Glacial tectonic lakes are examples. Lakes: characteristics and types

The uniqueness of natural lakes lies in a number of their special characteristics. They are characterized by slow water exchange, free thermal conditions, a unique chemical composition, and differences in water levels.

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

Geographical object "lake" (meaning)

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 km 3 . As a component of the hydrosphere, classic natural lakes are bodies of natural origin, which are lake bowls of 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 arose as a result of human activity.

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

Characteristics of lakes

To give an accurate description of a particular lake, you need to determine its origin, position (above or underground), type of water balance (wastewater or not), mineralization parameters (fresh or not), its chemical composition, etc.

In addition, you need to accurately determine the following parameters: total area water mirror, the total length of the shoreline, the maximum distance between opposite shores, 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 by origin factor 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 based on 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, are in Karelia and Finland: lakes appeared along the trajectory of the glacier along tectonic cracks.
• Oxbow lake, lagoon or estuary - a decrease in water level cuts off part of the river or ocean.
• Karst, suffusion, thermokarst, aeolian - 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 body of water by a land bridge.
• Water often also collects in mountain basins and craters of volcanoes or their eruption channels.
• And others.

The importance of lakes in nature and for humans

Lakes are natural reservoirs of water that can regulate river flow: receive excess water and, conversely, release part of it when the water level in the river generally decreases. A large water mass has a large thermal inertia, the effect of which can significantly soften the climate of nearby areas.

Lakes are an important object for fishing, organizing salt production, and laying waterways. Water from lakes is often used for water supply. Reservoirs can be used to organize the energy reservoir of a hydraulic 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 not deep (30 m);

(Lake Baikal)

Baikal - depth record (1620 meters!).

The average record holders for largest lakes are tectonic lakes.

A lake is a body of water that forms on the surface of land. Lakes do not have a direct connection with oceans and seas. Most of reservoirs are tectonic lakes. In total, on our planet they occupy almost two percent of the land surface.

Characteristics of lakes

After a long study of lakes, scientists have identified a number of characteristics characteristic of this type of reservoir.

1. Water mirror area.
2. Length coastline.
3. Length of the lake. To measure this indicator, the two most distant points of the coastline are taken. During measurement, the average width is determined - this is the ratio of area to length.
4. The volume of the basin, which is filled with water, is determined.
5. The average depth of the reservoir is established, and the maximum depth is also determined.

The largest lake in the world is the Caspian, and the deepest is Baikal.

Lake name	Max. surface area, thousand km 2	Max. depth, m	What continent is it located on?
Caspian lake
			North America
Victoria
			North America
Ladoga
Onega

Origin of lakes

All existing lakes are divided into underground and above-ground. The basins themselves can be of endo- and exogenous origin. This factor determines the shape and size of the reservoir. Tectonic lakes are located in the largest basins. They can be located in tectonic depressions, like Ilmen, in grabens (Baikal) or in foothills and mountain troughs.

Most of the large basins have complex tectonic origin. Rupture and folding movements took part in their formation. All tectonic lakes are distinguished by their large sizes and significant depths, and the presence of rocky slopes. The bottom of most reservoirs is located at the level of the World Ocean, and the mirrors are much higher.

There is a certain pattern in the location of tectonic lakes: they are concentrated along faults in the earth or in rift zones, but can frame shields. Examples of such lakes are Ladoga and Onega, located along the Baltic shield.

Types of lakes

There is a classification of lakes according to their water regime.

1. Drainless. Rivers flow into these types of reservoirs, but none of them flow out. Most of them are located in areas with insufficient humidity: in the desert, semi-desert. The Caspian Sea-lake belongs to this type.
2. Sewage. Rivers flow into these lakes and also flow out of them. Such species are most often found in areas of excess moisture. A different number of rivers flow into such lakes, but usually only one flows out. An example of a tectonic lake of the drainage type is Baikal, Teletskoye.
3. Flowing reservoirs. Many rivers flow into and out of these lakes. Examples are lakes Ladoga and Onega.

In any body of water, food comes from precipitation, rivers, and underwater resources. Some of the water evaporates from the surface of reservoirs, flows out or goes underground. Because of this feature, the amount of water in the pool fluctuates. For example, Chad during drought covers an area of ​​about twelve thousand square kilometers, but during the rainy season the basin occupies an area twice as large - about 24 thousand square kilometers.

The largest lakes in the world are of tectonic origin. An example would be Lake Baikal, Lake Ladoga and Lake Onega. Large Endogenous factors play a role in the origin of tectonic lakes. The basins of these reservoirs are formed on subsided areas of the earth's crust. Typically such basins are very elongated and deep.

Baikal

The deepest and big lake world with fresh water. Baikal is located in Siberia. The area of ​​this basin is more than 31 thousand square kilometers, the depth is over 1500 meters. If you look at Baikal in terms of water volume, it ranks only second after the Caspian Sea-lake. The water in Baikal is always cold: in summer - about nine degrees, and in winter - no more than three. The lake has twenty-two islands: the largest is Olkhon. 330 rivers flow into Baikal, but only one flows out - the Angara.

Baikal influences the climate of Siberia: it softens winters and makes summers cooler. average temperature in January - about -17 °C, and in summer +16 °C. In the south and north, different amounts of precipitation fall throughout the year - from 200 to 900 mm. From January to May Baikal is covered clear ice. This is due to the very clean and transparent water - you can see everything that happens in the water at a depth of up to forty meters.

Other types of reservoirs

There are glacial-tectonic lakes that arose as a result of the processing of tectonic depressions in the earth's crust by glaciers. Examples of such lakes are Onega and Ladoga. There are volcanic lakes in Kamchatka and the Kuril Islands. There are lake basins that appeared due to continental glaciations.

In the mountains, some lakes were formed due to rubble, for example Lake Ritsa in the Caucasus. Small bodies of water appear above karst sinkholes. There are saucer-shaped lakes that arise on loose rocks. When permafrost melts, shallow lakes can form.

Lakes of glacial-tectonic origin are located not only in the mountains, but also on the plains. Water fills basins literally plowed out by glaciers. As the glacier moved from northwest to southeast along the cracks, the ice seemed to make a furrow. It filled with water: this is how many reservoirs were formed.

Ladoga lake

One of the large glacial-tectonic lakes is Ladoga. It is located in the Leningrad region and Karelia.

The area of ​​the lake is more than seventeen thousand square kilometers: the width of the reservoir is almost 140 kilometers, and the length is 219 km. The depth throughout the entire basin is uneven: in the northern part it ranges from eighty to two hundred meters, and in the southern part - up to seventy meters. Ladoga is fed by 35 rivers, and only one begins - the Neva.

There are many islands on the lake, among which the largest are Kilpola, Valaam, and Mantinsari.

Lake Ladoga freezes in winter and opens in April. The water temperature on the surface is uneven: in the northern part it is about fourteen degrees, and in the southern part it is about twenty degrees.

The water in the lake is of the hydrocarbonate type with weak mineralization. It is clean, transparency reaches seven meters. Throughout the year there are storms (they are strongest in the fall), and calm (most often in the summer).

Onega and other lakes

The largest number of islands is on Onega Island: there are more than a thousand of them. The largest of them is Klimetsky. More than fifty rivers flow into this reservoir, and only the Svir originates.

There are many tectonic lakes in Russia, among which are the drainage basin that includes Ilmen, Saimaa, and Lake Onega.

There are lakes of similar origin in Krasnaya Polyana, for example Khmelevskie. Their formation was facilitated by the deflection that arose during the destruction of the earth's crust. The resulting deflections led to the formation of basins that were filled with water. As a result, Khmelevsky lakes were formed in this place, which became a national park. There are four large lakes and several small reservoirs and swamps.

Large lakes located on the territory of Russia are of great economic importance. These are huge reserves of fresh water. Shipping is developed in the waters of many large lakes. On the banks there are recreation centers equipped fishing spots. In very large lakes, such as Ladoga, fishing is carried out.

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 (basins) with water masses. Lakes have no connection with the ocean and, unlike rivers, have slow water exchange.

Each lake consists of three interconnected natural components:

1. basins - landforms of the earth's surface,
2. water mass with substances dissolved in it,
3. plants and animals inhabiting the reservoir.

Origin of lake basins

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

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

Basins of tectonic origin are formed as a result of the movement of sections of the earth's crust. Many lakes that arose in basins of tectonic origin occupy a vast area, are characterized by great depth and are of 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 processes of stretching and subsidence of the continental crust occur. Lake Baikal in Russia (which is the largest freshwater body of water and has a maximum depth of -1620 m among lakes), Lake Biwa in Japan (famous for the freshwater pearls mined there) and others have a similar origin. Basins are often confined to isometric troughs (Chad, Air) or large tectonic faults. The formation is also associated with tectonic processes residual lakes, which are the remnants of ancient oceans and seas. Thus, the 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 of extinct volcanoes or located among frozen lava fields. In the latter case, lake basins are formed when hot lava flows out from under a cooler surface lava horizon, which contributes to the subsidence of the latter (this is how Lake Yellowstone 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 basins. Moraine-dammed ones are formed when river valleys are dammed by glaciers. When the cirque basins are filled with water, small picturesque lakes with clean and cold water are formed.
On the plains, basins of glacial origin are common in areas subject to Quaternary glaciation. Among them we can distinguish basins of exaration, glacial-accumulative and moraine-dammed origin. Exaration basins are associated with negative forms of relief 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 river valley processed by a glacier. Thousands of lakes formed in basins of glacial plowing are found on 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 ​​moraine-plain relief are wide, oval in shape and shallow in depth (Chudskoe, Ilmen); in conditions of hilly-western and hilly-ridged relief, they have an irregular shape, islands, a complex coastline, dissected by peninsulas and bays (Seliger). Moraine-dammed basins arise when a moraine dams a pre-glacial river valley (for example, Lake Saimaa in Finland).

In permafrost areas, depressions of thermokarst origin, which owe their origin to the melting of fossil ice and frozen rocks and ground subsidence. Many tundra lake basins have this origin. All of them have a shallow depth and are small in area. Another area of ​​development of thermokarst basins is the area of ​​distribution of Quaternary fluvioglacial deposits. Here, when the cover glaciers melted, huge blocks were buried under the thickness of sediments carried out by melted glacial waters dead ice. Many of them melted only after hundreds of years, and in their place hollows appeared, filled with water.

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

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

Depressions of fluvial origin associated with the geological activity of rivers. Most often these are oxbow and delta lakes. Sometimes the formation of lakes is caused by the obstruction of a river bed by alluvial sediments from another river. For example, the formation of Lake St. Croix (USA) is associated with the damming of the river. Saint-Croix alluvial deposits of the river. Mississippi. Due to the dynamics of erosion and accumulative fluvial processes and not large sizes 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 by landslides, mountain falls or river mudflows. Typically, such lakes do not exist for long - a breakthrough of sediment occurs, forming a “dam”. So, in 1841 The Indus in what is now Pakistan was dammed by a landslide caused by an earthquake, and six months later the “dam” collapsed, releasing the 64 km long and 300 m deep lake 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 landslide also contributed to the formation of one of the “pearls” of the Caucasus - Lake Ritsa in Abkhazia. A giant collapse on the slope of Mount Pshegisha dammed the Lashipse River. The waters of the river flooded the gorge for more than 2 km (tracing a large tectonic fault in the rock strata), the water rose 130 m. A river with a different name emerges from under a natural stone dam - Yupshara (in Abkhazian “split”).

Lakes artificial origin are associated with the filling of artificial basins (quarries, etc.) with water, or with the damming of river flows by dams. 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 River, Volta on the Volta River and Kariba on the Zambezi River; the largest in volume in Russia is the Bratsk Reservoir on the Hangar). Some dams were built to produce electricity for aluminum smelting based on large bauxite deposits. It should be added that dams are not created only by humans. Dams built by beavers can be over 500 m long, but they only last for a short time.

Basins of coastal-marine origin are formed mainly as a result of separation sea ​​bays bars from the sea during the movement of alongshore sediment flow. At the initial stage, the basin is filled with salty sea waters; subsequently, the resulting salt lake is gradually desalinated.

Depressions of organogenic origin occur in 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.

Lakes exist relatively short-lived on geological time scales. 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 fill with sediment or become swamped.

Sedimentation in lakes

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

In lakes in humid areas, predominantly silty-clay 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 gyttiyu(from Swedish gyttja - silt, mud) - lake sediments consisting of organic remains. The organic matter of gyttia is formed mainly due to the decay products of plant and animal organisms living in water, and to a lesser extent due to the remains of land plants brought from the surrounding land. The mineral part consists of sandy-clayey 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 - “putrid silt”). In Lake Nero, located near the city of Rostov-Yaroslavsky (Rostov the Great), 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, the lakes are drainless with intense evaporation. Since rivers and groundwater always bring salt, and only evaporates pure water, then there is a gradual increase in the salinity of lake waters. The concentration of salts can increase so significantly that salt is deposited from water supersaturated with salts (brine) to the bottom of the lake (self-settling lakes). When continental lakes become salinized, carbonate, soda, sulfate, salt and other chemogenic deposits accumulate. In Russia, modern soda lakes are known in Transbaikalia and Western Siberia; Lake Natron in Tanzania and Lake Searles in California are very famous abroad. Deposits of natural soda are confined to the fossil deposits of such lakes.
In general, arid regions are characterized by halogen-carbonate deposits, poor in organic matter.

In some 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 sediments. Carbonates accumulate in karst lakes, sometimes with piles of rocks of landslide origin.

Familiarization with the varieties, geographical location, water temperature and chemical composition of lakes in Russia.

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

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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 Vilenovo 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 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 Sea, as well as lakes Elton and Baskunchak, where salt is eliminated.

Hydrographic characteristics of large lakes in Russia

There are different lakes and headwater pools.

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 the processing of liquid depressions in the glacial crust of the glacier: Imandra, Ladoga, Onega.

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

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

In the south of Western Siberia there are many saucer-shaped lakes that were created by stoning rocks. When ice melts on the surface of permafrost, shallow slab-like waters also form. Lake people are located on the floodplain plains of low-lying rivers. On the coast of the Black and Sea of ​​Azov There are estuary lakes.

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

In Baikal the harvest is omul. Lakes are also used for navigation - geoglobus.ru. Numerous minerals were acquired from the lakes: oil and mirbilite in the Caspian Lake, salt in Elton and Baskunchak. Freshwater lake water is used for drinking. On the shores of many lakes there are many sanatoriums and holiday homes.

There are nine lake districts in Russia:

1) northwestern 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-salty lakes;
5) Altai - marine view of lakes (Teletskoye, Markakol);
6) Transbaikalsky - the remaining lakes;
7) Lower Amur lakes, which have a hydrological connection with the Amur River;
8) Yakutia - lakes made of thermocouples;
9) Lake Kamchatka - lakes of volcanic origin (Kronotsky, Kurilsky).

Definition 1

In the aspect of planetology, a lake is an object that exists stably in space and time, which is filled with a substance in liquid form.

In a geographical sense, it can be represented as a closed depression of land into which water flows systematically. For a fairly long period of time, the chemical composition of lakes does not change. The liquid that fills it is renewed, but much less frequently than in a river. At the same time, the currents present in it do not act as the main factor by which it is possible to determine the general regime.

Note 1

Lakes mainly provide balancing of river flow, as complex chemical reactions occur in their waters.

In the process of interactions, some elements pass into liquid, others settle in bottom sediments. In some reservoirs that do not have such a flow, the salt content increases significantly due to evaporation. As a result, there is a radical change in the mineral and salt composition of the lakes. Large objects soften the climatic conditions of areas close to them through large-scale thermal inertia, thereby reducing seasonal and annual weather fluctuations.

Tectonic lakes: characteristics, examples

Definition 2

Tectonic lakes– reservoirs that were formed in areas of faults and shifts in the earth’s crust.

Basically, these objects are narrow and deep, and are also distinguished by straight, steep banks. Such lakes are located mainly in deep through gorges. Tectonic lakes in Russia (examples: Dalnee and Kurilskoye in Kamchatka) are characterized by a low bottom. Thus, the Kurilskoe reservoir flows in the southern part of Kamchatka, in a colorful deep basin. This area is completely surrounded by mountains. The maximum depth of the lake is about 360 m, and a huge amount of mountain streams constantly flow down from the steep banks. The Ozernaya River flows from this reservoir, along the banks of which quite hot springs come to the surface. In the center of the reservoir there is an island in the form of a small dome-shaped elevation, popularly called the “heart-stone”. Not far from the lake there are unique pumice deposits called Kutkhiny Bati. Today Lake Kurilskoye is considered a nature reserve and declared a natural zoological monument.

Interestingly, tectonic lakes are located only in explosion tubes and extinct craters. Such reservoirs are often found in European countries. For example, volcanic lakes are observed in the Eifel region (in Germany), near which weak manifestations of volcanic activity in the form of hot springs are recorded. A water-filled crater is the most common type of such reservoir.

Example 1

For example, the Crater lakes of the Mazama volcano in Oregon were formed approximately 6.5 thousand years ago.

Its diameter reaches 10 km, and its depth is more than 589 m. Part of the reservoir was formed by volcanic valleys in the process of blocking continuous lava flows, in which water accumulates over time and a lake is formed. This is how the Kivu reservoir appeared, which is a depression of the East African rift structure, which is located on the border of Zaire and Rwanda. Flowing out of Tanganyika more than 7 thousand years ago, the Ruzizi River flowed through the Kivu Valley to the northern regions, towards the Nile. But from that period, the channel was “sealed” with the eruption of a nearby volcano.

Profile of the bottom of tectonic lakes

Tectonic reservoirs of the world have a clearly outlined bottom relief, presented as a broken curve.

Accumulative processes and glacial deposits in sediments did not have a significant impact on the relief of the basin lines, but in a number of special cases the influence can be quite noticeable.

Glacial-tectonic lakes can have a bottom covered with “scars” and “mutton foreheads,” which can be observed on rocky shores and islands. The latter are formed mainly from hard rocks that are practically resistant to erosion. As a result of this process, a small rate of precipitation accumulation occurs. Geographers classify similar tectonic reservoirs in Russia into the following categories: a = 2-4 and a = 4-10. The deep-water surface (over 10 m) of the total volume reaches approximately 60-70%, shallow water (up to 5 m) - 15-20%. Such lakes are characterized by diverse waters in terms of thermal indicators. The low temperature of bottom waters persists during the period of maximum surface heating. This is due to thermally stable stratifications. Vegetation in these zones is extremely rare, since it can only be found along the shores of closed bays.

Features of the formation of reservoirs

Lakes arise for a variety of reasons. Their natural creators are:

• water;
• wind;
• tectonic forces.

Depressions on the earth's surface are often washed out by water. Due to the action of the wind, a depression is created, after which the glacier polishes the depression, and the mountain collapse gradually dams the river valley. This is how the bed for the future reservoir is formed.

Based on their origin, lakes are divided into:

• river reservoirs;
• seaside lakes;
• mountain reservoirs;
• glacial lakes;
• dammed reservoirs;
• tectonic lakes;
• sinkhole lakes.

Tectonic lakes appear as a result of small cracks in the crust filling with water. Thus, shifts formed the Caspian Sea - the largest body of water on the territory of Russia and the entire planet. Before the rise of the Caucasus Range, the Caspian Sea was directly connected with the Black Sea. Another striking example of a large-scale fault in the earth's crust is the East African structure, which extends from the southwestern region of the continent north to southeast Asia. There is a chain of tectonic reservoirs here. The most famous are Tanganyika, Albert Edward, Nyasa. Experts include the Dead Sea, the lowest tectonic lake in the world, in this same system.

Coastal lakes are estuaries and lagoons, which are mainly located in northern regions Adriatic Sea. One of the specific features of sinkhole reservoirs is their systematic disappearance and appearance. This natural phenomenon is directly dependent on the unique dynamics of groundwater. An ideal example of this object is Lake Ertsov, located in South Ossetia. Mountain reservoirs are located in ridge basins, and glacial lakes are formed when the thickness of multi-year ice shifts.

- 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 body of slow water exchange.

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

Main characteristics of the lake:

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

The largest lake on Earth by water surface area 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. 1.

Each lake has three interconnected components: basin, water mass, vegetation and animal world reservoir

Lakes of the world

By position In the lake basin, lakes are divided into above-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 could be like endogenous, so exogenous origin, which most significantly affects their size, shape, and 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 fault and fold movements are involved in their formation (Issyk-Kul, Balkhash, Victoria, etc.). All tectonic lakes are large in size, and most have significant depths and steep rocky slopes. The bottoms of many deep lakes lie below the level of the World Ocean, and the surface of the lake lies above the level. Certain patterns are observed in the location of tectonic lakes: they are concentrated along faults in the earth’s crust or in rift zones (Syrian-African, Baikal), or frame shields: along the Canadian shield are located the Great Bear Lake, the Great Slave Lake, the Great North American Lakes, along the Baltic Shield — Onega, Ladoga, etc.

Lake name	Maximum surface area, thousand km 2	Altitude above sea level, m	Maximum depth, m
Caspian Sea
				North America
Victoria
				North America
				North America
Aral Sea
Tanganyika
Nyasa (Malawi)
Big Bear				North America
Great Slave				North America
				North America
Winnipeg				North America
				North America
Ladoga
Maracaibo				South America
Bangweulu
Onega
Tonle Sap
Nicaragua				North America
Titicaca				South America
Athabasca				North America
				North America
Issyk-Kul
Bolshoye Solenoye				North America
				Australia

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

Along with lake basins created by 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 basins plowed by glaciers and in depressions between hills with uneven deposition of moraine. The lakes of Karelia and Finland, which are elongated in the direction of glacier movement from northwest to southeast along tectonic cracks, owe their origin to the destructive activity of ancient glaciers. In fact, Ladoga, Onega and other lakes have a mixed glacial-tectonic origin. Glacial basins in the mountains include numerous, but small carts lakes located in bowl-shaped depressions on mountain slopes below the snow line (in the Alps, Caucasus, Altai), and trogous lakes - in trough-shaped glacial valleys in the mountains.

The uneven accumulation of glacial deposits on the plains is associated with lakes among hilly and moraine terrain: in the north-west of the East European Plain, especially in the Valdai Upland, in the Baltic states, Poland, Germany, Canada and the northern 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 glacier tongues (Como, Garda, Würm in the Alps). In areas of ancient glaciations, there are numerous lakes in the hollows of the runoff of melted glacial waters; they are elongated, trough-shaped, usually small and shallow (for example, Dolgoe, Krugloe - near Moscow).

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

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

Thermokarst Lakes appear when permafrost soil melts 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 north-west of the East European Plain in the former periglacial zone.

Aeolian lakes arise in blowing 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 Murghab 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, river lakes are formed in bochagas - reaches; in river deltas there are small ilmen lakes, in place of channels, often overgrown with reeds and reeds (ilmen lakes of the Volga delta, lakes of the Kuban flood plains).

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

A special type is 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 - 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 fresh, although in dry climates they may eventually become salty.

Other lakes were part of the World Ocean - these are relict salty lakes (Caspian, Aral). But even in such lakes, primary sea water can be greatly transformed and even completely displaced and replaced by atmospheric waters (Ladozhskoye, etc.).

Table 2. Distribution of the main genetic groups of lakes by continent and part of the world

Genetic groups of lakes	Continents and parts of the world
	Western Europe	Foreign Asia	North America	South America		Australia
Glacial
Glacial-tectonic
Tectonic
Volcanic
Karst
Residual
Lagoon
Floodplain

Depending from water balance, t.s. According to the conditions of inflow and outflow, lakes are divided into drainage and drainageless. 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 drain into the World Ocean - drainless(Caspian, Aral, Bolshoye Solenoye). The water level in such lakes is subject to fluctuations of varying 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 promise long cycles of climate moisture and aridity.

Lake waters, like other natural waters, are characterized by different chemical compositions and varying degrees of mineralization.

Based on the composition of salts in the water, lakes are divided into three types: carbonate, sulfate, and chloride.

By degree of mineralization lakes are divided into fresh(less than 1%o), brackish(1-24.7%c), 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%, brackish - Caspian sea water - 12-13%, Bolshoye Solenoye - 137-300%, Dead Sea - 260-270%, in some years - up to 310%c.

The distribution of lakes with varying degrees of mineralization on the earth's surface shows geographic zonality, determined by the moisture coefficient. In addition, those lakes into which rivers flow are characterized by low salinity.

However, the degree of mineralization can vary within the same lake. For example, in the closed lake Balkhash, located in an 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 part only by a narrow (4 km) shallow strait, the water is brackish.

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

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

Freshwater lakes in the hot thermal zone are characterized by the warmest water at the surface, which gradually decreases with depth. This temperature distribution over depth is called direct thermal stratification. Lakes in the cold thermal zone have the coldest (about 0 °C) and lightest water at the top almost all year round; With depth, the water temperature increases (up to 4°C), the water becomes denser and heavier. This temperature distribution over depth is called reverse thermal stratification. Lakes in the temperate thermal zone have variable stratification by season: 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 constant temperature over depth is called homothermy(spring and autumn).

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

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

Dynamic phenomena in lakes include currents, waves and seiches. Discharge currents occur when a river flows into a lake and water flows out of 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, promotes mixing of water, penetration of oxygen into the lower layers, and uniform distribution of nutrients, which is important for the very diverse inhabitants of lakes.

By nutritional properties of water mass and the conditions for the development of life, lakes are divided into three biological types: oligotrophic, eutrophic, 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 nutrients, they are poor in plankton. Life is not rich, but there are fish and crustaceans. These are many mountain lakes, Baikal, Geneva, etc.

Eutrophic the 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 muddy with an abundance of organic residues. In summer, water blooms occur due to the strong development of phytoplankton. The lakes have a rich flora and fauna. They are most common in forest-steppe and steppe zones.

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

In the last decade, due to the increased supply of phosphorus and nitrogen compounds from 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, silt forms, and hydrogen sulfide appears. All this will create unfavorable living conditions for fish, waterfowl, etc.

Evolution of lakes occurs in different ways in humid 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 gentle shores are overgrown by pushing vegetation ecological zones from the periphery to the center. Eventually the lake becomes a grassy, ​​low-lying marsh.

Deep lakes with steep banks overgrow differently: by growing from above alloys(swell) - a layer of living and dead plants. It is based on plants with long rhizomes (cinquefoil, cinquefoil, whitewing), and other herbaceous plants and even shrubs (alder, willow) settle on the network of rhizomes. The float first appears on the shores, protected from the wind, where there is no waves, and gradually advances onto the lake, increasing in power. Some plants die and fall to the bottom, forming peat. Gradually, only “windows” of water remain in the ravine, and then they disappear, although the basin is not yet filled with sediments, and only over time the raft closes with the peat layer.

In dry climates, lakes eventually become salt marshes. This is facilitated by an insignificant amount of precipitation, intense evaporation, and a decrease in inflow river waters, 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 fresh lake may first turn into a salt lake (Big Salt Lake in North America), and then into the salt marsh.

Lakes, especially large ones, have a softening effect on the climate of the surrounding areas: they are warmer in winter and cooler in summer. Thus, at coastal weather 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.