Coastal marine processes and coastal landforms. Coastal marine processes and landforms coastal Relief of sea coasts

COASTAL STREETS There are several streets with this name in St. Petersburg. Two of them take place in the Vyborg region very close to each other. One is in Ozerki along the shore of Lake Verkhne, from the junction of Onezhsky Proezd and Erivanskaya Street. Its name has been known since 1889. Another

Shore- this is the boundary of land and sea where their interaction occurs. It is observed within a relatively wide band called coastal zone. This zone includes the surface part of the coast and the underwater coastal slope.

The coastal zone is affected by the following forces: sea waves; wave currents and tidal phenomena. The following also take part in the formation of coasts: rivers connecting delta coasts; tectonic movements; alive organisms.

Debris in the coastal zone, transported by waves and surf, is usually called marine sediments. The accumulation of sediment in the zone of the surf flow is usually called beach. Usually the beach is composed of larger sediments than the underwater coastal slope. The largest debris accumulates near the wave breaking zone, as maximum speeds flow - at the beginning of its movement.

Beaches are classified according to morphological characteristics full and incomplete profile.

Full profile beach is formed if there is free space ahead of the forming sediments. Then the beach takes on the appearance of a coastal rampart, which has a gentle and wide sea slope and a steeper slope facing the shore. If the beach is formed at the foot of the ledge, then sloping beach or incomplete profile beach, with one slope facing the sea.

With the transverse movement of sediment, various underwater and coastal accumulative forms arise. This underwater shafts, representing accumulative forms composed of sandy material and stretched along the coast parallel to each other. Usually there are 2-3 shafts, less often 5-6 shafts. Their height is from 1 to 4 meters and their length is from several hundred meters to several kilometers.

The origin of underwater shafts is associated with partial destruction of waves or the so-called by drilling. In this case, the shafts lose some of their energy and the material they carry is deposited on the bottom in the form of an underwater shaft. The zone of partial destruction of waves with a shallow bottom near the shore can be quite wide. They call her bubbling zone. The large number of underwater swells is due to the fact that waves of different magnitudes experience surfacing at different depths. Underwater swells are formed in places of the underwater slope, where partial destruction of waves of a certain magnitude occurs. Beaches, coastal and underwater levees are elementary accumulative forms. Larger accumulative formations include coastal bars or barriers.

Shore bars composed of material of bottom origin, usually shells and coral sand. Οʜᴎ stretch for tens and hundreds of kilometers along low-lying sea ​​shores and usually separate the coastal waters from the sea, which is usually called lagoon. The foot of the sea bars are located at a depth of 10-20 m, and above the water they rise 5-7 m, sometimes up to several tens of meters. Such high altitude achieved through dunes. Bars are widespread and are found along 10% of the world's ocean shores. It can be assumed that the formation of bars is associated with a rise in sea level in post-glacial times. At the same time, the surfaces of the flooded accumulative plains turn out to be too sloping and the waves carry large masses of sand towards the shore. Excess transported sediment falls out during movement and forms an underwater bar, which becomes an obstacle to sediment arriving from the underwater coastal slope. Their deposition on the sea side of the bar leads to its expansion in width. At the same time, the bar grows in height due to the accumulation of sediment on the ridge and the general movement of the bar to shallower depths. It can be assumed that the formation of coastal or island bars is associated with changes in the level of the world ocean in recent times.

Longitudinal movement of sediment. When waves approach the shore at an oblique angle, longitudinal, or alongshore sediment movement. Due to wave vibrations, sediment particles travel along a zigzag path and travel a certain distance along the coast. The surf flow, running up the beach, at the beginning maintains the direction of the wave movement, then deviates more and more from it under the influence of gravity. The reverse flow runs in the direction of the greatest slope. It describes an asymmetrical trajectory, resembling a parabola, and moves sediment particles along the coastline. The speed of such movement depends on the angle of approach of the wave to the shore. In this case, its optimal value is 45°. Under certain conditions, massive sediment movement occurs on the beach and on the underwater coastal slope. Such movement in one direction over a long period of time, for example a year, is usually called sediment flow. The flow is characterized by power, capacity and saturation.

Flow power- this is the amount of sediment that actually moves along the coast per year. Capacity- it is customary to call the amount of sediment that waves are capable of moving. If the power is equal to the capacity, this means that all the wave energy is spent only on transport. Neither bank erosion nor sediment deposition occurs in this case. For this reason saturation flow should be called the power-to-capacity ratio. If this ratio is less than 1, then the flow is unsaturated. In this case, part of the energy free from the work of transporting material will be directed to erosion of the coast. If the flow capacity is less than the sediment supply to a given area, we can talk about an increase in the intensity of sediment supply above the flow capacity. As a result, some of the material stops moving and is deposited, forming accumulative forms.

Accumulative forms during longitudinal movement of sediment. As the angle of approach of the waves to the shore decreases, the flow capacity decreases and the accumulation of material begins. This creates: accumulative forms of filling the shore contour. This category includes various accumulative underwater terraces at the tops of bays. Accumulative braids, which are formed when a flow bends around a shore protrusion. In this case, the wave front spreads and its energy decreases. The braids are attached to the shore only by their root part, and their growing end remains free. For this reason, such braids are called free accumulative forms. If the coast on the sea side is protected by a cape, then a closing form is formed at the entrance to the bay, which is usually called a bay-bar.

Abrasion. The destructive work of the sea is commonly called abrasion. It can be mechanical, chemical and thermal.

Mechanical abrasion- this is the destruction of rocks that make up the shores under the influence of impacts from surf waves and rock fragments carried by waves and surf.

Chemical abrasion- destruction of rocks due to their dissolution by sea water.

Thermal abrasion- destruction of banks composed of frozen rocks or ice as a result of the warming effect sea ​​water.

With a steep slope of the coastal slope, the waves come to the shore with a large supply of energy. They have a direct impact on the area adjacent to the coastline. For this reason, a recess is formed here, which is usually called wave-breaking niche. When it deepens, the cornice collapses. The mass of rock entering the water further accelerates the destruction of the shore. The process of cornice collapse is repeated repeatedly, which leads to the formation of a vertical ledge, that is abrasion cliff or clif. In front of the cliff, a platform is developed that is slightly inclined towards the sea, called Bench. The bench begins at the very foot of the cliff and continues below sea level. Expansion of the bench during abrasion leads to flattening of the profile and attenuation of the processes of bank destruction.

Straightening the coastline. The destruction of coastlines and the formation of accumulative coastal forms lead to the leveling of the coastline. Its initial outlines are currently determined by the penetration of sea water into relief depressions after the retreat of the glacier. Such shores are called ingressive. Among them are:

1. Fiord (fjord) shores, formed during the flooding of glacial valleys. Fjords- narrow and long winding bays (Norway, Canada, New Zealand).

2. Skerry shores, which were formed during the flooding of low glacial plains. Skerries- these are small rocky islands, which look like submerged sheep's foreheads, separated by narrow straits.

3. Rias shores, caused by flooding of river valleys mountainous countries. Rias are narrow, winding bays. For example, Sevastopol Bay.

4. Estuary shores, formed during the flooding of river valleys of the coastal plains. The bays that arise in this case - estuaries. ( North-West Black Sea region).

5. Dalmatian-type shores, which arose during the flooding of folded structures with a strike close to the general direction of the coast. In this case, bizarre archipelagos of islands are formed, stretched along the coast.

6. The banks of fault-block lobate dissection, which are formed during the flooding of tectonic depressions of grabens (Greek coast of the Aegean Sea).

All types of coasts are in different stages of leveling, which is associated with the unequal nature of the initial dissection and different geological structure. At the same time, some sections of the coast turned out to be leveled, others are being leveled, and others have become even more dismembered during the leveling. This happened due to the formation of bays or irrigation in place of rocks more susceptible to erosion, as well as during the formation of closing accumulative forms.

Some banks retain their original dissection. This applies to rias and fiord shores, as well as to the shores of tectonic dissection, composed of durable igneous rocks. Such shores are called shores, not changed by the sea. Their development occurs mainly under the influence of slope processes. They can be called denudation, and with great influence of the sea - abrasion-denudation.

Shores tidal seas. The seashores are affected not only by waves, but also by tides. At the same time, tides on deep shores intensify abrasion, since with increasing depth near the shore, the waves act more energetically on the cliff. The foot of the cliff on such shores is at high tide level. At low tide, only part of the suspended material is carried away by the ebb current. As a result, accumulative forms are formed near the shore, which are called dryings or watts. Gradually, the drying surface becomes higher than the tidal level, vegetation settles on it and a soil cover is formed - marches appear.

However, the accumulative activity of tides generally leads to the buildup of land. Within the coastal shallow waters, underwater accumulative forms can form: sand ridges and sand waves.

Sand ridges- these are large linear forms up to several kilometers long and 1-2 km wide. Their height is up to 20 m. They are located along the coast in the direction tidal currents.

Sand waves- these are formations that arose on the slopes of sand ridges and are oriented frontally in relation to the direction of tidal currents. Their sizes range from several hundred meters to several kilometers in length and up to several meters in height. Οʜᴎ resemble enlarged wave ripple marks.

Coral Shores and islands. In the formation of seashores on the coasts of tropical seas, some marine reef building organisms, which absorb lime from sea water. When they die, it forms coral or reef limestone. Accumulative forms built from such limestone are called coral reefs.

The following types of coral structures are distinguished:

- fringing or shore reefs;

- barrier reefs;

- ring or intralagoonal reefs.

Fringing reefs these are underwater coral-limestone terraces adjacent to the shore. Their outer side is covered with living colonies of corals. The surface of the reef is usually called reef flat. With distance from the outer zone, this surface is increasingly covered with sediment cover of gravel and sand. Near the shore it is bordered by a sand and gravel beach. The thickness of the fringing reef on tectonically stable shores usually does not exceed 50 m, which is due to the habitat conditions of reef-forming corals. Coral polyps live in symbiosis with unicellular green algae, which needs good lighting.

Barrier reefs these are coral-limestone ridges located considerable distances from the coast. The thickness of barrier reefs is many times greater than that of fringing reefs. It has been established that they arise during tectonic subsidence of their outer edge. The largest such reef is the Great Barrier Reef, which stretches along the northeastern edge of Australia for more than 2,300 km. If a barrier reef forms around a small subducting island, it becomes a ring-shaped reef, or atoll. In this case, a coral lagoon is formed inside the atoll, in which intralagoonal reefs can arise. In most cases, they take the form of columns, or giant pedestals, randomly scattered inside the lagoon. By merging with each other, the columns form large formations in area, which are called banks. Coral islands are often found in tropical seas. They are usually located on accumulative forms formed due to the activity of sea waves and consisting of coral sediments - sand, gravel, pebbles, and sometimes blocks of reef limestone.

As a result of repeated changes in ocean depth during glacial and interglacial eras, peculiar relief forms were formed in the coastal zones of the seas, which are called ancient coastlines.Οʜᴎ 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.Οʜᴎ record the position of the ancient coastline.

Taking into account the dependence of the reconstruction, the following are distinguished:

1. Accumulative terraces, that is, completely composed of coastal-marine sediments;

2. Abrasion terraces, which are composed only of bedrock;

3. 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.

Marine coastal landforms - concept and types. Classification and features of the category "Marine coastal landforms" 2017, 2018.

(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, crushing 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 ocean depth 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. The ancient coastlines corresponding to the lower level are now submerged 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:

1. Accumulative terraces, that is, completely composed of coastal-marine sediments;
2. Abrasion terraces, which are composed only of bedrock;
3. 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.

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

Origin of the shores

The following main types of shores are distinguished by origin.

1. Ingression shores formed as a result of the advance of the sea onto land:

A) fiordaceae, formed as a result of the influence of tectonic forces at different times, as well as water and glacial erosion. These shores are indented by long, narrow and deep bays and straits with high and very steep sides (fiords). Fiords are characterized by a winding coastline, deepening of the middle part and the presence of a depth threshold at the mouth;

b) skerry, formed as a result of flooding of a complex of glacial-denudation forms such as sheep's foreheads, large glacial outliers, and less commonly accumulative glacial forms (drumlins, eskers, etc.). They are characterized by fractional and complex dissection, an abundance of rocky islands, straits, bays, capes and peninsulas;

V) riaceae - the result of the sea flooding mountain river valleys. They are characterized by rias - narrow winding bays with high sides;

G) estuaries and lagoons, formed by flooding of lowland river valleys or coastal lowlands. An estuary is a shallow bay that protrudes deeply into the land with spits and bars, and a lagoon is a shallow bay stretched along the coast, connected to the sea by a small strait or separated from the sea by a spit. A characteristic feature of this type of coastline is the leveled coastline on the sea side.

2. Coasts formed by continental accumulation:

a) deltaic, formed as a result of the removal of sediments by rivers;

b) composed of aeolian deposits, such as dunes;

c) landslides, formed as a result of the sliding of land areas washed away by the sea. They are recognized by the accumulation of earth masses on the shore and the landslide relief of adjacent areas.

3. Coasts formed by tectonic movements, for example faults. Characterized by rectilinear outlines and steepness. Moreover, the underwater slope is as steep as the shore.

In addition to the listed types, there are shores that owe their origin to volcanic activity, the death of plants, the vital activity of corals, etc.

According to the nature of the relief, the coasts are divided into mountainous and flat. Mountainous coasts are usually high and well protect the coast from winds from the land, while low flat coasts open the way for the winds.

Depending on the bottom topography of the coastal zone, there are The shores are shallow and deep. On shallow shores the bottom slope is on average less than 0.01, and on deep shores it is more than 0.03.

A peculiar element of the coastal zone of tidal seas are drying areas (drying areas) - areas of the coastal zone that are flooded with water during high tide and dry out at low tide. The upper and lower boundaries of drying run respectively along the spring high and low tide marks.

The conditions for drilling operations within the drying zone are very unique: during high tide they are similar to drilling conditions in offshore conditions, and at low tide they are similar to drilling conditions on land. This periodic change in conditions complicates drilling operations and places special demands on them.