LONGSHORE CURRENT 



lithification — (or lithif action) . The processes of 

 induration, cementation, petrification, consoli- 

 dation, and crystallization which convert mag- 

 ma and newly deposited sediments into rock. 



lithofraction — Fragmentation of rocks by wave 

 action on beaches. 



lithoid tufa — Gray algal reeflike material form- 

 ing beds and the core of reef domes. 



lithology — The study and description of rocks 

 based upon magascopic and microscopic exami- 

 nation of samples. 



lithometeor — See meteor. 



lithosphere — The outer, solid portion of the 

 earth; the crust of the earth; usually used in 

 contexts wherein the lithosphere is said to make 

 contact with the atmosphere and the hydro- 

 sphere. See also biosphere, geosphere. (5) 

 {See figure for earth structure.) 



lithostrome — See lithotope. 



Lithothamnion ridge — A ridge, composed of the 

 calcium carbonate secretions of Lithothamnion 

 and other red calcareous algae, which rises about 

 3 feet above sea level at the seaward edge of a 

 reef flat. The secretions of Lithothamnion and 

 related genera may compromise 50 percent or 

 more of a coral reef. 



lithotope — An area and environment of uniform 

 sedimentation. The layer or deposit of uniform 

 or uniformly heterogeneous composition and tex- 

 ture produced in a lithotope is called a litho- 

 strome. 



littoral — (or intertidal) . The benthic zone be- 

 tween high and low water marks. According 

 to some authorities the benthonic zone between 

 the shore and water depths of approximately 

 100 fathoms (200 meters). It is also called the 

 littoral benthal which is subdivided into the 

 eulittoral and the sublittoral. The usage and 

 interpretation of this term varies widely in the 

 literature. {See figure for classification of ma- 

 rine environments.) 



littoral benthal — See littoral. 



littoral current — A current, caused by wave ac- 

 tion, that sets parallel to the shore; usually in 

 the nearshore region within the breaker zone. 

 See longshore current. 



littoral deposits — Deposits of littoral drift, that 

 is, sand, gravel, and other material which moves 

 along the shore between high and low water 

 marks. Littoral drift also refers to the long- 

 shore movement or littoral transport of such 

 material by longshore currents. 



littoral drift — The material moved in the littoral 

 zone under the influence of waves and currents. 

 (61) See littoral deposits. 



littoral transport — The movement of material 

 along the shore in the littoral zone by waves and 

 currents. (61) <See littoral deposits. 



littoral zone — See intertidal zone. 



live weight — See biomass. 



load — The quantity of sediment transported by a 

 current. It includes the suspended load of 

 small particles, which float in suspension distrib- 

 uted through the whole body of the current, and 

 the traction load, bottom load, or bed load of 

 large particles which move along the bottom by 

 traction, that is, saltation, rolling, and sliding. 



loam — A soil composed of clay, silt, sand, and 

 organic matter. The term occasionally is used 

 to describe a marine sediment. (2) 



lobes — If a three-dimensional representation of a 

 transducer directivity is made by rotating the 

 two-dimensional directivity pattern these sec- 

 tors generate zones, or regions, on the constant 

 distance surface. These regions are known as 

 lobes. The term is also used with reference to 

 the corresponding portions of the directivity 

 pattern. The region, or sector, which includes 

 the reference axis is known as the primary lobe; 

 the remaining regions, or sectors, are known as 

 the secondary lobes. (28) 



local winds — Winds which, over a small area, dif- 

 fer from those which would be appropriate to 

 the general pressure distribution, or which po- 

 sess some other peculiarity. ( 5 ) 



loch — (or lough). An inlet or arm of the sea, 

 often nearly landlocked. ( 68 ) 



log line — A graduated line used to measure the 

 speed of a ship through the water, or to measure 

 the speed of the current from a ship at anchor. 

 (59) 



lolly ice — See frazil ice. 



longcrested wave — A wave, the crest width of 

 which is long compared to the wavelength. 

 (73) 



longitudinal wave — (also called pressv/re wave, 

 compressional laave, irrotational wave). A 

 wave in which the direction of displacement of 

 each particle in the medium is perpendicular to 

 the wave front. 



long-period constituent — A tide or tidal current 

 constituent with a period that is independent 

 of the rotation of the earth but which depends 

 upon the orbital movement of the moon or of 

 the earth. The period is usually longer than a 

 day and in genei'al a half month or larger. See 

 constituent. 



longshore bar — (or ball). See ball, bar. 



longshore current — (also called littoral current) . 

 The resultant current produced by waves being 

 deflected at an angle by the shore. In this 

 case the current runs roughly parallel to the 

 shoreline. {See figure for nearshore current 

 system.) 



The longshore current is capable of carrying 

 a certain amount of material depending upon its 

 velocity and the particle size of the material; 

 however, any obstruction, such as a submarine 

 rock ridge or a land point cutting across the 

 path of the current will cause loss of velocity 

 and consequent loss of carrying power. 



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