My Spodosol


The 12-foot deep excavation for the garage revealed a nice soil profile - we have a spodosol!

Spodosols are fairly rare. Spodosols form in sandy parent materials under cool, humid forest settings in the Great Lakes region, Northern Idaho mountains, northern New England mountains, and southern Alaska. Their distinctive E horizon (leached) and Bh /Bhs horizon (accumulated) make them distinct. A colorful "spodic" horizon develops when large amounts of water infiltrates into the soil during one season (spring snowmelt here in Alaska) year after year. This seasonal flushing leaches Al, Fe and organic compounds from one subsoil horizon and deposits it lower down in the soil profile. A whitish eluvial horizon overlies a reddish illuvial horizon. The red horizon is the diagnostic one.

The soil in my yard classifies as a variant of the Talkeetna Series: a deep, well-drained, acidic soil developed on forested mountain slopes in volcanic ash-influenced loess overlying Pleistocene glacial till below the alpine zone. Soil nerds would say "medial over loamy-skeletal, amorphic over mixed, superactive Andic Humicryod."

The photos show a light gray leached horizon (eluviated E) horizon over a reddish to black horizon (illuviated Bs/Bsh with organic matter + Al and Fe oxides). You have to ignore the thick accumulations of disturbed top soil - its the fill associated with land clearing in the 1970s. Also, the E horizon isn't as well developed as it could be (could be whiter). I confirmed my hasty interpretation, shown here, with Dr. Paul McDaniel, an andic soils expert and professor at University of Idaho. Nejirigama tool is 12" long.

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