Established Series


The Breakneck series consists of moderately deep, well drained soils on strongly sloping to very steep summits and side slopes in the high elevations of the Southern Blue Ridge mountains, MLRA 130B. They formed in residuum affected by soil creep in the upper part, and weathered from low-grade metasedimentary rocks, primarily metasandstone. Slope ranges from 8 to 95 percent.

TAXONOMIC CLASS: Fine-loamy, isotic, frigid Typic Humudepts

TYPICAL PEDON: Breakneck channery loam, on a 25 percent slope at 6,600 feet in elevation, forested

Oe--0 to 3 inches; moderately decomposed plant material and root mat

A--3 to 12 inches; black (10YR 2/1) channery loam; moderate fine and medium granular structure; friable; common fine, coarse and very coarse roots; 19 percent by volume metasandstone channers; very strongly acid; abrupt wavy boundary. (Combined thickness of the A horizon is 8 to 18 inches.)

Bw--12 to 28 inches; dark yellowish brown (10YR 4/4) channery loam; weak coarse subangular blocky structure; friable; few fine roots; 34 percent by volume metasandstone channers; very strongly acid; abrupt wavy boundary. (12 to 24 inches)

R--28 inches; Thunderhead metasandstone with widely spaced fractures greater than 4 inches apart.

TYPE LOCATION: Sevier County, TN (Great Smoky Mountains National Park); near the summit of Clingmans Dome, between the observation tower and the Appalachian Trail; USGS Clingmans Dome topographic quadrangle lat. 35 degrees 33 minutes, 46 seconds N, long. 83 degrees, 29 minutes, 58 seconds W, NAD 27.

RANGE IN CHARACTERISTICS: Solum thickness and depth to bedrock ranges from 20 to 40 inches. The content of rock fragments is less than 35 percent by volume throughout. Reaction is extremely acid to strongly acid.

The A horizon has a hue of 10YR, value of 2 or 3, and chroma of 1 to 3. Texture is clay loam or loam in the fine earth fraction.

The Bw horizon has a hue of 7.5YR or 10YR , value of 4 or 5, and chroma of 3 to 8. Texture is loam or sandy loam in the fine earth fraction.

The BC or C horizon, where present, has colors and textures similar to the Bw horizon.

Some pedons have a thin Cr horizon that is highly weathered metasandstone bedrock.

The R horizon is metasandstone bedrock. Some interbedding with slate occurs. Excavation difficulty is very high with very strongly cemented hardness.

COMPETING SERIES: These are the Burton, Cataloochee, Guyot, Oconaluftee, Tanasee, and Wayah series. Burton and Wayah soils formed in residuum and Tanasee in colluvium from high-grade metamorphic rocks and contain fragments of those rocks. Cataloochee and Guyot soils have paralithic contacts at depths of 20 to 40 inches and 40 to 60 inches, respectively. Oconaluftee, Tanasee and Wayah soils have bedrock at depths greater than 60 inches.

GEOGRAPHIC SETTING: Breakneck soils are on strongly sloping to very steep side slopes, summits, and on heath balds in the high elevations of the Southern Blue Ridge mountains, MLRA 130B. Slope ranges from 8 to 95 percent. Elevation ranges from 4,200 feet to over 6,600 feet. Breakneck soils formed in residuum that is affected by soil creep in the upper part, and weathered from low-grade metasedimentary rock, primarily metasandstone. Some interbedding with slate occurs. Moist atmospheric conditions in the form of fog and cloud cover are prevalent throughout the year in these high mountain areas. Near the type location, mean annual air temperature is about 45 degrees F., and mean annual precipitation is about 85 inches.

GEOGRAPHICALLY ASSOCIATED SOILS: In addition to the competing Guyot, and Oconaluftee series, these include the Chiltoskie, Clingman, Heintooga, Horsetrough, Pinnacle, and Pullback series. Chiltoskie, Heintooga, and Horsetrough soils formed in colluvium. Heintooga soils are in a loamy-skeletal particle-size class. Horsetrough soils are in a sandy-skeletal particle-size class and are poorly drained. Clingman and Pinnacle soils are comprised of organic soil material. Pullback soils formed in residuum and have a lithic contact at less than 20 inches

DRAINAGE AND PERMEABILITY: Well-drained. Runoff is slow where forest litter has not been disturbed or only partially removed. Permeability is moderate.

USE AND VEGETATION: Most of the acreage is in public ownership and is used for watershed protection, recreation, and wildlife habitat. In areas higher than about 5,400 feet, red spruce and fraser fir are the dominant trees. At the lower elevations, northern red oak, chestnut oak, American beech, yellow birch, black cherry, sugar maple, eastern hemlock, and yellow buckeye are common trees. Common understory plants are serviceberry, striped maple, American chestnut sprouts, silverbell, pin cherry, rhododendron, flame azalea, and blueberry. Common forbs are hay-scented fern, woodfern, New York fern, Solomons seal, yellow mandarin, and trillium. A small acreage is covered by heath balds. These balds are vegetated with rhododendron, mountain laurel, blueberry, flame azalea, hawthorn, and mountain ash. Vegetation ranges for spruce/fur to northern hard woods, heath and grass balds.

DISTRIBUTION AND EXTENT: Higher elevations of the Southern Blue Ridge mountains, MLRA 130B of Tennessee and North Carolina. This series is of moderate extent.


SERIES ESTABLISHED: Buncombe County, North Carolina, 2006.

REMARKS: Laboratory PSA (pipette method) and corresponding field texture estimates (feel method) indicate control section clay contents of generally 12 to 24 percent, with most pedons marginally coarse-loamy. Fine-loamy particle-size class placement is based on the presence of amorphous (non-crystalline) clay-size material associated with the relatively high organic matter content found in these soils. Although field estimates, laboratory measurements, and calculated values may vary, clay content in the particle-size control section is generally less than 25 percent. Although Breakneck soils may exhibit some of the characteristics of andic soil properties, they lack the volcanic glass found in soils of similar taxa in the Western United States.

Revisions made 9/07(HCD) adjusted OSD to reflect Lab Data.

Diagnostic horizons and other feature recognized in this soil are:

Umbric epipedon -- the zone from the mineral soil surface to 12 inches (A horizon)

Cambic horizon -- the zone from 12 to 28 inches (Bw horizon)

Lithic contact -- the occurrence of hard bedrock at depth of 28 inches

Isotic mineralogy class - In more than one-half of the control section, a 1500 kPa water to clay ratio of 0.6 or more and a pH in NaF solution of more than 8.4.

ADDITIONAL DATA: Characterization data are available from the National Soil Survey Laboratory, Lincoln, NE for the following pedons: S01TN-009-002, S01TN-155-009, S01TN-155-002.

NASIS Data Map Unit ID: NASIS data for the typical pedon in the Great Smoky Mountains National Park are represented by DMU #432209.

Revised 02/11-BPS: Taxonomic Classification -- 11th Keys, update competing and associated series, MLRA clarification

National Cooperative Soil Survey