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. So, Caspian lake separated from the Mediterranean and Black Seas as a result of tectonic movements of the earth's crust.

Basins of volcanic origin confined to craters and calderas extinct volcanoes or located among frozen lava fields. In the latter case, lake basins are formed when hot lava flows out from under a cooler surface lava horizon, which contributes to the subsidence of the latter (this is how Lake Yellowstone was formed), or in the case of rivers and streams 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 (Chudskoye, 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 genesis are found in steppe and semi-desert zones 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 erosional and accumulative fluvial processes and the small size of the basins, the latter are relatively quickly filled with sediment and overgrown in some places and re-formed in others.

Some lake basins are formed as a result of damming by landslides, mountain falls or mudflows of rivers. 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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Genetic types of lakes, thermal regime and life in them. Lakes associated with river activity. Tectonic, volcanic and glacial lakes.

Characteristics of some large lakes

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General information about Eastern Siberia as one of the largest regions of Russia.

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Study of the history of the formation of Lake Ladoga.

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Ecological significance of the lake’s aquatic environment, its flora and fauna.

Technogenic impact on the lake ecosystem.

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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 most big 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 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 of Russia's largest and largest lakes are frequently 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).

The lake is an element of the hydrosphere. This is a body of water that has arisen naturally or artificially. It is filled within its bed with water and has no direct connection with the sea or ocean. There are about 5 million such reservoirs in the world.

general characteristics

In terms of planetology, a lake is an object that exists stably in space and time, filled with matter in liquid form. In a geographical sense, it is represented as a closed depression of land into which water enters and accumulates. The chemical composition of lakes remains constant for a relatively long time. The substance filling it is renewed, but much less frequently than in the river. At the same time, the currents present in it do not act as the predominant factor determining the regime. Lakes provide regulation. Chemical reactions take place in the waters. During interactions, some elements settle in bottom sediments, others pass into the water. In some bodies of water, which usually do not have a flow, the salt content increases due to evaporation. As a result of this process, a significant change in the salt and mineral composition of the lakes occurs. Due to large thermal inertia, large objects soften the climatic conditions of adjacent zones, reducing seasonal and annual meteorological fluctuations.

Bottom sediments

When they accumulate, significant changes occur in the relief and size of lake basins. When reservoirs become overgrown, new forms are formed - flat and convex. Lakes often form barriers to groundwater. This, in turn, causes waterlogging of nearby land areas. There is a continuous accumulation of mineral and organic elements in the lakes. As a result, thick layers of sediment are formed. They change along the way further development bodies of water and turning them into land or swamps. Under certain conditions, bottom sediments are transformed into rock minerals of organic origin.

Features of education

Ponds arise for a variety of reasons. Their natural creators are wind, water, and tectonic forces. On the surface of the earth, depressions can be washed out by water. Due to the action of the wind, a depression is formed. The glacier polishes the depression, and the mountain collapse dams the river valley. This creates a bed for the future reservoir. Once filled with water, a lake appears. In geography, bodies of water are classified depending on the method of formation, the presence of life, and salt concentration. Only the saltiest lakes lack living organisms. Most of the reservoirs were created as a result of displacements of the earth's crust or volcanic eruptions.

Classification

According to their origin, reservoirs are divided into:

Volcanic reservoirs

Such lakes are located in extinct craters and explosion tubes. Such reservoirs are found in Europe. For example, volcanic lakes are present in the Eifel region (in Germany). Near them there is a weak manifestation of volcanic activity in the form of hot springs. The most common type of such lakes is a crater filled with water. Oz. The Mazama volcano crater in Oregon was formed more than 6.5 thousand years ago. Its diameter is 10 km, and its depth is 589 m. Some of the lakes were formed in the process of blocking volcanic valleys with lava flows. Gradually, water accumulates in them and a reservoir is formed. So, for example, a lake appeared. Kivu is a depression of the East African Rift structure located on the border of Rwanda and Zaire. Flowing once from the lake. Tanganyika r. The Ruzizi flowed north through the Kivu Valley towards the Nile. But from the moment the channel was blocked after the eruption of a nearby volcano, it filled the depression.

Other types

Lakes can form in limestone voids. Water dissolves this rock, forming huge caves. Such lakes can arise in areas of underground salt deposits. Lakes may be artificial. They are usually intended to store water for various purposes. Often, the creation of artificial lakes is associated with various types of excavation work. However, in some cases their appearance is a side effect. For example, artificial reservoirs are formed in mined-out quarries. Among the largest lakes it is worth noting Lake. Nasser, located on the border of Sudan and Egypt. It was formed by damming the river valley. Nile. Another example of a large artificial lake is Lake. Mid. It appeared after the installation of a dam on the river. Colorado. As a rule, such lakes are served by local hydroelectric power stations and provide water to nearby settlements and industrial zones.

Largest glacial-tectonic lakes

One of the main reasons for the formation of reservoirs is due to this displacement in a number of cases, the sliding of glaciers occurs. Ponds are very common on the plains and in the mountains. They can be found both in basins and between hills in depressions. Glacial-tectonic lakes (examples: Ladoga, Onega) are quite common in the Northern Hemisphere. Avalanches left quite deep depressions behind. Melt water accumulated in them. Sediments (moraine) dammed the depressions. This is how reservoirs in the Lake District were formed. At the foot of the town of Bolshoi Arber there is a lake. Arbersee. This body of water remained after the Ice Age.

Tectonic lakes: examples, characteristics

Such reservoirs are formed in areas of shifts and faults in the crust. Typically, the world's tectonic lakes are deep and narrow. They are distinguished by steep, straight banks. These reservoirs are located mainly in through deep gorges. Tectonic lakes Russia (examples: Kuril and Dalnee in Kamchatka) are characterized by a low bottom (below the ocean level). Yes, lake. Kurilskoe is located in the southern part of Kamchatka, in a picturesque deep basin. The area is surrounded by mountains. The maximum depth of the reservoir is 360 m. It has steep banks from which many mountain streams flow. The river flows from the reservoir. Ozernaya. Hot springs come to the surface along the banks. In the center of the lake there is a small hill - an island. It is called the "heart stone". Not far from the lake there are unique deposits of pumice. They are called Kutkhin bats. Today the lake Kurilskoye is a nature reserve and declared a zoological natural monument.

Bottom profile

The glacial-tectonic lakes of the world have a sharply defined relief. It is presented in the form of a broken curve. Glacial deposits and accumulative processes in sediments may not have a significant effect on the clarity of basin lines. However, in some cases the impact can be quite noticeable. Glacial tectonic lakes may have a bottom covered with “scars.” They are quite clearly visible on islands and rocky shores. The latter are composed mainly of hard rocks. They are weakly susceptible to erosion, which, in turn, causes a low rate of sediment accumulation. Such tectonic ones are classified as a=2-4 and a=4-10. The deep-water zone (over 10 m) of the total volume is 60-70%, shallow water (up to 5 m) - 15-20%. Tectonic lakes are characterized by heterogeneity of water in terms of thermal parameters. During maximum heating of the surface, it remains low temperature bottom waters. This is due to stable thermal stratifications. Vegetation is quite rare. It can be found along the shores in closed bays.

Spreading

Where, besides Kamchatka, are tectonic lakes found? The list of the most famous bodies of water in the country includes such formations as:

1. Sandalwood.
2. Sundozero.
3. Palier.
4. Randozero.
5. Salvilambi.

These reservoirs are located in the Suna River basin. Tectonic lakes are also found in the forest-steppe Trans-Urals. Examples of reservoirs:

1. Welgi.
2. Argayash.
3. Shablish.
4. Quiet.
5. Sugoyak.
6. Kaldy.
7. B. Kuyash and others.

The depth of reservoirs on the Trans-Ural Plain does not exceed 8-10 m. Based on their origin, they are classified as lakes of the erosion-tectonic type. Their depressions changed accordingly under the influence of erosion processes. Many reservoirs in the Trans-Urals are confined to ancient river hollows. These are, in particular, tectonic lakes such as Kamyshnoye, Alakul, Peschanoye, Etkul and others.

Unique body of water

In the southern part of Eastern Siberia there is a lake. Baikal is a tectonic lake. Its length is more than 630 km, and its length coastline- 2100 km. The width of the reservoir varies from 25 to 79 km. The total area of ​​the lake is 31.5 square meters. km. This reservoir is considered the deepest on the planet. It contains the largest volume fresh water on Earth (23 thousand m3). This is 1/10 of the world supply. Complete renewal of water in the reservoir occurs in 332 years. Its age is about 15-20 million years ago. Baikal is considered one of the oldest lakes.

Terrain

Baikal lies in a deep depression. It is surrounded by mountain ranges covered with taiga. The area around the reservoir has a complex, deeply dissected topography. Not far from the lake itself there is a noticeable expansion of the mountain strip. The ridges run parallel to each other here in the direction from northwest to southeast. They are separated by basin-like depressions. River valleys run along their bottom, and in some places small tectonic lakes are formed. Shifts of the earth's crust take place in this area today. This is indicated by relatively frequent earthquakes near the basin, hot springs coming to the surface, as well as subsidence of large areas of the coast. The water in the lake is blue-green. It is distinguished by exceptional transparency and purity. In some places you can clearly see stones lying at a depth of 10-15 m and thickets of algae. The white disk, lowered into the water, is visible even at a depth of 40 m.

Distinctive features

The shape of the lake is a nascent crescent. The reservoir stretches between 55°47" and 51°28" north. latitude and 103°43" and 109°58" east. longitude The maximum width in the center is 81 km, the minimum (opposite the Selenga River delta) is 27 km. The lake is located above sea level at an altitude of 455 m. 336 rivers and streams flow into the reservoir. Half of the water comes from the river. Selenga. One river flows out of the lake - the Angara. It should be said, however, that in scientific community There are still ongoing discussions about the exact number of streams flowing into the reservoir. Most scientists agree that there are fewer than 336.

Water

The liquid substance filling the lake is considered unique in nature. As mentioned above, the water is surprisingly transparent and clean, rich in oxygen. In the recent past, it was even considered healing. Baikal water was used to treat various diseases. In spring its transparency is higher. In terms of indicators, it is approaching the standard - the Sargasso Sea. Its water transparency is estimated at 65 m. During the period of mass algal blooms, the lake’s indicator decreases. Nevertheless, even at this time, in a lull, the bottom can be seen from the boat at a fairly decent depth. High transparency is caused by the activity of living organisms. Thanks to them, the lake is slightly mineralized. The structure of the water is similar to that of distilled water. The importance of the lake Baikal is difficult to overestimate. In this regard, the state provides special environmental protection to this area.

Tectonic lakes are formed in places of faults and shifts in the earth's crust. As a rule, these are deep narrow reservoirs with straight steep banks, located in deep through gorges. The bottom of such lakes located in Kamchatka is below ocean level. Tectonic lakes include Dalnee and Kurilskoye. Kuril 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 shores are steep. Numerous mountain streams flow from them. The lake is drainage; the Ozernaya River originates from it. Hot springs come to the surface along the shores of the lake.

Tectonic basins result from movements of the earth's crust, and many lake basins of tectonic origin have large area and ancient age. They occupy depressions that arise as a result of tectonic movements of the earth's crust: faults, faults, grabens, intermountain and plain troughs. As a rule, they are very deep, some tectonic lakes exceed the sea. It is no coincidence that the Caspian and Aral lakes are called seas. The Caspian Lake is 4 times larger than the White Lake, almost 3 times larger than the Adriatic and 2 times - Aegean seas. And the most deep lakes world - Baikal and Tanganyika - are much deeper than our northern seas - Barents, Kara, East Siberian and others.

Tectonic processes manifest themselves in different ways. For example, the Caspian Sea is confined to a trough at the bottom ancient sea Tethys. In the Neogene there was an uplift, as a result of which the Caspian basin. Its waters gradually desalinated under the influence of precipitation and river runoff. Lake basin Victoria in East Africa formed as a result of the uplift of the surrounding land. Big Salt Lake in Utah also arose due to the tectonic uplift of the territory through which the lake previously drained. Tectonic activity often results in the formation of faults (cracks in the Earth's crust), which can become lake basins if the area then undergoes a reverse fault or if a block enclosed between the faults subsides. In the latter case, they say that the lake basin is confined to a graben. Several lakes within the East African Rift System have this origin. Among them is the lake. Tanganyika, formed about 17 million years ago and characterized by a very great depth (1470 m). Continuing this system to the north are the Dead Sea and Lake Tiberias. Both of them are very ancient. The maximum depth of Lake Tiberias is currently only 46 m. ​​Lake Tahoe on the border of California and Nevada in the USA, Biwa (a source of freshwater pearls) in Japan and Lake Baikal are also confined to the grabens. The bottom profile of tectonic lakes is sharply outlined and has the appearance of a broken curve. Glacial deposits and sediment accumulation processes 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 rocks that are poorly susceptible to erosion, which is one of the reasons for the weak sedimentation process. The waters of the lakes are thermally heterogeneous: during the period of 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. As a result of the movement of the earth's crust, depressions are formed in some places over time. Tectonic lakes arise in these depressions. The three largest lakes in Kyrgyzstan: Issyk-Kul, Son-Kul and Chatyr-Kul were formed tectonically.

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 . Being a component of the hydrosphere, classical 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 important object for fishing, organizing salt production, 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 the 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. Coastline length.
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. Installed average depth reservoir, 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 a 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 occupies an area of ​​about twelve thousand square kilometers during drought, 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 Baikal, 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. Usually such basins are very elongated and deep.

Baikal

The deepest and largest fresh water lake in the world. 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 Leningrad region and in 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.

Ladoga lake It 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.