Glacial tectonic lakes are examples. 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 type 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 are formed in places of faults and shifts in the earth's 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 warming 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 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 largest lakes in 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 deepest 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 temperate zone.

Geography of Lake Baikal

Lake Baikal is located in the south of Eastern Siberia. In the shape 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. Length coastline about 2000 km. The area of ​​the water table, determined at the water edge of 454 m above sea level, 31470 square kilometers. Maximum depth lakes 1637 m, average depth - 730 m. 336 permanent rivers and streams flow into Baikal, while half of the water flowing into the lake is brought by the Selenga. 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 the 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.

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 most deep lakes formed on site (Baikal - depth 1620 m; - 1470 m). The depth of most lakes tectonic origin usually less than 1000 m. Donya of the deepest lakes lie below sea 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, Kronotskoe lake on, lakes and Java;
• glacial... These are lakes formed in territories subjected 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. Is not large lakes, and zones or crater. Outside of these groups were karst lakes, since their food 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 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. 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 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 climates, 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... Lakes also affect the relief, as they also carry out erosional and accumulative work.

They are formed in places of faults and shifts in the earth's 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 and looks like a broken curve. Glacial deposits and the 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 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 warming 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 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 largest lakes in Kyrgyzstan: Issyk-Kul, Son-Kul and Chatyr-Kul are formed tectonically.

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.).

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- a body of water 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 delayed water exchange.

The total area of ​​lakes in 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 mirror area;
• coastline length - length of the water's edge;
• lake length - the shortest distance between the two most distant points of the coastline, average width - area to length ratio;
• lake volume - the volume of the basin filled with water;
• average depth - the ratio of the volume of the water mass to the area;
• maximum depth - is 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 Lake Baikal (1620 m).

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

In each lake, three interrelated components are distinguished: a basin, water mass, vegetation and animal world reservoir.

Lakes of the world

By position lacustrine hollows lakes are subdivided into ground and underground. The latter are sometimes filled with juvenile water. The subglacial lake in Antarctica can also be referred to the number of underground lakes.

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 intermontane troughs, in grabens (Baikal, Nyasa, Tanganyika). Most of the large lacustrine basins have a complex tectonic origin, both discontinuous and folded movements (Issyk-Kul, Balkhash, Victoria, etc.) are involved in their formation. All tectonic lakes are large in size, and most of them are also significant depths, steep rocky slopes. The bottoms of many deep lakes lie below the level of the World Ocean, and the mirror of the ox - above the level. In the location of tectonic lakes, certain patterns are observed: they are concentrated along the faults of the earth's crust either in rift zones (Syrian-African, Baikal), or are framed by shields: along the Canadian Shield there are Big Bear Lake, Big Slave, Great North American Lakes, along the Baltic Shield - Onega, Ladoga, etc.

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

Along with the 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 plains and in mountains, located both in hollows plowed by glaciers, and in depressions between hills with uneven deposition of moraine. The destructive activity of ancient glaciers owes their origin to the lakes of Karelia and Finland, which are elongated in the direction of movement of the glacier from northwest to southeast along tectonic cracks. In fact, Ladoga, Onega and other lakes have a mixed glacial-tectonic origin. Glacial basins in the mountains include numerous, but small tar lakes located in bowl-shaped depressions on the slopes of mountains below the snow border (in the Alps, 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 in the Valdai Upland, in the Baltic States, Poland, Germany, Canada and in the north of the United States. These lakes are usually shallow, wide, with lobed shores, with islands (Seliger, Valdai, etc.). In the mountains, such lakes arose on the site of the former tongues of glaciers (Como, Garda, Wurmskoe in the Alps). In the areas of ancient glaciations, there are numerous lakes in the troughs of the melt glacial waters runoff, they are elongated, trough-shaped, usually small and shallow (for example, Dolgoe, 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 depressions of subsidence origin at the place of intensive removal of fine-earth and mineral particles by groundwater (south of Western Siberia).

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

Aeolian lakes arise in the blow-out hollows (Lake Teke in Kazakhstan).

Zaprudnye lakes are formed in the mountains, often after earthquakes, as a result of avalanches 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 the subsequent straightening of channels; when the rivers dry up, river lakes are formed in the basins - reaches; in the river deltas there are shallow lakes-ilmeni, in place of channels, often overgrown with reeds and reeds (ilmeni of the Volga delta, lakes of the Kuban floodplain).

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

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

These are the main genetic types of lake basins, caused by natural processes. Their location on the continents is presented in table. 2. But lately there are more and more “man-made” lakes created by man - so-called anthropogenic lakes: lakes - reservoirs on rivers, lakes - ponds in quarries, in salt mines, in the place 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 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, etc.).

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

Depending on on the water balance, t. s. according to the conditions of inflow and runoff, the lakes are divided into drainage and internal 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 (Angara from Lake Baikal, Neva from Lake Ladoga and etc.). Lakes that do not have a drain into the World Ocean - 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 the lakes and the properties of water masses change. This is especially noticeable on lakes in arid regions, which promise long cycles of moisture and aridity of the climate.

Lake waters 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 subdivided into insipid(less than 1% o), brackish(1-24.7% s), salty(24.7-47% o) and mineral(more than 47% c). An example of a fresh lake is Baikal, the salinity of which is 0.1% c \ salty - Caspian seafood - 12-13% o, Big Salt - 137-300% o, the Dead Sea - 260-270% o, in some years - up to 310% c.

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

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

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

An important role in the life of lakes is played by thermal regime.

Fresh lakes of the hot heat zone are characterized by the most warm water at the surface, it gradually decreases with depth. This temperature distribution over depth is called direct thermal stratification. The lakes of the cold heat zone have the coldest (about 0 ° C) and lightest water at the top almost all year round; with depth, the water temperature rises (up to 4 ° C), the water becomes denser and heavier. This temperature distribution over depth is called reverse thermal stratification. The lakes of the temperate heat zone have variable stratification according to the seasons of the year: direct in summer, reverse in winter. In spring and autumn, there come such 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 the 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 ° С) - 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 up, opening. The process of ice formation and melting is similar to that of rivers. The lakes are usually covered with ice for 2-3 weeks longer than the rivers of the region. The thermal regime of the freezing salt lakes resembles the regime of the seas and oceans.

Dynamic phenomena in lakes include currents, waves and seiches. Stock currents arise when the river flows into the lake and the 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 non-flowing 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 even distribution of nutrients, which is important for a very diverse lake dweller.

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

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

Eutrophic the lakes have a high content of nutrients, especially nitrogen and phosphorus compounds, shallow (up to 1015 m), well warmed up, with brownish-green water. The oxygen content decreases with depth, which is why fish and other animals are killed in winter. The bottom is peaty or silty with an abundance of organic remains. In summer, water blooms 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 the 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, as well as animals. These lakes are common in highly wetlands.

In the last decade, under conditions of increased input 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 are formed, and hydrogen sulfide appears. All this will create unfavorable conditions for the life of fish, waterfowl, etc.

Evolution of lakes occurs in different ways in a humid and dry climate: 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 remnants of the animal population, which together form organic residues. Temporary streams and rivers carry mineral deposits. Shallow lakes with gently sloping shores are overgrown by pushing vegetation ecological zones from the periphery to the center. Ultimately, the lake becomes a grassy lowland bog.

Deep lakes with steep banks are overgrown differently: by growing from above alloys(zybuna) - 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 the net of rhizomes. The raft first appears at the shores protected from the wind, where there is no roughness, and gradually approaches the lake, increasing in thickness. Some of the plants die off, fall to the bottom, forming peat. Gradually, only “windows” of water remain in the raft, and then they disappear, although the basin is not yet filled with sediments, and only with time the raft merges with the peat layer.

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, 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 concentration of salts increases, and even a fresh lake can first turn into a salt lake (Big Salt Lake v North America), and then into a salt marsh.

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

Tectonic lakes are formed in places of faults and shifts in the earth's crust. As a rule, these are deep narrow reservoirs with rectilinear steep banks, located in deep through gorges. The bottom of such lakes located in Kamchatka is below ocean level. Tectonic lakes include Dalneye and Kurilskoe. 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. Hot springs come to the surface along the shores of the lake.

Tectonic depressions arise from crustal movements, and many tectonic lake basins are large in area and ancient in age. They occupy depressions resulting from tectonic movements of the earth's crust: faults, faults, grabens, intermontane and lowland troughs. As a rule, they are very deep; some tectonic lakes exceed the seas. It is not by chance that the Caspian and Aral lakes are called seas. Caspian lake 4 times more than White, almost 3 times more than the Adriatic and 2 times - Aegean seas... And the deepest lakes in the world - Baikal and Tanganyika - are much deeper than ours northern seas- Barents, Karsky, East Siberian and others.

Tectonic processes manifest themselves in different ways. For example, the Caspian Sea is confined to the trough at the bottom of the ancient Tethys Sea. In the Neogene, an uplift took place, as a result of which the Caspian depression became isolated. Its waters were gradually desalinated under the influence of atmospheric precipitation and river runoff. The basin of the lake. Victoria in East Africa formed as a result of the uplift of the surrounding land. The Great Salt Lake in Utah also arose from the tectonic uplift of the territory through which the lake used to drain. Tectonic activity often leads to the formation of faults (cracks in the earth's crust), which can turn into lacustrine basins if the area is then reversed or if a block enclosed between the faults subsides. In the latter case, it is said that the lake basin is confined to the graben. Several lakes within the East African Rift System have this origin. Among them - the lake. Tanganyika, formed about 17 million years ago, is very deep (1470 m). The continuation of this system to the north is the Dead Sea and Lake Tiberias. Both are very ancient. The maximum depth of Lake Tiberias is currently only 46 m. ​​Lakes Tahoe on the border of the states of California and Nevada in the USA, Biwa (a source of freshwater pearls) in Japan and Lake Baikal are also confined to grabens. The bottom profile of tectonic lakes is sharply delineated and looks like a broken curve. Glacial deposits and the 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 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. The waters of the lakes are thermally inhomogeneous: during the period of the greatest warming 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. 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 largest lakes in Kyrgyzstan: Issyk-Kul, Son-Kul and Chatyr-Kul are formed tectonically.