| Term | Definition |
|---|
| alluvial fan | A cone- or fan-shaped accumulation of sediment deposited where a stream widens abruptly as it leaves a mountain front for an open valley. |
| antecedent stream | A stream that existed before the present topography was created and so maintained its original course despite changes in the structure of the underlying rocks and in topography. |
| base level | The elevation at which a stream ends by entering a large standing body of water, such as a lake or ocean. |
| bed load | The material a stream carries along its bed by sliding and rolling. |
| bottomset bed | A thin, horizontal bed of mud deposited seaward of a delta and then buried by continued delta growth. |
| braided stream | A stream whose channel divides into an interlacing network of channels, which then rejoin in a pattern resembling braids of hair. |
| capacity | The total sediment load carried by a flow. |
| channel | The trough through which the water in a stream flows. |
| competence | The ability of a flow to carry material of a given size. |
| delta | A depositional platform built of sediments deposited in an ocean or lake at the mouth of a stream. |
| dendritic drainage | An irregular stream drainage network that resembles the limbs of a branching tree. |
| discharge | 1) The volume of groundwater leaving an aquifer in a given time. 2) the volume of water that passes a given point in a given time as it flows through a channel of a certain width and depth. |
| distributary | A smaller stream that receives water and sediment from the main channel, branches off downstream, and thus distributes the water and sediment into many channels. |
| divide | A ridge of high ground along which all rainfalls runs off down one side of the rise or the other. |
| drainage basin | An area of land, bounded by divides, that funnels all its water into the network of streams draining the area. |
| drainage network | The pattern of connections of tributaries, large and small, of a stream system. |
| dune | An elongated ridge of sand formed by wind or water. |
| floodplain | A flat area about level with the top of a channel that lies on either side of the channel. It is the part of the valley that is flooded when a stream spills over its banks, carrying with it silt and sand from the main channel. |
| foreset bed | A gently inclined deposit of fine-grained sand and silt, resembling large-scale cross-beds, on the outer front of a delta. |
| graded stream | A stream in which the slope, velocity, and discharge combine to transport its sediment load, with neither sedimentation nor erosion. |
| laminar flow | A flow in which straight or gently curved streamlines run parallel to one another without mixing or crossing between layers. |
| longitudinal profile | The smooth, concave-upward curve that represents a cross-sectional view of a stream, from notably steep near its head to almost level near its mouth. |
| meander | A curve or bend in a stream that develops as the stream erodes the outer bank of a bend and deposits sediment against the inner bank. Meanders are usual in streams flwing on low slopes in plains or lowlands, where channels typically cut through unconsolidated sediments or easily eroded bedrock. |
| natural levee | A ridge of coarse material that confines a stream within its banks between floods, even when water levels are high. |
| oxbow lake | A crescent-shaped, water-filled loop created in the former path of a stream when it abandons a meander and takes a new coarse. |
| point bar | A curved sandbar deposited alon the inside bank of a stream, where the current is slower. |
| pothole | A hemispherical hole in the bedrock of a streambed, formed by abrasion of small pebbles and cobbles in a strong current. |
| recurrence interval | The average time interval between the occurence of two ruptures on the same fault that produce earthquakes of approximately equal magnitude. |
| ripple | A sedimentary structure consisting of a very small dune of sand or silt whose long dimension is at right angles to the current. |
| river | A major branch of a stream system. |
| saltation | The transportation of sand or fine sediment by currents of water or air in such a manner that they move along in a series of short intermittent jumps. |
| settling velocity | The speed at which particles of various weights suspended in a stream settle to the bottom. |
| stream | Any flowing body of water, large or small. |
| superposed stream | A stream that erodes a gorge in resistant formation because its course was established at a higher level on uniform rocks before downcutting began. A superposed stream tends to conitnue the pattern it developed earlier rather than adjusting to its new conditions. |
| suspended load | All the material temporarily or permanently suspended in the flow of a stream. |
| terrace | A flat, steplike surface that lines a stream above the floodplain. |
| topset bed | A horizontal bed of sediments formed at the top of a delta and overlying hte foreset beds. |
| tributary | A stream that discharges water into a larger stream. |
| turbulent flow | A flow in which streamlines mix, cross, and form swirls and eddies. |
| valley | The entire area betwen the tops of the slopes on both sides of a stream. |
| deflation | The removal of dust, silt, and sand from dry soil by strong winds that gradually scoop out shallow depressions in the ground. |
| desertification | Changes in a region's climate that transform semiarid lands into deserts. |
| desert pavement | A remanent ground surface of gravel too large for the wind to transport, left when continued deflation removes the finer-grained particles from a mixture of gravel, sand, and silt in sediments and soils. |
| desert varnish | A distinctive dark brown, sometimes shiny coating found on many rock surfaces in the desert that is a mixture of clay minerals with smaller amounts of manganese and iron oxides. Hypothesized to form very slowly from a combination of dew, chemical weathering, and the adhesion of windblown dust to exposed rock surfaces. |
| dry wash | A desert valley that carries water only briefly after a rain. Called a wadi in the Middle East. |
| eolian | Pertaining to geological processes powered by the wind. |
| loess | A blanket of unstratified, wind-deposited, fine-grained sediment rich in clay minerals. |
| pediment | A broad, gently sloping platform of bedrock left behind as a mountain front erodes and retreats from its valley. |
| playa | A flat bed of clay, sometimes encrusted with precipitated salts, that forms by the complete evaporation of a playa lake. |
| playa lake | A permanent or temporary lake that occurs in arid mountain valleys or basins. As the lake water evaporates, dissolved weathering products are concentrated and gradually precipitated. |
| sandblasting | The erosion of rock outcrops, boulders, and pepples by abrasion caused by the impact of high-speed sand grains carried by the wind. |
| slip face | The steep lee slope of a dune on which sand is deposited in cross-beds at the angle of repose. |
| ventifact | A wind-faceted pebble having several curved or almost flat surfaces that meet at sharp ridges. Each surface or facet is made by sandblasting of the pebble's windward side. |
| abyssal hill | A hill on the slope of a mid-ocean ridge, typically 100 m or so high and lineated parallel to the ridge crest, formed primarily by normal faulting of the basaltic oceanic crust as it moves out of the rift valley. |
| abyssal plain | A wide, flat plain that covers large ares of the ocean floor at depths of about 4000 to 6000 m. |
| active margin | A continentaly margin characterized by volcanic activity and frequent earthquakes and associated with subduction or transform faulting. |
| barrier island | A long offshore sandbar that guilds up to form a barricade between open ocean waves and the main shoreline. |
| continental margin | The shoreline, shelf, and slope of a continent. |
| continental rise | An apron or muddy and sandy sediment extending form the continental slope into the main ocean basin. |
| continental shelf | A broad, flat, sand- and mud-covered platform that is a slightly submerged part of a continent and extends to the edge of the continental slope. |
| continental slope | A steep, mud-covered slope between the continental shelf and continental rise. |
| foraminiferal ooze | A sandy and silty sediment composed of the shells of dead foraminifers. |
| guyot | A large, flat-topped seamount resulting from erosion of an island volcano when it was above sea level. |
| hurricane | A great storm that forms over tropical parts of Earth's oceans, between 8 and 20 degrees latitude, in areas of high humidity, light winds, and warm sea-surface temperatures. They produce winds of at least 119 km/hour and large amounts of rainfall. |
| hurricane intensity scale | A scale used to estimate the potential property damage and flooding expcted along hte coast from hurricane landfall. It is analogous to the Mercalli sclae for earthquakes. |
| longshore current | A shallow-water current that runs parallel to the shore. |
| passive margin | A continental margin far from a plate margin, with no active volcanoes and few earthquakes. |
| pelagic sediment | An open-ocean sediment composed of fine-grained terrigenous and biochemically precipitated particles that slowly settle from the surface to the bottom. |
| sand budget | The inputs and outputs caused by erosion and sedimentation of a beach. |
| seamount | A submerged volcano, usually extinct, found on the seafloor. |
| silica ooze | A biochemically precipitated pelagic sediment consisting of the remains of the silica shells of diatoms and radiolarians. |
| storm surge | A dome of seawater formed by a hurricane at levels higher than the surrounding ocean surface. |
| submarine canyon | A deep valley eroded into the continental shelf. |
| tidal flat | A muddy or sandy area that lies above low tide but is flooded at high tide. |
| tide | The twice-daily rise and fall of the sea caused by the gravitational attraction of the Moon and, to a lesser degree, the Sun. |
| turbidite | A graded bed of sand, silt, and mud deposited by a turbidity current on the abyssal plain. |
| turbidity current | A flow of turbid, muddy water down a slope. The suspended load of mud makes the turbid water denser than the overlying clear water, so that the turbidity current flows beneath the clear water. |
| wave-cut terrace | A level surface formed by wave erosion of coastal bedrock beneath the surf zone. May be visible at low tide. |
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