Lakes of tectonic origin. Glacial lakes of Russia

A lake is a body of water with a slowed down water exchange. Lakes are classified according to various criteria: in origin (tectonic, volcanic, dammed, glacial, sinkhole, karst, etc.); by salinity (fresh, brackish, saline, brine, etc.); by trophicity (oligotrophic, mesotrophic, eutrophic, etc.); by position in the landscape (lowland, floodplain, highland, etc.); in depth (shallow, deep, superdeep); by morphology (rounded, elongated, ribbon-like, sickle-shaped, distinct, etc.); by flow (closed, low flow, periodically flow, temporary, relic); by types of use (fishery, for water supply, for the extraction of salt, sapropel ore, therapeutic mud, etc.); by condition (clean, polluted, overgrown, etc.).

How many years do lakes live?

Most often, it is relatively short - several thousand or tens of thousands of years. This applies primarily to glacial and old lakes. Karst, volcanic and especially tectonic lakes can exist for millions and tens of millions of years. For example, one of the lakes in Australia was formed about 700 million years ago.

How many lakes are there on Earth?

The exact calculation has not yet been made. There are probably about 2 million lakes in Canada and Alaska, about 100 thousand in Finland and the Scandinavian Peninsulas. About 100 thousand in Great Britain and Ireland as well as Denmark, Belgium, Holland and France. Hydrologists believe that there are about 5 million lakes on the earth.

Tectonic lakes.

They form in places of faults and displacements. crust... As a rule, these are deep narrow reservoirs with straight-sided steep banks, located in deep through gorges The bottom of such lakes located in Kamchatka is located below ocean level. Tectonic lakes include Dalneye and Kurilsk. Kuril Lake is located in the south of Kamchatka in a deep picturesque basin surrounded by mountains. The maximum depth of the lake is 306 m. Its shores are steep. Numerous mountain streams flow from them. The lake is a waste water, from which the Ozernaya river originates. On the shores of the lake, hot springs come to the surface, and in the middle there is an island called the Heart-stone. Not far from the lake there is a unique outcrop of pumice, which is called Kutkhiny baty. Currently, the lake is declared a nature reserve and a zoological natural monument.

The bottom profile of tectonic lakes is sharply delineated, has the form of a broken curve. Glacial deposits and the processes of accumulation of sediments have little changed the clarity of the tectonic lines of the lake basin. The influence of the glacier on the formation of the basin is noticeable; it leaves traces of its presence in the form of scars, sheep's foreheads, which are clearly visible on rocky shores and islands. The shores of the lakes are composed mainly of hard-stone rocks that are poorly eroded, which is one of the reasons for the weak sedimentation process. These lakes belong to the group of lakes of normal depth (a = 2-4) and deep (a = 4-10). The deep-water zone (more than 10 m) of the total volume of the lake is 60-70%, shallow water (0-5m) 15-20%. The waters of the lakes are thermally inhomogeneous: during the period of the greatest heating surface waters low bottom temperatures remain, which is facilitated by stable thermal stratification. Aquatic vegetation is rare, only in a narrow strip along the shores of closed bays. Typical lakes in the river basin. The Suna are large and medium-sized: Palje, Sundozero, Sandal, as well as the very small lakes Salvilambi and Randozero, located on the private catchments of the Palje and Sandala lakes.

As a result of the movement of the earth's crust, depressions are formed in some places over time. It is in these depressions that tectonic lakes arise. The three most large lakes and Kyrgyzstan: Issyk-Kul, Son-Kul and Chatyr-Kul are formed tectonic way.

There are many lakes in the forest-steppe Trans-Urals. Here such large reservoirs as Uelgi, Shablish, Argayash, B. Kuyash, Kaldy, Sugoyak, Tishki, etc. The depths of the lakes in the Trans-Ural plain are noticeably reduced and do not exceed 8-10 m. By their origin, these lakes belong to the erosion-tectonic type. Tectonic depressions have been modified as a result of the impact of erosion processes. Many lakes of the Trans-Urals are confined to the ancient hollows of river runoff (Etkul, Peschanoe, Alakul, Kamyshnoe, etc.).

Lake Baikal. General information

Lake Baikal

Baikal - a freshwater lake in the south Eastern Siberia, it stretched from 53 to 56 ° N. and from 104 to 109 ° 30''E. Its length is 636 km, and the coastline is 2100 km. The width of the lake varies from 25 to 79 km. The total area of ​​the lake (mirror area) is 31,500 sq. Km.

Baikal is the most deep lake in the world (1620 m). It contains the largest reserves of fresh water on earth - 23 thousand cubic kilometers, which is 1/10 of the world's fresh water supply. A complete change of such a huge amount of water in Lake Baikal has been taking place for 332 years.

This is one of the oldest lakes, its age is 15 - 20 million years.

336 rivers flow into the lake, including the Selenga, Barguzin, Upper Angara, and only one Angapa flows out. There are 27 islands on Lake Baikal, the largest of which is Olkhon. The lake freezes in January, opens up in May.

Baikal lies in a deep tectonic depression and is surrounded by mountain ranges covered with taiga; the area around the lake has a complex, deeply dissected relief. Near Lake Baikal, the strip of mountains is noticeably expanding. Mountain ranges stretch here parallel to one another in the direction from northwest to southeast and are separated by basin-like depressions, along the bottom of which rivers flow and in some places lakes are located. The height of most of the ranges of Transbaikalia rarely exceeds 1300 - 1800, but the highest ranges reach high values. For example, xp. Khamar-Daban (Sokhor peak) - 2 304 m, and the Barguzinsky ridge. about 3000 m.

Tectonic movements continue here to this day. This is evidenced by frequent earthquakes in the area of ​​the basin, outcrops of hot springs and, finally, sinking of significant parts of the coast.

The waters of Lake Baikal have a blue-green color, are distinguished by exceptional purity and transparency, often even greater than in the ocean: you can clearly see stones and thickets of greenish algae lying at a depth of 10-15 m, and a white disk immersed in the water is visible at a depth of 40 m.

Baikal lies in the belt temperate climate.

Geography of Lake Baikal

Lake Baikal is located in the south of Eastern Siberia. In the form of a nascent crescent, Baikal stretches from southwest to northeast between 55 ° 47 "and 51 ° 28" north latitude and 103 ° 43 "and 109 ° 58" east longitude. The length of the lake is 636 km, the maximum width in the central part is 81 km, the minimum width opposite the Selenga delta is 27 km. Baikal is located at an altitude of 455 m above sea level. The length of the coastline is about 2000 km. The area of ​​the water table, determined at the water edge of 454 m above sea level, is 31,470 square kilometers. The maximum depth of the lake is 1637 m, average depth- 730 m. 336 permanent rivers and streams flow into Baikal, while the Selenga brings half of the water flowing into the lake. The only river that flows out of Baikal is the Angara. However, the question of the number of rivers flowing into Baikal is rather controversial, most likely there are fewer of them than 336. There is no doubt that Baikal is the deepest lake in the world, the closest contender for this title, the African lake Tanganyika, is 200 meters behind. There are 22 islands on Lake Baikal, although, as mentioned above, there is no unanimity on this issue. Most large island- Olkhon.

Age of Lake Baikal

Usually the age of the lake is given in the literature as 20-25 million years. In fact, the question of the age of Lake Baikal should be considered open, since the use of various methods for determining the age gives values ​​from 20-30 million to several tens of thousands of years. Apparently, the first estimate is closer to the truth - Baikal is in fact a very ancient lake.

It is believed that Baikal arose as a result of tectonic forces. Tectonic processes are still going on, which is manifested in the increased seismicity of the Baikal region. If we assume that the age of Baikal is indeed several tens of millions of years, then this is the oldest lake on Earth.

origin of name

Numerous scientific studies are devoted to the problem of the origin of the word "Baikal", which indicates a lack of clarity in this issue. There are about a dozen possible explanations for the origin of the name. Among them, the most likely is the version of the origin of the name of the lake from the Turkic-speaking Bai-Kul - a rich lake. Of the other versions, two more can be noted: from the Mongolian Baigal - rich fire and Baigal Dalai - big lake... The peoples who lived on the shores of the lake called Baikal in their own way. Evenks, for example, - Lamu, Buryats - Baigal-Nuur, even the Chinese had a name for Baikal - Beihai - North Sea.

The Evenk name Lamu - More was used for several years by the first Russian explorers in the 17th century, then they switched to the Buryat Baigal, slightly softening the letter "g" by phonetic substitution. Quite often Baikal is called the sea, simply out of respect, for its violent disposition, for the fact that the distant opposite shore often hides somewhere in a haze ... At the same time, the Maloye More and the Big Sea are distinguished. Small Sea is located between the northern coast of Olkhon and the mainland, everything else is the Big Sea.

Baikal water

Baikal water is unique and amazing, like Baikal itself. It is extraordinarily transparent, clean and oxygenated. In not so ancient times, it was considered curative, with its help diseases were treated. In spring, the transparency of Baikal water, measured with the Secchi disk (a white disk with a diameter of 30 cm), is 40 m (for comparison, in the Sargasso Sea, which is considered the standard of transparency, this value is 65 m). Later, when a massive algae bloom begins, the transparency of the water decreases, but in calm weather, the bottom is visible from the boat at a fairly decent depth. Such high transparency is explained by the fact that Baikal water, due to the activity of living organisms inhabiting it, is very weakly mineralized and close to distilled. The volume of water in Lake Baikal is about 23 thousand cubic kilometers, which is 20% of the world's fresh water reserves.

The origin of lake basins
Sedimentation in lakes

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

Each lake is made up 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 inhabiting the reservoir.

The origin of lake basins

Basins of lakes arise as a result of various relief-forming processes and are divided into several groups by origin.

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

Basins of tectonic origin are formed as a result of the movement of sections of the earth's crust. Many lakes, which have arisen in depressions of tectonic origin, occupy a vast area, are characterized by great depth and have an 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 extension and subsidence of the continental crust take place. Lake Baikal in Russia (which is the largest freshwater body of water and has the maximum depth among lakes -1620 m), Lake Biwa in Japan (known for the freshwater pearls mined in it) and others have a similar origin. Depressions are often confined to isometric troughs (Chad, Eyr) 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.

Basins of volcanic origin confined to craters and calderas extinct volcanoes or located among frozen lava fields. In the latter case, lake basins are formed when hot lava flows out from under a colder surface lava horizon, which contributes to the subsidence of the latter (this is how Yellowstone Lake was formed), or in the case of damming rivers and streams with lava or mud flow during volcanic eruptions. Depressions 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 of various groups of lake basins.

A large number of lake basins have glacial origin... Their formation can be associated with the activity of mountain and lowland glaciers. In the mountains, glacial lake basins are represented by moraine-dammed and tarred ones. Moraine dams are formed when river valleys are dammed by glaciers. Small picturesque lakes with clean and cold water are formed when the tarry depressions are filled with water.
On the plains, hollows of glacial origin are widespread in the territory subjected to Quaternary glaciation. Among them, one can distinguish depressions of exaration, glacial-accumulative and moraine-dammed origin. Examination basins are associated with negative relief forms developed by moving ice. 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 glacial plowing basins are found in the Scandinavian Peninsula in northern Canada. Glacial-accumulative basins are formed in the area of ​​development of moraine deposits. The lacustrine depressions in the moraine-lowland relief are wide, oval and shallow (Chudskoe, Ilmen); in the conditions of hilly-depression and hilly-ridged relief they have an irregular shape, islands, complex coastline, dissected by peninsulas and bays (Seliger). Moraine dam basins arise when a moraine preglacial river valley is dammed up (for example, Lake Saimaa in Finland).

In areas permafrost formed basins of thermokarst origin, owing their origin to the melting of fossil ice and frozen rocks and soil subsidence. Many basins of tundra lakes have such an origin. All of them are shallow and small in area. Another area of ​​development of thermokarst basins is the area of ​​distribution of quaternary fluvioglacial deposits. Here, during the melting of the ice sheets, huge blocks were buried under the layer of sediments carried by the melted glacial waters. dead ice... Many of them melted only after hundreds of years, and in their place there were basins filled with water.

Lakes basins of karst origin are formed in areas composed of soluble (karst) rocks. Dissolution of rocks leads to the formation of deep, but usually insignificant basins in area. Here, failures often occur due to the collapse of the vaults of underground karst cavities. Examples of karst basins are the famous "Proval" in Pyatigorsk (known from the novel by Ilf and Petrov "Twelve Chairs") and the lake. Fat in the French Alps, with a depth of -99 m with an area of ​​only 57 hectares.

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

Basins of fluvial origin associated with the geological activity of rivers. Most often these are old and delta lakes. Sometimes the formation of lakes is due to the obstruction of the river bed by alluvial sediments of another river. For example, the formation of Lake St. Croix (USA) is associated with the damming of the river. St. Croix alluvial deposits of the river. Mississippi. Due to the dynamism of erosional and accumulative fluvial processes and the small size of the 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 damming up by landslides, mountain falls 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 p. The Indus on the territory of modern Pakistan was dammed by a landslide caused by an earthquake, and six months later the "dam" collapsed, and the 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 rocks. 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 among the lakes in the world).
The process of damming the river with a powerful avalanche contributed to the formation of one of the "pearls" of the Caucasus - Lake Ritsa in Abkhazia. A giant landslide on the slope of Mount Pshegisha dammed up the Lashipsa River. The waters of the river flooded the gorge for more than 2 km (tracing a large tectonic fault in the strata of rocks), the water rose 130 m. From under a natural stone dam, a river with a different name - Yupshara (in Abkhazian "split") is knocked out.

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

Basins of coastal marine origin are formed mainly as a result of the separation of sea bays by bars from the sea water area during the movement of alongshore sediment flow. At the initial stage, the basin is filled with salty sea water, later formed salt Lake gradually desalinates.

Organogenic basins occur on sphagnum bogs of 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.

On a geologic time scale, lakes are relatively short-lived. The only exceptions are some lakes with depressions of tectonic origin, confined to active zones of the earth's crust, and large residual lakes. Over time, the basins are filled with sediment or waterlogged.

Sedimentation in lakes

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

In the lakes of humid regions, mainly silty-clayey sediments accumulate, often with a large amount of organic matter. Dead organisms, as well as material carried into the lake, are deposited at the bottom and form gittia(from Swedish gyttja - silt, mud) - lacustrine sediments, consisting of organic remains. The organic matter of gittia is formed mainly due to the decay products of plant and animal organisms living in the 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. Gittia is also called sapropel(from the Greek sapros - rotten and pelos - silt, mud - "putrid silt"). In Lake Nero, located near the city of Rostov-Yaroslavsky (Rostov the Great), the sapropel layer 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, the lakes are closed-flowing with intense evaporation. Since rivers and underground waters always bring salt, and only evaporate pure water, then there is a gradual increase in the salinity of lake waters. The concentration of salts can increase so significantly that salt precipitates from the water oversaturated with salts (brine) to the bottom of the lake (self-sedimentary lakes). With salinization of continental lakes, carbonate, soda, sulfate, salt and other chemogenic deposits accumulate. In Russia, modern soda lakes are known in Transbaikalia and in Western Siberia; overseas, Lake Natron in Tanzania and Lake Searles in California are well known. Deposits of natural soda are confined to the fossil deposits of such lakes.
In general, halogen-carbonate deposits, poor in organic matter, are characteristic of arid regions.

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

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

Study of the location, area and depth indicators of the largest domestic water bodies - Lake Baikal, Ladoga and Onega lakes.

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

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

In particular, in the Vilenovsky hollows, West Siberian Plain and in the northwestern layer of Europe - in Karelia. All of these areas are too humid. In the south, in the steppe and semi-sedimentary zone with a mild 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 removed.

Hydrographic characteristics of large lakes in Russia

There are different lakes and pool sources.

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

Ice-tectonic lake basins were created as a result of treatment of 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 the mountain valleys, there was a lake of the 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 stones being hammered. When ice melts on the surface of the permafrost, shallow, plate-like waters also form. Lake people are located on the floodplains of low-lying rivers. On the Black coast and Sea of ​​Azov there are estuary lakes.

All major and largest lakes Russia is often used in the national economy. Catch and catch in them. Especially many fish, including the most valuable sturgeon, find their way to the Caspian Sea.

The harvest in Baikal is omul. Lakes are also used for navigation - geoglobus.ru. Numerous minerals were acquired in the lakes of the lakes: oil and myrbilite in the Caspian Lake, salt in Elton and Baskunchak. Freshwater lake water 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 of 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-salt lakes;
5) Altai - sea view of lakes (Teletskoe, Markakol);
6) Zabaikalsky - the remaining lakes;
7) Lower Amur lakes, which have a hydrological connection with the Amur River;
8) yakuti - lakes from thermocouples;
9) Lake Kamchatka - lakes of volcanic origin (Kronotsky, Kuril).

It has no direct connection to the sea. Lakes cover about 1.8% of the land surface, but are extremely unevenly distributed.

The lakes are very diverse in size. Especially large ones are even called seas ().

By the origin of the lake depressions, there are:

• tectonic... These are usually the deepest lakes formed on site (Baikal - depth 1620 m; - 1470 m). The depth of most lakes of tectonic origin is usually less than 1000 m. The deepest lakes lie below the ocean level (the bottom of Baikal is 1165 m below sea level;
• volcanic... These are lakes formed in craters or in calderas, as well as in depressions on the surface of lava flows: lakes, Lake Kronotskoye, lakes and Java;
• glacial... These are lakes formed in areas exposed to continental glaciation... They are created either as a result, or as a result of the glacial. The erosional glacial type includes lakes located in, in (), (Russia), in the northeastern. The shape of these lakes is long, narrow, and they are elongated in the direction of movement of the glacier. Lakes that have arisen as a result of lacustrine accumulation are confined to areas of hilly-moraine relief (see Glaciation). Some lakes occupy lowlands between hills and are usually lobed and shallow (). Others arose among the moraine relief. They are wide, oval and small:, White;
• karst... They are located in or in karst sinkholes and occur in areas composed of soluble rocks. Thermokarst basins are formed in the regions, owing to the origin of the melting of fossil and frozen ice, as well as soil subsidence. Many tundra lakes are thermokarst;
• coastal lakes... They were formed as a result of the separation of a part of the sea from the rest by deposits of sand or silt. There are many estuaries and lagoons on the coast and;
• dammed lakes occur when the watercourse is dammed by landslides, landslides, lava flows, etc. So in 1911, Lake Sarez was formed with a depth of 505 m. It was dammed by a colossal mountain collapse. Dammed lakes are also frequent. Many lakes of Sikhote-Alin (Russia), Lake Sevan, Lake Tana () were formed as a result of damming the river with lava flows;
• - ponds and;
• oxbow lakes formed during meandering of river beds.

The water mass of lakes is mainly of origin and enters the lake by condensation on the water surface, when water flows from rivers and streams and due to groundwater supply. The discharge of lake water is carried out through evaporation, and flow into. In some lakes, the modern water mass has replaced the sea mass that occupied the basin in the recent geological past. On the site of the modern, Ladoga and, as well as in the glacial time, there was the Yoldiev Sea. After its disintegration, lakes were formed, first with salty sea water, and then with fresh water. Such lakes are called relict or residual. The animals that live there adapt to the lake habitat.

According to the arrival and discharge of the water mass, all lakes are divided into:

• well flowing... Rivers flow into and out of them. The water in these lakes is constantly changing. Such lakes are located in zones of excessive atmospheric moisture (Baikal, Geneva);
• low-flow... Rivers also flow into them, but much less flows out of them. These lakes are located in an area with insufficient moisture (Balaton, Tanganyika);
• drainless... Formed in zones and. Rivers flow into such lakes, but not a single one flows out (, Dead Sea);
• deaf... They feed on rain or melt water, since rivers do not flow into them and do not flow out of them. These are small lakes and zones or craters. Outside of these groups were karst lakes, since their feeding is carried out primarily at the expense of.

By its own lake can also be divided into:

• insipid(their salinity does not exceed 1% o);
• salty(their salinity is from 1 to 47% o);
• (their salinity exceeds 47% o). Salts can precipitate from them (Elton, Baskunchak).

Salinity of the Dead Lake 270% ©.

Lakes. In countries with warm climates, it fluctuates slightly throughout the year. In summer, the water temperature decreases with depth. In winter, the upper layer of water cools below freezing, and the lake is covered with ice, and the water temperature rises with depth. How saltier water, the lower its freezing point. Large and deep lakes do not freeze longer than shallow ones. So, Baikal freezes only at the beginning of January, when all the water bodies around are already covered with ice for a long time.

According to their biological properties, the lakes are divided into:

• to a depth of 1 m thickets of sedge, arrowhead, etc. are located;
• to a depth of 2-3 m - reeds, reeds;
• to a depth of 4m - submerged plants: pondweed and others.
• nutrient-poor lakes. They are transparent, deep and cold;
• lakes with rich. They are usually shallow, well warmed up;
• lakes, poor in life, with brown water in which there is not enough oxygen.

Most lakes are characterized by abundant vegetation, especially in the coastal zone. It is arranged in tiers:
Lakes go through several stages in their development. In more humid climate they overgrow and turn into. In dry climates, lakes dry up; they become salty and with poor vegetation.

The movement of water in lakes, as well as in the seas, manifests itself in the form of currents, but very slow, as well as waves that reach large sizes only in large lakes. For example, up to 2-2.5 m are observed in and on. With differences in different parts of the lake, standing waves are also observed.

Lakes play a very important role both in nature and in human life. Like the seas, they have a warming effect on the world around them. Lakes also affect the relief, as they also carry out erosional and accumulative work.

The uniqueness of natural lakes lies in a number of their special characteristics. They are characterized by slow water exchange, free thermal regime, peculiar chemical composition, drops in water level.

In addition, they create their own microclimate and cause changes in the adjacent landscape. They accumulate mineral and organic substances, some of which are valuable and useful.

Geographic feature "lake" (meaning)

There are about 5,000,000 lakes in our world. Lakes on Globe occupy almost 2% of the surface, which is almost 2.6 million km 3. As a component of the hydrosphere, the classic natural lakes, are reservoirs of natural origin, which are lake bowls with water that do not have direct contact (contact) with the sea or ocean. There is a whole science that studies them - limnology. However, there are also man-made lakes that have arisen as a result of human activities.

If we consider the lake as geographic feature, then its definition becomes clearer: it is a pit on land with closed edges, into which flowing water falls and as a result accumulates there.

Characteristics of lakes

To give a specific lake an accurate description, you need to determine its origin, position (above or below the ground), type of water balance (waste or not), mineralization parameters (fresh or not), its chemical composition etc.

In addition, the following parameters must be accurately determined: the total area of ​​the water surface, the total length of the coastline, the maximum distance between opposite banks, the average width of the lake (calculated by dividing the area by the previous indicator), the volume of water that fills it, its average and maximum depth ...

Lake types by origin

The generally accepted classification of lakes according to the factor of origin is as follows:

1. Anthropogenic (artificial) - created by man;
2. Natural - arose naturally (exogenous or endogenous - either from within the Earth, or as a result of processes on its surface), without human intervention.

Natural lakes, in turn, have their own division according to the principle of origin:

• Tectonic - cracks in the earth's crust that have arisen for one reason or another are filled with water. The most famous lake of this type is Baikal.
• Glacial - the glacier melts and the resulting water creates a lake in the basin of the glacier itself or any other. Such lakes, for example, in Karelia and Finland: lakes appeared along the trajectory of the glacier along tectonic cracks.
• Old woman, lagoon or estuary - a decrease in water level cuts off part of the river or ocean.
• Karst, suffusion, thermokarst, eolian - leaching, subsidence, thawing, blowing, respectively, create a depression that is filled with water.
• A dam occurs when a landslide or earthquake cuts off a part of the water surface from the main water body by a land bridge.
• Water often collects in mountain basins and craters of volcanoes or channels of their eruption.
• Other.

The value of lakes in nature and for humans

Lakes are natural reservoirs of water that can regulate river flow: take in excess water and, conversely, give away part of it with a general decrease in the water level in the river. A large mass of water has a large thermal inertia, the effect of which can significantly soften the climate of nearby territories.

The lakes are important subject for fishing, organizing salt extraction, laying waterways. Water from lakes is often used for water supply. The reservoirs can be used to organize an energy reservoir for a hydroelectric plant. Sapropels are mined from them. Some lake mud has medicinal properties and are used in medicine. The importance of lakes in the ecosystem of the planet can hardly be overestimated; they are an organic element of the entire natural mechanism.

The largest lakes in the world

Among the lakes, there are two main record holders:

The Caspian Sea is the largest in area (376,000 km 2), but relatively shallow (30 m);

(Lake Baikal)

Baikal is a depth record (1620 meters!).

Tectonic lakes are the average size record holders in the lake community.

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. This is how the deepest lake in the world - Baikal and the largest in area - the Caspian Sea were formed. In the East African rift system, a large rift has formed, where a number of lakes are concentrated:

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

By their form, tectonic lakes are very narrow and deep bodies of water, with distinct shores. Their bottom is usually located below ocean level. It has a clear outline that resembles a curved, broken, curved line. At the bottom, you can find traces of various forms of relief. The shores of tectonic lakes are composed of hard rocks, and they are poorly 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

The Suna river basin has both large and medium tectonic lakes:

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

Among the lakes of tectonic origin in Kyrgyzstan, Son-Kul, Chatyr-Kul and Issyk-Kul should be named. On the territory of the Trans-Ural Plain, there are also several lakes formed as a result of a tectonic fault in 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, Biwa and Van.

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

Tectonic lakes are located on plains or in the area of ​​intermontane troughs. They are of considerable depth and enormous size. Not only folds of the lithosphere, but also ruptures of the earth's crust take part in the formation of lake depressions. The bottom of tectonic lakes is below ocean level. Such reservoirs are found on all continents of the earth, but their greatest number is located precisely in the fault zone of the earth's crust.