Define what a lake is. Tectonic lakes. Origin of lake basins

Origin lake basins
Sedimentation in lakes

lakes – natural reservoirs with stagnant or low-flowing water, formed as a result of flooding of land depressions (hollows) with water masses. Lakes have no connection with the ocean and, unlike rivers, have a slow water exchange.

Each lake consists of three interconnected natural components:

1. hollows - landforms of the earth's surface,
2. water mass with substances dissolved in it,
3. plants and animals that inhabit the water.

Origin of lake basins

Lake basins arise as a result of various relief-forming processes and are divided into several groups according to their origin.

The manifestation of endogenous activity is associated with the formation of tectonic and volcanic basins.

Hollows tectonic origin formed as a result of the movement of parts of the earth's crust. Many lakes that have arisen in basins of tectonic origin occupy a vast area, are characterized by great depth and have ancient age. Typical examples of lakes belonging to this group are the Great African lakes(including Tanganyika with a depth of -1470 m), confined to the East African rift system, where the processes of stretching and subsidence of the continental crust take place. Lake Baikal in Russia (which is the largest freshwater reservoir and has a maximum depth of -1620 m among lakes), Lake Biwa in Japan (famous for freshwater pearls mined in it) and others have a similar origin. Basins are often confined to isometric troughs (Chad, Eyre) or large tectonic faults. Formation is also associated with tectonic processes. residual lakes, which are the remains of ancient oceans and seas. So, Caspian lake separated from the Mediterranean and Black Seas as a result of tectonic movements of the earth's crust.

Hollows volcanic origin confined to the craters and calderas of extinct volcanoes or located among solidified lava fields. In the latter case, lake basins are formed when hot lava flows from under a colder surface lava horizon, which contributes to the subsidence of the latter (this is how Yellowstone Lake was formed), or when rivers and streams are dammed by lava or mud flow during volcanic eruptions. Basins of this origin are found in areas of modern or ancient volcanic activity (Kamchatka, Transcaucasia, Iceland, Italy, Japan, New Zealand and etc.).

The variety of exogenous processes leads to the formation various groups lake basins.

A large number of lake basins have glacial origin. Their formation may be associated with the activity of mountain and lowland glaciers. In the mountains, glacial lake basins are represented by moraine-dammed and cirque. Moraine-dammed ones are formed when river valleys are dammed up by glaciers. When the cirque basins are filled with water, small picturesque lakes with clean and cold water.
On the plains of the basin glacial origin distributed in the territory subjected to the Quaternary glaciation. Among them, one can distinguish hollows of exaration, glacial-accumulative and moraine-dammed origin. Exaration basins are associated with mined-out moving ice by negative relief forms. A famous example of a lake that owes its origin to the destructive activity of glaciers is Loch Ness in Scotland, formed in a glaciated river valley. Thousands of lakes formed in the basins of glacial ploughing, are found in the territory Scandinavian Peninsula, in northern Canada. Glacial-accumulative basins are formed in the area of ​​development of moraine deposits. Lake basins in the area of ​​the moraine-plain relief are wide, have an oval shape and shallow depth (Chudskoye, Ilmen); in conditions of hilly-western and hilly-ridged terrain, they have an irregular shape, islands, complex coastline, dissected by peninsulas and bays (Seliger). Moraine-dammed basins arise when a moraine pre-glacial river valley is dammed up (for example, Lake Saimaa in Finland).

In areas of permafrost, thermo basins karst origin , which owe their origin to the melting of fossil ice and frozen rocks and subsidence of the soil. Many basins of tundra lakes have this origin. All of them have a small depth and are small in area. Another area of ​​development of thermokarst basins is the area of ​​distribution of Quaternary fluvioglacial deposits. Here, during the melting of ice caps, huge blocks were buried under a layer of sediments carried out by melted glacial waters. dead ice. Many of them melted only after hundreds of years, and in their place there were basins filled with water.

Lake basins of karst origin are formed in areas composed of soluble (karst) rocks. The dissolution of rocks leads to the formation of deep, but usually insignificant basins. Here, failures often occur due to the collapse of the vaults of underground karst cavities. Examples of karst basins are the famous "Failure" in Pyatigorsk (known from the novel by Ilf and Petrov "The Twelve Chairs") and Lake. Zhirot in french alps, having a depth of -99 m with an area of ​​​​only 57 hectares.

Lake basins of suffusion origin are formed during subsidence of soils due to the removal of loose silt particles by groundwater. Basins of this genesis are found in the steppe and semi-desert zones. Central Asia, Kazakhstan and the West Siberian Plain.

Basins of fluvial origin associated with the geological activity of rivers. Most often these are oxbow and deltaic lakes. Sometimes the formation of lakes is due to the obstruction of the riverbed by alluvial sediments of another river. For example, the formation of Lake St. Croy (USA) is associated with the damming of the river. St. Croy alluvial deposits of the river. Mississippi. Due to the dynamism of erosive and accumulative fluvial processes and the small size of basins, the latter are relatively quickly filled with sediment and overgrown in some places and re-formed in others.

Some lake basins are formed as a result of springing by landslides, mountain landslides or mudflows of rivers. Usually such lakes do not exist for long - there is a breakthrough of sediments that form a "dam". So, in 1841. The Indus in present-day Pakistan was dammed by a landslide caused by an earthquake, and six months later the "dam" collapsed, and a lake 64 km long and 300 m deep was drained in 24 hours. Lakes in this group can remain stable provided that excess water is drained through erosion-resistant hard rock. For example, Lake Sarez, formed in 1911 in the valley of the river. Murghab in the Eastern Pamirs still exists and has a depth of -500 m (the tenth deepest lake in the world).
The process of damming the river with a powerful collapse also contributed to the formation of one of the "pearls" of the Caucasus - Lake Ritsa in Abkhazia. A giant landslide on the slope of Mount Pshegish dammed the Lashipse River. The waters of the river flooded the gorge for more than 2 km (tracing a large tectonic fault in the strata rocks), the water rose to 130 m. A river with a different name, Yupshara (in Abkhazian for “split”), is knocked out from under a natural stone dam.

lakes artificial origin associated with the filling of artificial basins (quarries, etc.) with water, or with the damming of river flows. During the construction of dams, reservoirs of various sizes are formed - from small ponds to huge reservoirs(located in Africa are the Victoria reservoirs on the Victoria Nile, Volta on the Volta and Kariba on the Zambezi; the largest in Russia is Bratsk reservoir on the Angara River). Some dams were built to generate electricity for aluminum smelting from large deposits of bauxite. It should be added that dams are created not only by man. Dams built by beavers can reach lengths of more than 500 m, but they exist only for a short time.

Basins of coastal marine origin formed mainly as a result of the separation sea ​​bays bars from the sea area during the movement of the alongshore sediment flow. On initial stage the basin is filled with salty sea waters, which later formed salt Lake gradually softens.

Hollows of organogenic origin occur in the sphagnum swamps of the taiga, forest-tundra and tundra, as well as on coral islands. In the first case, they owe their origin to the uneven growth of mosses, in the second - to coral polyps.

Lakes on the scale of geological time exist for a relatively short time. The only exceptions are some lakes with basins of tectonic origin, confined to active zones of the earth's crust, and large residual lakes. Over time, the basins are filled with sediments or become swampy.

Sedimentation in lakes

Lake deposits are represented by terrigenous, chemogenic and organogenic sediments. The composition of sediments accumulating in lakes is primarily determined by climatic zoning.

In the lakes of humid areas, predominantly silt-clay deposits accumulate, often with big amount organics. Dead organisms, as well as material carried into the lake, are deposited at the bottom and form gyttia(from Swedish gyttja - silt, mud) - lake deposits, consisting of organic residues. The organic matter of gyttium is formed mainly due to the decay products of plant and animal organisms living in water, to a lesser extent due to the remains of terrestrial plants brought from the surrounding land. The mineral part consists of sandy-clay material and oxides of calcium, iron and magnesium precipitated from water. Gyttia is also called sapropel(from the Greek sapros - rotten and pelos - silt, mud - "putrefactive silt"). In Lake Nero, located near the city of Rostov-Yaroslavsky (Rostov Veliky), the layer of sapropel reaches 20 m. Sapropels are used as fertilizer or as a mineral feed for livestock; sometimes for balneological purposes (mud therapy).

In semi-desert and desert arid zones, lakes are endorheic with intense evaporation. Since rivers and underground waters always bring salts, and only pure water evaporates, there is a gradual increase in the salinity of lake waters. The concentration of salts can increase so significantly that from the water (brine) supersaturated with salts, salt is deposited on the bottom of the lake (self-settling lakes). Salinization of continental lakes accumulates carbonate, soda, sulfate, salt and other chemogenic deposits. In Russia, modern soda lakes known in Transbaikalia and in Western Siberia; abroad, Lake Natron in Tanzania and Lake Searls in California are very famous. Natural soda deposits are associated with fossil deposits of such lakes.
In general, arid regions are characterized by halogen-carbonate deposits, poor in organic matter.

In a number of cases, the origin of lake basins plays a decisive role in the nature of sedimentation. Glacial lakes are characterized by banded clays formed by a combination of lacustrine and glacial deposits. In karst lakes, carbonates accumulate, sometimes heaps of blocks of landslide origin.

Familiarization with varieties, geographical location, temperature regime of waters and chemical composition of lakes in Russia.

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Significant water reserves are concentrated in lakes. There are more than 2.5 million lakes in Russia. The largest lakes are the Caspian, Ladoga, Onega and Baikal.

Caspian lake is the most big lake in the world, the deepest is Lake Baikal. The lakes are very unevenly distributed.

In particular, in the Vilenovsky basins, the West Siberian Plain and the northwestern layer of Europe - in Karelia. All these areas are in too much humidity. In the south, in the zone of the steppe and semi-sedimentary zone with a weak climate, the number of lakes decreases sharply, and many lakes have salt or salt. Salt is such huge large lakes as the Caspian, as well as lakes Elton and Baskunchak, where salt is eliminated.

Hydrographic characteristics of large lakes in Russia

Eat different lakes and the origins of the basins.

Lakes of tectonic origin are located in trenches and cracks in the earth's crust. The largest tectonic lake Baikal is located in the Graben, reaching a depth of 1637 m.

Ice-tectonic lake basins were created as a result of processing liquid depressions of the glacial crust of the glacier: Imandra, Ladoga, Onega.

in Kamchatka and Kuril Islands The lake is mainly of volcanic origin. In the northwest of the European Plain, the sources of lake basins are associated with continental ice. Many caves are located between the hills of the sea: Seliger, Valdai.

Due to landslides in mountain valleys there was a lake of a lake: Sarez in the Pamirs, Ritsa in the Caucasus. Small lakes are formed by karst nests.

In the south of Western Siberia, there are many lakes in the form of plates, which were created as a result of stoning stones. When ice melts on the surface of the permafrost, shallow slab-like waters also form. Lake people are located on the flood plains of low-lying rivers. On the Black and Sea of ​​Azov there are estuary lakes.

All the largest and largest lakes in Russia are often used in the national economy. Catch and catch in them. Especially a lot of fish, including the most valuable sturgeon, end up in the Caspian.

In Baikal, the harvest is omul. Lakes are also used for navigation - geoglobus.ru. Numerous minerals were acquired in the lakes of lakes: oil and mirbilite in the Caspian lake, salt in Elton and Baskunchak. Water for freshwater lakes is used for drinking. There are many sanatoriums and rest houses on the shores of many lakes.

There are nine lake districts on the territory of Russia:

1) northwest lake, iceberg icebergs;
2a) Azov-Black Sea estuaries associated with marine activities;
2b) North Caucasian - glacial and karst lake;
3) salt formation of the Caspian Lake;
4) West Siberian-Tuscan and bitter-salty lakes;
5) Altai - sea ​​view lakes (Teletskoye, Markakol);
6) Zabaikalsky - the remaining lakes;
7) Lower Amur lakes, which have a hydrological connection with the Amur River;
8) Yakuti - lakes of thermocouples;
9) Lake Kamchatka - lakes of volcanic origin (Kronotsky, Kurilsky).

Lake - a component of the hydrosphere, which is a naturally occurring body of water filled within the lake bowl (lake bed) with water and not having direct connection with the sea (ocean). Lakes are the subject of study of the science of limnology.

From the point of view of planetology, a lake is an object that exists stably in time and space, filled with a substance in the liquid phase, the size of which is intermediate between the sea and the pond.

From the point of view of geography, the lake is a closed depression of the land, into which water flows and accumulates. Lakes are not part of the oceans.

Although the chemical composition of the lakes remains relatively long time constant, in contrast to the river, the substance filling it is updated much less frequently, and the currents present in it are not the predominant factor determining its regime. Lakes regulate the flow of rivers, retaining hollow waters in their basins and releasing them in other periods. Chemical reactions take place in lake waters. Some elements pass from water to bottom sediments, others - vice versa. In a number of lakes, mostly without runoff, the concentration of salts increases due to the evaporation of water. The result is significant changes in the mineralization and salt composition of lakes. Due to the significant thermal inertia of the water mass, large lakes soften the climate of the surrounding areas, reducing the annual and seasonal fluctuations of meteorological elements.

The shape, size and topography of the bottom of lake basins change significantly with the accumulation of bottom sediments. Overgrowth of lakes creates new landforms, flat or even convex. Lakes and, especially, reservoirs often create groundwater backwater, causing waterlogging of nearby land areas. As a result of the continuous accumulation of organic and mineral particles in lakes, thick strata of bottom sediments are formed. These deposits are modified with the further development of water bodies and their transformation into swamps or dry land. Under certain conditions, they are transformed into rocks of organic origin.

Lake classification

By origin, the lakes are divided into:

• Tectonic: formed by filling cracks in the earth's crust. A striking example of a tectonic lake is Lake Baikal.
• Glacial: formed by a melting glacier. A typical glacial lake left from the last ice age is the Arbersee, located at the foot of the Great Arber mountain (1456 m) - the most high mountain Bohemian forest.
• River(or old lady).
• seaside(lagoons and estuaries). The most famous lagoon is the Venetian lagoon, located in the northern part of the Adriatic Sea.
• Failed(karst, thermokarst). A feature of some failed lakes is their periodic disappearance and appearance, depending on the peculiar dynamics groundwater. A typical representative is Lake Ertso in South Ossetia.
• Zavalno-dammed: formed during the collapse of a part of a mountain (for example, Lake Ritsa in Abkhazia).
• Mountain: located in mountain basins.
• Crater: located in the craters of extinct volcanoes and explosion tubes. In Europe, similar lakes are located in the Eifel region (Germany). Near them, weak manifestations of volcanic activity in the form of hot springs are observed.
• artificial(reservoirs, ponds). The creation of such lakes can be an end in itself, for example, to create reservoirs for various purposes. Often this creation is associated with more or less significant earthworks. But in some cases, such lakes appear as a side effect of such work, for example, in depleted quarries.

According to the position of the lake are divided into (in relation to the planet Earth):

• Ground, whose waters take an active part in the water cycle in nature and groundwater, whose waters, if they take part in it, then only indirectly. Sometimes these lakes are filled with juvenile, that is, native water.
• Underground. The subglacial lake in Antarctica can also be attributed to the number of underground lakes.

According to the water balance, the lakes are divided into:

• sewage(have a drain, mainly in the form of a river).
• Drainless(they do not have surface runoff or underground water drainage to neighboring watersheds. Water consumption occurs due to evaporation).

By type of mineralization

• fresh;
• ultra-fresh

mineral (salty).

• brackish
• salty

According to the chemical composition of water, mineral lakes are divided into

• carbonate (soda)
• sulfate (bitter-salty)
• chloride (salty)

According to the nutritional value of the substances contained in the lake (trophicity), three types of lakes are distinguished:

• Oligotrophic (with a small amount of nutrients) - lakes are usually characterized by large or medium depths, a significant mass of water below the temperature jump layer, high transparency, water color from blue to green, a gradual drop in O2 content to the bottom, near which water always contains significant amounts of O2 (at least 60% of its content on the surface)
• Eutrophic (with a high content of nutrients) - well-heated lakes (the layer below the temperature jump is very small), transparency is low, the color of the water is from green to brown, the bottom is covered with organic silt. The water is rich in nutrient salts, the O2 content drops sharply towards the bottom, where it often disappears completely.
• Dystrophic (poor in nutrients) - swampy lakes with little transparency and yellow or brown (from great content humic substances) water color. The mineralization of water is low, the content of O2 is low due to its consumption for the oxidation of organic substances.

In modern hydrology and hydroecology, intermediate levels of trophic classification are distinguished: mesotrophic (between oligotrophic and eutrophic) and hypertrophic.

According to their location on celestial bodies, lakes are divided into:

• earthly;
• extraterrestrial.

The largest lakes of the Earth

total area lakes the globe makes up about 1.8% of the land (about 2.7 million km²).

The science of limonology deals with the study of lakes. By origin, scientists distinguish several types, among which there are tectonic lakes. They are formed as a result of the movement of lithospheric plates and the appearance of depressions in the earth's crust. Thus, the deepest lake in the world, Baikal, and the largest in area, the Caspian Sea, were formed. A large fault has formed in the East African rift system, where a number of lakes are concentrated:

• Tanganyika;
• Albert;
• Nyasa;
• Edward;
• The Dead Sea (is the lowest-lying lake on the planet).

In their form, tectonic lakes are very narrow and deep reservoirs, with sheer shores. Their bottom, as a rule, is located below the level of the ocean. It has a clear outline, resembling a curved broken curved line. Traces of various landforms can be found at the bottom. coast tectonic lakes They are made up of hard rocks and are weakly eroded. On average, the deep-water zone of lakes of this type is up to 70%, and shallow water - no more than 20%. The water of tectonic lakes is not the same, but in general it has a low temperature.

The largest tectonic lakes in the world

There are both large and medium-sized tectonic lakes in the Suna river basin:

• Randozero;
• Palier;
• Salvilambi;
• Sandal;
• Sundozero.

Among the lakes of tectonic origin in Kyrgyzstan, Son-Kul, Chatyr-Kul and Issyk-Kul should be mentioned. On the territory of the Trans-Ural Plain there are also several lakes formed as a result of a tectonic fault of the solid shell of the earth. These are Argayash and Kaldy, Uelgi and Tishki, Shablish and Sugoyak. In Asia, there are also tectonic lakes Kukunor, Khubsugul, Urmia, Biva and Van.

In Europe, there are also a number of lakes of tectonic origin. These are Geneva and Weettern, Como and Constance, Balaton and Lake Maggiore. Among the American lakes of tectonic origin, the Great North American Lakes should be mentioned. The same type of Winnipeg, Athabasca and the Great Bear Lake.

Tectonic lakes are located on the plains or in the area of ​​intermountain troughs. They have considerable depth and enormous dimensions. Not only the folds of the lithosphere, but also ruptures of the earth's crust take part in the process of formation of the lake basins. The bottom of tectonic lakes is below the ocean level. Such reservoirs are found on all continents of the earth, however, the largest number of them is located precisely in the fault zone of the earth's crust.

A lake is a closed depression of land filled with water. It has a slow water exchange, unlike rivers, and does not flow into the waters of the oceans, unlike the seas. These reservoirs on our planet are distributed unevenly. The total area of ​​the Earth's lakes is about 2.7 million km 2, or about 1.8% of the land surface.

The lakes have a number of differences among themselves both in external parameters and in the composition of the water structure, origin, etc.

Classification of lakes by origin

Glacial reservoirs were formed due to the melting of glaciers. This happened during periods of severe cooling, which fettered the continents repeatedly over the past 2 million years. As a result of the ice ages modern lakes located on the territory North America and Europe, namely in Canada, Baffin Island, Scandinavia, Karelia, the Baltic States, the Urals and other areas.

Huge blocks of ice, under the weight of their weight, and also because of their movements, formed considerable pits in the thickness of the earth's surface, sometimes even pushed apart tectonic plates. In these pits and faults, after the melting of ice, reservoirs were formed. One of the representatives glacial lakes can be called a lake. Arbersee.

The cause of the occurrence was the movement of lithospheric plates, as a result of which faults were formed in the earth's crust. They began to fill with water from melting glaciers, which led to the emergence of this type of reservoir. The brightest example is Lake Baikal.

River lakes appear when some sections of flowing rivers dry up. In this case, the formation of chain reservoirs arising from one river takes place. The second variant of river formations are floodplain lakes, which appear due to water barriers that interrupt the water channel.

Seaside lakes are called estuaries. They appear when lowland rivers are flooded by the waters of the seas or as a result of the lowering of sea coasts. In the latter case, a strip of land or shallow water appears between the newly formed bay and the sea. In estuaries, which appeared from the confluence of the river and the sea, the water has a slightly salty taste.

Karst lakes are earthen pits that are filled with water underground rivers. Pit pits are failures of the lithosphere, consisting of limestone rocks. Due to the failure, limestone rocks line the bottom of the reservoir, which affects the transparency of its filled waters: they are crystal clear.

Karst lakes have one distinguishing feature- they are periodic in their appearance. That is, they can disappear and form again. This phenomenon depends on the level of underground rivers.

They are located in mountain valleys. They are formed in several ways. Due to mountain landslides that block the river flow and thereby form lakes. The second way of formation is the slow descent of huge blocks of ice, which leave behind deep land failures - basins that are filled with water from melted ice.

Volcanic-type lakes appear in the craters of dormant volcanoes. Such craters are of significant depth and high edges, which prevents flows and inflows river waters. It does volcanic lake practically isolated. Craters fill with rainwater. The specific location of such objects is often reflected in the composition of their waters. Increased content carbon dioxide make them dead, unfit for life.

These are reservoirs and ponds. They are created intentionally for industrial purposes. settlements. Also, artificial lakes can be the result of earthworks, when the remaining earthen pits are filled with rainwater.

Above was a classification of lakes depending on the origin.

Types of lakes by position

It is possible to make a classification of lakes depending on their position in relation to the earth as follows:

1. Terrestrial lakes are located directly on the surface of the land. These are involved in the constant water cycle.
2. Underground lakes are located in underground mountain caves.

Mineralization classification

You can classify lakes by the amount of salts as follows:

1. Fresh lakes are formed from rainwater, melting glaciers, groundwater. The waters of such natural objects do not contain salts. In addition, fresh lakes are a consequence of the overlapping of river beds. The largest fresh lake is Baikal.
2. Salt water bodies are subdivided into brackish and saline.

Brackish lakes are common in arid areas: steppes and deserts.

Salt lakes in terms of the content of salts in the thickness of their waters resemble oceans. Sometimes the salt concentration of lakes is somewhat higher than in the seas and oceans.

Classification by chemical composition

The chemical composition of the lakes of the Earth is different, it depends on the amount of impurities in the water. Lakes are named based on this:

1. In carbonate lakes, there is an increased concentration of Na and Ca. Soda is mined from the depths of such reservoirs.
2. Sulfate lakes are considered curative due to the content of Na and Mg in them. In addition, sulfate lakes are a place for the extraction of Glauber's salt.
3. Chloride lakes are salt lakes, which are the place where common table salt is mined.

Water balance classification

1. Waste lakes are endowed with the help of which a certain amount of water is discharged. As a rule, such reservoirs have several rivers flowing into their basin, but there is always one flowing one. An excellent example is the large lakes - Baikal and Teletskoye. The water of sewage lakes is fresh.
2. Endorheic lakes are saline lakes, since the flow of water in them is more active than its inflow. They are located in the desert and steppe zones. Sometimes they produce salt and soda on an industrial scale.

Classification according to the amount of nutrients

1. Oligotrophic lakes contain a relatively small amount of nutrients. The peculiarities are the transparency and purity of the waters, the color from blue to green, the depth of the lakes is significant - from medium to deep, the decrease in oxygen concentration closer to the bottom of the lake.
2. Eutrophic plants are saturated with a high concentration of nutrients. The peculiarities of such lakes are the following phenomena: the amount of oxygen sharply decreases towards the bottom, there is an excess of mineral salts, the color of the water is from dark green to brown, which is why the transparency of the water is low.
3. Dystrophic lakes are extremely poor in minerals. There is little oxygen, the transparency is low, the color of the waters can be yellow or dark red.

Conclusion

The water basin of the Earth is made up of: rivers, seas, oceans, glaciers of the oceans, lakes. There are several types of lake classifications. They have been reviewed in this article.

Lakes, like other bodies of water, are the most important Natural resources which are actively used by man in various fields.

A lake is a closed depression of land filled with water and not directly connected to the ocean. Unlike lakes, these are reservoirs of slow water exchange. The total area of ​​the Earth's lakes is about 2.7 million km2, or about 1.8% of the land surface. Lakes are ubiquitous, but uneven. On the geographical location of the lakes big influence the climate that determines their nutrition and evaporation, as well as factors contributing to the formation of lake basins. There are many lakes in the regions, they are full-flowing, fresh and mostly flowing. In areas with a dry climate, ceteris paribus, there are fewer lakes, often they are shallow, more often drainless, and therefore often saline. Thus, the distribution of lakes and their features are determined geographically.

4. Karst lakes, the basins of which arose as a result of sinkholes, soil subsidence and erosion (limestone, gypsum, dolomite). The dissolution of these rocks with water leads to the formation of deep, but insignificant lake basins.

5. Damped (dammed, or dammed) lakes arise as a result of blocking the channel (valley) of the river with blocks of rocks during landslides in the mountains (Sevan, Tana, many lakes of the Alps, and other mountainous ones). From a large mountain collapse in 1911, Sarez Lake was formed with a depth of 505 m.

A number of lakes are formed by other reasons:

• estuary lakes are common on the shores of the seas - these are coastal areas of the sea, separated from it by means of coastal spits;
• oxbow lakes - lakes that have arisen in old riverbeds.

According to the origin of the water mass, lakes are of two types.

1. Fresh lakes - the salinity of which does not exceed 1‰ (one ppm).

2. Brackish - the salinity of such lakes is up to 24‰.

3. Salty - with a content of dissolved substances in the range of 24.7-47‰.

4. Mineral (47‰). These lakes are soda, sulfate, chloride. In mineral lakes, salts can precipitate. For example, self-sustaining lakes Elton and Baskunchak, where salt is mined.

Usually sewage lakes are fresh, as the water in them is constantly updated. endorheic lakes more often they are salty, because evaporation prevails in their water consumption, and all minerals remain in the reservoir.

Lakes, like rivers, are the most important natural resources; are used by man for navigation, water supply, fishing, obtaining mineral salts and chemical elements. In some places, small lakes are often artificially created by man. Then they are also called.