to its very moist nature, the soil is very unstable.  Tokul is a part of glacial soils (soils left behind from the retreating of glaciers).  As it was mentioned how moist these deposited soils are, they often need assistance in the dewatering process.  A few examples of areas of glacial soils and erosion from glaciers are the banks of Lake Washington, Cedar River, May Creek and Coal Creek.

Tokul Soil Profile

  

Tokul Horizons

O-Horizon = 1-2 inches

A-Horizon = 2-6 inches, Andic soil properties from 2 to 33 inches

B-Horizon = 6-62 inches, Redox concentrations at 17 inches with aquic conditions (depletions with chroma of 2 and concentrations) at 33 inches, Cemented pan at 33 inches.

Tokul Soil Profile
Surface layer: organic material Subsurface layer: very dark grayish brown gravelly loam Subsoil - upper: dark brown gravelly loam Subsoil - lower: light yellowish brown gravelly loam Substratum: light brownish gray and dark gray gravelly sandy loam (very hard, dense glacial till cemented by a combination of iron, aluminum, and organic matter)

(click here 
https://soilseries.sc.egov.usda.gov/OSD_Docs/T/TOKUL.html )

Loess Soils

Palouse Region map, and areas of Loess deposits

The Palouse Region of southeastern Washington, northeastern Oregon, and northwestern Idaho is home to completely different fertile soils, Loess soils.  These soils are also found in Tokul soils.  Loess soils are mixed with clay and give off a yellowish color.  These loess soils are also left over from retreating glaciers.  The difference between Loess soils and Tokul soils is simply precipitation.  The heavy rains on the western slopes of the Cascades keep the Tokul soils very moist, whereas the eastern side of the Cascades is must drier and more arid.  Loess means “loose” in German, which is where the name is applied.  Loess soils are formed by wind-blown accumulation of silt.  This silt is comprised of Aeolian sediments.  This silt is a source of rich nutrients and perfect for growing wheat, lentils, and peas in the Palouse Region.  

The beautiful farmland of the Palouse Region

Tokul soils and Loess soils are great examples of why the Pacific Northwest is a lush and fertile area.  It is also evidence of major land changes from glacier formations from the ancient past.





Work Cited.

Gleization: Geography-Dictionary.org. n.d. WEB. 9 March 2013. <http://geography.geography-dictionary.org/Physical-Geography-Dictionary/Gleization>.

Howe, Alicia. Soil Types in Washington State. n.d. WEB. 9 March 2013. <http://www.ehow.com/list_6008741_soil-types-washington-state.html>.

Loess: wikipedia.org. n.d. WEB. 9 March 2013. <http://en.wikipedia.org/wiki/Loess>.

U.S. Department of Agriculture. National Cooperative Soil Survey: Tokul Survey. March 1999. WEB. 9 March 2013. <https://soilseries.sc.egov.usda.gov/OSD_Docs/T/TOKUL.html>.

—. Tokul -- Washington State Soil. n.d. WEB. 9 March 2013. <ftp://ftp-fc.sc.egov.usda.gov/NSSC/StateSoil_Profiles/wa_soil.pdf>.