R layer Continuous bedrock. Refer to soil horizon and Appendix II.
r-selected In ecological theory, that group of organisms in soil that rapidly proliferate in response to an abundance of resources. Analogous to zymogenous microorganisms.
radial drainage pattern A drainage pattern in which consequent streams radiate or diverge outward, like the spokes of a wheel from a high central area; a major collector stream is usually found in a curvilinear alignment around the bottom of the elevated topographic feature. It is best developed on the slopes of a young domal structure, a volcanic cone, or isolated hills (erosional remnant; Schoeneberger and Wysocki, personal communication, 2013; Way, 1973; Jackson, 1997).
radius ratio A ratio between the radii of a cation and a coordinating anion.
railroad bed The trace or track of a railroad route, commonly constructed slightly above the adjacent land, and composed mostly of earthy materials (gravel, rock fragments, etc.). Abandoned or reclaimed beds may no longer be topographically or visually distinct, but the materials used to construct them may still be a significant portion of the soil zone (Schoeneberger and Wysocki, personal communication, 2013).
rainfall erosivity index Refer to erosion, rainfall erosivity index.
rainfall interception Refer to precipitation interception.
raised beach
An ancient (relict) beach occurring above the present shoreline and separated from the present beach, having been elevated above the high-water mark either by local crustal movements (uplift) or by lowering of sea or lake level, and which may be bounded by inland cliffs (Jackson, 1997).
raised bed Refer to bed.
raised bog An area of acid, peaty soil, especially that developed from moss, in which the center is higher than the margins. Compare pocosin, Carolina Bay, moss peat. [Note: raised peat bog (not preferred)-use highmoor bog; Schoeneberger and Wysocki, personal communication, 2013; Bates and Jackson, 1987].
rating curve A graph of the flow rate of an open channel at a discharge point as a function of the water level or stage. Refer to discharge curve.
ravine A small stream channel; narrow, steep-sided, commonly V-shaped in cross section and larger than a gully, cut in unconsolidated materials. General synonym (not preferred) gulch. Compare arroyo, draw, gully (Hawley and Parsons, 1980).
reaction, soil (no longer used in SSSA publications) The degree of acidity or alkalinity of a soil, usually expressed as a pH value. Descriptive terms commonly associated with certain ranges in pH are: extremely acid,<4.5; very strongly acid, 4.5–5.0; strongly acid, 5.1–5.5; moderately acid, 5.6–6.0; slightly acid, 6.1–6.5; neutral,6.6–7.3; slightly alkaline, 7.4–7.8; moderately alkaline,7.9–8.4; strongly alkaline, 8.5–9.0; and very strongly alkaline, >9.1.
recessional moraine An end or lateral moraine, built during a temporary but significant halt in the retreat of a glacier. Also, a moraine built during a minor readvance of the ice front during a period of general recession. Compare end moraine, ground moraine, terminal moraine ( Jackson, 1997).
recharge Movement of water into the aquifer or a recharge area.
recharge wetland [soil hydrology] A wet area which focuses surface water infiltration and subsurface recharge into the surrounding landscape; a type of wetland. Compare discharge wetland.
reclaimed land (a) A land area composed of earthy fill material that has been placed and shaped to approximate natural contours, commonly part of land-reclamation efforts after mining operations; (b) A land area, commonly submerged in its native state, that has been protected by artificial structures (e.g., dikes) and drained for agricultural or other purposes (e.g., polder)(Schoeneberger and Wysocki, personal communication, 2013).
rectangular drainage pattern A drainage pattern in which the tributaries join the main streams at right-angles, and exhibit sections of approximately the same length which form rectangular shapes; it is indicative of streams following prominent bedrock fault, joint, or foliation systems that break the rocks into rectangular blocks. It is more irregular than the trellis drainage pattern, as the side streams are not perfectly parallel and not necessarily as conspicuously elongated, and secondary tributaries need not be present. The stronger or more harsh the pattern, the thinner the soil cover. These patterns commonly form in slate, schist, and gneiss, in resistive sandstone in arid climates, or in sandstone in humid climates if little soil has developed (Schoeneberger and Wysocki, personal communication, 2013; Way, 1973; Jackson, 1997).
Red Desert soil [soil classification] (obsolete; not used in soil taxonomy) A zonal great soil group consisting of soils formed under warm-temperate to hot, dry regions under desert-type vegetation, mostly shrubs (Baldwin et al., 1938).
red earth [soil classification] (obsolete; not used in soil taxonomy) Highly leached, red clayey soils of the humid tropics, usually with very deep profiles that are low in silica and high in sesquioxides (Baldwin et al., 1938).
Red-Yellow Podzolic soils [soil classification](obsolete; not used in soil taxonomy) A combination of the zonal great soil groups, Red Podzolic and Yellow Podzolic, consisting of soils formed under warm-temperate to tropical, humid climates, under deciduous or coniferous forest vegetation and usually, except for a few members of the Yellow Podzolic Group, under conditions of good drainage (Thorp and Smith, 1949).
redistribution (of soil water) The process of soil-water movement to achieve an equilibrium energy state of water throughout the soil.
redox Reduction-oxidation.
redox concentrations Zones of apparent accumulation of Fe-Mn oxides in soils.
redox depletions Zones of low chroma (two or less) where Fe-Mn oxides alone or both Fe-Mn oxides and clay have been stripped out of the soil.
redox-potential Refer to EH and pe.
redoximorphic features Redoximorphic concentrations, redoximorphic depletions, reduced matrices, and other features indicating the chemical reduction and oxidation of iron and manganese compounds resulting from saturation.
reduced matrix A soil matrix which has a low chroma in situ, but undergoes a change in hue or chroma within 30 minutes after the soil material is exposed to air. The color change is due to the oxidation of iron.
reduction The gain of one or more electrons by an ion or molecule.
reef A ridge-like or mound-like structure, layered or massive, built by sedentary calcareous organisms, especially corals, and consisting mostly of their remains; it is wave-resistant and stands above the surrounding contemporaneously deposited sediment. Reefs can also include a mass or ridge of rocks, especially coral and sometimes sand, gravel, or shells, rising above the surrounding estuary, sea or lake bottom to or nearly to the surface (Schoeneberger and Wysocki, personal communication, 2013; Subaqueous Soil Subcommittee, 2005; Jackson, 1997).
reel and gun irrigation (traveling gun) Refer to irrigation.
reference electrode An electrode that maintains an invariant potential under the conditions prevailing in an electrochemical measurement and thereby permits measurement of the potential of an ion-selective or a platinum (redox) electrode.
reflectance The ratio of the radiant energy reflected by a body to that incident upon it. The suffix (-ance) implies a property of that particular specimen surface.
regolith All the unconsolidated materials above solid rock. It includes material weathered in place from all kinds of bedrock and alluvial, glacial, eolian, lacustrian, and pyroclastic deposits. Soil scientists regard as soil that part of the regolith that is modified by organisms and soil-forming processes (Schoeneberger and Wysocki, personal communication, 2013; Hawley and Parsons, 1980). (Approximately equivalent to the term “soil” as used by many engineers.) Compare residuum, bedrock.
Regosol [soil classification] (obsolete; not used in soil taxonomy) Any soil of the azonal order without definite genetic horizons and developing from or on deep, unconsolidated, soft mineral deposits such as sands, 1oess, or glacial drift (Baldwin et al., 1938).
Regur [soil classification] An intrazonal group of dark calcareous soils high in clay, which is mainly montmorillonitic, and formed mainly from rocks low in quartz; occurring extensively on the Deccan Plateau of India. (Not used in current U.S. system of soil taxonomy.)
relative humidity The ratio, at a given temperature, of the water vapor pressure to the saturated water vapor pressure; used as a measure of water potential by meteorologists.
relative yield The harvestable or biomass yield with or without supplementation of the nutrient in question expressed as a percentage of the yield with the nutrient in adequate amounts.
relict (adjective) Pertaining to surface landscape features for example, landforms, geomorphic surfaces, and paleosols that have never been buried and yet are predominantly products of past environments (Hawley and Parsons, 1980). Compare exhumed, buried, ground soil.
relict-tidal inlet A channel remnant of a former tidal inlet. The channel was cutoff or abandoned by infilling from migrating shore sediments (Subaqueous Soil Subcommittee, 2005). Compare inlet, tidal inlet.
relief The relative difference in elevation between the upland summits and the lowlands or valleys of a given region (e.g., broad scale; Jackson, 1997). Compare local relief.
remnant (not preferred) use erosion remnant.
remote sensing Refers to the full range of activities that collects information from a distance, for example, the utilization at a distance (as from aircraft, spacecraft, or ship) of any device for measuring electromagnetic radiation, force fields, or acoustic energy. The technique employs such devices as the camera, lasers, and radio frequency receivers, radar systems, sonar, seismographs, gravimeters, magnetometers, and scintillation counters.
Rendolls [soil classification] A suborder of Mollisols of humid regions and formed in highly calcareous parent materials (e.g., limestone, chalk, limestone-rich drift, or shell bars). These soils have a mollic epipedon that may overly a carbonate-rich cambic horizon. Rendolls have a cryic soil temperature regime or a udic soil moisture regime, or both, and are not saturated with water for periods long enough to limit their use for most crops (USDA, 1999).
Rendzina [soil classification] (obsolete; not used in soil taxonomy) A great soil group of the intrazonal order and calcimorphic suborder consisting of soils with brown or black friable surface horizons underlain by light gray to pale yellow calcareous material developed from soft, highly calcareous parent material under grass vegetation or mixed grasses and forest in humid and semiarid climates (Baldwin et al., 1938).
reservoir tillage Refer to tillage.
residence time The time required for an individual solute ion or molecule to travel through the soil.
resident concentration The solution concentration, mass of solute per volume of soil, at a point in the soil.
residual fertility The available nutrient content of a soil carried over to subsequent crops.
residual material Unconsolidated and partly weathered mineral materials accumulated by disintegration of consolidated rock in place. Refer to residuum.
residual shrinkage Refer to shrinkage, soil.
residual soil A generic term for any soil formed in regolith, derived in place from the weathering of underlying bedrock; minimal displacement is presumed. Compare colluvial soil.
residue processing Refer to tillage, residue processing.
residuum Unconsolidated, weathered, or partly weathered mineral material that accumulates by disintegration of bedrock in place. Compare saprolite, regolith, colluvium.
resilient soil soil that has the ability to maintian or regain the capacity for function or to perform its functions (i.e., in relation to soil quality/health) when challenged (by erosive forces, excessive residue removal, tillage, etc.).
resolution The ability of an entire remote sensor system, including lens, antennae, display, exposure, processing, and other factors, to render a sharply defined image.
respiratory quotient (RQ)
The number of molecules of CO2 liberated for each molecule of O2 consumed.
restriction enzyme A class of highly specific enzymes that make double stranded breaks in DNA at specific sites near where they combine.
retardation factor The capability of a soil for slowing or retarding the movement of a solute, and is defined for solutes subject to equilibrium reactions with the soil matrix.
retentivity profile, soil A graph showing the retaining capacity of a soil as a function of depth. The retaining capacity may be for water, for water at any given tension, for cations, or for any other substances held by soils.
reticulate mottling A network of mottles with no dominant color, most commonly found in deeper horizons of soils containing plinthite.
Revised Universal Soil Loss Equation, version 2 (RUSLE2) Refer to erosion, Revised Universal Soil Loss Equation (RUSLE2). Compare USLE.
reworked lake plain (obsolete) Refer to till-floored lake plain.
Reynolds number (Re) A dimensionless parameter calculated from the pore water velocity (v), pore diameter (d), fluid density (ρ), and the fluid viscosity (μ): Re= ρvd/μ. Values below 2000 indicate laminar flow and values above 2000 indicate turbulent flow.
rhizobacteria Bacteria that aggressively colonize plant roots.
rhizobia Bacteria able to live symbiotically in roots of leguminous plants, from which they receive energy and often utilize molecular nitrogen. Collective common name for the genus Rhizobium.
rhizobia free Any material that does not contain rhizobia able to nodulate leguminous plants of interest. The material need not be void of all rhizobia. Compare rhizobia populated.
rhizobia populated Any material that contains rhizobia able to nodulate leguminous plants of interest. Contrast with rhizobia free.
rhizocylinder The plant root plus the adjacent soil that is influenced by the root. Compare rhizosphere.
rhizoplane Plant root surfaces usually including the adhering soil particles.
rhizosphere The zone of soil immediately adjacent to plant roots in which the kinds, numbers, or activities of microorganisms differ from that of the bulk soil.
rhythmite
An individual unit of a succession of beds developed by rhythmic sedimentation; for example, a cyclothem. The term implies no limit as to the bedding thickness or complexity and it denotes no time or seasonal connotation (Jackson, 1997). Compare varves, cyclothem.
rib A small, high angle, tertiary spur ridge or mini-interfluve that is a constituent part of rib and groove topography; (slopes generally 20-90%, ); common on the mid and lower hillslopes of well dissected uplands. Compare finger ridge, groove, rib and groove topography (Schoeneberger and Wysocki, personal communication, 2013).
rib and groove topography A local scale topography composed of repeating, small, high-angle (slopes generally 20-90%), tertiary spur ridges or mini-interfluves (ribs) separated by small, natural, narrow drainageways (grooves); the overall effect is a corrugated transverse surface, common on the mid and lower slopes of well dissected uplands in semi-arid to humid environments (e.g., Basin and Range, Ozarks, etc.). Micro-elevational differences generally range from < 3 to < 15 m (Schoeneberger and Wysocki, personal communication, 2013).
ribbed fen A nutrient-rich wetland with a surface pattern of ridges and depressions.
rice paddy An anthropogenic, nearly level impoundment that is inundated for long periods typically for wetland rice production. It is applied to areas that have been used in this fashion for a long enough period of time to significantly change the original soil morphology (especially redoximorphic features; Schoeneberger and Wysocki, personal communication, 2013).
Richards' equation The partial differential equation used to represent transient flow through unsaturated porous media.
Richards' law A positive water pressure is required for water to freely move out of soil and into an open channel.
Richards’ equation The partial differential equation used to represent transient flow through unsaturated porous media.
Richards’ law A positive water pressure is required for water to freely move out of soil and into an open channel.
ridge [geomorphology] A long, narrow elevation of the land surface, usually sharp crested with steep sides and forming an extended upland between valleys. The term is used in areas of both hill and mountain relief (Hawley and Parsons, 1980).
ridge planting Refer to tillage, ridge planting.
ridge [tillage] Refer to tillage, ridge.
rift valley A valley that has developed along a long, narrow continental trough that has down-dropped and is bounded by normal faults; a graben of regional size. It marks part of a zone along which the entire thickness of the lithosphere has ruptured under crustal extension (Schoeneberger and Wysocki, personal communication, 2013; Jackson, 1997).
rill [erosion] Refer to erosion, rill.
rill [geomorphology] A very small channel with steep sides caused by erosion and cut in unconsolidated materials by concentrated but intermittent flow of water, usually during and immediately following moderate rains or after ice/snow melt. Generally, a rill is not an obstacle to wheeled vehicles and is shallow enough (e.g., < 0.5 m) to be obliterated by ordinary tillage. Compare gully (Schoeneberger and Wysocki, personal communication, 2013).
rim The border, margin, edge, or face of a landform, such as the curved brim surrounding the top part of a crater or caldera; specifically the rimrock of a plateau or canyon ( Jackson, 1997).
ring silicate
A mineral containing a circular arrangement of silica tetrahedra that share two oxygens per tetrahedra; silicon-oxygen ratio is SiO32-; example: beryl, Be3Al2(SiO3)6; cyclosilicate.
riparian Land adjacent to a body of water that is at least periodically influenced by flooding. Compare flood plain, tidal flats, and wetland.
ripple mark
An undulating surface of alternating, subparallel, small-scale ridges and depressions, commonly composed of loose sand. It is produced on land by wind and under water by the agitation of water by currents or wave action, and generally tends at right angles or obliquely to the direction of flow of the moving fluid. Compare giant ripple mark (Jackson, 1997).
rise [geomorphology] A geomorphic component of flat plains (e.g., lake plain, low coastal plain, low-gradient till plain) consisting of a slightly elevated but low, broad area with low slope gradients (e.g., 1-3% slopes); typically a microfeature but can be fairly extensive. Commonly soils on a rise are better drained than those on the surrounding talf (Schoeneberger and Wysocki, personal communication, 2013). Compare talf.
riser [geomorphology] A geomorphic component of terraces, flood-plain steps, and other stepped landforms consisting of the vertical or steep side slope (e.g., escarpment) typically of minimal aerial extent. Commonly a recurring part of a series of natural, step-like landforms such as successive stream terraces. Characteristic shape and alluvial sediment composition are derived from the cut and fill processes of a fluvial system. Compare tread (Schoeneberger and Wysocki, personal communication, 2013).
river
[streams] (a) A general term for a natural, freshwater surface stream of considerable volume and generally with a permanent base flow, moving in a defined channel toward a larger river, lake, or sea. (b) (not recommended: colloquial New England, USA) A small watercourse which elsewhere in the USA is known as a creek. Compare stream (Jackson, 1997).
river valley An elongate depression of the Earth’s surface; carved by a river during the course of development. Compare valley side, valley floor ( Jackson, 1997).
river wash [soil survey] A miscellaneous area (map unit) applied to barren alluvial areas of unstablilized sand, silt, clays or gravel frequently flooded, washed, and reworked by stream activity (USDA, 19939).
road bed The trace or track of a wheeled vehicle route that may or may not be raised slightly above the adjacent land, and composed of earthy fill material (gravel, rock fragments, etc.) or local soil material. Traffic can alter various soil properties primarily by compaction. Abandoned or reclaimed beds may no longer be topographically or visually distinct. However, materials used to construct beds or changes in soil properties may continue to have a significant impact on soil management or plant growth (Schoeneberger and Wysocki, personal communication, 2013).
roche moutonnée A small elongate protruding knob or hillock of bedrock, so sculptured by a large glacier as to have its long axis oriented in the direction of ice movement, an upstream (stoss or scour) side that is gently inclined, smoothly rounded, and striated, and a downstream (lee or pluck) side that is steep and rough. It is usually a few meters in height, length, and breadth ( Jackson, 1997).
rock anhydrite A sedimentary rock (evaporite) composed chiefly of mineral anhydrite (anhydrous CaSO4); The rock is generally massive, cryptocrystalline, and may exhibit rhythmic sedimentation (rhymites; Schoeneberger and Wysocki, personal communication, 2013). Compare rock gypsum, rock halite.
rock halite A sedimentary rock (evaporite) composed primarily of halite (NaCl; Schoeneberger and Wysocki, personal communication, 2013).
rock land Areas containing frequent rock outcrops and shallow soils. Rock outcrops usually occupy from 25 to 90% of the area. Compare miscellaneous area.
rock outcrop [soil survey] A miscellaneous area (map unit) applied to natural exposures of dominantly barren bedrock (other than lava flows and rock-lined pits; USDA, 1993).
rock fragments Discrete pieces of hard rock 2 mm in diameter or larger that are strongly cemented or more resistant to rupture. Refer to Table 4 for terms that are used to classify rock fragments in soils. Compare artifact, coarse fragments, pararock fragments.
rock glacier
A mass of poorly sorted angular boulders and fine material, with interstitial ice a meter or so below the surface (ice-cemented) or containing a buried ice glacier (ice-cored). It occurs in a permafrost area, and is derived from a cirque wall or other steep cliff. Rock glaciers have the general appearance and slow movement of small valley glaciers, ranging from a few hundred meters to several kilometers in length, and having a distal area marked by a series of transverse, arcuate ridges (Jackson, 1997).
rock gypsum
A sedimentary rock (evaporite) composed primarily of mineral gypsum (CaSO4∙2H2O). The rock is generally massive, ranges from coarse crystalline to fine granular, may show disturbed bedding due to hydration expansion of parent anhydrite (anhydrous CaSO4), and may exhibit rhythmic sedimentation (rhymites; Jackskon, 1997). Compare gypsite.
rock pediment An erosion surface of low relief, cut directly into and across bedrock and composed of either bare rock or thinly veneered pedisediment or residuum (e.g., <1.5 m) over bedrock; it occurs along the flanks of mountain fronts, or at the base of mountains or high hills. Its surface grades to the backwearing mountain slopes or hillslopes above, and generally grades down to and merges with a lower-lying alluvial plain, piedmont slope or valley floor below (Schoeneberger and Wysocki, personal communication, 2013; Peterson, 1981).
rock spread [mass movement] The process, associated sediments (rock spread deposit) or resultant landforms characterized by a very rapid type of spread dominated by lateral movement in a rock mass resulting from liquefaction or plastic flow of underlying materials that may be extruded out between intact units; rock bodies predominate. Compare debris spread, earth spread, landslide (Schoeneberger and Wysocki, personal communication, 2013; Varnes, 1978).
rock topple [mass movement] The process, associated sediments (rock topple deposit) or resultant landform characterized by a localized, very rapid type of fall in which large blocks of rock material literally fall over, rotating outward over a low pivot point; rock bodies predominate (little fine earth). Portions of the original material may remain intact, although reoriented, within the resulting deposit. Compare earth topple, debris topple, landslide (Schoeneberger and Wysocki, personal communication, 2013).
rock varnish
A thin, dark, shiny film or coating, composed of iron oxide accompanied by traces of manganese oxide and silica, formed on the surfaces of pebbles, boulders, and other rock fragments, commonly on rock outcrops in arid regions. It is believed to be caused by exudation of mineralized solutions from within and deposition by evaporation on the surface (Jackson, 1997).
rockfall [mass movement] The process, associated sediments (rockfall deposit) or resultant landform characterized by a very rapid type of fall dominated by downslope movement of detached rock bodies which fall freely through the air or by leaps and bounds (lacks an underlying slip face); also spelled rock fall. Compare debris fall, soil fall, landslide (Schoeneberger and Wysocki, personal communication, 2013).
rockfall avalanche [mass movement] The process, associated sediments (rockfall avalanche deposit) or resultant landform characterized by an extremely rapid, large type of rock-fragment flow (a type of landslide) that starts as a rockfall but turns into a flow and characteristically deposits rock-dominated debris long distances from the failure face (such as 10–20 times the fall height); occurs only when huge rockfalls and rockslides involving millions of metric tons of material attain extremely rapid speeds; most common in a rugged mountainous area; for example, the 1903 Franks, Alberta, Canada avalanche. Sometimes loosely referred to as a long run-out landslide. Compare rock fragment flow, flow, landslide (Schoeneberger and Wysocki, personal communication, 2013).
rod weeding Refer to tillage, rod weeding.
rolling Refer to tillage, rolling.
root mean square Refer to modeling, root mean square.
root bed Refer to tillage, root bed.
root penetration The process by which plant roots elongate through soil.
root zone The portion of the soil profile from which plants absorb water and nutrients.
rotary hoeing Refer to tillage, rotary hoeing.
rotary tilling Refer to tillage, rotary tilling.
rotational debris slide [mass movement] The process, associated sediments (rotational debris slide deposit) or resultant landform characterized by an extremely slow to moderately rapid type of slide, composed of comparatively dry and largely unconsolidated earthy material, portions of which remain largely intact and in which movement occurs along a well-defined, concave shear surface and resulting in a backward rotation of the displaced mass; sediments have substantial proportions of both fine earth and coarse fragments. The landform may be single, successive (repeated up and down slope), or multiple (as the number of slide components increase). Compare rotational earth slide, rotational rock slide, translational slide, lateral spread, landslide (Schoeneberger and Wysocki, personal communication, 2013; Varnes, 1978).
rotational earth slide [mass movement] The process, associated sediments (rotational earth slide deposit) or resultant landform characterized by an extremely slow to moderately rapid type of slide, composed of comparatively dry and largely unconsolidated earthy material, portions of which remain largely intact and in which movement occurs along a well-defined, concave shear surface and resulting in a backward rotation of the displaced mass; sediments predominantly fine earth (< 2 mm). The landform may be single, successive (repeated up and down slope), or multiple (as the number of slide components increase). Compare rotational debris slide, rotational rock slide, translational slide, lateral spread, landslide. (Schoeneberger and Wysocki, personal communication, 2013; Varnes, 1978).
rotational landslide (not preferred) use rotational slide.
rotational rock slide [mass movement] The process, associated sediments (rotational rock slide deposit) or resultant landform characterized by an extremely slow to moderately rapid type of slide, composed of comparatively dry and largely consolidated rock bodies, portions of which remain largely intact but reoriented, and in which movement occurs along a well-defined, concave shear surface and resulting in a backward rotation of the displaced mass. The landform may be single, successive (repeated up and down slope), or multiple (as the number of slide components increase). Compare rotational debris slide, rotational earth slide, translational slide, lateral spread, landslide (Schoeneberger and Wysocki, personal communication, 2013; Varnes, 1978).
rotational slide [mass movement] The process, associated sediments (rotational landslide deposit) or resultant landforms characterized by an extremely slow to moderately rapid type of slide, composed of comparatively dry and largely soil-rock materials, portions of which remain largely intact and in which movement occurs along a well-defined, concave shear surface and resulting in a backward rotation of the displaced mass. The landform may be single, successive (repeated up and down slope), or multiple (as the number of slide components increase). Compare rotational debris slide, rotational earth slide, rotational rock slide, translational slide, lateral spread, landslide.
rotational slump (not recommended) use rotational slide.
rough broken land (obsolete) An informal term for areas with very steep topography and numerous intermittent drainage channels but usually covered with vegetation. Compare miscellaneous areas and badland. (Not used in current U.S. system of soil taxonomy.)
rubble An accumulation of loose angular rock fragments, commonly overlying outcropping rock; the unconsolidated equivalent of a breccia ( Jackson, 1997). Compare scree, talus.
rubble land [soil survey] A miscellaneous area (map unit) applied to areas with ≥90% or more of the surface covered with cobbles, stones, and or boulders. Commonly occurs as colluvium at the base of mountains, but some areas may be left on mountainsides by glaciation or periglacial processes. A miscellaneous area (USDA, 1993).
runoff That portion of precipitation or irrigation on an area that does not infiltrate, but instead is discharged from the area. That which is lost without entering the soil is called surface runoff. That which enters the soil before reaching a stream channel is called throughflow, ground water runoff or seepage flow from ground water. (Note: In soil science, runoff usually refers to the water lost by surface flow; in geology and hydraulics runoff usually includes both surface and subsurface flow.). Refer to Hortonian flow.
RUSLE2 Refer to erosion, Revised Universal Soil Loss Equation.