LOCATION RUMUNG FM+ PBEstablished Series
TAXONOMIC CLASS: Clayey-skeletal, mixed, semiactive, isohyperthermic Lithic Hapludalfs
TYPICAL PEDON: Rumung gravelly silt loam - on a 19 percent northeast-facing convex slope in a degraded anthropic savannah. When described (4/15/80), the soil was dry in the upper 2 inches of the profile. (Colors are for moist soil unless otherwise noted.)(About 60 percent of the surface is covered with iron-coated chlorite schist and amphibolite gravel .1 to 2 inches in size.)
A1--0 to 4 inches; dark brown (10YR 3/3) gravelly silt loam, brown (10YR 5/3) dry; strong very fine granular structure; hard, very friable, slightly sticky and slightly plastic; many very fine and medium roots; many very fine interstitial pores and common very fine tubular pores; approximately 25 percent by volume subangular high grade chlorite schist fragments 1 to 2 inches in size; slightly acid (pH 6.4, 1:1 water); clear wavy boundary. (3 to 8 inches thick)
B2--4 to 11 inches; strong brown (7.5YR 5/8) very gravelly clay; many fine distinct light olive brown (2.5Y 5/4) mottles; moderate medium and coarse subangular blocky structure; firm, slightly sticky and moderately plastic; common very fine and fine roots, and few coarse roots; many very fine and fine tubular pores, few medium tubular pores and common fine interstitial pores; approximately 40 percent by volume subrounded hard chlorite schist and amphibolite fragments .8 to 2 inches along long axis; moderately acid (pH 6.0, 1:1 water); clear wavy boundary. (4 to 16 inches thick)
C--11 to 19 inches; pale olive (5Y 6/4) extremely gravelly clay; moderate medium and coarse subangular blocky structure; firm, slightly sticky and moderately plastic; few very fine roots; common very fine tubular pores; approximately 80 percent by volume hard chlorite schist and amphibolite fragments .8 to 2 inches along the long axis; moderately acid (pH 5.7, 1:1 water); abrupt irregular boundary. (0 to 10 inches thick)
R--19 inches; pale green (5G 6/2) uptilted high grade highly fractured chlorite schist and amphibolite; contains interlayered crystals of olivine; approximately 25 percent of the horizon is weathered.
TYPE LOCATION: Weloy Municipality, Yap Island and State, Federated States of Micronesia; about .8 mile N. of the village of Okau by road and about 1.9 miles E. on the over-island road above a small rock quarry S. of the road. Site is about 125 feet S. of the road; lat. 9 degrees 32 minutes 38.26 seconds N. and long. 138 degrees 6 minutes 17.59 seconds E.
RANGE IN CHARACTERISTICS: Depth to bedrock ranges from 10 to 20 inches. Thickness of the solum ranges from 7 to 20 inches.
The A horizon has hue of 10YR or 2.5Y, value of 2, 3, or 4 moist, and chroma of 2 or 3. It is dominantly gravelly silt loam but ranges to gravelly clay loam, gravelly silty clay loam, or very gravelly silt loam. By volume, the A horizon is 15 to 40 percent moderately hard and hard schist gravel .1 to 3 inches in size and 0 to 15 percent cobbles 3 to 6 inches in size. Reaction in 1:1 water is moderately acid or slightly acid.
The B horizon has moist color in hue of 10YR, 7.5YR, or 5Y, value of 4 or 5, and chroma of 3 through 8. It is clay loam, silty clay loam, silty clay, or clay and is very gravelly. The B horizon pebble content ranges from 0 to 10 percent by volume and 3 to 6 inches in size. Reaction in 1:1 water is strongly acid through slightly acid.
The C horizon has moist color with hue of 5Y, 2.5Y, or 5G, value of 4, 5, or 6, and chroma of 2 through 6. It is extremely gravelly clay loam or extremely gravelly clay. By volume, the C horizon is 50 to 85 percent gravel 1 to 30 inches in size and 10 to 20 percent cobbles 3 to 6 inches in size. Total coarse fragment content ranges from 60 to 90 percent by volume. Reaction in 1:1 water is strongly acid through slightly acid.
COMPETING SERIES: This is the Weloy series. Weloy soils are deeper than 20 inches, and have a mollic epipedon.
GEOGRAPHIC SETTING: Rumung soils are on hills and low mountains that have convex relief. Slopes are 2 to 75 percent. The soils formed in uptilted hard and soft green, chlorite, or talc schist or volcanic breccia containing schist fragments. Elevation ranges from 3 to 567 feet. The mean annual temperature is 81 degrees F. and does not vary by more than 34 degrees F from month to month. Mean annual maximum temperature is 88 degrees F. and mean annual minimum temperature is 75 degrees F. Mean annual rainfall is about 122 inches (and presumably higher in the higher elevations) and varies from 90 to 149 inches from year to year, with the driest months of February, March, and April averaging 6 inches per month.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Gitam, Yap, and the competing Weloy soils. Gitam soils are moderately deep to a paralithic contact and have a high water table. Yap soils are very deep and have an oxic horizon.
DRAINAGE AND PERMEABILITY: Well drained; slow through very high runoff; moderate permeability.
USE AND VEGETATION: Most areas are in degraded anthropic savannah or broadleaf evergreen forest. Forest areas are used for a minor amount of firewood collecting.
DISTRIBUTION AND EXTENT: Rumung soils are inextensive in Yap.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California
SERIES ESTABLISHED: Weloy Municipality, Yap Island and State, Federated States of Micronesia, 1981.
REMARKS: The Rumung soils typically have a calcium-magnesium imbalance in the B horizon.
Taxonomic Version: Keys to Soil Taxonomy, 10th edition 2006.