V-shaped valley A valley having a pronounced cross profile suggesting the form of the letter “V”, characterized by steep sides and short tributaries; specifically a narrow valley resulting from downcutting by a stream. The “V” becomes broader as the downcutting progresses. Compare U-shaped valley ( Jackson, 1997).

vadose water Water in the vadose zone.

vadose zone The aerated region of soil above the permanent water table.

valence state The number of electrons required to fill the outermost shell of an atom or alternatively the number of electrons which can be lost or shared in the outermost shell.

valley An elongate, relatively large, externally drained depression of the Earth’s surface that is primarily developed by stream erosion or glacial activity (Hawley and Parsons, 1980). Compare basin.

valley floor A general term for the nearly level to gently sloping, lowest surface of a valley. Landforms include axial stream channels, the flood plain, flood-plain steps, and, in some areas, low terrace surfaces. Compare flood-plain landforms, meander, braided channel, valley side (Hawley and Parsons, 1980).

valley side The sloping to very steep surfaces between the valley floor and summits of adjacent uplands. Well-defined, steep valley sides have been termed valley walls (not recommended). Note: Scale, relief, and perspective may require use of closely related terms such as hill slope or mountain slope (Hawley and Parsons, 1980).

valley train A long narrow body of outwash confined within a valley beyond a glacier; it may, or may not, emerge from the valley and join an outwash plain ( Jackson, 1997).

valley fill The unconsolidated sediment deposited by any agent (water, wind, ice, mass wasting) so as to fill or partly fill a valley (Hawley and Parsons, 1980).

valley flat A generic term for the low or relatively level ground lying between valley walls and bordering a stream channel; especially the small plain at the bottom of a narrow, steep-sided valley. The term can be generally applied noncommittally to a flat surface that cannot be identified with certainty as a floodplain or terrace. Compare backswamp, meander belt ( Jackson, 1997).

valley floor remnant Hills that are now erosional remnants of a former valley or basin floor, composed mostly of unconsolidated valley/basin fill sediments (e.g., alluvium) and typically lie well above the modern valley floor and flood plain. Former basin floor surfaces have become dissected and irregular and consist of hillslope positions (shoulder, backslope, etc.) and hill components (interfluve, headslope, etc.); common in large valleys of the western USA (Schoeneberger and Wysocki, personal communication, 2013).

valley wall (not recommended) use valley side.

valley-border surfaces A general grouping of valley-side geomorphic surfaces of relatively large extent that occur in a stepped sequence graded to successively lower stream base levels, produced by episodic valley entrenchment; for example, multiple stream terrace levels, each with assemblages of constituent landforms (e.g., interfluves, hillslopes, fans, etc.) that dominate the margins of large river valleys (Schoeneberger and Wysocki, personal communication, 2013; Hawley and Parsons, 1980).

value, color The degree of lightness or darkness of a color in relation to a neutral gray scale. On a neutral gray scale, value extends from pure black to pure white; one of the three variables of color. Compare Munsell color system, hue, and chroma.

Van der Waals forces Binding force which arises from an induced dipole in a normal molecule which induces a dipole in another molecule thus causing an attraction between them.

vapor flow The gaseous flow of water vapor in soils from a moist or warm zone of higher potential to a drier or colder zone of lower potential.

variable charge A solid surface carrying a net electrical charge which may be positive, negative, or zero, depending on the activity of one or more species of a potential-determining ions in the solution phase contacting the surface. For minerals and other materials common in soils(e.g., soil organic matter, and oxides), the potential-determining ion usually is H+ or OH-, but any ion that forms a complex with the surface may be potential-determining. Compare constant-potential surface and pH dependent charge.

variant Refer to soil variant.

varnish Refer to desert varnish.

varve A sedimentary layer, lamina, or sequence of laminae, deposited in a body of still water within 1 year; specifically, a thin pair of graded glaciolacustrine layers seasonally deposited, usually by meltwater streams, in a glacial lake or other body of still water in front of a glacier ( Jackson, 1997). Compare rhythmite.

vegetative cell The growing or feeding form of a microbial cell, as opposed to a resistant resting form.

ventifact A stone or pebble that has been shaped, worn, faceted, or polished by the abrasive action of windblown sand, usually under arid conditions. When the pebble is at the ground surface, as in a desert pavement, the upper part is polished while the lower or below ground part is angular or subangular. ( Jackson, 1997; Hawley and Parsons, 1980).

vermiculite A highly charged particle, averages about 159 cmolc kg_-1 for soil vermiculites but has a very wide range, layer silicate of the 2:1 type that is formed from mica. It is characterized by adsorption preference for potassium, ammonium, and cesium over smaller exchange cations. It may be dior trioctahedral. Compare Appendix I, Table A3.

vernal pool A natural, seasonal pond in a small closed depression (microlow) which supports a semi-aquatic or aquatic ecosystem adapted to annual cycles of standing water in the springtime followed by drying in the summer/autumn; commonly recognized in California (Schoeneberger and Wysocki, personal communication, 2013).

vertical mulching Refer to tillage, vertical mulching.

Vertisols [soil taxonomy] An order of clay-rich, high shrink-swell, and deep-cracking mineral soils that have 30% or more clay, deep wide cracks when dry, and either gilgai microrelief, intersecting slickensides within 1 m of the surface, or wedge-shaped structural aggregates tilted at an angle from the a horizontal plane. Vertisols have a cryic or warmer soil temperature regime. Soil moisture regime is commonly ustic, but can range through aridic, ustic and xeric (USDA, 1999; Appendix I).

very coarse sand A soil separate. Compare soil separates.

very fine sand (a) A soil separate. Compare soil separates. (b) A soil textural class. Compare soil texture.

very fine sandy loam A soil textural class. Compare soil texture.

vesicles (a) Unconnected voids with smooth walls.(b) Spherical structures, formed intracellularly, by vesicular arbuscular endomycorrhizal fungi.

viable but not culturable microorganisms Soil microorganisms that cannot be cultured on common laboratory media but can be detected based on sequences of DNA extracted directly from soil.

viscosity Property of a fluid indicating its resistance to movement due to the internal friction in the fluid, as measured by the force per unit area resisting flow.

Vitrands [soil taxonomy] A suborder of Andisols that are coarse textured and more or less well drained. Characteristically, Vitrands have an ochric or mollic epipedon and a cambic horizon. Vitrands have a frigid or warmer soil temperature regime and an ustic or udic soil moisture regime (USDA, 1999; Appendix I).

vitric Pyroclastic material that is more than 75% glass ( Jackson, 1997).

void ratio The ratio of the volume of soil pore (or void) space to the solid-particle volume.

volcanic (adjective) Pertaining to (i) the deep seated (igneous) processes by which magma and associated gases rise through the crust and are extruded onto the earth’s surface and into the atmosphere, and (ii) the structures, rocks, and landforms produced (Hawley and Parsons, 1980). Compare extrusive, volcaniclastic.

volcanic breccia A volcaniclastic rock composed mostly of angular rock fragments greater than 2 mm in size. The name volcanic breccia is not synonymous with pyroclastic breccia (volcanic breccia forms in different ways; Jackson, 1997).

volcanic plug A consolidated crater-filling of lava, the surrounding material of which has been largely removed by erosion leaving an isolated hill or knob (Schoeneberger and Wysocki, personal communication, 2013; Jackson, 1997). Compare neck [volcanic].

volcanic cone A conical hill of lava and/or pyroclastics that is built up around a volcanic vent ( Jackson, 1997).

volcanic crater A basin-like, rimmed structure, usually at the summit of a volcanic cone. It may be formed by collapse, by an explosive eruption or by the gradual accumulation of pyroclastic material into a surrounding rim. Compare caldera ( Jackson, 1997).

volcanic dome A steep-sided, rounded extrusion of highly viscous lava squeezed out from a volcano, and forming a dome-shaped or bulbous mass of congealed lava above and around the volcanic vent ( Jackson, 1997).

volcanic field A more or less well defined area that is covered with volcanic rocks of much more diverse lithology and distribution than a lava field, or that is so modified by age and erosion that it’s original topographic configuration, composition and extent is uncertain (Schoeneberger and Wysocki, personal communication, 2013). Compare lava field, lava plain.

volcanic neck A vertical, pipe-like tower of solidified lava or consolidated fragmental igneous rock that represents a former volcanic vent whose surrounding material (e.g., tuff and tephra) has been largely removed by erosion (Schoeneberger and Wysocki, personal communication, 2013; Jackson, 1997; Green and Short, 1971). Compare plug [volcanic], diatreme.

volcaniclastic Pertaining to the entire spectrum of fragmental materials with a preponderance of clasts of volcanic origin. The term includes not only pyroclastic materials but also epiclastic deposits derived from volcanic source areas by normal processes of mass movement and stream erosion. Examples: welded tuff, volcanic breccia.

volcano (a) A vent in the surface of the Earth through which magma and associated gases and ash erupt; also, the form or structure, usually conical, that is produced by the ejected material. (b) Any eruption of material, for example, mud, sand, etc., that resembles a magmatic volcano ( Jackson, 1997).

volume weight (no longer used in SSSA publications) Refer to bulk density, soil.

volumetric heat capacity The heat required to raise the temperature of 1 cm3 of soil by 1°C. The change in heat content of unit volume of soil per unit change in soil temperature.

volumetric water content The soil-water content expressed as the volume of water per unit bulk volume of soil.

vughs Relatively large voids, usually irregular and not normally interconnected with other voids of comparable size; at the magnifications at which they are recognized they appear as discrete entities.