Tectonic lakes. Tectonic lakes: examples, list

They are formed in places of faults and shifts of the earth's crust. As a rule, these are deep narrow reservoirs with straight sheer shores, located in deep through gorges. Kurile Lake is located in the south of Kamchatka in a deep picturesque basin surrounded by mountains. The greatest depth of the lake is 306 m. Its banks are steep. Numerous mountain streams flow from them. The lake is sewage, the Ozernaya River originates from it. Hot springs come to the surface along the shores of the lake, and in its middle there is an island called the Heart-stone. Not far from the lake there is a unique outcrop of pumice stones, which are called Kutkhin Baty. Currently, the lake has been declared a nature reserve and a zoological monument of nature.

The profile of the bottom of tectonic lakes is sharply defined and has the form of a broken curve. Glacial deposits and processes of sediment accumulation have little changed the clarity of the tectonic lines of the lake basin. The influence of the glacier on the formation of the basin can be noticeable, it leaves traces of its presence in the form of scars, sheep's foreheads, which are clearly visible on the rocky shores and islands. The shores of the lakes are composed mainly of hard stone rocks that are weakly susceptible to erosion, which is one of the reasons for the weak process of sedimentation. 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 heterogeneous: during the period of the greatest heating of 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 suns are large and medium-sized: Palye, Sundozero, Sandal, as well as very small lakes Salvilambi and Randozero, located on private watersheds of lakes Palye and Sandal.

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

There are many lakes in the forest-steppe Trans-Urals. Here are such large reservoirs as Uelgi, Shablish, Argayash, B. Kuyash, Kaldy, Sugoyak, Tishki, etc. The depths of lakes in the Trans-Ural Plain noticeably decrease and do not exceed 8-10 m. By 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 ancient hollows of river flow (Etkul, Peschanoe, Alakul, Kamyshnoe, etc.).

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

In addition, they create their own microclimate and cause changes in the surrounding landscape. They accumulate mineral and organic substances, some of them have value and usefulness.

Geographical object "lake" (value)

There are about 5,000,000 lakes in our world. Lakes on the globe occupy almost 2% of the surface, which is almost 2.6 million km3. As a component of the hydrosphere, classical 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 anthropogenic lakes that have arisen as a result of human activities.

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

Characteristics of lakes

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

In addition, you need to accurately determine the following parameters: the total area of ​​​​the water mirror, 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 .

Types of lakes 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. by the most famous lake 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.
• An oxbow, lagoon or estuary - a decrease in the 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 dammed lake occurs when a landslide or earthquake cuts off part of the water surface from the main water body with a land bridge.
• In mountain basins and craters of volcanoes or channels of their eruption, water often also collects.
• And others.

The importance 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 it away with a general decrease in the water level in the river. A large water mass has a large thermal inertia, the action of which can significantly moderate the climate of nearby territories.

Lakes are an important object for fishing, organizing the extraction of salt, laying waterways. Water from lakes is often used for water supply. Reservoirs can be used to organize an energy reservoir for a hydroelectric installation. Sapropels are extracted from them. Some lake muds have medicinal properties and are used in medicine. The importance of lakes in the planet's ecosystem 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 - depth record (1620 meters!).

The average record holders in terms of size in the lake brotherhood are tectonic lakes.

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. basins - landforms 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 are of ancient age. Characteristic 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.

Basins of volcanic origin confined to craters and calderas extinct volcanoes or located among the frozen 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 of various groups of 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 clear and cold water are formed.
On the plains, basins of glacial origin are common in the territory subjected to 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 on the territory of the 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 the conditions of a hilly-recessional and hilly-ridged relief, they have an irregular shape, islands, and a 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, basins of thermokarst 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. Girot in the 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 of 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 (tracing a large tectonic fault in the strata of rocks) for more than 2 km, the water rose by 130 m. A river with a different name, Yupshara (in Abkhazian “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 river; the largest in Russia is the Bratsk reservoir on the river Angara). 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 are formed mainly as a result of the separation of sea bays by bars from the sea in the process of movement of the alongshore sediment flow. At the initial stage, the basin is filled with salty sea waters; later, the formed salt lake is gradually desalinated.

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 regions, predominantly silty-argillaceous deposits 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 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 salt, and only pure water, then 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 are known in Transbaikalia and 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.

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

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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.

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 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

There are different lakes and sources of 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 connected with continental ice. Many caves are located between the hills of the sea: Seliger, Valdai.

Because of the landslides in the 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 permafrost, shallow waters plate-like. Lake people are located on the flood plains of low-lying rivers. On the Black 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 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) northwestern lake, iceberg iceberg;
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).

- a reservoir formed on the surface of the land in a natural depression. Since the lake does not have a direct connection with the ocean, it is a reservoir of slow water exchange.

The total area of ​​lakes on the globe- about 2.7 million km 3, which is 1.8% of the land surface.

The main characteristics of the lake:

• lake area - water surface area;
• length coastline - water edge length;
• lake length - the shortest distance between the two most distant points on a coastline, average width - ratio of area to length;
• lake volume - the volume of the basin filled with water;
• average depth - ratio of water mass volume to area;
• maximum depth - found by direct measurements.

The largest lake in terms of water surface area on Earth is the Caspian (376 thousand km 2 at a water level of 28 m), and the deepest is Baikal (1620 m).

The characteristics of the largest lakes in the world are given in Table. one.

In each lake, three interconnected components are distinguished: the basin, the water mass, the vegetation and fauna of the reservoir.

Lakes of the world

By position lake basin lakes are divided into ground and underground. The latter are sometimes filled with juvenile water. The subglacial lake in Antarctica can also be classified as an underground lake.

Lake basins can be like endogenous, and exogenous origin, which most significantly affects their size, shape, water regime.

The largest lake basins. They can be located in tectonic depressions (Ilmen), in foothill and intermountain troughs, in grabens (Baikal, Nyasa, Tanganyika). Most large lake basins have a complex tectonic origin, both discontinuous and folded movements are involved in their formation (Issyk-Kul, Balkhash, Victoria, etc.). All tectonic lakes are large, and most of them have significant depths, steep rocky slopes. The bottoms of many deep lakes lie below the level of the World Ocean, and the mirror of the oxen is above the level. Certain regularities are observed in the location of tectonic lakes: they are concentrated along the faults of the earth's crust, either in rift zones (Syrian-African, Baikal), or frame shields: along the Canadian Shield there are the Great Bear Lake, the Great Slave Lake, the Great North American Lakes, along the Baltic Shield - Onega, Ladoga, etc.

Volcanic lakes occupy craters and calderas of extinct volcanoes (Kronopkoye Lake in Kamchatka, lakes of Java, New Zealand).

Along with lake basins created by the internal processes of the Earth, there are very numerous lake baths formed due to exogenous processes.

Among them, the most common glacial lakes on the plains and in the mountains, located both in hollows plowed by the glacier, and in depressions between hills with uneven deposition of moraine. The destructive activity of ancient glaciers owes its origin to the lakes of Karelia and Finland, which are elongated in the direction of glacier movement from northwest to southeast along tectonic cracks. In fact, Ladoga, Onega and other lakes have a mixed glacial-tectonic origin. The glacial basins in the mountains include numerous, but small car lakes located in bowl-shaped depressions on the slopes of mountains below the snow line (in the Alps, in the Caucasus, Altai), and trough lakes - in trough-shaped glacial valleys in the mountains.

The uneven accumulation of glacial deposits on the plains is associated with lakes among the hilly and moraine relief: in the northwest of the East European Plain, especially on the Valdai Upland, in the Baltic States, Poland, Germany, Canada and in the north of the USA. These lakes are usually shallow, wide, with lobed shores, with islands (Seliger, Valdai, etc.). In the mountains, such lakes arose on the site of former tongues of glaciers (Como, Garda, Würm in the Alps). In areas of ancient glaciation, there are numerous lakes in the hollows of the flow of melted glacial waters, they are elongated, trough-shaped, usually small and shallow (for example, Dolgoye, Krugloye - near Moscow).

Karst lakes are formed in places where rocks are leached by underground and partly surface waters. They are deep, but small, often rounded in shape (in the Crimea, the Caucasus, in the Dinaric and other mountainous regions).

Suffusion lakes are formed in basins of subsiding origin at the site of intensive removal of fine earth and mineral particles by groundwater (south of Western Siberia).

Thermokarst Lakes are created when permafrost is burned or ice melts. Thanks to them, the Kolyma Lowland is one of the most lake regions in Russia. Many relict thermokarst lake basins are located in the northwest of the East European Plain in the former periglacial zone.

eolian lakes arise in blowout basins (Lake Teke in Kazakhstan).

Zaprudnye lakes are formed in the mountains, often after earthquakes, as a result of landslides and landslides blocking river valleys (Lake Sarez in the Murgab valley in the Pamirs).

In the valleys of lowland rivers, the most numerous are floodplain oxbow lakes of a characteristic horseshoe shape, formed as a result of meandering of rivers and subsequent straightening of channels; when rivers dry up in bochagas - reaches, river lakes are formed; in river deltas there are small ilmen lakes, in place of channels, often overgrown with reeds and reeds (ilmens of the Volga delta, lakes of the Kuban floodplains).

On the low coasts of the seas, coastal lakes are characteristic in place of estuaries and lagoons, if the latter are separated from the sea by sandy alluvial barriers: spits, bars.

A special type are organogenic lakes among swamps and coral buildings.

These are the main genetic types of lake basins, determined by natural processes. Their location on the continents is presented in Table. 2. But recently, more and more "man-made" lakes created by man have appeared - the so-called anthropogenic lakes: lakes - reservoirs on rivers, lakes - ponds in quarries, in salt mines, on the site of peat mining.

By genesis of water masses There are two types of lakes. Some have water of atmospheric origin: precipitation, river and groundwater. Such lakes insipid, although in dry climates they can eventually become salty.

Other lakes were part of the World Ocean - these are relic salty lakes (Caspian, Aral). But even in such lakes, the primary sea ​​water can be strongly transformed and even completely displaced and replaced by atmospheric waters (Ladoga and others).

Table 2. Distribution of the main genetic groups of lakes by continents and parts of the world

depending from water balance, t.s. According to the conditions of inflow and runoff, lakes are divided into waste and non-drainage. Lakes that discharge part of their waters in the form of river runoff - sewage; a special case of them are flowing lakes. Many rivers can flow into the lake, but only one flows out (the Angara from Lake Baikal, the Neva from Lake Ladoga, etc.). Lakes that do not have a runoff into the oceans - drainless(Caspian, Aral, Big Salt). The water level in such lakes is subject to fluctuations of different duration, which is primarily due to long-term and seasonal climate changes. At the same time, the morphometric characteristics of lakes and the properties of water masses change. This is especially noticeable on lakes in arid regions, which are predicted to have long cycles of humidification and aridity of the climate.

The waters of the lakes, like others natural waters, are characterized by different chemical composition and varying degrees of mineralization.

According to the composition of salts in the water, the lakes are divided into three types: carbonate, sulfate, chloride.

By degree of mineralization lakes are divided into insipid(less than 1% o), brackish(1-24.7% s), salty(24.7-47% o) and mineral(more than 47% c). Baikal can serve as an example of a fresh lake, the salinity of which is 0.1% c \ brackish - the Caspian Sea - 12-13% o, the Big Salt - 137-300% o, the Dead Sea - 260-270% o, in some years - up to 310% s.

In the distribution of lakes with different degrees of mineralization on the earth's surface, geographic zoning is traced, due to the coefficient of moisture. In addition, those lakes into which rivers flow are distinguished by low salinity.

However, the degree of mineralization can be different within the same lake. So, for example, in drainless lake Balkhash, located in the arid zone, in the western part, where the river flows. Or, the water is fresh, and in the eastern part, which is connected to the western part only by a narrow (4 km) shallow strait, the water is brackish.

When the lakes are oversaturated from the brine, the salts begin to precipitate and crystallize. Such mineral lakes are called self-planting(for example, Elton, Baskunchak). mineral lakes, in which lamellar finely dispersed needles are deposited, are known as mud.

plays an important role in the life of lakes thermal regime.

Fresh lakes of the hot thermal zone are characterized by the warmest water near the surface, with depth it gradually decreases. This distribution of temperature over depth is called direct thermal stratification. Lakes of the cold thermal zone have the coldest (about 0 ° C) and light water at the top for almost the entire year; with depth, the water temperature rises (up to 4 ° C), the water becomes denser, heavier. This distribution of temperature over depth is called reverse thermal stratification. Lakes of the temperate thermal zone have a variable stratification according to the seasons of the year: direct in summer, reverse in winter. In spring and autumn there come moments when the vertical temperature is the same (4 °C) at different depths. The phenomenon of temperature constancy over depth is called homothermy(spring and autumn).

The annual thermal cycle in lakes of the temperate zone is divided into four periods: spring heating (from 0 to 4 °C) is carried out due to convective mixing; summer heating (from 4 °C to maximum temperature) - by molecular heat conduction; autumn cooling (from maximum temperature to 4 °C) - by convective mixing; winter cooling (from 4 to 0 ° C) - again by molecular heat conduction.

In the winter period of freezing lakes, the same three phases are distinguished as in rivers: freezing, freezing, opening. The process of formation and melting of ice is similar to rivers. The lakes are usually covered with ice for 2-3 weeks longer than the rivers of the region. The thermal regime of freezing salt lakes resembles that of the seas and oceans.

Dynamic phenomena in lakes include currents, waves and seiches. Stock currents occur when a river flows into a lake and outflow of water from the lake into the river. In flowing lakes, they can be traced throughout the entire water area of ​​the lake, in stagnant lakes - in areas adjacent to the mouth or source of the river.

The height of the waves on the lake is less, but the steepness is greater compared to the seas and oceans.

The movement of water in lakes, along with dense convection, contributes to the mixing of water, the penetration of oxygen into the lower layers, and the uniform distribution of nutrients, which is important for a wide variety of lake inhabitants.

By nutritional properties of the water mass and the conditions for the development of life, lakes are divided into three biological types: oligotrophic, eutrophic, and dystrophic.

Oligotrophic- low-nutrient lakes. These are large deep transparent lakes with greenish-blue water, rich in oxygen, so organic residues are intensively mineralized. Due to the small amount of biogenic elements, they are poor in plankton. Life is not rich, but there are fish, crustaceans. It's many mountain lakes, Baikal, Geneva, etc.

Eutrophic lakes have a high content of nutrients, especially nitrogen and phosphorus compounds, are shallow (up to 1015 m), well heated, with brownish-green water. The oxygen content decreases with depth, which is why fish and other animals die in winter. The bottom is peaty or silty with an abundance of organic remains. In summer, there is a "bloom" of water due to the strong development of phytoplankton. The lakes are rich in flora and fauna. They are most common in forest-steppe and steppe zones.

Dystrophic lakes are poor in nutrients and oxygen, they are shallow. The water in them is acidic, slightly transparent, brown due to the abundance of humic acids. The bottom is peaty, there are few phytoplankton and higher aquatic vegetation, animals too. These lakes are common in heavily wetlands.

In the last decade, under the conditions of increased supply of phosphorus and nitrogen compounds from the fields, as well as the discharge of wastewater from some industrial enterprises, eutrophication of lakes has been observed. The first sign of this unfavorable phenomenon is a strong bloom of blue-green algae, then the amount of oxygen in the reservoir decreases, silts form, and hydrogen sulfide appears. All this will create unfavorable conditions for the life of fish, waterfowl, etc.

The evolution of lakes occurs in different ways in wet and dry climates: in the first case, they gradually turn into swamps, in the second, into salt marshes.

In a humid (humid) climate, the leading role in filling the lake and turning it into a swamp belongs to vegetation, partly to the remains of the animal population, which together form organic remains. Temporary streams and rivers bring mineral deposits. Small lakes with gently sloping shores are overgrown by pushing vegetative ecological zones from the periphery to the center. Eventually the lake becomes a grassy fens.

Deep lakes with steep banks overgrow in a different way: by growing from above alloys(quick) - a layer of living and dead plants. It is based on plants with long rhizomes (cinquefoil, watch, calla), and other herbaceous plants and even shrubs (alder, willow) settle on a grid of rhizomes. The raft first appears near the coast, protected from the wind, where there is no excitement, and gradually moves towards the lake, increasing in power. Part of the plants dies, falls to the bottom, forming peat. Gradually, only “windows” of water remain in the quagmire, and then they disappear, although the basin is not yet filled with sediments, and only with time does the raft merge with a layer of peat.

In dry climates, lakes eventually become salt marshes. This is facilitated by an insignificant amount of precipitation, intense evaporation, a decrease in the inflow of river waters, and the deposition of solid sediments brought by rivers and dust storms. As a result, the water mass of the lake decreases, the level decreases, the area decreases, the salt concentration increases, and even a fresh lake can first turn into a salt lake (Big Salt Lake in North America), and then to the salt marsh.

Lakes, especially large ones, have a softening effect on the climate of the surrounding areas: it is warmer in winter and cooler in summer. So, at coastal weather stations near Lake Baikal, the temperature in winter is 8-10 °С higher, and in summer by 6-8 °С lower than at stations outside the influence of the lake. The air humidity near the lake is higher due to increased evaporation.

Not directly connected to the sea. Lakes occupy about 1.8% of the land surface, but are extremely unevenly distributed.

The area of ​​the lake is very diverse. Especially large ones are even called seas ().

According to the origin of lake depressions, there are:

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

The water mass of lakes is predominantly of origin and enters the lake by condensation on the water surface, when water enters from rivers and streams and due to ground feeding. The consumption of lake water is carried out through evaporation, and runoff in. In some lakes, the modern water mass has replaced the marine one, which occupied the basin in the recent geological past. On the site of modern, Ladoga and, as well as in ice age, there was the Yoldian Sea. After its collapse, lakes were formed, first with salty sea, and then with fresh water. Such lakes are called relict or residual. Animals that live there adapt to lake habitat conditions.

According to the inflow and outflow of 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 of them flow out. These lakes are located in a zone 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 these groups were karst lakes, since their nutrition is carried out primarily at the expense of.

According to their lakes 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). Of these, salts can precipitate (Elton, Baskunchak).

The salinity of the Dead Lake is 270% ©.

Ozer. In countries with a warm climate, it fluctuates slightly throughout the year. In summer, the water temperature decreases with depth. In winter, the top layer of water cools below freezing, and the lake is covered with ice, and the temperature of the water rises with depth. The saltier the 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 have long been covered with ice.

According to their biological properties, lakes are divided into:

• up to a depth of 1 m there are thickets of sedge, arrowhead, etc.;
• to a depth of 2-3 m - reeds, reeds;
• up to a depth of 4 m - submerged plants: pondweeds and others.
• lakes poor in nutrients. They are transparent, deep and cold;
• lakes with a rich They are usually shallow, well warmed up;
• lakes poor in life, with brown water lacking oxygen.

Most lakes are characterized by abundant vegetation, especially in the coastal zone. It is arranged in tiers:
Lakes in their development go through several stages. In a wetter climate, they overgrow and turn into. In a dry climate, 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, reaching 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. Lakes also influence the relief, as they also carry out erosive and accumulative work.