TribeTerm used to designate a federally recognized group of American Indians and their governing body. Tribes may be composed of more than one band.
TributaryA creek, stream, or river that feeds a larger stream or river, or lake.
TroposphereThe layer of the atmosphere closest to the Earth's surface.
TsunamiOcean wave produced by earthquakes or underwater landslides.
TuffVolcanic rock made up of rock and mineral fragments in volcanic ash matrix. Tuffs commonly are composed of much shattered volcanic rock glass—chilled…
TurbidityThe relative clarity of water, which may be affected by material in suspension in the water.
U.S. Environmental Protection AgencyThe independent federal agency, established in 1970, that regulates federal environmental matters and oversees the implementation of federal environmental…
Unconsolidated shore wetlandsIncludes all wetland habitats having three characteristics: (1) unconsolidated substrates with less than 75% areal cover of stones, boulders, or bedrock…
UnderflowThe movement of groundwater through the soil or a subsurface stratum, or under a structure; specifically, the water flowing beneath the bed of a stream…
UnderstoryThe trees and other woody species growing under a relatively continuous cover of branches and foliage formed by the overstory trees.
United States Code (USC)(USC)A compilation of the general and permanent federal laws of the United States. It is divided into 51 titles that represent broad areas subject to federal…
Unrest (episode)Usually non-eruptive volcanic activity (e.g., ground deformation, steam plumes, degassing) that may be interpreted as a precursor to an eruption.
Unstable slopesSlopes considered unstable due to their incline (or critical angle of repose), applied to slopes made of unconsolidated material.
UplandThe portion of the landscape above the valley floor or stream.
UplightingLight directed upward at greater than 90° above nadir, generally upward into the sky.
Upper-air soundingAn upper-air observation of the vertical profile of an atmospheric variable such as temperature or wind.
UpwarpA broad anticline with gently sloping limbs formed as a result of differential uplift.
Utility scale facilitiesFacilities that generate large amounts of electricity that is delivered to many users through transmission and distribution systems.
Valley floorThe gently sloping to nearly level bottom surface of a valley.
VentA component of a heating or ventilation appliance used to conduct fresh air into, or waste air or combustion gases out of, an appliance or interior space.
Vernal poolSeasonally-flooded depressions found on soils with an impermeable layer such as a hardpan, claypan, or volcanic basalt.
VertebrateAny species having a backbone or spinal column including fish, amphibians, reptiles, birds, and mammals.
Vertical angle of viewElevation of viewer relative to the elevation of the proposed action, and the resulting angle of difference.
View durationLength of time a proposed action is in view. Impacts that are viewed for a long period of time are generally judged to be more severe than those viewed…
Viewer distanceThe distance from a viewpoint to a seen object or landscape element.
ViewpointA point from which a landscape view is analyzed and/or evaluated.
ViewshedThe total landscape seen or potentially seen from all or a logical part of a travel route, use area, or water body.
Visibility factorsConditions or other phenomena that affect the visibility or appearance of an object or a landscape.
Visual absorption capabilityThe physical capacity of a landscape to accept human alterations without loss of its inherent visual character or scenic quality.
Visual attentionNoticing and focusing of vision on a particular object or landscape element.
Visual clutterThe complex visual interplay of numerous disharmonious landscape characteristics and features resulting in a displeasing view.
Visual contrastOpposition or unlikeness of different forms, lines, colors, or textures in a landscape.
Visual disharmonyA state of disagreement, incongruity, or disproportionate arrangement of forms, lines, colors, and textures in the visual elements of a seen landscape.
Visual featureAn element, such as a land or water form, vegetation, or structure in the seen landscape.
Visual harmonyA pleasing array of visual elements in a landscape, usually as a result of a sense of visual order, compatibility, and completeness between and among the…
Visual impactAny modification in land forms, water bodies, or vegetation, or any introduction of structures, which negatively or positively affect the visual character…
Visual intrusionAny human-caused change in the land form, water form, vegetation, or the addition of a structure which creates a visual contrast in the basic elements…
Visual mitigationActions taken to avoid, eliminate, or reduce potential adverse impacts on scenic resources.
Visual Resource Management (VRM) Class Designations(VRM)Class I objective is to preserve the existing character of the landscape. The level of change to the characteristic landscape should be very low and must…
Visual Resource Management (VRM) Classes(VRM)Categories assigned to BLM lands, utilizing the Visual Resource Inventory Classes in the RMP process, with an objective which prescribes the amount of…
Visual Resource Management (VRM) System(VRM)BLM's system for minimizing the visual impacts of surface-disturbing activities and maintaining scenic values for the future.
Visual resourcesRefers to all objects (man-made and natural, moving and stationary) and features such as landforms and water bodies that are visible on a landscape.
Visual sensitivityPublic concern for the maintenance of scenic quality in a particular landscape setting.
Visual unityThe quality or state of appearing to be united in principles and relationships or to be logically and aesthetically connected because of the visual…
Volatile organic compound (VOC)(VOC)Any organic compound that participates in atmospheric photochemical reactions except those designated by the EPA as having negligible photochemical…
Volcanic AshConsists of rock, mineral, and volcanic glass fragments smaller than 2 millimeters (mm) (0.
Volcanic chainA linear sequence of volcanoes that occurs within a tectonic plate. As the plate moves over a stationary hot spot, new volcanoes are created.
Volcanic coneA landform built by the material ejected from a volcanic vent and piled up around the vent in the shape of a cone with a central crater.
Volcanic ventThe opening at the Earth's surface through which volcanic materials issue forth.
VolcanismThe process by which magma and associated gases rise to the Earth's crust and are extruded, or expelled, onto the surface and into the atmosphere.
VolcanoA vent (opening) in the surface of the Earth through which magma erupts. It is also the landform that is constructed by the erupted material.
Volcanoclastic rockSedimentary rocks such as sandstones formed by the aggregation of rock fragments (clasts) of volcanic origin.
Voluntary relinquishmentTo voluntarily relinquish possession with the intent of terminating ownership, but without vesting it in any other person.
Wake effectEnhanced plume dispersion due to mechanical turbulence and zones of turbulent eddies, primarily downwind of a building, which results in increased…
WashA normally dry stream bed that occasionally fills with water.
Waste managementProcedures, physical attributes, and support services that collectively provide for the identification, containerization, storage, transport, treatment…
Waste minimizationActions, policies, or procedures that collectively serve to reduce the amount of wastes generated as a result of operation of an activity or facility.
WastewaterWater that typically contains less than 1% concentration of organic hazardous waste materials.
Water codeA type of legislation that is specific to the management of water resources.
Water qualityA term used to describe the chemical, physical, and biological characteristics of water, usually with respect to its suitability for a particular purpose.
Water rightA legal entitlement of an individual or entity to extract water from a water source (surface water or groundwater) and to use it for a beneficial use (e.g.
Water TableThe upper level of ground water; the level below which soil and rock are saturated with water.
WatershedAll land area from which run-off water may enter a pond or lake.
Watt (W)(W)The unit of electrical power equal to 1 ampere under a pressure of one volt. A Watt is equal to 1/746 horsepower.
WetlandsArea having specific hydric soil and water table characteristics supporting or capable of supporting wetlands vegetation.
WickiupTemporary dwelling framed of arched poles covered by brush, bark, rushes, or mats.
Wild and Scenic Rivers (WSR) Act(WSR)Primary river conservation law enacted in 1968. The Act was specifically intended by Congress to balance the existing policy of building dams on rivers…
Wild horses and burrosUnbranded and unclaimed horses or burros roaming free on public lands in the western United States and protected by the Wild Free-Roaming Horse and Burro…
WildernessAll lands included in the National Wilderness Preservation System by public law, generally defined as undeveloped federal land retaining its primeval…
Wilderness characteristicsWilderness characteristics include (1) Naturalness: the area generally appears to have been affected primarily by the forces of nature, with the imprint…
WildfireAny nonstructural fire that occurs in the wildland.
Wildlife corridorLinear spaces that connect various areas of an animal's habitat (i.e., links between feeding, watering, resting, breeding, or seasonal habitats).
Wind RoseA diagram that indicates the average percentage of time that the wind blows from different directions, on a monthly or annual basis.
WinnowingSelective sorting or removal of fine particles by wind or water.
WithdrawalA withdrawal is money you take out of your banking, brokerage firm, or other accounts.
Xeric (habitat)Low in moisture. Dry environmental conditions. Habitats or sites characterized by their limited water availability.
YardangA wind-carved rock ridge feature found in desert environments.