ACCRETION The opposite of erosion. On a beach, sediment accumulation results in beach widening and seaward growth.
ADHESION RIPPLES A feature formed when dry sand blown over a wet beach adheres to the damp surface, to form an irregular, warty bed form.
AEOLIANITE See eolianite.
ANTIDUNES Small, current-formed, asymmetric ripple-like features roughly parallel to the shoreline that develop in the swash zone, only inches high, with their steep face oriented opposite the direction of backflow. They form on beach surfaces where rapid seaward backwash returns over fine-grained sand. Antidunes are usually washed out on the falling tide but leave a distinctive striped pattern on the beach. Somewhat larger antidunes also form in channels where the flow velocity is high.
ARMORED MUD BALL A piece of mud that has rolled on the beach to become coated with sand and coarser material, often shell fragments, which “armor” the mud, slowing the ball’s attrition.
BACKSHORE That part of the beach landward of the normal high-tide line.
BACKWASH The seaward flow of water return from wave swash, down the beach face.
BARRIER ISLAND A narrow sandy island, usually close to and paralleling the coast, but facing the open ocean and bounded on each end by tidal inlets. Barrier islands make up about 12 percent of the world’s open-ocean shoreline and are characteristic of trailing-edge coasts (e.g., the Frisian Islands of the Dutch-German North Sea Coast and the East and Gulf Coasts of the United States).
BARRIER ISLAND MIGRATION The landward movement of an island in response to either a rising sea level (Colombia’s Pacific Coast) or a loss of sand supply (Nile Delta).
BEACH BISCUITS An informal name for biscuit-shaped lumps of cohesive sand on the upper beach surface, often occurring in a regularly spaced pattern. In some instances, these are the resistant caps that lead to the eventual formation of pedestals.
BEACH GLASS Collectors’ informal name for rounded pieces of broken glass found on beaches. Also called mermaid’s tears and lucky tears.
BEACH GROOMING Any cleaning of a beach by raking, sweeping, or mechanical sifting to remove wrack and debris.
BEACH NOURISHMENT The artificial rebuilding of a beach by the addition of sand from an outside source to hold the shoreline in place. Also called beach replenishment, and dredge and fill.
BEACH PROFILE A line representing the silhouette of the beach as viewed when looking parallel to the shoreline.
BEACH RIDGE An elevated berm above normal high tide, typical of a beach that is accreting or building seaward. The term is also used to describe the first row of dunes landward of the back beach.
BEACH ROCK Cemented beach sand that forms ledges between the high- and low-tide lines.
BEACH SCRAPING / BEACH BULLDOZING A procedure in which a layer of sand is bulldozed or pushed from the intertidal zone and forebeach to the back of the beach in order to form an artificial dune or sand dike. This is usually done to protect buildings.
BEDFORM A small-scale feature formed on the surface of the beach or dune. Also called sedimentary structures. Examples include lineations, rills, and ripples.
BERM A depositional terrace-like feature on the upper beach.
BERM CREST The seaward edge of the berm, beyond which is the steep berm face, sloping seaward.
BIOGENIC A term that refers to sediment produced by organisms.
BIOTURBATION Sedimentary structures (seen in cross section or in a ditch) disturbed or destroyed by the activity of animals and plants (e.g., plant roots or crab burrows).
BLACK SAND See heavy minerals.
BLISTER A small bedform on the beach resulting from trapped air pushing up a miniature mound of sand, usually circular or oval in plan view. Characterized by an internal air cavity.
BLOWOUT A bowl-shaped or flat area in a dune field where the sand has been blown away (eroded). This erosion usually proceeds until the groundwater table is reached, at which point the wet sand hinders further sand removal. This results in a flat blowout floor. This is the only large-scale erosional feature formed by winds.
BREAKWATER Hard structure placed offshore, usually parallel to the shore, designed to cause waves to break, lessening erosion on the beach immediately behind the breakwater. Breakwaters interrupt longshore drift and cut off sand supply to downdrift beaches.
BUBBLE TRAINS Lines of bubbles formed by air escaping from a hole in the beach into the water layer of the swash or backwash. The bubble line may be straight or curved depending on how the swash is moving across the beach.
BUBBLY SAND Sand with cavities or very large visible pores that are formed when air bubbles are trapped in the sand. See soft sand.
BULKHEAD A relatively low and small seawall designed not to protect buildings from waves, but to keep land from eroding from behind wall.
CALCAREOUS A term used to describe material composed of calcium carbonate (CaCO3). On beaches this is usually shells, skeletal material such as coral, and the sand derived from these sources.
CARBONATE FRACTION The calcareous portion of the sediment composed of grains of calcium carbonate (CaCO3).
CHIMNEY STRUCTURE The resistant rim and burrow-tube lining that protrudes out on a beach surface when exposed by swash erosion.
COASTAL PLAIN A broad, gently seaward-sloping plain, often tens to hundreds of miles wide and underlain by sedimentary rocks, that borders the coast. Coastal plains occur primarily on trailing-edge coasts (e.g., eastern North and South America and East Africa).
COLLISION OR LEADING-EDGE COAST A coast that borders the colliding oceanic and continental plates. Usually the continental margins here are narrow and steep and bordered by mountain ranges, and the beaches tend to have relatively high waves (e.g., western North and South America).
CONTINENTAL SHELF The very gently sloping surface extending from the beach out to where the steeper continental slope begins, usually at depths greater than 300 ft (90 m). The width of the continental shelf is an important control of the size of the waves that strike the beach; narrow shelves (Peru, Chile, eastern Japan) favor high waves, and wide shelves (Argentina, western Australia, eastern China) favor low waves.
COQUINA Calcareous rock, composed mostly of shell material, cemented by calcium carbonate.
CRESCENT MARK A scour mark around any small object on the beach, such as a shell or pebble, that results from wind or water flow around the object. Also called an obstacle mark.
CROSS BEDDING Inclined laminations and beds that form in a sand dune. Successive sets of laminations show different orientations.
CROSS RIPPLE See interference ripple.
CURRENT RIPPLE MARK A type of asymmetric ripple mark that forms by water current or wind flow on the beach or dune surface. The steep face of the ripple mark faces in the direction of current flow.
CUSPATE FORELAND A triangular coastal landform (e.g., a cape) resulting from deposition of sediment transported by longshore currents, usually from two directions, and fringed by beaches. Called a ness in Great Britain.
CUSPS Regularly spaced (3 to 9 ft [1 to 3 m]) small embayments (of variable size), separated by small ridges or horns, along a beach that give the shoreline a sinuous or cuspate appearance. The spacing can be considerably greater depending on the size of the waves that formed these features.
DISSIPATIVE BEACH Above the low-tide line these are low, flat, and narrow beaches with a wide surf zone (often more than 325 ft [100 m] wide) on the broad underwater portion of the beach. Offshore sandbars are usually well-developed. Waves are characteristically high, and because of the gentle slope of the offshore beach, the waves lose much of their energy as they first break well offshore, re-form, and break again close to the exposed beach.
DOWNDRIFT The dominant direction of the longshore current flow; analogous to downstream in rivers.
DOWNWELLING The flow of surface water into deeper water. This occurs when onshore winds pile up water on the beach, which then escapes by flowing down the surface of the shoreface.
DRAG MARKS Marks on a beach surface resulting from objects being dragged over the sand by waves or swash, scouring the surface. The object or tool may be a shell, seaweed, foam, or other flotsam, and each object leaves a unique mark.
DREDGING / DREDGE AND FILL The removal of sand by dredges to provide sand to nourish a beach.
DRIFT LINE An accumulation of natural and artificial debris (e.g., seaweed, driftwood, plastic refuse, bottles, fishing net floats, lumber) at the most landward extent of the wave swash. See wrack.
DRY BEACH See wet-dry beach line.
DUNE A feature formed on land from the accumulation of windblown sand, either bare or covered with vegetation. Internally cross bedded due to sand deposition on the various slope faces of the dune.
DUNE CROSS BEDDING A feature in dunes created by the wind building consecutive layers of sand on top of each other that are inclined at different angles. Each single layer indicates a former surface of the dune.
DYNAMIC EQUILIBRIUM The natural balance between processes and materials in the formation of any landform, including beaches. Sea level, wave energy, and sediment supply will produce a specific equilibrium beach profile. A change in any factor will cause the beach profile or beach location to change, moving to a new equilibrium.
EBB CURRENT A tidal current formed when the tide is falling, or “going out.”
EBB TIDAL DELTA The body of sand that protrudes seaward of an inlet formed by sand carried by ebb tidal currents and shaped by waves.
EMBRYONIC DUNE A small sand dune formed by the initial process of dune formation when a sand deposit forms in the wind shadow of a large obstacle or around a clump of vegetation.
EOLIANITE Windblown dune sand cemented into rock, usually a limestone as a result of dissolution of some calcium carbonate grains and then re-precipitation as cement. Primarily found in the tropics.
EROSION A term used to describe shoreline retreat. The opposite of accretion.
ESTUARY The mouth of a river valley flooded by the rising sea where fresh water and salt water mix.
FETCH The distance of open water over which the wind can blow to form waves. The greater this fetch, the larger the potential wave height.
FLASER RIPPLE MARKS Ripple marks with thin layers of mud in the trough between the crests.
FLAT-TOPPED RIPPLE MARK A ripple mark resulting from a reversal of flow that truncates the crest of a previously formed ripple, leaving a flat top; common on tidal flats where the tidal currents reverse direction.
FLOATING SAND Patches of sand grains floating on a calm water surface, as on standing water in a runnel or at the uppermost fringes of the swash. The sand grains float as a result of the normal surface tension of water.
FLOOD CURRENT A tidal current formed as the tide is rising.
FLOOD TIDAL DELTA The body of sand deposited landward of an inlet, formed by flood-tidal currents.
FOREDUNE The first dune line at the back of a beach.
FULGURITE A rare tubular structure of natural glass found in sand dunes and at the back of dry beaches; formed when lightning struck the sand, causing it to melt and fuse.
GRADED BED A bed that is coarser at the base and becomes finer toward the top as viewed in cross section. The opposite pattern is reverse grading.
GROIN (GROYNE) A hard erosion-control structure installed perpendicular to the beach, designed to trap sand traveling with the longshore current. Shorter than jetties, groins are usually placed in groups (or fields). Groins cause sand accretion on the updrift side but erosion on the downdrift side.
GROUNDWATER Water stored underground in the fractures or in pore spaces between the grains of sand. In a beach, the groundwater may be fresh from overland runoff, or salty from wave and tide waters soaking into the beach.
GROUNDWATER TABLE The top of the zone of saturation where groundwater completely fills the pores. On beaches where the water table intersects the surface, seeps or springs may emerge at low tide.
HARD STABILIZATION Any hard engineering structure designed to trap sand or dissipate wave energy in order to hold the shoreline in place, usually to protect buildings.
HARROW STRUCTURES Linear sand deposits that form in the lee or wind shadow of any obstacle. Miniature harrow structures occur on damp surfaces where larger particles form similar obstacles to fine-sand movement.
HEAVY MINERALS Minerals that weigh more than quartz and feldspar (the light minerals). Commonly these are found in patches of black sand that form during storms. They become concentrated by the winnowing effect of wind and water (placering). Most concentrations of heavy minerals in beach sand are black, often due to the abundance of black grains of magnetite. Sometimes heavy minerals impart other colors to beach sand, such as green sand from olivine (Hawaii) or reddish brown sand from garnet (Labrador).
HOLOCENE A unit (Epoch) of geologic time extending from about ten thousand years ago to the present.
IMBRICATION A pattern of overlap stacking of pebbles or cobbles (clasts), common where these pebbles have a flat shape. This stacking results from waves or currents pushing the clast over in the direction of flow, so the resulting orientation of individual pebbles is sloping down in the direction from which the wave or current came. Shingle beaches usually show imbrication.
INLET A narrow waterway between two barrier islands or barrier spits that connects the sea and the lagoon and is maintained by tidal currents.
INNER BAR The landward bar where two or more submerged sandbars occur off a beach.
INTERFERENCE RIPPLE A compound ripple mark resulting from one set of ripples superposed on an earlier set, and produced by waves or currents coming from more than one direction. See also ladderback ripple. Found in runnels and on tidal flats.
INTERTIDAL ZONE The area of the beach between the high-tide line and the low-tide line. The wet portion of the beach exposed at low tide.
JETTY A long, shore-perpendicular engineering structure, often placed in pairs on the sides of inlets to stabilize a navigational channel and to prevent longshore-transported sediment from clogging the channel.
LADDERBACK RIPPLE A compound ripple mark produced when one set of wave ripple marks forms atop of a previous set at nearly a right angle. The resulting pattern looks like a stepladder or is a checkered pattern. Usually produced by changing wave directions during the falling tide, and commonly found on tidal flats.
LAG DEPOSIT A residual layer of coarser sediment that forms on a beach surface when finer sediment is preferentially removed.
LAGOON The body of water between a barrier island and the mainland; the area in which salt marshes develop.
LAMINAE Very thin layers of sediment, usually deposited by a short-term event such as an individual wave or a burst of wind. A lamination, or lamina, may be no more than the thickness of a single layer of sand grains.
LITTORAL DRIFT The sediment transported along a shore by longshore currents. The “net littoral drift” is the volume of sand moved in one direction minus the volume moved in the other direction over a year’s time.
LONGSHORE CURRENT A surf- and breaker-zone current that flows parallel to a beach, created by waves striking the shore at an angle. This is the current that transports sand and carries swimmers away from their beach towel.
MACROFAUNA Animals large enough to be visible to the naked eye.
MANGROVE SWAMP A tropical to subtropical marine wetland that is dominated by mangrove trees and bushes; similar in position and biological role to salt marshes which grow in cooler waters.
MEGARIPPLES Large ripple marks with crest spacing between 2 and 20 ft (0.6 and 6 m) deposited by strong currents such as on tidal deltas.
MEIOFAUNA Tiny animals that live between the sand grains of the beach.
MERMAID’S TEARS See beach glass.
MICROFAUNA Microscopic animals.
MIDDEN An accumulation of waste material from a cultural site occupied by a group of people (e.g., a fishing or hunting camp) over a long period. In coastal areas, middens usually consist of shell heaps from shellfishing cultures. Also called kitchen midden.
MINERAL SUITE The group of minerals that make up the heavy-mineral fraction of a particular beach. The minerals reflect the composition of their source rocks, as well as their history of weathering and transport.
MUD BALL A ball-shaped clump of clay or peat of variable size produced by the erosion of clay or peat outcrops on the beach. Sometimes mud balls result from beach nourishment using muddy sand.
MUD CRACKS A pattern of cracks or lines formed on the surface of a mud layer due to its drying out and shrinking (desiccating).
NAIL HOLE An informal term for holes in a beach produced by air escape or truncation of air cavities in the beach; so named because of their range of sizes similar to nails. Also called sand holes.
NEAP TIDE The minimum tidal range at a beach (least difference between high and low tides), occurring during the first or third quarters of the moon.
NESS See cuspate foreland.
NOURISHED BEACH An artificial beach that has been maintained or widened by the import and addition of new sediment.
OBSTACLE MARK See crescent mark.
OFFSHORE BAR An underwater sand ridge offshore from the beach, often identifiable by a line of waves breaking on the bar.
OOIDS Sand-size spherical grains formed by the precipitation of calcium carbonate in concentric layers around some tiny nucleus. The grains usually form in shallow, wave-agitated marine waters. Also called oolites.
OSCILLATION RIPPLE MARK A ripple with a symmetric cross section, produced by the to-and-fro motion of waves. Characterized by a sharp, straight crest and rounded trough. Also called wave ripple.
OUTER BAR The outermost sandbar where two or more bars occur off a beach. The biggest waves break on this seaward-most bar.
OVERWASH Beach sand that has been transported inland beyond the beach by storm waves or the process of waves crossing the beach and moving into the dunes.
OVERWASH FAN See washover fan.
PARABOLIC DUNE A U-shaped dune, often formed where a breach or blowout occurs in a foredune in coastal areas.
PARTING LINEATION Faint linear patterns on beach surfaces produced by the swash orientation of the grains. Sand grains usually have at least one axis longer than the other two, so individual grains can be aligned preferentially by the swash, resulting in parallel streaks; like brush marks.
PEAT BALL See mud ball.
PEDESTAL STRUCTURE A toadstool-shaped feature formed by differential wind erosion of damp and dry sand layers, or by removal of sand from around an obstacle, leaving it standing atop a small column of sand.
PELLETS Fecal material from organisms of various kinds, often cylindrical in shape and often found on a beach surface surrounding burrows.
PIT Any small depression in the beach formed by a variety of processes including collapse (e.g., blister or air-bubble collapse) and impacts (e.g., raindrop impressions).
PLANE BED A sand layer that has accumulated in a parallel, planar fashion to produce a bed of sediment.
PLANT ARC An arc-shaped ring or other traced pattern in the sand produced by the wind movement of the end of a plant frond, leaf, or rootlet. See scribe marks.
PLATE TECTONICS The theory that the uppermost crust of the earth is divided into plates that move about and interact with one another.
PLEISTOCENE A unit (Epoch) of geologic time that extends from about 2 million years ago to the beginning of the Holocene Epoch (ten thousand years ago); informally called the Ice Age.
PLUNGING BREAKER A type of breaking wave that forms on a moderate beach slope (usually 3 to 11 degrees). The breaker curls over, forming a barrel or tube of air as it collapses. This is the most forceful type of breaker in terms of generating sand movement on the seafloor and also the one that surfers dream about.
POCKET BEACH A beach confined between two headlands.
POSITIVE INTERFERENCE When two (or more) waves from different sources meet in phase (crest to crest or trough to trough), they are additive. The resulting wave is the combined height of the two original waves. On the open ocean, this phenomenon can result in very large rogue waves.
PSAMMON General term for all of the tiny plants and animals that live in the beach or move through the sand.
REFLECTIVE BEACH A steep beach without offshore bars, subjected to relatively low waves. The waves travel right up to the beach and break on it. The intertidal zone is narrow, but often the dry beach is wide. Reflective beaches form a continuum of intermediate forms with dissipative beaches.
REVETMENT A common type of seawall built directly on a surface such as the seaward slope of a dune. Revetments are frequently constructed of boulders; the large rocks provide ample interstitial cavities that absorb some of the water from a breaking wave, thereby reducing sand-removing wave reflection and backwash.
RHOMBOID RIPPLE MARK Diamond-shaped ripples generated by backwash over the beach surface. Most common on the falling tide. The apex of the resulting V pattern points landward, or upslope.
RIDGE AND RUNNEL The ridges of a ridge-and-runnel system are sandbars on the beach surface. Runnels are the troughs between the ridges on the beach. See trough.
RILL MARKS The small erosional channels in the beach face, carved out by either fresh- or saltwater draining out of the beach at low tide. Seaward ends of rills have small deltas (micro deltas).
RINGS A ring pattern on the beach surface produced when a blister or arched sand layer is truncated. Rings are more pronounced where laminae of different colors (heavy minerals) or grain size occur in the beach.
RIP CURRENT A narrow, fast-moving water current that flows seaward from the beach through the surf zone. A major hazard for swimmers.
RIPPLE MARKS Small-scale ridges separated by troughs or depressions in the sand, typically in a repetitive pattern, and usually less than 2 in (5 cm) in amplitude. These bedforms occur in a wide variety of shapes and patterns depending on air, water, and wave conditions.
RIPPLE TRAIN A set of current ripples moving together.
ROGUE WAVE A rare wave that forms when waves coming from more than one direction converge in phase to create a wave with a very large amplitude. It is believed that some rogue waves have struck beaches.
RUNNEL See trough.
SALCRETE Thin sand layers that form fragile crusts, weakly cemented by salt from seawater; they are slightly more resistant or cohesive than underlying dry sand layers.
SALT MARSH The vegetated wetland of the upper intertidal zone in sheltered coastal areas such as lagoons and estuaries, and characterized by salt-tolerant grasses (e.g., Spartina sp.), herbs, and shrubs. Such marshes are usually dissected by tidal creeks.
SALT PRUNING The characteristic seaward-sloping profile of a coastal near-beach vegetation line due to the negative impact of windblown salt spray that prevents leaf formation.
SALTATION A type of sand movement, usually by wind, in which the grains are lifted off of the bed by the current (wind or water) and then fall and strike another grain, launching it into a similar arclike motion.
SAND A size term for grains made up of anything (minerals such as quartz or magnetite, or bits of shells) that range from 1/16 to 2 mm in diameter.
SANDBAR See offshore bar.
SAND HOLE See nail hole.
SAND VOLCANO A miniature cone structure of sand formed when water escapes from a hole in the beach, either due to the tidal effect or when a burrowing organism forces water out though its burrow opening.
SAND WAVE Submerged depositional features formed by strong currents that have crest-to-crest spacing of greater than 18 ft (5.5 m). They are common where tidal currents flow, as in inlets or over tidal deltas.
SCARP A shore-parallel vertical sand “cliff” as high as 7 feet (2 m) on the beach (berm scarp) or at the toe of the dune (dune scarp), usually indicating rapid erosion (often in storms). Scarps are very common on nourished beaches.
SCRIBE MARKS Marks in the sand surface of a dune or back of beach produced when a plant leaf, frond, or exposed root is moved by the wind against the sand. Often circular or semicircular in form.
SEA Locally generated waves in a chaotic surface pattern that is choppy and irregular (confused).
SEA FOAM Foam that is produced during storms; when the bottom is stirred up, organic matter is released and, when churned by the waves, forms foam.
SEA LEVEL The average elevation of the water surface of the sea.
SEAWALL A general term for any hard structure such as a wall, revetment, or bulkhead installed parallel to the shore on the upper beach in an effort to prevent shoreline retreat and loss of property.
SEDIMENT BUDGET A listing of all the sources of sand that contribute to a beach, including rivers, shoreline erosion, and waves pushing sediment ashore from the continental shelf.
SEDIMENTARY STRUCTURE A general and broadly applied term that includes surface bed-forms and internal beach and dune structures, such as cross bedding, produced by sedimentary agents such as waves and currents.
SHADOW DUNE See embryonic dune.
SHELL HASH A general term for any concentration of broken shell material on a beach.
SHOALING Becoming shallower, as in a shoaling wave.
SHOREFACE The narrow, relatively steep surface extending seaward from the low-tide line out to the point where the seafloor slope flattens and merges into the continental shelf, often at depths of 30 to 60 ft (9 to 18 m). The shoreface is an extension of the beach on sandy coasts and is the surface of active sand exchange between the inner shelf and the beach.
SINGING SAND Beach or dune sand that produces any sound when subjected to pressure such as walking on the beach, or the wind blowing over a dune. The sound is produced by the shearing of grains against each other and goes by a variety of names including singing, chirping, barking, whistling, and croaking. The low-frequency sound produced by sliding sand on a dune surface is usually described as booming.
SOFT SAND An informal term for beach sand into which one’s feet sink deeper than on a firm beach, making it difficult to walk. The softness can be due to the presence of bubbly sand, trapped air in the beach, or noncohesiveness attributable to a combination of factors including amount of water saturation, grain size, and seaweed content.
SOFT STABILIZATION Any approach to holding a shoreline in place through the use of non-hardening techniques, but most commonly the artificial placement of sediment on the beach (e.g., dredge and fill; beach replenishment). Also includes the use of vegetation to stabilize dunes.
SORTING A measure of the range of grain sizes in a sediment. A well-sorted sand has a narrow range of grain sizes and a poorly-sorted sand has a wide range of grain sizes.
SPILLING BREAKER A wave that breaks on a relatively flat beach slope (typically 3 degrees or less). The wave crest spills over the top of the wave but does not curl like a plunging breaker.
SPIT A sandbar or fingerlike beach extending from the land and formed by longshore sediment transport; typically curved or hooklike on its seaward end. Spits extend into inlets and mouths of bays. Spit formation can be an initial stage in the formation of barrier islands.
SPRING TIDE The highest tidal range at a beach, occurring during a full or new moon.
STANDING WAVE A smooth wave that forms and stays in place on a current of high-velocity flow, as seen in beach channels. The sediment on the bottom of the channel has a form similar to the water’s surface.
STORM SURGE The superelevation of the water surface due to the combination of low atmospheric pressure at the center of a storm, wind stresses pushing water onshore, and wave setup. Storm surge approaching a coast also is affected by the bottom physiography as water is pushed into shallower depths. Shoreline configuration can also add to the storm-surge effect (e.g., funnel-shaped shorelines are highly susceptible to surges).
SUPRATIDAL FLAT A flat land area landward of the highest tide line, which is occasionally occupied by water from storms. In Abu Dhabi, the supratidal flats are areas of formation of evaporite minerals.
SURF ZONE A band of water within which waves are breaking adjacent to the beach.
SURGING BREAKER A wave that comes ashore on a steep bottom slope (generally greater than 11 degrees) but does not break like spilling or plunging breakers.
SWASH The last remnant of the final breaking wave as it runs up the beach.
SWASH MARK A sinuous line of sand, shell debris, seaweed, or other fine detritus, left at the edge of the uppermost wave swash. A line that marks the maximum advance of a dissipating wave onto the beach.
SWASH ZONE The area of the beach where wave swash and backwash are running up and down the beach slope. The swash zone moves up and down with the tides.
SWELL Regularly spaced waves, with long wavelength and continuous crests, that were formed by winds far from the beach.
TAR BALL Similar to a mud ball but formed from blobs of tar from oil spills or less commonly from natural oil seeps. These are the final remnant of spilled oil left behind as the more volatile fraction evaporates away.
TERRIGENOUS A term describing sediment derived from land.
TIDAL FLAT A more or less flat surface exposed at low tide, sometimes composed of sandy mud. Sandy tidal flats are often covered with extensive fields of ripple marks and the tracks, trails, traces, and burrow openings of animals living on or in the sediment.
TIDE The daily rise and fall of the local water level caused by the gravitational pull of the moon and sun on the ocean’s waters as the Earth rotates.
TIDE RANGE The vertical difference between normal high and low tides; synonymous with tidal amplitude.
TOMBOLO A body of sand, usually perpendicular to the shoreline, which connects the beach to an offshore island or rock. Tombolos often connect offshore breakwaters with the beach.
TRAILING-EDGE COAST Coasts usually bordered by coastal plains where the oceanic tectonic plate is moving along with (not colliding with) the tectonic plate that the continent is on. As a rule, the beaches on trailing-edge coasts tend not to be rocky, the continental shelves are wider, and the beaches have sand that is finer and more quartz rich than that of beaches on colliding or leading-edge margins. Examples are the east coasts of North and South America.
TRANSVERSE DUNE See foredune.
TROUGH A channel-like feature between berm crests or sandbars (ridges) exposed at low tide; also called a runnel. The trough is usually visible as a drainage channel at low tide and is a locale of current ripples.
TSUNAMI An immense, fast-travelling wave formed as the result of an earthquake, submarine landslide, or underwater volcanic eruption. Tsunami waves are small in the open ocean, but in shallow water, they peak up (increase in height).
UPDRIFT The direction opposite the direction of net longshore drift of sand. Analogous to upstream in rivers, and the opposite of downdrift.
UPWELLING Water moving from deep water to the surface. On beaches this usually occurs when winds are blowing offshore, causing water to upwell to replace water that has moved away from the beach.
VENTIFACTS Rocks that have been abraded, grooved, or otherwise shaped by wind-blown sand that usually comes from a desert floor. The result is similar to sand blasting.
WASHOVER FAN A fan-shaped sand deposit resulting from storm waves that carry sediment beyond the back of the beach into the dunes or backing salt marsh and lagoon. Where adjacent fans merge or coalesce, they form a washover apron.
WATER-SATURATED BEACH A beach in which the pores are completely filled with water and the water table in effect is the surface of the beach. Such beaches often give a mirror-like appearance in the distance, reflecting the sky or skyline.
WATER TABLE The surface of the zone of groundwater saturation. See groundwater table.
WAVE The form water takes as energy is transferred from the wind to the sea surface, and consists of the crest (high point) and trough (low point). A wave moves through the water from its wind source area of formation to the coastline. Waves move water in a circular or elliptical rotation, not in a forward direction with the wave form.
WAVE AMPLITUDE Half of the vertical distance between the wave crest and trough.
WAVE BASE The greatest depth at which waves stir up the bottom.
WAVE CLIMATE The characteristic wave conditions (height, period, direction, storm magnitude and frequency) over time for a particular area, and an important factor in determining the type of beach that forms on any given coast. For example, ocean beaches in southern Iceland are usually subjected to high waves, while beaches in Georgia (U.S.) commonly experience very low waves.
WAVE CREST The line formed along the highest point of a wave.
WAVE FREQUENCY The inverse of the wave period, or the fraction of a wave that passes a given point in one second.
WAVE HEIGHT The vertical distance between the wave crest and trough.
WAVELENGTH The horizontal distance between wave crests.
WAVE ORBITAL The internal water movement caused by the passage of a wave. Orbitals are circular in deep water and elliptical in shallow water.
WAVE PERIOD The time it takes for two adjacent wave crests to pass a given point.
WAVE REFRACTION The bending of waves as they come ashore and begin to feel bottom, or change in the direction of the wave front as the wave encounters obstructions such as islands or headlands.
WAVE RIPPLE A type of ripple mark formed by waves and also referred to as a long-crested ripple mark.
WAVE SETUP Water that piles up along a coastline due to continually incoming waves. Water brought in by waves comes in faster than it can drain back to sea, elevating the local water level during storms.
WAVE STEEPNESS The steepness of a wave, measured by the ratio of the wave height to the wavelength.
WAVE TRAIN A group of waves of similar size and speed moving together in the same direction.
WAVE TROUGH The lowest point of a wave.
WET-DRY BEACH LINE The high-tide line marked by the limit of wet sand. The width of the dry beach is one measure of the health of recreational beaches.
WIND RIPPLE MARK A long, parallel-crested ripple mark formed by wind, usually of lower amplitude than water-wave ripples. Typically found on the backshore of the beach and in sand dunes.
WIND SETUP The piling up of water along a coastline due to onshore winds. Winds blow water up against the beach, elevating the local water level, especially during storms, and causing offshore flow of water along the seafloor.
WIND SHADOW The area protected from the wind in the lee of an object or obstacle to the wind, usually resulting in sediment deposition in this position.
WINTER-SUMMER BEACH A highly variable and site-specific characteristic of beaches reflecting the higher waves and more common storms in the winter relative to the summer.
WRACK The general term for debris, whether natural or artificial, that has washed up on a beach, usually accumulating at the edge of the last high-tide line (wrack line) or from the edge of the swash during the last storm. See drift line. Flotsam and jetsam from shipping are a common source, but increasingly wrack is dominated by refuse having a land origin.
WRINKLE MARKS Tiny ripple-like structures that form on a mud surface when covered with a thin film of water and subjected to a wind current.