Before proceeding to the characterization of coastal marine processes and the forms of relief they create, let us dwell on the definition of some concepts.

Coastline (shoreline) - the line along which the horizontal water surface of the sea (or lake) intersects with the land. Since the level of water bodies does not remain constant, the coastline is a conditional concept used in relation to some average long-term position of the water body level.

Coast - a strip of land adjacent to the coastline, the relief of which is formed by the sea at a given average level of the reservoir.

An underwater coastal slope is a coastal strip of the seabed, within which waves are able to carry out active work (erode the bottom, move sediments).

The coastal zone includes the coast and the underwater coastal slope.

Depending on the nature (morphology) of the coast, there are coastlines: high (for example, the coast of the Kola Peninsula) and low (northern coast of the Caspian Sea); dissected (the Black Sea coast between the Crimean Peninsula and the Danube mouth) and leveled (the Black Sea coast between Gelendzhik and Sochi); deep, with significant slopes of the underwater coastal slope with the predominant development of abrasion (destructive) processes (the Black Sea coast south of Novorossiysk), shallow, characterized by small angles of inclination of the underwater coastal slope, with a predominance of material accumulation processes (the coast of the Northern Caspian).

A complex of forces acts in the coastal zone, which determine its morphological appearance. These are ebb and flow and associated currents; in non-tidal seas with shallow shores - surge phenomena and currents caused by them; tsunami - sea gravity waves of long length, arising from underwater earthquakes; constant sea currents; activity of organisms; activity of rivers forming a special type of banks (potamogenic banks). However, the main operating factor determining the morphology and dynamics of the coast is waves and associated wave currents.

Waves. The wind, acting on the water surface, causes oscillatory movements of water in its surface thickness. Particles of water begin to make orbital movements in a plane perpendicular to the surface of the sea, and movement along these orbits occurs in the direction of the wind. Distinguish between deep sea waves and shallow water waves. Since wave movements attenuate with depth, the division of sea waves into these categories is carried out according to the criterion: the depth of the sea is greater or less than the depth of penetration of wave movements. At a depth equal to or more than half the wavelength, wave oscillations, and, consequently, their impact on the bottom of the reservoir, attenuate.



In a sea wave, the height h, the length L, the period T, the propagation speed V and such elements as the crest and trough of the wave, the front and rear slopes, the front and the moons of the wave are distinguished (Fig. 153). The time during which a water particle describes a full orbit is called the period, and the value obtained by dividing the wavelength by its period is called the propagation velocity.

Figure: 153. Wave elements:

height; L - length; 1 - wave crest; hollow; 3 - rear slope of the wave; the front slope of the wave. Arrows indicate wind direction

Wave parameters depend on the strength of the wind and its duration, on the nature of the underwater coastal slope, and on the wave acceleration length. Like the energy of a stream, the total energy of waves can be expressed by the formula: E \u003d VsPgh 2 L, where E is the wave energy, p is the density of water, g is the acceleration of gravity, h is the wave height, L is the wavelength. Considering that p and g vary within insignificant limits, we can say that the wave energy is proportional to the length and the square of the wave height.

Shallow water waves, in contrast to the waves of the open sea, affect the bottom (on the underwater coastal slope) and themselves experience its effect. As a result, they spend energy on transforming the bottom topography, on the transfer of debris particles lying on the bottom. The waves of the open sea consume energy only to overcome internal friction and interact with the atmosphere.

The more energy is expended by the waves when passing over the underwater coastal slope, the less it reaches the coastline. As a result of interaction with the bottom when

Figure: 154. The nature of the orbits of wave particles in the wave of shallow water (according to N.E. Kondratiev)



when walking over shallow water, the waves change their profile, become asymmetric: the front slope becomes steeper, and the back one flattens out. External asymmetry corresponds to the asymmetry of the orbits arising in shallow water waves along which water particles move. Orbits from round become elliptical, and the ellipses themselves are irregular, flattened from below (Fig. 154). Accordingly, the equality of orbital velocities is lost. Movement velocities directed towards the coast (i.e., when passing through the upper part of the orbit) become higher than the velocities of the reverse motion (along the lower part of the orbit). This ratio of velocities is of fundamental importance for understanding the processes of sediment movement and relief formation in the coastal zone.

The increase in the steepness of the front slope of the wave reaches a critical value above the depth equal to the wave height. It becomes vertical and even overhanging. The wave crest collapses, as a result, the wave motion of the water is replaced by a fundamentally new type of motion - a surf stream, or coasting. The breaking of the wave itself is called surf.

The surf flow is formed from the mass of water formed when the wave breaks. It runs up the coastal slope, and the direction of the flow roughly coincides with the direction of the wave that caused it, but still noticeably deviates from the initial one under the influence of gravity (Fig. 155). The speed of the surf stream decreases as it moves away from the place of origin, i.e. from where the wave breaks. The deceleration of the flow is associated with the expenditure of energy to overcome the force of gravity, to overcome friction against the surface on which it runs up, to move and process sediments, as well as to the loss of a part of the mass of water to seep into the ground.

Bottom-

The point where the speed at- ................ * ......... x x

Sea

combat flow decreases to zero, called

Figure: 155. Trajectories of a surf stream on the beach with an oblique approach of waves to the shore. X marks the top of the splash
the top of the splash. From here, the mass of water not yet wasted on infiltration flows down the slope in the direction of the greatest slope. This "branch" of the surf flow is called the reverse surf flow, or rollback.

Consequently, the upper and lower boundaries of the coastal zone are determined by the boundaries of the wave impact on the coast, namely: the lower boundary is located at a depth equal to half the wavelength, i.e. that isobath, on which the wave deformation begins, and the upper is determined by the splash line formed by the set of surf peaks. According to the available data on the length of oceanic waves, reaching 350 m, the lower boundary of the underwater coastal slope in the oceans can be traced at depths of up to 150 m, in the seas - up to 50 m.

To understand wave processes on the shores of the seas, it is necessary to have an idea of \u200b\u200brefraction. Refraction is the reversal of the wave front as it approaches the coast, and this process is carried out in such a way that the wave front tends to take a position parallel to the coast. On a flat coast, with the full implementation of refraction, this is the case, and on a rugged one, due to the fact that each segment of the front tends to be parallel to the corresponding segment of the coast, there is, as it were, a compression of the front at the capes and its stretching in the bays. As a result, there is a concentration of wave energy at the headlands and scattering in the concavities of the coastal contour (Fig. 156). The result is "cutting" (abrasion) of the capes, the accumulation of material in the concavities (bays) and, as a result, the leveling of the coast, and in essence, the equalization of the energy of the waves approaching the coast.

It should be noted that the actual orbits along which water particles move during waves are somewhat open due to

h ____ -------- ^ - J

Figure: 156. Scheme of wave refraction at flat (A) and bay (B) coasts (according to V.P. Zenkovich): 1 - wave fronts; 2 - rays of waves; 3 - the base of the underwater slope

with pulsating (uneven) wind impact on the water surface. Due to the open ™ orbits, not only the waveform moves, but also the actual movement of the water mass in the direction of wave propagation, i.e. towards the coast. This creates a rise in sea level off the coast compared to the offshore position. The level imbalance causes the formation of compensation currents.

When waves approach at right angles to the coast with a gentle underwater slope, the first breakdown of waves occurs at a considerable distance from it. The mass of water accumulating near the coast is dampened by the "living wall" of the surf until it finds a way out in some area where this "wall" is somewhat lower. Then the masses of water break through from the coast towards the sea, forming a discontinuous current (Fig. 157). Discontinuous currents, due to their "turbulent" nature, develop speeds of up to several meters per second and are capable of carrying out from the coastal strip to the outer zone of the underwater coastal slope a large number of turbid sediments. This is one of the reasons for sediment leakage from the coastal strip of the coastal zone.

01 S2

When waves approach a deep shore, the outflow of excess water from the shore is carried out

Figure: 157. Wave currents: A - bottom countercurrent; B - along-coastal current: C - discontinuous current; 1 - direction of wave propagation; 2 - direction of currents

ny current directed from the coast towards the sea - bottom countercurrent (Fig. 157, A). It also facilitates the carryover of debris from the coastal strip to the outer coastal zone.

From what has been said, it can be seen that wave movements and the wave currents caused by them lead to the movement of sediment perpendicular to the coast - this is called transverse movement of sediment, or along the coast - alongshore movement of sediment. Both of these factors lead to the formation of specific landforms within the coastal zone.

(lakes, rivers) are called the shore.

The shores are subdivided depending on their steepness (sloping, steep) and the nature of the materials composing them (silty, sandy, pebble, stony). From the side of the water area, a strip of the seabed adjoins the coast, which is constantly affected by wave movements of water. This strip is called the underwater coastal slope.

The coast and the underwater coastal slope together form coastal zone of the sea, within which the complex interaction of the lithosphere, hydrosphere, atmosphere and biosphere is constantly carried out. This zone is characterized by inconstancy of relief forms and their various combinations within the limits of even small areas. The work of sea water is manifested in the destruction of the coast - abrasion, as a result of which they retreat into the interior of the land, as well as in the deposition of destruction products - accumulation, which leads to a change in the underwater relief of the coastal zone and to the formation of new types of coast. The shores formed mainly as a result of the destructive work of waves are called abrasion, and the shores created by sedimentation are called accumulative.

The main factor in the formation of abrasion shores is the destructive work of surf waves, as a result of which a depression is formed at the base of the slope - wave-breaker niche... Over time, this niche deepens more and more, the overhanging parts of the slope fall into the sea, splitting into a mass of debris, with the help of which the surf waves continue the further destruction of the coastal scarp.

The creative work of the sea is expressed in the accumulation of materials thrown out by the sea (sand, pebbles, shells of sea animals, etc.) off the coast. Pebbles and sand on the surface of the abrasion platform are constantly moving within its boundaries under the influence of the surf. As a result, relief forms of accumulative origin are created.

As a result of multiple changes in the depth of the ocean during the glacial and interglacial epochs, peculiar forms of relief were formed in the coastal zones of the seas, which are called ancient coastlines. They can sometimes be located on land and correspond to a higher sea position than at present. The ancient coastlines corresponding to the lower level are now flooded by the sea.

Raised coastlines are expressed as sea \u200b\u200bterraces... These are steps along the coast.

Each terrace is distinguished by: the surface of the terrace; ledge; brow; back seam.They fix the position of the ancient coastline.

Depending on the structure, there are:

  1. Accumulative terraces, that is, completely folded by coastal marine sediments;
  2. Abrasive terraceswhich are composed only of bedrocks;
  3. Basement terraceswith a root base covered by marine sediments.

To reveal the history of the development of the coast, the so-called spectra of terraces,which make it possible to compare different parts of the coast and contain information on neotectonic movements.

Shore types (byD.G. Panov)

(a - riass, b - fiord, c - skerry, d - estuary, e - Dalmatian, f - watt (1 - watts, 2 - runoff troughs), g - thermal abrasion, h - coral, and - volcanic).

Literature.

  1. Smolyaninov V. M. General geography: lithosphere, biosphere, geographic envelope. Study guide / V.M. Smolyaninov, A. Ya. Nemykin. - Voronezh: Origins, 2010 - 193 p.

Coast - a narrow zone within which the interaction of land and sea takes place. Shore-forming processes include waves, currents and tidal events. The coastal zone consists of the coast itself - its surface and an underwater coastal slope. The lower boundary of the coast is a depth equal to half the wavelength; it is at this depth that the impact of the wave on the coast begins. The upper boundary is the line drawn along the tops of the wave breaks.

Coast - a strip of land that includes modern and ancient coastlines. The main process that determines the originality of coastal relief forms is excitement. The wave produces destructive and accumulative work in the coastal zone, causing the development of abrasion and accumulative forms. The destructive work of the waves is called abrasion... Distinguish between mechanical, chemical and thermal abrasion. Mechanical abrasion- This is the destruction of rocks under the influence of waves and surf and bombardment with debris. Chemical abrasion occurs when rocks dissolve sea \u200b\u200bwater... Thermal abrasion - the destruction of the coast, composed of frozen rocks, as a result of the warming effect of sea waters. The prevalence of abrasion or accumulation in the coastal zone depends on the steepness of the coast and the properties of the rocks that compose it. Abrasive landforms prevail on a steep slope composed of solid rock formations. In this case, a wave with high energy affects the coast, and at the level of the coastline a wave-breaking niche is formed.

Its further deepening causes the collapse of the cornice and the development of a vertical ledge - qlipha... As the cliff recedes towards the coast, a platform grows at its foot - bench... The bench begins at the foot of the cliff and continues below sea level; at low tide, the bench can dry out. The abrasion rate on the shores composed of clays and marls can reach several meters per year. Accumulative forms are formed on shallow shores, their originality depends on the angle of the wave approach to the shore. Transverse and alongshore movement of sediments is distinguished. If the wave approaches perpendicular to the coast, a lateral movement of sediments is formed. Gradually, the coast, composed of sediments of the same size, takes the form of dynamic equilibrium. It happens as follows. At a depth equal to half the wavelength, the wave begins to affect the coast. The preponderance of forward velocities (towards the coast) is still small compared to reverse ones. But since the particle is on a slope, it moves slightly down the slope. The closer to the coast, the higher the forward speeds, at the neutral point they become equal to the reverse speeds. At the neutral point, the particle performs only oscillatory motion. Above the slope, the particle will move to the shore, causing the accumulation of material on the shore, below the neutral point, the material will be carried down the slope. With the transverse movement of sediments, the material is delivered to the shore from the bottom, which is mainly sand, pebbles, and shells. Landforms formed by the lateral movement of sediments include underwater coastal ramparts, underwater and island bars, beaches and terraces. At a depth of X / 2, the wave begins to break down, material accumulates at the bottom in the burying zone, and an accumulative underwater coastal shaft... There can be several underwater shafts, they are located parallel to each other and the coast. The height of the shafts reaches 1 - 4 m with a length of up to several kilometers. The formation of several rows of underwater coastal swells is explained by the approach of waves of different wavelengths, therefore, their burying is observed at different depths. When material accumulates, the shafts are converted to underwater bars... The crest of an underwater bar may appear on the surface, in which case the bar becomes island and represents? a chain of islands stretching along the coast. It is believed that island bars can only arise if the World Ocean Level changes. The bars stretch for hundreds of kilometers along low-lying seashores and separate from the sea a coastal area called a lagoon. The feet of the bars are located at a depth of 10 - 20 m, they rise above the water by 5 - 7 m. Bars are very common on the sea shores, 10% of the coastline falls on the shores bordered by bars. A beach is formed on the surface of the coast during the lateral movement of sediments. Beaches of complete and incomplete profile are distinguished by morphological characteristics. A full profile beach is formed in free space. Then the beach looks like a coastal wall with gentle slopes.

Beachan incomplete profile is formed at the foot of the scarp; it has one slope facing the sea. If the sea level drops, the beach becomes an accumulative sea \u200b\u200bterrace... When waves approach the coast at an angle less than 90 °, an alongshore sediment flow is formed. Sediments move along the coast towards an obtuse angle and consist of products of bank destruction and river alluvium supplied to the coast. The optimal angle of approach of the wave to the shore is 45 °. At this approach angle, the maximum amount of sediment is transferred. When the coastal contour changes, the rate of material inflow turns out to be excessive and accumulation begins. An accumulative terrace is formed at the concave coast at the tops of the bays. Since the relief form adjoins the coast along its entire length, it is called adjoined. When bending around the bank ledge, the speed of material movement decreases, at this point an accumulative form is formed - scythe... The braid is attached to the shore by only one part, its end remains free. This form is called free. On the coastal area protected by the island, the accumulation of material leads to the appearance tombolo (take). If the coast is protected from the sea side by a far protruding promontory, a pour... In the course of growth, the barrow can reach the opposite shore and block the bay. In this case, the accumulative form is called the closing one. Depending on the outlines of the coastline and the complex of processes occurring on the coast, they are divided into several types.

1. Primary dissected shores, slightly altered by the sea (ingression). The dismemberment of the coast is created by non-wave processes, the sea waters only fill the relief depressions. Such shores include fiord shores - formed during the flooding of glacial and trough valleys, skerry - formed during flooding of the relief of "curly" rocks (sheep's foreheads).

Such shores are typical for Scandinavia, the northern shores of Canada, while skerries are developed in the Baltic Sea. Rias shores arise when the sea floods the mouths of mountain rivers, such shores include the coast of the Iberian Peninsula. Dalmatian coasts are formed when negative fold structures parallel to the coast are inundated by the sea. This creates chains of islands along the coast and long narrow bays. This coastline is typical for the Adriatic Sea. Estuary banks are formed due to the flooding of estuarine parts of river valleys on low-lying coastal plains. Typical estuaries are characteristic of the Don and Dnieper rivers.

2... Non-wave shores. Such shores are created by tides, rivers, organisms, slope or tectonic processes. Tidal shores include watts - they are flooded twice a day by the lowest quadrature tide, marches are rarely flooded, only by high syzygium tides. The deposition of a large amount of alluvium on the banks causes the creation of a delta coast.

The Lena, Volga and Nile rivers have large deltas. On the coasts of tropical seas, organisms, especially corals, play an active role in coastal formation. Organogenic coral banks are formed here. Tectonic shores can form in tectonically active zones, sometimes tectonics activates slope processes, and then talus and landslides are formed.

3. Wave shores proper. Aligned abrasion shores arise where abrasion is actively occurring. As a rule, these banks are steep, composed of easily eroded rocks. Due to the high rate of retreat, the shores are quickly leveled out, forming a leveled abrasive shore. The leveled accumulative banks are characteristic of the gentle underwater slopes. The accumulation process comes to the fore on this bank. The transitional types of shores include bay and lagoon shores. Abrasion is observed on the bay shores on the capes, and accumulation in the bays. On the lagoon coast, the separation of the lagoon by the growing slant has not yet ended, therefore, the formation of a leveled accumulative coast continues.

The bottom relief of the World Ocean

In the topography of the ocean floor there are four geotecture. Three geotectures are located entirely within the ocean floor: ocean floor, transition zone, mid-ocean ridges; the latter, the underwater edge of the continent, is a part of the geotecture - the continental ledge.

Mainland ledge.A significant part of the continental ledge (about 35%) is flooded by ocean waters. This part is called underwater outskirts of the continents.Approximately 2/3 e falls in the Northern Hemisphere and only 1/3 - in the Southern.

Submarine outskirts of the mainland has a continental type of the earth's crust. With an increase in the ocean level, the area of \u200b\u200bthe underwater part increases, with a decrease in the level, the share of land increases. The submarine edge of the mainland consists of shelf, or the continental shelf, continental slopeand continental foot.

The coastal, relatively shallow-water part of the underwater margin, directly adjacent to the coast, is called the shelf, or continental shoal. In the polar regions, the shelf relief is complicated by glacial morphosculpture; in temperate latitudes and at the equator, river valleys are preserved on the shelf. In tropical and equatorial latitudes, offshore coral reefs are very typical.

Below the edge of the shelf the continental slope is located. It is characterized by a noticeable increase in the slope up to 5 - 7 °, sometimes up to more than 50 °. Very often the continental slope has a stepped profile. If the steps have significant areas, they are called edge plateaus (underwater Blake Plateau off the Florida Peninsula).

Underwater canyons are widespread within the continental slope. These are deeply incised hollows with steep slopes, the incision depth reaches 2000 m. The underwater canyons resemble river valleys of mountainous countries and are often their underwater extensions.

At a depth of about 2.5 km, the continental slope smoothly turns into the continental foot. It looks like a sloping plain adjacent to the base of the slope. If the shelf, slope and foot cannot be distinguished, then such areas are called borderland(California coast). There are underwater and surface ledges within the oceans. They are separated from the continents by a wide strip of bottom with an oceanic crust. Similar

formations are called micro-continents. For instance, Seychelles, underwater outskirts of New Zealand, underwater uplift of the Naturalist, etc.

Ocean bed... This geotecture consists of deep-sea abyssal basinsand separating them underwater ridgesand volcanic mountains.The ocean floor has an oceanic type of the earth's crust The most widespread, especially in Pacific, have hilly plains, the relief of which is complicated by seamounts and swell-like uplifts of various sizes. Among them, there are oceanic ridges, mainly of tectonic origin, chains of volcanic mountains and individual volcanoes. Flat-topped mountains known as guyots are widespread on the ocean floor. The sedimentation rate of material on the ocean floor is several centimeters per year.

Transition zone.Several transition zones are located along the eastern edge of the Eurasian continent, two zones are observed off the coast of North and South America. The transition zone consists of depressions of the marginal sea, island arcand deep-sea trough.

A definite relationship is noted between the depths of the basins and the thickness of sediments at the bottom: the deeper the sea, the less the thickness of the sediments. In the Sea of \u200b\u200bOkhotsk at a depth of 3.5. km, the thickness of precipitation is 5 km. In the Bering Sea, which has a depth of 4 km, the thickness of precipitation decreases to 2.5 km.

Deep-sea trenches are narrow depressions - troughs in the earth's crust, in the form of an arc. There are currently 35 known deep trenches, 28 of them in the Pacific Ocean. Five troughs have a depth of more than 10 000 m, the Mariansk Trench - I 034 m. The steepness of the slopes increases to the bottom: in the upper part of the slope it is 5 - 6 °, in the lower part it can increase up to 25 °. The slopes are stepped and cut by underwater canyons. Earthquake foci are confined to deep-water canyons.

Island arcs are huge ridges usually located on the inner side of a deep-sea trench. The island arcs are characterized by volcanism and high seismic activity. Island arcs can be double, they distinguish between inner and outer ridges, separated by depression ( Kurile Islands). At a certain stage of development

island arcs merge with each other, forming a large island or peninsula (Kamchatka, Japanese islands). Sometimes at the edge of a deep-sea trench there is only an underwater uplift; there are no islands.

Mid-ocean ridges.They represent the largest, elongated in the meridional direction, underwater uplifts. Mid-ocean ridges can be 2,000 km wide and 6 km high. Mid-ocean ridges form a single system that stretches across all oceans. In the Atlantic Ocean, the ridge is located almost in the center, in the Pacific Ocean it approaches the coast of the Americas, in Indian Ocean runs along the coast of Africa. By relief and tectonic activity, rift and non-rift ridges are distinguished. The relief of the rift ridges is complex, rugged: rift valleys, narrow mountain ranges, giant transverse faults. Submarine and surface volcanoes and islands are common. The non-rift ridges are characterized by the absence of a rift valley and less complex relief. For example, most of the Pacific arch uplift does not have a rift valley. The mid-oceanic ridges are cut by a grandiose system of transverse faults, called transform faults, along which the blocks move relative to each other. The ridges correspond to the riftogenic type of the earth's crust.

Before proceeding to the characterization of coastal marine processes and the forms of relief they create, let us dwell on the definition of some concepts.

Coastline (edge \u200b\u200bline) - the line along which the horizontal water surface of the sea (or lake) intersects with the land. Since the level of water bodies does not remain constant, the coastline is a conditional concept used in relation to some average long-term position of the water body level.

Coast - a strip of land adjacent to the coastline, the relief of which is formed by the sea at a given average level of the reservoir.

Underwater coastal slope - the coastal strip of the seabed, within which the waves are able to carry out active work (erode the bottom, move sediments).

Coastal zone includes the coast and the underwater coastal slope.

Depending on the nature (morphology) of the coast, there are coastlines: high (for example, the coast of the Kola Peninsula) and low (northern coast of the Caspian Sea); dismembered (the Black Sea coast between the Crimean peninsula and the mouth of the Danube) and aligned (the Black Sea coast between Gelendzhik and Sochi); deep, having significant slopes of the underwater coastal slope with predominant development abrasive (destructive) processes (the Black Sea coast south of Novorossiysk), shallow, characterized by small angles of inclination of the underwater coastal slope, with a predominance of material accumulation processes (the coast of the Northern Caspian).

A complex of forces acts in the coastal zone, which determine its morphological appearance. These are the ebb and flow and associated currents; in non-tidal seas with shallow shores - surge phenomena and currents caused by them; tsunami - sea gravity waves of long length, arising from underwater earthquakes; constant sea currents; activity of organisms; the activity of rivers that form a special type of banks ( potamogenic shores). However, the main operating factor that determines the morphology and dynamics of the coast is waves and associated wave currents.

Waves. The wind, acting on the water surface, causes oscillatory movements of water in its surface thickness. Particles of water begin to make orbital movements in a plane perpendicular to the surface of the sea, and movement along these orbits occurs in the direction of the wind. Distinguish deep sea wavesand shallow water waves. Since wave movements attenuate with depth, the division of sea waves into these categories is carried out according to the criterion: the depth of the sea is greater or less than the depth of penetration of wave movements. At a depth equal to half the wavelength or greater than it, wave oscillations, and, consequently, their impact on the bottom of the reservoir, attenuate.

In the sea wave they distinguish height h, length L, period T, propagation speed v and items like crest and wave trough, front and rear slopes, front and wave beam (fig.19.1). The time during which a water particle describes a full orbit is called a period, and the value obtained by dividing the wavelength by its period is propagation speed.

Figure: 19.1.

h - height; L - length; 1 - wave crest; 2 - hollow; 3 - back slope of the wave; 4 - front slope of the wave. Arrows indicate wind direction

Figure: 19.2.

Wave parameters depend on the strength of the wind and its duration, on the nature of the underwater coastal slope, and on the wave acceleration length. Like the energy of a stream, the total energy of the waves can be expressed by the formula: E \u003d l / 8pgh2L, Where E - wave energy, r is the density of water, g is the acceleration of gravity, h - wave height, L is the wavelength. Considering that png vary within insignificant limits, we can say that the wave energy is proportional to the length and the square of the wave height.

Shallow water waves, in contrast to the waves of the open sea, affect the bottom (on the underwater coastal slope) and themselves experience its effect. As a result, they spend energy on transforming the bottom topography, on the transfer of debris particles lying on the bottom. The waves of the open sea consume energy only to overcome internal friction and interact with the atmosphere.

The more energy is expended by waves when passing over an underwater coastal slope, the less it reaches the coastline. As a result of interaction with the bottom, when passing over shallow water, the waves change their profile, become asymmetric: the front slope becomes steeper, and the rear one flattens out. The external asymmetry corresponds to the asymmetry of the orbits arising in shallow water waves along which the water particles move. Orbits from round become elliptical, and the ellipses themselves are irregular, flattened from below (see Fig. 19.2). Accordingly, the equality of orbital velocities is lost. Movement velocities directed towards the coast (i.e., when passing through the upper part of the orbit) become higher than the velocities of the reverse motion (along the lower part of the orbit). This ratio of velocities is of fundamental importance for understanding the processes of sediment movement and relief formation in the coastal zone.

The increase in the steepness of the front slope of the wave reaches a critical value above the depth equal to the wave height. It becomes vertical and even overhanging. The wave crest collapses, as a result, the wave motion of water is replaced by a fundamentally new type of motion - surf stream, or coasting. The very destruction of the wave is called surf.

The surf flow is formed from the mass of water formed when the wave breaks. It runs up the coastal slope, and the direction of the flow roughly coincides with the direction of the wave that caused it, but nevertheless noticeably deviates from the original under the influence of gravity (Fig. 19.3). The speed of the surf stream decreases as it moves away from the place of origin, i.e. from where the wave breaks. The deceleration of the flow is associated with the expenditure of energy to overcome the force of gravity, to overcome the friction against the surface on which it runs up, to move and process sediments, as well as the loss of a part of the mass of water to seep into the ground.

Figure: 19.3.

The point where the speed of the surf falls to zero is called the top of the whiff. From here the mass of water not yet wasted on infiltration flows down the slope in the direction of the greatest slope. This "branch" of the surf stream was named reverse surf stream, or rollback.

Consequently, the upper and lower boundaries of the coastal zone are determined by the boundaries of the wave impact on the coast, namely: the lower boundary is located at a depth equal to half the wavelength, i.e. the isobath on which the wave deformation begins, and the upper is determined a whisk line, formed by a set of surf splash peaks. According to the available data on the length of oceanic waves reaching 350 m, the lower boundary of the underwater coastal slope in the oceans can be traced at depths of up to 150 m, in the seas - up to 50 m.

To understand wave processes on the shores of the seas, it is necessary to have an idea of \u200b\u200brefraction. Refraction is called the reversal of the wave front as it approaches the coast, and this process is carried out in such a way that the wave front tends to take a position parallel to the coast. On a flat coast, with the full implementation of refraction, this is the case, and on a rugged one, due to the fact that each segment of the front tends to be parallel to the corresponding segment of the coast, there is, as it were, a compression of the front at the capes and its stretching in the bays. As a result, there is a concentration of wave energy at the headlands and scattering in the concavities of the coastal contour (Fig. 19.4). The result of this is the "cutting" (abrasion) of the capes, the accumulation of material in the concavities (bays) and, as a result, the leveling of the coast, and in essence, the equalization of the energy of the waves approaching the coast.

It should be noted that the actual orbits along which water particles move during waves are somewhat open due to the pulsating (uneven) effect of the wind on the water surface. Due to the openness of the orbits, not only the movement of the waveform occurs, but also the actual movement of the water mass in the direction of wave propagation, i.e. towards the coast. This creates a rise in sea level off the coast compared to the offshore position. Level imbalance causes formation compensatory currents.


Figure: 19.4.

  • (according to V.P. Zenkovich):
    • 1 - wave fronts; 2 - rays of waves;
    • 3 - the base of the underwater slope

When waves approach at right angles to the coast with a gentle underwater slope, the first breakdown of waves occurs at a considerable distance from it. The mass of water accumulating near the coast is bounded by the “living wall” of the surf until it finds an outlet in some area where this “wall” is somewhat lower. Then the masses of water break through from the coast towards the sea, forming an explosive flow (fig.19.5). Discontinuous currents, due to their "violent" nature, develop speeds of up to several meters per second and are capable of carrying a large amount of turbid sediment from the coastal strip into the outer zone of the underwater coastal slope. This is one of the reasons for sediment leakage from the coastal strip of the coastal zone.

When the waves approach shallow shore at an acute angle, the outflow of excess water occurs along the coast. As a result, alongshore wave current (fig.19.5, B). It also has significant velocities and, along with proper wave movements, is an important means of moving sediment along the coast.

When the waves approach deep coast the outflow of excess water from the coast is carried out by the bottom current directed from the coast towards the sea, - bottom countercurrent (fig.19.5, A). It also facilitates the carryover of debris from the coastal strip to the outer coastal zone.

From what has been said, it is obvious that wave movements and the wave currents caused by them lead to the movement of sediment perpendicular to the coast - this is called lateral movement of sediments,or along the coast - alongshore sediment movement. Both of these factors lead to the formation of specific landforms within the coastal zone.

Figure: 19.5.

AND -bottom countercurrent; B - alongshore current:

Coastline (shoreline) - the line along which the horizontal water surface of the sea (or lake) intersects with the land. Since the level of water bodies does not remain constant, the coastline is a conditional concept used in relation to some average long-term position of the water level.

An underwater coastal slope is a coastal strip of the seabed, within which waves are capable of active work (eroding the bottom, moving sediments). The coastal zone includes the coast and the underwater coastal slope.

The banks are: ♠ High (for example, the coast of the Kola Peninsula) ♠ Low (the northern coast of the Caspian Sea); ♠ Dismembered (Black Sea coast between the Crimean Peninsula and the Danube estuary); Leveled (Black Sea coast between Gelendzhik and Sochi); ♠ Shallow, with significant slopes of the underwater coastal slope with the predominant development of abrasion (destructive) processes (the Black Sea coast south of Novorossiysk), ♠ Shallow, characterized by small angles of inclination of the underwater coastal slope, with a predominance of material accumulation processes (the coast of the North Caspian Sea).

Waves. The wind, acting on the water surface, causes oscillatory movements of water in its surface thickness. Particles of water begin to make orbital movements in a plane perpendicular to the surface of the sea, and movement along these orbits occurs in the direction of the wind.

Shallow water waves, in contrast to the waves of the open sea, affect the bottom (on the underwater coastal slope) and themselves experience its effect. The waves of the open sea consume energy only to overcome internal friction and interact with the atmosphere.

Waves carry eroded material parallel to the shore, depositing it elsewhere, creating shoals or sand bars that can develop into a chain of barrier islands.

The masses of debris transported in the coastal zone by waves are called marine sediments. If the coast is accumulative, that is, the seabed near it is composed of sediments, an accumulation of sediments forms above the coastline in the surf zone - a beach (French plage - a gentle sea coast).

Owing to the alongshore transport, the bays shallowly protruding into the land are filled with sediment. Where the flow of sediment cannot turn along a coastline that goes out to the side, spits can form - long ridges that rise slightly above the water. If some obstacle - an island, a shoal, a half-sunken ship, an artificial structure - impedes the movement of waves, creates a wave shadow, the accumulation of sediments usually leads to the creation of a bridge between the coast and this obstacle - a jumper, or tombolo (Italian tombolo - roller, dune) ... The ridge of the lintel can be below sea level, it can protrude above it constantly or only at low tide

If there is a tectonic rise or a decrease in the level of the World Ocean, flat coastal areas that were previously below the water level turn out to be higher than it, characteristic coastal forms are formed - sea terraces with a flat area and a relatively steep ledge to the water or a terrace of a lower tier.

Coast - a strip of land adjacent to the coastline, the relief of which is formed by the sea at a given average level of the reservoir.

Root coast - a coast, composed of bedrock rocks, often stationed. It is opposed to the banks, composed of alluvial (in river valleys, loose sea) or organogenic (seashore, coral reefs) formations.

flat is a bank with simple outlines. Found in lowland countries; bay - typical of mountainous coasts. Heavily cut; riassic - formed when mountain ranges approach the sea at an angle or perpendicular. In this case, the sea floods intermontane depressions, forming long wedge-shaped bays (for example, the coast of Spain); Dalmatian - typical of the Adriatic coast. At the same time, the sea heats up the mountains, which were cut by gorges like a lattice. As a result, numerous islands are formed, separated by wide longitudinal and narrow transverse bays; fjord - typical for the coast of Norway, Greenland and Novaya Zemlya. The sea floods ancient river valleys and tectonic depressions, worked by the glacier, and forms long and narrow bays with high and steep rocky shores that cut deep into the land. Such bays are called fjords. Some of them are more than 200 km long, depth up to 1000 m and more;

skerny - originated on the coasts, composed of crystalline rocks, also subjected to the treatment of glaciers. As a result, a mass of small islands is formed, located close to each other and from the coast. The skerry type of coast is typical for the south of the Scandinavian Peninsula, for the shores of Finland and Iceland. In Russia, this type of coast is found in the Ladoga and Onega lakes; estuary - by its origin is close to the rice one, arises when the mouths of river valleys of low-lying coasts are flooded. Over time, the shallow bay, called the estuary, is separated from the sea by a shallow water zone or spit. With complete separation, an estuary lake appears. This type of coast is typical for the Black and Azov seas; lagoon - develops on young lowlands formed by loose sediments. Distributed in the southern outskirts of the Baltic Sea. Long sandbanks are formed parallel to the coastline, which are separated from the open sea by chains of lagoons stretching along the coast.