Coastal relief. Coastal landforms. "coastal landforms" in books

Coastal landforms

abrasive and accumulative. Abrasion forms: a steep, often steep coastal ledge, or cliff, a wave-breaking niche and a coastal, or abrasion, platform; surf carrs, miniature quest-like beds, gigantic cauldrons. Coastal accumulative forms are very diverse. Based on morphological characteristics, three types are distinguished: joined– accumulative surface formations adjacent to the shore throughout; free– narrow alluvial strips of land, adjacent to the coast at only one end, and then moving away from it at an increasingly increasing angle; closing– connecting to the shore with both its root part and its growing end. According to the conditions of formation and the composition of the constituent material, accumulative coastal landforms are divided into beaches, beach festoons, coastal levees, underwater levees, bars, spits, bay-bars and tombolos, or plains. Beach is a cloak of loose material made of pebbles, gravel, sand and shell detritus covering the abrasion platform. Beach festoons – a series of rollers, parallel to the coastline, is created by the surf flow at the sea edge of the beach. Coastal ramparts – a double-sloping beach of full profile, composed of sand, pebbles or shells. Submerged shafts – linear sandy swells forming a series, appearing parallel to the shore and isobath lines by transverse movements along the coastal sediments caused by wave movements. Bars – underwater shafts brought to the surface position. Braids – free linear accumulative forms of simple and complex structure, straight and crescent-shaped in plan, connected to the shore at one end. Peresyp – linear accumulative forms blocking bays. Tombolo

– narrow linear, usually sandy forms that tie islands to the shores.. Geography. Modern illustrated encyclopedia. - M.: Rosman. 2006 .

Edited by prof. A. P. Gorkina

See what “coastal landforms” are in other dictionaries: Formed as a result of the accumulation of g.p., brought by water, wind, ice, etc. They are usually correlatively associated with denudation forms, due to the destruction of which they arose. There are F. r. a.: subaerial, which include: 1)… …

Landforms formed within the seashore due to the accumulation of marine sediments. The main factors in the formation of B. a. f. sea waves and surf. Depending on the angle of approach of the waves to the shore and the nature of the movement of sediments, B. a.... ...

They are formed under the influence of waves and currents. A distinction is made between adjacent forms, i.e. those connected to the main shore over a long distance with their inner side (terraces, beaches, coastal ramparts, ditches); free connected to the land by one... ... Formed as a result of the accumulation of g.p., brought by water, wind, ice, etc. They are usually correlatively associated with denudation forms, due to the destruction of which they arose. There are F. r. a.: subaerial, which include: 1)… …

A border strip between land and sea, characterized by the distribution of modern and ancient coastal landforms. It consists of a coastal zone - a land zone with ancient sea terraces, a coastal zone, where modern coastal forms are presented... ... Geographical encyclopedia

It is distinguished by a highly rugged coastline due to numerous islands, peninsulas, bays and bays with winding outlines. It arises as a result of sea ingression, flooding the aeolian relief (dunes, blow basins, sand dunes, etc.), and... ... Formed as a result of the accumulation of g.p., brought by water, wind, ice, etc. They are usually correlatively associated with denudation forms, due to the destruction of which they arose. There are F. r. a.: subaerial, which include: 1)… …

Forms of relief of the coastal zone created by the sea at a relatively lower or higher level compared to the modern one. Based on their origin, they distinguish between accumulative, abrasion and basement (accumulative abrasion) terraces.… … Great Soviet Encyclopedia

GKINP 02-121-79: Guidelines for interpreting aerial photographs for topographic surveys and updating plans at scales 1:2000 and 1:5000- Terminology GKINP 02 121 79: Guidelines for interpreting aerial photographs for topographic surveys and updating plans at scales 1:2000 and 1:5000: 7.8.43. “Bushes” of piles in the water are the remains of pile bridges, some dams and other structures on rivers with... ... Dictionary-reference book of terms of normative and technical documentation

United States of America USA, state in North. America. Name includes: geogr. the term states (from English, state), this is how self-governing territorial units are called in a number of countries; definition united, i.e. included in the federation,... ... Geographical encyclopedia

The main part of the United States is divided into eight provinces based on topography: Appalachia, Coastal Plains, Inland Uplands, Inland Plains, Lake Superior Upland, Rocky Mountains, Intermountain Plateaus and Pacific Coasts... ... Collier's Encyclopedia

The science of the structure and history of the development of the Earth. The main objects of research are rocks, which contain the geological record of the Earth, as well as modern physical processes and mechanisms operating both on its surface and in the depths... ... Collier's Encyclopedia

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

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

Shore- 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- a coastal strip of the seabed, within which waves are capable of carrying out active work (eroding the bottom, moving sediment).

Coastal zone includes the shore and the underwater coastal slope.

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

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

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

In the sea wave there are height h, length L, period T, propagation speed v and elements like crest And wave trough, front And back slopes, front And wave ray(Fig. 19.1). The time it takes a water particle to describe full orbit, is called a period, and the value obtained by dividing the wavelength by its period is speed of spread.

Rice. 19.1.

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

Rice. 19.2.

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

Shallow water waves as opposed to waves open sea influence the bottom (the underwater coastal slope) and themselves experience its influence. As a result, they spend energy on transforming the bottom topography and transporting debris particles lying on the bottom. Waves of the open sea expend energy only to overcome internal friction and interact with the atmosphere.

The more energy expended by waves when passing over an underwater coastal slope, the less of it reaches the coastline. As a result of interaction with the bottom when passing over shallow water, the waves change their profile and become asymmetrical: the front slope becomes steeper, and the back slope flattens. External asymmetry corresponds to the asymmetry of orbits that arises in shallow water waves, along which water particles move. The orbits change from round to elliptical, and the ellipses themselves are irregular, flattened from below (see Fig. 19.2). Accordingly, the equality of orbital velocities is lost. The speeds of movement directed towards the coast (i.e. when passing the upper part of the orbit) become greater than the speeds of the reverse movement (along the lower part of the orbit). This speed ratio 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 a depth equal to the height of the wave. It becomes vertical and even overhanging. The wave crest collapses, as a result, the wave movement of water is replaced by a fundamentally new type of movement - surf stream, or coasting. The destruction 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 approximately coincides with the direction of the wave that caused it, but still noticeably deviates from the original one under the influence of gravity (Fig. 19.3). The speed of the surf flow decreases as it moves away from the place of origin, i.e. from the place where the wave breaks. The slowdown of the flow is associated with the expenditure of energy to overcome the force of gravity, to overcome friction with the surface along which it runs up, to move and process sediment, as well as with the loss of part of the mass of water due to seepage into the ground.

Rice. 19.3.

The point where the speed of the surf flow decreases to zero is called the top is a notch. From here, the mass of water not yet spent on infiltration flows down the slope in the direction of the greatest slope. This “branch” of the breaking stream is called reverse surf flow, or rollback

Consequently, the upper and lower boundaries of the coastal zone are determined by the boundaries of the wave action on the coast, namely: the lower boundary is located at a depth equal to half the wavelength, i.e. the isobath at which wave deformation begins, and the upper one is determined edging line, formed by a set of surf splash peaks. According to available data on the length of ocean 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 understanding of refraction. Refraction is called the reversal of the wave front as it approaches the shore, and this process is carried out in such a way that the wave front tends to take a position parallel to the shore. On a flat coast, with full refraction, this happens, but on a rugged coast, due to the fact that each segment of the front tends to be parallel to the corresponding section of the coast, there is a kind of compression of the front at the capes and its stretching in the bays. As a result, wave energy is concentrated at capes and dissipated in the concavities of the coastal contour (Fig. 19.4). The result of this is the “cutting off” (abrasion) of capes, the accumulation of material in concavities (bays) and, ultimately, the leveling of the coast, and in essence, the leveling of the energy of waves approaching the shore.

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 wave shape moves, but also the actual movement of the water mass in the direction of the wave propagation, i.e. towards the shore. This creates a rise in sea level near the coast compared to the level in the open sea. Level imbalance causes formation compensatory flows.

Rice. 19.4.

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

When waves approach a shore with a gentle underwater slope at right angles, the first destruction of the waves occurs at a considerable distance from it. The mass of water accumulating near the shore is dammed by the “living wall” of the surf until it finds an outlet in some area where this “wall” is slightly lower. Then masses of water break from the shore towards the sea, forming a rupture flow(Fig. 19.5). Rip currents, due to their “turbulent” nature, develop speeds of up to several meters per second and are capable of carrying a large amount of agitated sediment from the coastal strip to the outer zone of the underwater coastal slope. This is one of the reasons for sediment leakage from the coastal zone.

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

When the waves approach deep shore the outflow of excess water from the shore is carried out by a bottom current directed from the shore towards the sea - bottom countercurrent(Fig. 19.5, A). It also contributes to the transport of debris from the coastal zone to the outer coastal zone.

From the above, it is obvious that wave movements and the wave currents caused by them lead to the movement of sediment perpendicular to the shore - this is called transverse movement of sediments, or along the shore - alongshore sediment movement. Both of these factors lead to the formation of specific relief forms within the coastal zone.

Rice. 19.5.

A-bottom countercurrent; B- alongshore current:

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

Coastline (edge line) is the line along which the horizontal water surface of the sea (or lake) intersects with the land. Since the level of reservoirs does not remain constant, the coastline is a conditional concept applied relative to some average long-term position of the reservoir 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 capable of active work (eroding the bottom, moving sediment).

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

Depending on the nature (morphology) of the coast, coasts are distinguished: high (for example, the coast of the Kola Peninsula) and low (the northern coast of the Caspian Sea); dismembered (the Black Sea coast between the Crimean Peninsula and the mouth of the Danube) and leveled (the Black Sea coast between Gelendzhik and Sochi); deep, having 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 processes of accumulation of material (the coast of the Northern Caspian).

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

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

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

Rice. 153. Wave elements:

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

Wave parameters depend on the wind strength and its duration, on the nature of the underwater coastal slope, and on the wave acceleration length. Similar to the flow energy, the total energy of the waves can be expressed by the formula: E = 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 square of the wave height.

Shallow water waves, unlike open sea waves, act on the bottom (on the underwater coastal slope) and themselves experience its impact. As a result, they spend energy on transforming the bottom topography and transporting debris particles lying on the bottom. Waves of the open sea expend energy only to overcome internal friction and interact with the atmosphere.

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

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

When moving over shallow water, the waves change their profile and become asymmetrical: the front slope becomes steeper, and the back slope flattens out. External asymmetry corresponds to the asymmetry of orbits that arises in shallow water waves, along which water particles move. The orbits change from round to elliptical, and the ellipses themselves are irregular, flattened from below (Fig. 154). Accordingly, the equality of orbital velocities is lost. The speeds of movement directed towards the coast (i.e., when passing the upper part of the orbit) become greater than the speeds of the reverse movement (along the lower part of the orbit). This speed ratio 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 a depth equal to the height of the wave. It becomes vertical and even overhanging. The wave crest collapses, and as a result, the wave movement of water is replaced by a fundamentally new type of movement - a surf flow, or run-up. The breaking of the wave itself is called breaking.

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 approximately coincides with the direction of the wave that caused it, but still noticeably deviates from the original one under the influence of gravity (Fig. 155). The speed of the surf flow decreases as it moves away from the place of origin, i.e. from the place where the wave breaks. The slowdown of the flow is associated with the expenditure of energy to overcome the force of gravity, to overcome friction with the surface along which it runs up, to move and process sediment, as well as with the loss of part of the mass of water due to seepage into the ground.

Bottom-

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

Sea

the fighting flow is reduced to zero, called

Rice. 155. Trajectories of the surf flow on the beach with waves approaching the shore obliquely. Crosses mark the top of the splash
the top of the splash. From here, the mass of water not yet spent 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 action on the coast, namely: the lower boundary is located at a depth equal to half the wavelength, i.e. the isobath at which wave deformation begins, and the upper one is determined by the splash line formed by the set of surf splash peaks. According to available data on the length of ocean 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 understanding of refraction. Refraction is the reversal of the wave front as it approaches the shore, and this process is carried out in such a way that the wave front tends to take a position parallel to the shore. On a flat coast, with full refraction, this happens, but on a rugged coast, due to the fact that each segment of the front tends to be parallel to the corresponding section of the coast, there is a kind of compression of the front at the capes and its stretching in the bays. As a result, wave energy is concentrated at capes and dissipated in the concavities of the coastal contour (Fig. 156). The result of this is the “cutting off” (abrasion) of capes, the accumulation of material in concavities (bays) and, ultimately, the leveling of the coast, and in essence, the leveling of the energy of waves approaching the shore.

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

h____ -------- ^ - J

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

with a pulsating (uneven) effect of wind on the water surface. Thanks to the open™ orbits, not only the wave shape moves, but also the actual movement of the water mass in the direction of the wave propagation, i.e. towards the shore. This creates a rise in sea level near the coast compared to the level in the open sea. The level imbalance causes the formation of compensatory flows.

When waves approach a shore with a gentle underwater slope at right angles, the first destruction of the waves occurs at a considerable distance from it. The mass of water accumulating near the shore is dammed by the “living wall” of the surf until it finds a way out in some area where this “wall” is slightly lower. Then masses of water break through from the shore towards the sea, forming a rip current (Fig. 157). Due to their “turbulent” nature, rip currents develop speeds of up to several meters per second and are capable of carrying a large amount of agitated sediment from the coastal strip to the outer zone of the underwater coastal slope. This is one of the reasons for sediment leakage from the coastal zone.

01 S2

When waves approach a deep shore, the outflow of excess water from the shore occurs bottom-up.

Rice. 157. Wave currents: A - bottom countercurrent; B - along-shore current: B - rip current; 1 - direction of wave propagation; 2 - direction of currents

a strong current directed from the shore towards the sea - bottom countercurrent (Fig. 157, A). It also contributes to the transport of debris from the coastal zone to the outer coastal zone.

From the above it is clear that wave movements and the wave currents caused by them lead to the movement of sediment perpendicular to the shore - 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 relief forms within the coastal zone.

Shore- a narrow zone within which interaction between land and sea occurs. The processes that shape the coast include waves, currents and tidal phenomena. The coastal zone consists of the coast itself - its surface part and the underwater coastal slope. The lower boundary of the shore is a depth equal to half the wavelength; it is at this depth that the wave’s impact on the shore begins. The upper limit is a line drawn along the tops of the wave splashes.

Coast- a strip of land that includes modern and ancient coastlines. The main process that determines the originality of forms coastal relief, is excitement. The wave produces destructive and accumulative work in the coastal zone, causing the development of abrasive and accumulative forms. The destructive work of waves is called abrasion. There are 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 are dissolved by sea water. Thermal abrasion is the destruction of coastlines composed of frozen rocks as a result of the warming influence of sea waters. The predominance of abrasion or accumulation in the coastal zone depends on the steepness of the coast and the properties of the rocks composing it. On a steep slope composed of strong rocks rocks, abrasion forms of relief predominate. In this case, a wave with high energy acts on the shore, 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 - clif. As the cliff retreats towards the shore, 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 become dry. The rate of abrasion on banks 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 approach of the wave to the shore. There are transverse and alongshore movement of sediments. If a wave approaches perpendicular to the shore, a transverse movement of sediment occurs. Gradually, the coast, composed of sediments of the same size, takes on the form of dynamic equilibrium. This happens as follows. At a depth equal to half the wavelength, the impact of the wave on the shore begins. The advantage of forward speeds (towards the shore) is still small compared to the reverse ones. But since the particle is on an inclined surface, it moves down the slope a little. The closer to the shore, the greater the forward speeds; at the neutral point they become equal to the reverse speeds. At the neutral point, the particle performs only oscillatory movements. Higher up the slope, the particle will move toward the shore, causing the accumulation of material on the shore; below the neutral point, material will be carried down the slope. During the transverse movement of sediment, the material delivered to the shore from the bottom is mainly sand, pebbles, and shells. Landforms created by the lateral movement of sediment include submarine shore bars, submarine and island bars, beaches and terraces. At depth X/2, wave destruction begins, material accumulates in the blistering zone at the bottom, and accumulative underwater shore wall. There can be several underwater shafts; they are located parallel to each other and the shore. 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 ridges is explained by the approach of waves of different lengths, so their formation is observed at different depths. When material accumulates, the shafts are converted into underwater bars. The crest of an underwater bar may appear on the surface, in which case the bar becomes island and represents? is a chain of islands stretching along the coast. It is believed that island bars can only appear if the World Ocean Level changes. The bars stretch for hundreds of kilometers along the low-lying sea coasts and separate the coastal waters, called the lagoon, from the sea. The bases 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 sea shores, 10% of the coastline is on the shores bordered by bars. On the above-water part of the coast, with the transverse movement of sediments, a beach is formed. Based on morphological characteristics, beaches with a complete and incomplete profile are distinguished. A full profile beach is formed in free space. Then the beach looks like a coastal rampart with gentle slopes.

According to the conditions of formation and the composition of the constituent material, accumulative coastal landforms are divided into beaches, beach festoons, coastal levees, underwater levees, bars, spits, bay-bars and tombolos, or plains. of an incomplete profile is formed at the foot of the ledge; it has one slope facing the sea. If sea level drops, the beach becomes accumulative sea terrace. When waves approach the shore at an angle of less than 90°, an alongshore sediment flow is formed. Sediment moves along the coast towards an obtuse angle and consists of products of coastal destruction and river alluvium supplied to the coast. The optimal angle of wave approach to the shore is 45°. At this angle of approach, the maximum amount of sediment is transported. When the shore contour changes, the rate of material supply turns out to be excessive and accumulation begins. An accumulative terrace forms near the concave coast at the tops of the bays. Since the landform is adjacent to the shore along its entire length, it is called adjacent. When going around the shore protrusion, the speed of movement of the material drops, and an accumulative form is formed in this place - braid. The spit is attached to the shore in only one part, its end remains free. This form is called free. On a section of the coast protected by an island, the accumulation of material leads to the appearance tombolo (take over). If the coast is protected from the sea by a far protruding cape, a overspray. As it grows, the bay bar can reach the opposite shore and block the bay. In this case, the accumulative form is called closing. Depending on the outlines of the coastline and the complex of processes occurring on the banks, they are divided into several types.

1. Primary dissected shores, slightly modified by the sea (ingression). The dismemberment of the coast is created by non-wave processes; sea waters only fill depressions in the relief. Such shores include fiord shores - formed during the flooding of glacial and trough valleys, skerry shores - formed during the flooding of the relief of “curly” rocks (ram’s foreheads).

Such shores are typical for Scandinavia, northern shores Canada, while skerries are developed in the Baltic Sea. Rias shores arise when estuaries are flooded by the sea mountain rivers, such shores include the coast of the Iberian Peninsula. The Dalmatian coasts are formed when negative folded structures parallel to the coast are flooded by the sea. This creates chains of islands stretching along the coast and long narrow bays. This kind of shore is typical for Adriatic Sea. Estuary banks are formed due to the flooding of the mouths 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, marshes - they are rarely flooded, only by high spring tides. The deposition of large amounts of alluvium on the banks causes the creation of a deltaic coast.

There are large deltas near the Lena, Volga, and Nile rivers. On the coasts of tropical seas, organisms, especially corals, play an active role in the formation of coasts. Organogenic coral shores are formed here. In tectonically active zones, tectonic shores can form; sometimes tectonics activates slope processes, and then talus and landslide shores are formed.

3. The actual wave banks. Leveled abrasion banks appear where abrasion is actively occurring. As a rule, these shores are steep, composed of easily eroded rocks. Due to the high speed of retreat, the banks quickly level out, forming a leveled abrasion coast. Leveled accumulative shores are characteristic of gentle underwater slopes. On this shore, the process of accumulation comes first. Transitional types of shores include bay and lagoon shores. Abrasion is observed on bay shores on capes, and accumulation is observed in bays. On the lagoon coast, the separation of the lagoon by the growing spit has not yet finished; therefore, the formation of a leveled accumulative coast continues.

Relief of the ocean floor

In the relief of the ocean floor there are four geotextures. Three geotextures are located entirely within the ocean floor: ocean floor, transition zone, mid-ocean ridges; the latter - the underwater edge of the continent - is part of the geotexture - the continental protrusion.

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

The underwater edge of the continent has a continental type of crust. As the sea level rises, the area of the underwater part increases, and as the level decreases, the share of land increases. The underwater continental margin consists of shelf, or continental shallows, continental slope And continental foothills.

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

Below the shelf edge there is a continental slope. It is characterized by a noticeable increase in 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 marginal plateaus (Blake Submarine Plateau off the Florida Peninsula).

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

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 it is impossible to distinguish the shelf, slope and foot, then such areas are called borderland(California coast). Within the oceans there are underwater and surface protrusions. They are separated from the continents by a wide strip of bottom with an oceanic type of crust. Similar

formations are called microcontinents. For example, Seychelles, underwater margin of New Zealand, underwater rise of Naturalista, etc.

ocean bed. This geotexture consists of deep-sea abyssal basins and separating them underwater ridges And volcanic mountains The ocean bed has an oceanic type of crust. It is most widespread, especially in Pacific Ocean, have hilly plains, the topography 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. At the bottom of the ocean there are flat-topped mountains - guyots. The rate of sedimentation 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 Northern and South America. The transition zone consists of basins of the marginal sea, island arc And deep-sea trench.

There is a certain connection 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 Okhotsk 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 - deflections in the earth's crust, having the shape of an arc in plan. Currently, 35 deep-sea trenches are known, 28 of them in the Pacific Ocean. Five trenches have a depth of more than 10,000 m, the Mariana Trench is 034 m. The steepness of the slopes increases towards the bottom: in the upper part of the slope it is 5 - 6°, in the lower part it can increase to 25°. The slopes are stepped and dissected by underwater canyons. The sources of earthquakes are confined to deep-sea canyons.

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

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

Mid-ocean ridges. They are the largest underwater rises elongated in the meridional direction. Mid-ocean ridges can reach 2000 km in width and 6 km in relative height. Mid-ocean ridges form a single system stretching across all oceans. IN Atlantic Ocean the ridge is located almost in the center; in the Pacific Ocean it approaches the coast of both Americas, in Indian Ocean runs along the coast of Africa. Based on relief and tectonic activity, rift and non-rift ridges are distinguished. The relief of rift ridges is complex, rugged: rift valleys, narrow mountain ranges, giant transverse faults. Underwater and surface volcanoes and islands are often found. Non-rift ridges are characterized by the absence of a rift valley and less complex terrain. For example, most of the Pacific arch uplift does not have a rift valley. Mid-ocean ridges are cut by a grandiose system of transverse faults, called transform faults, along which blocks move relative to each other. The ridges correspond to a riftogenic type of the earth's crust.

(lakes, rivers) is called the shore.

The shores are divided depending on their steepness (sloping, steep) and the nature of the materials composing them (mud, sand, pebbles, rocky). On the side of the water area, a strip of seabed adjoins the shore, which is constantly exposed to wave movements of water. This strip is called the underwater coastal slope.

The shore and the underwater coastal slope together form coastal zone of the sea, within which the complex interaction of the lithosphere, hydrosphere, atmosphere and biosphere constantly takes place. This zone is characterized by the variability of relief forms and their various combinations within even small areas. The work of sea water is manifested in the destruction of shores - abrasion, as a result of which they retreat inland, as well as in the deposition of destruction products - accumulation, which leads to a change in the underwater relief of the coastal zone and the formation of new types of shores. Shores formed primarily as a result of the destructive action of waves are called abrasive, and shores created by sediment deposition are called accumulative.

The main factor in the formation of abrasion shores is the destructive action of breaking waves, as a result of which a depression is formed at the base of the slope - wave-breaking niche. Over time, this niche deepens more and more; the overhanging parts of the slope fall into the sea, breaking up into a mass of fragments, with the help of which breaking waves continue further destruction of the coastal ledge.

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 repeated changes in the depth of the ocean during glacial and interglacial eras, peculiar relief forms 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. Ancient coastlines corresponding to more low level, are now flooded by the sea.

Elevated coastlines are expressed as sea terraces. These are steps stretched along the shore.

In each terrace the following are distinguished: the surface of the terrace; ledge; edge; back seam. They record the position of the ancient coastline.

Depending on the structure there are:

Accumulative terraces, that is, completely composed of coastal-marine sediments;
Abrasion terraces, which are composed only of bedrock;
Basement terraces, having a bedrock base covered by marine sediments.

To identify the history of coastal development, so-called spectra of terraces, which make it possible to compare different sections of the coast and contain information about neotectonic movements.

Types of banks (according toD. G. Panov)

(a – rias, b – fiord, c – skerry, d – estuary, e – Dalmatian, f – watt (1 – watts, 2 – runoff hollows), g – thermal abrasion, h – coral, i – volcanic).

Literature.

Smolyaninov V. M. General geoscience: lithosphere, biosphere, geographical envelope. Educational manual / V.M. Smolyaninov, A. Ya. Nemykin. – Voronezh: Origins, 2010 – 193 p.

It might be useful to read: