Until now, we have been talking about the transporting and accumulative activity of sea waves and surf. But these same factors often cause the destruction of the coast. The destructive work of the sea is called abrasion. There are three types of abrasion - mechanical, chemical and thermal.
Mechanical abrasion is the destruction of rocks that make up the shores under the influence of waves and surf and bombardment by debris carried by waves and surf. This is the main type of sea abrasion work, which is always present in chemical and thermal abrasion.
Chemical abrasion is the destruction of bedrock that makes up the shore and underwater coastal slope as a result of their dissolution by sea water. The main condition for the manifestation of chemical abrasion, like karst, is the solubility of the rocks that make up the shore.
Thermal abrasion is the destruction of coastlines composed of frozen rocks or ice as a result of the warming effect of sea water on the ice contained in the frozen rock or composing coastal glaciers.
We already know that the concentration of wave energy near the headlands of the indented coast and the undersaturation of the coastal zone with sediment contribute to the occurrence of the abrasion process. The most important prerequisite for the development of the abrasion coast is also the steep slope of the initial profile of the underwater coastal slope. Under this condition, the energy consumption of the wave when passing over the underwater coastal slope occurs only within a narrow zone of the bottom, so the waves arrive at the coastal shore with large reserves of energy. During the destruction of waves, i.e., during the surf, which in these conditions is particularly violent, the maximum mechanical impact on the rocks that make up the shore occurs in the area immediately adjacent to the coastline. As a result, a recess is formed here - a wave-breaking niche. Further deepening of the niche leads to the collapse of the cornice hanging above it. A mass of rock fragments enters the surf zone. They now serve as material with the help of which the surf, bombarding the formed ledge with them, destroys the shore even more intensively.
The process of excavating a wave-breaking niche and collapsing the cornice hanging above it is repeated several times. Gradually, a vertical or almost vertical ledge is developed - an abrasion cliff, or cliff. As the cliff retreats under the blows of waves and surf, a platform slightly inclined towards the sea, called a bench, is formed in front of its foot. The bench begins at the very foot of the cliff, that is, at the wave-breaking niche, and also continues below sea level.
The more the cliff retreats, i.e. the longer and more intensely the abrasion works, the more positioned the part of the bench that is adjacent to the cliff becomes. Due to this, the profile of the abrasion bank gradually takes on the appearance of a curve convex upward. The flattened upper part of the profile becomes wider and wider, and over time the waves, in order to reach the shore, have to overcome a very wide strip of shallow water formed. A large expenditure of wave energy when passing over shallow water ultimately leads to attenuation, and then to the complete cessation of abrasion. Thus, abrasion itself, as it develops, creates conditions that set a limit to the abrasion process.
The rate of abrasion is estimated by the amount of retreat of the edge or foot of a cliff over a certain period of time, for example, over a year. It depends on the wave parameters, but there are a number of other conditions that determine it. Thus, high banks recede more slowly than low ones. Shores composed of stronger rocks erode more slowly than shores composed of loose or weakly cemented rocks. It has been noticed, for example, that coastlines composed of crystalline igneous rocks often do not show any noticeable signs of retreat at all. The shores, composed of clays, marls, loams, sands or weakly cemented sandstones, retreat very quickly, by several meters per year.

ABRASION is the process of mechanical destruction by waves and currents of indigenous areas. Abrasion is especially intense near the shore under the influence of surf (roll-up). G. p. experience impact, corrosion destruction under the influence of impacts of stones and grains of sand, dissolution, and other influences. Underwater water flows less intensely, although its effect on the bottom of seas and lakes extends to a depth of several tens of meters, and in the oceans to 100 m or more. A. should be distinguished from erosion, which destroys loose, often Holocene exc. This interpretation of aeration and erosion is used in oceanology. In general geology and geomorphology, abrasion is usually understood as the process of destruction of bedrock and loose soils. Peculiar abrasion processes occur on the shores of polar regions, often formed by frozen soils, containing villages. ice. Under the influence of waves, frozen areas are thawed with complete or partial removal of the thawed material. The process of destruction of such shores by waves is called thermal abrasion.

Geological Dictionary: in 2 volumes. - M.: Nedra. Edited by K. N. Paffengoltz et al.. 1978 .

Abrasion

(from Latin abrasio - scraping, shaving * A. abrasion; n. Abrasion; f. abrasion; And. abrasion) - mechanical process. destruction and demolition of hydraulic structures in the coastal zone of water bodies (oceans, seas, lakes, reservoirs) by waves and surf, as well as by the influence of moving and suspended debris in the water. As a result, A. specific ones are created. relief forms: abrasion ledges (cliffs), wave-cut niches ("spurs"), underwater abrasion terraces or platforms (benches), etc. This process is often called. A. mechanical, as opposed to A. thermal (thermal abrasion), i.e. destruction of coasts composed of permafrost and ice, and A. chemical (destruction of coasts as a result of the chemical influence of water). The less stable the g.p., the larger the adjacent bottom zone and the greater the strength of the waves, the higher the speed of A. The most intense A. in the surf zone. The length of abrasion areas on the shores of reservoirs around the globe is approx. 400 thousand km (51% of the total length). On average, 3.45 billion m 3 per year of clastic material enters reservoirs from cliffs, and 7.4 billion m 3 per year from benches. The sand, gravel and larger material formed during A. make up an underwater accumulative terrace attached to the bench, and accumulative coastal and underwater ones (spits, embankments, etc.), with which coastal-marine deposits are connected and deposits are being built. materials. When developing coastal deposits of gravel and sand, it is necessary to coordinate the scale of their extraction with the rate of supply of clastic material. Sediments of abrasion origin suspended in water migrate along the coastal strip or are carried by currents beyond the coastal zone and deposited in deeper parts of reservoirs. Yu. F. Chemekov.

Mountain encyclopedia. - M.: Soviet Encyclopedia. Edited by E. A. Kozlovsky. 1984-1991 .

See what “Abrasion” is in other dictionaries:

- (from Latin abrasio scraping), destruction, grinding and demolition of rocks under the influence of wind, water or ice. Abrasion is most intense as a result of the action of surf and corrosion on the seashore (dissolution of rocks under the influence of chemical ... ... Marine Dictionary

- (lat.). Painful irritation of the stomach from strong substances. Dictionary of foreign words included in the Russian language. Chudinov A.N., 1910. abrasion (lat. abrasio scraping) 1) geol. destruction of the shores of seas, lakes, large... ... Dictionary of foreign words of the Russian language

Scraping, destruction Dictionary of Russian synonyms. abrasion noun, number of synonyms: 5 scraping (7) ... Dictionary of synonyms

abrasion- Mechanical destruction of the shores of seas, lakes, rivers and reservoirs by waves. [Terminological dictionary of construction in 12 languages ​​(VNIIIS Gosstroy USSR)] abrasion Mechanical destruction by waves and currents of bedrock and loose rocks of marine and... ... Technical Translator's Guide

A type of natural disaster in insurance. This is how the demolition, erosion and destruction by the water element, sea surf, of the land surface immediately adjacent to the water is determined. Applies to seas, rivers, lakes and reservoirs. Dictionary… … Dictionary of business terms

- (from the Latin abrasio scraping), the process of destruction by breaking waves of rocks in the coastal zone of reservoirs (oceans, seas, lakes, reservoirs). The total length of the abrasion areas is 51% of the total length of the coastline of water bodies on the globe. WITH… … Modern encyclopedia

- (from Latin abrasio scraping) the process of destruction by waves and surf of the shores of seas, lakes and reservoirs ... Big Encyclopedic Dictionary

Destruction of shores and coastal sections of the seabed by sea waves... Geological terms

ABRASION, in geology, mechanical wear of rocks under the influence of mutual abrasion by rock fragments in contact with it. The main agents of abrasion are water flows, debris at the base of glaciers, as well as sand,... ... Scientific and technical encyclopedic dictionary

- (from Latin abrasio scraping), the erosive process of eroding the shores of seas and reservoirs under the influence of wave impacts, weathering or human economic activity. As a result, abrasion zones are created on shores exposed to erosion... ... Ecological dictionary

Books

• Life safety. Protection of territories and economic facilities in emergency situations, Onoprienko M.. Organizational, legal and technical issues of life safety are outlined, as well as the impact on the human body and its habitat of negative factors of natural,...

Shore abrasion speed

The rate of abrasion depends on many factors and is rarely constant. Typically, during a storm, much more coastal damage can occur within a few hours than during a long period of good weather. The presence and structure of cliffs is of great importance in determining the nature and rate of shore erosion, greater than the exposure of the shore relative to the waves.

Apparently, there is some relationship between the height of the cliff and the rate of erosion of the shore, since height is one of the important factors of its stability. The nature of the rocks composing the cliff plays a significant role. The erosion rate is also affected by the position of protective structures.

Protection of the shore from abrasion

When considering the issue of protecting banks from abrasion, one should keep in mind only banks composed of rocks that are easily eroded. Shores composed of durable rocks do not require additional protection. The erosion resistance of these rocks is quite sufficient to withstand abrasion.

Natural protection

Where the coast is potentially susceptible to destruction due to low height or poor stability of the rocks, a sufficiently developed beach provides a natural protection against abrasion. It absorbs wave energy and prevents waves from crashing directly onto the walls of the cliffs or onto the surface of the bench. On a low coast in the absence of cliffs, the best natural protection is dunes composed of sand coming from the beach and secured by the roots of psammophyte plants. Vegetation is of great importance as the primary trap for sand in the process of dune formation.

Artificial protection

Since the best natural defense of a shore is a wide and high beach, any method of artificially reproducing this form seems most desirable in seeking ways to prevent or stop abrasion. An artificial beach can be built in two ways. First of all, a beach can be created using sea booms. However, these structures are not always safe for the shore. The purpose of groins, usually built at almost right angles to the shoreline, is to catch sediment moving along the shore in order to raise the level of the beach surface. The danger of groynes, as well as breakwaters and some other structures, is that the “leeward” area may experience a sediment deficiency due to the interception of material, which helps to accelerate the erosion process.

Speaking about the significance of the groynes, it is worth noting that their location and character must correspond to the selected section of the coast, since it is impossible to make final conclusions and recommendations on these characteristics of the groynes in advance. Their length must correspond to the width of the sediment flow zone; where this zone is narrow, the groins must be made shorter, but taking into account that all the small amount of sediment available can accumulate in the upper part of the beach, where there is a special need for this. On pebble beaches, the groins should only be short, ending only a few yards from where the beach becomes sandy.

As for the height of the groynes, it should not exceed the maximum height of the level to which sediment accumulation on the beach is expected. The buna should be gently inclined, going under the level of the beach with its lower end; the angle of its inclination must correspond to the slope of the beach surface, which depends on the mechanical composition of the material composing it. As for the distance between the groins, it should be equal to their length. Longer groins can be spaced one and a half lengths apart.

Another way to protect low banks is to construct an artificial embankment located on the inside of the bank.

In some areas, the only possible method of protecting the coast and structures is the construction of coastal wave walls. Such walls can simultaneously be used for walks by vacationers. In other areas, coastal walls are needed to protect low-lying land from flooding during storm surges. This purpose can be served by earthen embankments, similar to those that fence many rivers, protecting their banks from tidal waves, floods or wave erosion.

The walls also help build up the beach. A concrete wall is an extremely strong structure that can withstand the blows of the surf. The force of the reverse surf flow is especially high due to the absence of water loss due to filtration. The drift of material towards the sea, which increases with strong sea winds, contributes to the destruction of the beach directly at the foot of the wall. There are no sand reserves necessary to cushion and stabilize the upper part of the beach. Reducing the height and width of the beach leads to the concentration of wave energy in a narrower zone, which increases their destructive power.

There is another method of shore protection that deserves mention. This is a method of artificial recovery of material washed from the beach, widely used in the United States and called “bypassing”.

Bypassing comes down to the fact that the sediment deficit in any area is replenished by transferring this sediment to it from a neighboring accumulation area.

The scooping of sand from the burring zone initially caused intense erosion of the beach in its “leeward” part, which once again indicates the need to intervene with great caution in the natural process of alongshore sediment movement. The material needed for beach restoration may come from some areas of the shore that are upwind of the scour obstructions or from an entirely different source unrelated to sediment flow. If the initial ratio between the inflow and outflow of material is achieved, the process of sand deposition will be generally equivalent to its loss during erosion and the coast will acquire stability. In order to correctly determine what the material should be, careful collection and examination of samples of sediment currently composing the beach is necessary, including collection of samples from all areas of the beach. The results of these analyzes must be compared with the nature of the material used for filling. The mechanical composition of sediments used to form the beach must be within the limits of changes in the mechanical composition of the material of natural beaches. To obtain an optimal result, the filling material should be somewhat larger than the natural sediment, not altered by erosion, and better sorted.

Conclusion: The abrasion activity of the sea has a dual effect on the coast. On the one hand, it leads to the accumulation of material, the formation of beaches, spits, and dams, and on the other hand, to the destruction of the shores by impact and their gradual retreat.

The place where the sea (or any other body of water) is in direct contact with a solid surface is called the shore. It is here that there is a constant confrontation between two elements: water and earth. Over time, the shores are destroyed and take on completely new forms.

Abrasion is... Definition and origin of the term

In the broadest sense, abrasion is the process of mechanical destruction of something. The term itself comes from the Latin word abrasio, which translates as “scraping” or “scraping.”

The term is used in many sciences and areas of human activity. For example, there is such a thing as dental abrasion. This is the process of physical abrasion of the hard tissues of teeth due to direct contact of their surfaces.

This term can be found in several scientific disciplines at once - in geology and geomorphology, medicine, gynecology, numismatics, etc. So, in numismatics, abrasion is the wear and tear of metal coins during their circulation. And in medicine, this concept refers to irritation of the walls of the stomach due to exposure to potent chemicals.

Coastal erosion - what is it? Types of shores

The coastline is heterogeneous; it is constantly being destroyed and modified. The culprits for this are two processes: sea surf and gravity. On the other hand, all the coastal strips of any water bodies in the world, one way or another, were formed under the continuous influence of waves arising in the same water bodies.

Marine abrasion is the process of destruction of bedrock and loose rocks of the coast. It is logical to assume that it depends on three main factors:

• strength and degree of wave impact;
• density and stability of rocks;
• steepness of the coastal slope.

Indeed, the steeper the coastal slope, the more intensely it will be destroyed. And the strength of the waves themselves, of course, also affects the process of marine abrasion.

In modern geomorphology, there are several main types of shores:

• Abrasion-denudation (formed under the influence of sea waves and slope processes).
• Fiords (formed as a result of flooding of glacial valleys by sea or ocean waters).
• Skerries (consist of many small rocky islands separated by narrow straits).
• Estuary (formed as a result of flooding by the sea of ​​the estuarine areas of river valleys).
• Rias (formed as a result of the flooding of narrow river valleys in mountainous areas by sea waters).

Abrasive shore and its elements

What is an abrasive bank? And what does he look like?

This is the name given to a special, specific form of relief. In simple terms, this is a steep and rather high shore of a body of water (sea, ocean, lake, artificial reservoir), which is destroyed under the constant influence of the surf. As a result of the work of waves, it seems to retreat towards land and is “eaten up” by the waters of the sea or ocean.

Geomorphologists were able to identify four main elements in the structure of the abrasive shore. This:

• cliff (shore ledge);
• wave-breaking niche;
• bench - abrasive underwater slope;
• underwater accumulative terrace of alluvial type.

The formation of any abrasive shore involves two opposing but complementary processes. This is actually abrasion (destruction of coastal rocks by waves) and accumulation (accumulation of loose products of this destruction).

In different parts of the world you can see the most beautiful abrasive shores: in England and Scotland, France and Poland, Russia, the USA, Australia. For example, on the southern coast of the island of Sicily there is a unique natural site - Scala dei Turchi. here it is composed of sedimentary rock - marl. Under the influence of waves for many years, these rocky cliffs have been smoothed and turned into smooth natural steps of dazzling white color. You can see what it looks like in the photo below.

How are the shores destroyed?

The process of forming an abrasive bank begins with the formation of a tiny excavation at the base of its slope. Gradually it increases in size, turning into a large niche. The “tongue” of rocks that hangs over this niche collapses over time and forms a small coastal ledge - a cliff.

Coastal cliffs may consist of pebbles, sand, gravel and larger debris. Sometimes it takes on rather bizarre shapes and outlines. Thus, on the California coast there is the city of Mendocino, which is known for its unusual “Bowling Ball Beach”. The sea surf gradually destroyed the solid rocky shore, and the resulting fragmentary material was ground into the sea into round stone balls. It all looks quite interesting (see photo below).

In general, the total length of abrasive shores on the planet is about 400 thousand kilometers. On average, approximately 10 billion cubic meters are lost annually from cliffs and benches into water bodies. m of fragmentary material.

Abrasion protection

Marine erosion causes a lot of trouble in many countries around the world. Scientists are constantly trying to develop more effective methods to combat it.

Protection against this phenomenon can be either natural or artificial (man-made). For example, the beach is an excellent natural means of protection against the destructive effects of abrasion. After all, it takes the brunt of the sea waves, absorbing their energy.

Artificial protection of the coast from abrasion consists of the construction of embankments on the inner side of the coast and the construction of powerful concrete walls along the coast. Breakwaters also help to cope with the process we are considering. These are long concrete structures that are built perpendicular to the coastline. Their name speaks for itself: breakwaters seem to “cut” sea waves, significantly reducing their destructive power.

Abrasion of sea shores

Abrasion

Abrasion is the process of destruction of the shores of water bodies by waves and surf. Abrasion also extends to the bottom of reservoirs to a depth of several tens of meters, and in the oceans - up to 100 meters or more. Debris material moves along the coast, is carried away and deposited offshore where wave energy weakens, and in depressions of the bottom. As a result of abrasion, various forms of relief of the abrasion coast are created.

There are mechanical (basic), chemical and thermal abrasion.

Mechanical abrasion occurs under the influence of mechanical impact of waves and dragged debris.

Chemical abrasion is the destruction of shores composed of soluble rocks (carbonates, sulfates, halogens). Under the influence of salts and carbon dioxide contained in chemically aggressive sea water, dissolution and leaching of rocks occurs.

Thermal abrasion occurs mainly in the polar zones on the shores of seas composed of loose permafrost or ice. Here the coast is destroyed not only under the influence of the mechanical energy of waves, but also as a result of the fact that the temperature of sea water is higher than the temperature of frozen rocks, and the latter thaw, loosen and are more easily destroyed. Chemical and thermal abrasion are always accompanied by mechanical, which is ultimately the main one. Abrasion occurs most intensely on deep coastlines, i.e. where there is a steep underwater slope. Then the waves approach the shore without wasting their energy, as happens when waves overturn on shallow shores, and all the kinetic energy of the waves goes to destroy the shore. First, at the edge of the sea, a depression is formed at the base of the coastal cliff - an abrasion or wave-breaking niche (in conditions of permanent permafrost, a thermal abrasion niche), and then with its further deepening and the collapse of the bedrock cornice overhanging it, a steep abrasion ledge, or cliff, is formed. The intensity and speed of abrasion depend not only on the energy of the waves, but also on the height of the coast, the composition and structure of the rocks composing it, i.e. on their resistance to erosion. Metamorphic, igneous, and cemented sedimentary rocks are durable and strong. If the coast is composed of soft rocks, then its destruction is especially intense and is often accompanied by sliding or subsidence of rock blocks with the formation of steep walls. In this case, the abrasion niche does not form (does not have time to form).

The average rate of abrasion on such shores is 0.6-1 m/year, although during strong storms the shore can retreat by 10 m at once. If the shore is composed of hard rocks, then large fragmentary material formed during their destruction remains at the foot of the cliff, and smaller ones are carried out to sea by reverse currents and deposited on an underwater slope, gradually forming an underwater accumulative terrace. As the cliff is destroyed and retreats inland, a slightly inclined seaward or horizontal abrasion platform - a bench - is formed in front of its foot. The surface of the bench articulates with an underwater accumulative terrace, forming an inclined abrasion-accumulative surface, which subsequently, being brought to the surface from the area of ​​wave processes (as a result of uplifting the coast), forms a marine terrace.

Sometimes, when a rocky coast is destroyed and retreats, individual rocks - kekurs - remain in the coastal zone. As the bench expands and coarse material accumulates at the foot of the cliff, a continuous block or boulder, depending on the lithology of the rocks and the duration of their processing by the sea, a blind area or flooring is formed. This blind area protects the shore from erosion. The bench can be developed in clayey rocks, then there is no blind area. The surface of the bench is either flat, or ridged, or stepped, depending on the angle of inclination and the uniformity of the eroded rocks and their composition. According to the degree of development, cliffs are divided into modern, or active, currently being formed, dying and ancient, already extinct. Over time, the bench and the accumulative underwater terrace expand, and the underwater slope flattens. Waves passing over the forming shallow water expend significantly more energy, and the abrasion gradually weakens and fades.

The underwater slope turns from deep to shallow, on which sediment accumulates and accumulative forms begin to form - underwater and surface levees. In this case, the bench, covered with sediments, becomes buried. Thus, the abrasive activity of the sea can naturally be replaced by accumulative activity. The processes of abrasion and accumulation in natural conditions lead to the leveling of the coast - the cutting off of capes protruding into the sea and the filling of bays with sediments.