What is the origin of the lakes? The largest lakes on earth. Ecology, population of the lake bottom

Distribution of lakes on the globe. Types of lakes.

Lakes are natural bodies of water, which are water-filled depressions in the earth's surface with a coastal zone profile developed by the influence of wind waves and currents and slow water exchange. A lake differs from a river, as a rule, in the absence of a current due to the slope of the channel, and from the sea - in the absence of a two-way connection with the ocean.

Each lake consists of three mutually interconnected components: 1) basins - landforms earth's crust, 2) water and substances dissolved in it - part of the hydrosphere and 3) the plant and animal population of a reservoir - part of the living matter of the planet.

Morphometric characteristics of reservoirs.

Lake morphometry is associated with quantitative assessments and changes in the shape of the lake and its elements. Morphometric indicators are determined from a plan or map of a reservoir in isobaths and relate to a certain water level. Lake length L (km) - the shortest distance between the two points most distant from each other coastline a body of water measured across its surface.

Lake width B (km): average width Vsr. - the quotient of dividing the surface area of ​​a reservoir F by its length; maximum width Bmax - the greatest distance between the banks perpendicular to the length of the reservoir.

The length of the coastline L (km) is measured along the water edge (zero isobath). The ruggedness of the shoreline characterizes the degree of irregularity of the outline of the shores and is defined as the ratio of the length of the shoreline of the lake to the circumference of a circle having an area equal to the area of ​​the lake. Surface area (mirror) of lake F (km2) - water surface area without islands. Depth: maximum Нmax (m) is found according to measurements; average Havg (m) - calculated as the quotient of the volume of the water mass (V) divided by the area of ​​its mirror (F). The volume of water mass V (km3) is calculated as the sum of the volumes of individual layers contained between two adjacent horizontal planes drawn along isobaths. Horizontal layers are considered as truncated cones or prisms.

Lake classification

Based on their origin, lakes are divided into:

Tectonic: are formed by filling cracks in the earth's crust. A striking example of a tectonic lake is Lake Baikal.

Glacial: formed by a melting glacier. Typical glacial lake, a remnant of the last ice age is Arbersee, located at the foot of the Great Arber mountain (1456 m) - the most high mountain Bohemian forest.

River (or oxbow lakes).

Coastal (lagoons and estuaries). The most famous lagoon is the Venetian lagoon, located in the northern part of the Adriatic Sea.

Failed(karst, thermokarst). A feature of some sinkhole lakes is their periodic disappearance and reappearance, depending on the peculiar dynamics of groundwater. A typical representative is Lake Ertso in South Ossetia.

Volcanic: located in craters extinct volcanoes. In Europe, similar lakes are located in the Eifel region (Germany). Near them there are weak manifestations of volcanic activity in the form of hot springs.

Dammed: formed when part of a mountain collapses (for example, Lake Ritsa in Abkhazia).

Crater.

Artificial (reservoirs, ponds). The creation of such lakes can be an end in itself, for example, for creating reservoirs for various purposes. Often this creation is associated with more or less significant excavation work. But in some cases, such lakes arise as a side effect of such work, for example, in mined-out quarries.

According to their position, lakes are divided into (in relation to planet Earth):

Ground, the waters of which take an active part in the water cycle in nature and underground waters, the waters of which, if they take part in it, are only indirect. Sometimes these lakes are filled with juvenile, that is, native water.

Underground. The subglacial lake in Antarctica can also be classified as an underground lake.

According to water balance, lakes are divided into:

Sewage(have a drainage, mainly in the form of a river).

Drainless(they do not have surface runoff or underground drainage of water to neighboring watersheds. Water consumption occurs due to evaporation).

By type of mineralization

fresh;

ultra-fresh

mineral (salty).

brackish

salty

According to the chemical composition of water, mineral lakes are divided into:

carbonate (soda)

sulfate (bitter-salty)

chloride (salty)

Based on its location on celestial bodies lakes are divided into:

earthly;

extraterrestrial.

Lake water dynamics. The movement of water in lakes ensures its mixing and, therefore, promotes the distribution of oxygen, aeration of the lower layer and the distribution of nutrients.

The most significant is the vertical circulation of water associated with the thermal regime. Where it is not present, the gas regime of the lake is not favorable for life. For example, in Tanganyika there is no oxygen below the temperature jump layer; 0.9 of the volume of this lake is lifeless.

Despite the fact that the lakes are reservoirs of slow water exchange, most of them have currents. Near the mouths of tributary rivers, inertial currents form, fanning out and fading towards the center of the lake. Their area is proportional to the river flow. In flowing lakes, under the pressure of tributaries and the suction action of outflowing rivers, waste currents arise. Their volume and intensity are determined by the water balance of the lake. Thus, in Lake Constance, through which the Rhine flows, the current is similar to that of a river, only at a lower speed. The larger the volume of the lake, the relatively smaller the waste currents; they are absent in lakes with little flow.

Winds cause wind currents. They are usually temporary. In large closed lakes, wind and inertial currents form a slow movement of water along the shores in the form of circular coastal currents, moving in accordance with the Coriolis force counterclockwise.

Waves are of great importance for the thermal and gas regime of lakes. There are two types of waves in lakes: wind waves, already described in the section on seas, and seiches. Seiches are standing waves that arise under the influence of rapidly changing atmospheric pressure, or the impact of wind falling from the mountains, or, finally, heavy rain in one part of the lake. Since water is incompressible, the force applied to it causes a rocking motion: at one shore the water level rises, at the other it decreases, then vice versa. This is a single-node seiche - with one antinode. There are also binodal ones - with two antinodes - in the middle and near the coast.

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Classification of lakes. What types of lakes are there?

There are several types of classification of lakes: types of lakes are divided according to the nature of the basins, according to the water regime and according to the chemical composition. Let's look at each of them.

Based on the nature of lake basins, there are the following types of lakes:

1. Dam Lakes- a type of lake formed by a landslide, a glacier, or sediments that blocked a valley.

In turn, dam lakes are:

• river – a seasonal phenomenon that occurs during the dry season, when a river, as a result of a decrease in flow, turns into a chain of lakes separated from each other by dry sections of the riverbed.
• floodplain- in other words, oxbow lakes - are formed in place of the old river bed when the river makes a new path for itself.
• valley– are formed in narrow mountain valleys due to rock collapse. In the photo: valley dam lake Malaya Ritsa, Abkhazia.
• coastal– are divided into lagoons and estuaries.

Lagoons– shallow bays or bays separated from the sea by spits or river sediments.

Estuaries– river mouths flooded by the sea.

2. Moraine lakes- a type of lakes formed as a result of the activity of glaciers mainly of the Quaternary period. As the glacier retreats, it leaves behind huge masses of clastic material (moraines), which consists of clay, sand, crushed stone, rock fragments, etc. The uneven distribution of the moraine forms a hilly area with closed relief depressions. The latter, when filled with water, form moraine lakes. In Russia, moraine lakes can only be found in the north and northwest. Usually these are small lakes no more than 10 meters deep with heavily indented shores. However, there are also quite large lakes of this type - Seliger, Chudsko-Pskovskoye, Ilmen. (Pictured: moraine Lake Seliger, Russia)

3. Tarn lakes - a type of lakes that also owe their formation to the activity of glaciers. They are water-filled depressions that appeared on the surface of the earth as a result of the combined action of ice, firn and frost weathering. Typical for high mountain regions, located above the snow line. This type of lake is characterized by its small size, round shape and slightly indented coastline. The banks are steep and vertical, the bottom is flat and flat. Karas are formed on the site of small glaciers, accumulations of snow in depressions on the slopes of mountains. Snow and ice, melting, gradually deepen and widen the depression - this is how a carcass appears. (In the photo: tarn lake at the foot of Teachers Peak, Kyrgyzstan)

4. Karst lakes - a type of lake formed by underground and surface waters through the dissolution of substances and the removal of fine clay particles (suffusion) and the appearance of underground voids as a result of this activity. Over time, the soil above the voids settles, causing the appearance of funnel-shaped depressions in the relief. If they are filled with water, karst lakes appear. Karst lakes also include water-filled depressions in the ground formed in permafrost zones as a result of the melting of underground ice layers. Such lakes received a special name - thermokarst. (In the photo: karst lake Kara-Gol, “Bath of Youth”, Crimea, Russia).
5. Deflationary (aeolian) lakes - a type of lakes, which are water-filled spaces between barchans and dunes, as well as lakes that arise in basins formed in the process of blowing out small particles of soil. Aeolian lakes are formed mainly in areas with a dry, hot climate and sparse vegetation. Aeolian lakes got their name from the ancient Greek god Aeolus, the lord of the winds. (In the photo: aeolian (deflationary) Lake Teke, Kazakhstan. Satellite photo.)
6. Tectonic lakes – a type of lakes, the emergence of which is associated with tectonic processes occurring in the earth’s crust. As a rule, they are huge in size. This type of lakes includes Baikal, Issyk-Kul, Sevan, etc.
7. Volcanic lakes – a type of lake associated with volcanic activity. They form in craters of volcanoes, in depressions on the surface of solidified lava, in river valleys due to the blocking of a river bed by a lava flow.

According to water balance, there are the following types of lakes:

• sewage- type of lakes with flow, mainly in the form of a river;
• drainless- a type of lakes that do not have surface flow or underground drainage of water into neighboring catchment areas. Water consumption occurs due to evaporation.

Based on the chemical composition of water, there are the following types of lakes:

• fresh
• mineral (salty)

Elements of the lake bed and coastal area. The parts of a lake are the lake bottom and the shore.

A depression filled with water, in contrast to depressions not filled with water, has a naturally constructed relief, i.e. structure of the lake bottom and its shores.

The shape of lake basins under the influence of water loses its original appearance: the slopes become gentle, the bottom is level, and the slopes are clear.

Elements of the coastal area of ​​the lake basin (bottom and shores of the lake):

• Root Bank (Yar)- a coastal slope delimiting the lake basin from the surrounding area. Surrounds the lake on all sides. Foundation of the indigenous lake shore lies on the boundary of wave action.
• Brow - the upper border of the molar lake shore, the line where the slopes meet the surface of the adjacent area.
• Coast - divided into dry part, only periodically exposed to water: during strong waves, during floods, etc., and on underwater part– shallow area lake bottom, the formation of which is influenced by lake waves.
• Shoal– follows the underwater part of the coast and ends with an underwater slope.
• Submarine slope - the boundary between the slope and lake bottom- part of a lake basin filled with water.

Rice. 1. Zones of the coastal region of the lake basin. Parts of the lake shore.

The coast and the coastal shallows are combined into one zone - coastal or littoral. Its lower limit is determined by the depth of action of waves, sometimes by the depth of penetration of sunlight. The deep part of the lake - profundal. Between the littoral and profundal - sublittoral .

Overgrowing of lakes.

The lake bottom gradually rises due to increasing amounts of mineral sediments and organic silt. As a result, it happens lake overgrowing and a swamp may form in its place.

If the shores of the lake are flat , then wetland vegetation advances onto the lake from the shores, gradually narrowing the mirror of clear water.

Figure 2 shows the plant zones characteristic of shallow lakes with gently sloping shores.

Rice. 2. Scheme of overgrowing of shallow lakes.

1 - sedge peat, 2 - reed and reed peat, 3 - sapropel peat, 4 - sapropelite.

If the shores of the lake are steep and the lake itself is deep, then lake overgrowing starts from the middle. First, small rafts appear - islands of vegetation attached to the mineral shore or completely torn off from the shores. Gradually growing, the rafts cover the entire surface of the lake with a continuous veil.

Rice. 3. Scheme of overgrowing of a deep lake through the formation of rafts.

Origin, types and morphology of lake basins

Lakes are called basins or depressions the earth's surface, filled with water and not having a direct connection with the sea.

The sizes of lakes vary over a very wide range. According to the above definition, lakes can also include such large bodies of water as the Caspian and Aral seas, as well as relatively small temporary accumulations of water in depressions of the area, formed, for example, during the period of spring snowmelt.

Sometimes, in contrast to flowing waters (rivers), lakes are defined as bodies of water with slow flow or slow water exchange.

In the presence of a depression, the formation of a lake will occur when the influx of water into this depression exceeds the losses due to filtration and evaporation.

Reservoir -And artificial lake .

Pond -small reservoir .

Pond - natural lakes in which aquatic vegetation is widespread.

Types of lakes according to the nature of the basins. Despite the wide variety of lakes found in nature, certain types can be distinguished among them, having similarities in a number of characteristics.

First of all, certain types of lakes can be distinguished depending on the conditions of formation of the lake bed.

By the nature of the basins that served as the basis for the formation of the lake can be distinguished:

1. Dam lakes - are formed when a valley is blocked in some place by a landslide, glacier, sediment, etc.; This group also includes artificial lakes - reservoirs.

Among the dam lakes we can distinguish

- river - may arise as temporary formations as a result of a sharp decrease in the flow of individual rivers during the dry season; in this case, rivers often turn into a chain of lakes lying in a valley and separated from each other by dry sections of the channel.

- floodplain - are directly related to the process of formation of oxbow lakes, which arise as a result of the blocking of individual branches of the river by a ridge of sediment and the formation of a new channel by the river.

- valley - arise in the mountains from rubble. Lakes of dammed origin are formed as a result of blockage of a narrow valley by the products of destruction of their slopes.

- coastal lakes There are two types: lagoons and estuaries.

Lagoons arise when shallow bays, or bays, are separated from the sea by alluvial sandy-clayey shafts, or spits.

Estuaries They represent the mouth of the valley flooded by the sea.

2. Moraine lakes owe their origin to the activity of glaciers, especially the powerful ice sheets of the Quaternary period, which buried vast spaces beneath them. After the retreat (melting) and disappearance of such an ice sheet, in its place there remained fragmentary material that the glacier carried with it: clay, sand, crushed stone, large blocks of rock, etc.

A large accumulation of this material (moraine) in some places and insignificant in others creates a relief characterized by hilliness, continuous and frequent alternation of hills and depressions, and the depressions are usually closed. Filled with water, they form moraine lakes of round or irregular shape, with many branches and bays. In the moraine landscape there are many lakes that are also of the dam type.

3. Tarn lakes occupy depressions developed during glacial times by the combined action of ice, firn and frost weathering.

4. Karst lakes are the result of the chemical (solvent) activity of ground and surface waters. The removal of dissolved substances, as well as fine clay particles (suffusion), can lead to the formation of underground voids and subsidence of the roof over these voids, which will cause the appearance of craters on the surface of the earth; If these sinkholes are filled with water, karst lakes will appear in their place.

A peculiar variety of karst type lakes are thermokarst lakes , arising as a result of the filling of depressions on the surface of the earth with water, formed in areas of permafrost development due to the melting of underground layers or lenses of ice. The melting of this ice not only contributes to the formation of the lake basin, but also largely supplies water to fill the basin.

5. Deflationary lakes are located in basins created as a result of the blowing process, and in depressions between barchans and dunes.

Many basin lakes arise as a result of volcanic and tectonic processes.

6. Tectonic lakes . Tectonic processes cause the appearance of huge basins. Therefore, tectonic lakes usually deep. Examples include lakes Issyk-Kul, Baikal, Sevan, etc.

7. Volcanic lakes arise either in the crater of an extinct volcano, or in depressions on the surface of a lava flow formed during its solidification, or in a river valley due to its blocking by a lava flow.

According to water balance lakes are divided into:

- sewage- have a drainage, mainly in the form of a river);

- drainless- do not have surface runoff or underground drainage of water to neighboring watersheds. Water consumption occurs due to evaporation.

By chemical composition The lake waters are divided into:

Fresh

Mineral (salty)

Elements of the lake bed and coastal area. A depression located on the ground and filled with water has a naturally constructed relief that distinguishes it from depressions not occupied by water.

The original shape of the basins changes under the influence of erosion, both by surface runoff into the lake and by waves: the slopes of the basin are flattened, the unevenness of the bottom topography is smoothed out, filled with sediments, and the shore slopes acquire a stable profile.

The section of lake science, which examines the patterns manifested in the formation of the relief of lake basins, is called lake morphology .

Lake basin separated from the surrounding area indigenous shore, forming coastal slope, or yar; the base of this shore is located at the upper limit of the influence of the lake wave.

The main bank ends edge, or line connecting the slopes with the surface of the adjacent area.

The part of the basin filled with water to the height of the maximum rise in level is called lake bed, or lake bowl.

In the lake basin, first of all, one can distinguish coastal And deep areas.

In the coastal area There are three zones:

1) coastal slopes (yar)- part of the lake slope that surrounds the lake on all sides and is not exposed to the effects of wave surf;

2) coast - includes dry part , which is exposed to water only during strong waves and especially when the water is high, floodable , which is covered with water periodically - when the water level of the lake rises, and underwater , which usually lies below the surface of the water and, unlike the deeper parts of the coastal region, is exposed to the action of waves when it is rough;

3) coastal sandbar - ends with an underwater slope, which is the boundary between the slope and the bottom of the lake bed; the upper part of the coastal shallows corresponds to the lower limit of the impact of the wave surf on the coastal area.

The indicated zones of the coastal region of the lake basin are shown schematically in Fig. 1.

Rice. 1. Scheme of dismemberment of the coastal area of ​​the lake basin

The coast and the coastal sandbank are combined into one zone - coastal or littoral. Its lower limit is determined by the depth of action of the wave, sometimes by the depth of penetration of sunlight. The deep part of the lake - profundal. Between the littoral and profundal - sublittoral.

Formation of a lake bed under the influence of waves and sediment deposition. Waves, depending on the strength of the wind, the depth and size of the lake, affect the coastal area of ​​the lake basin for a long period, destroy the rocks composing it and carry eroded material down the slopes and to the bottom of the lake. As a result of this, the size of the coast and the erosion shallows increases, while at the same time the area of ​​alluvium increases and decreases due to the deep area of ​​the lake.

Thus, the lake is gradually covered by the action of waves. The degree of intensity of this process, of course, largely depends on the geological composition of the rocks that make up the lake shore.

However, whatever the coastal material, under the influence of waves and weathering it eventually turns into small stone, gravel and sand.

In addition to waves, the shape of the lake bed is significantly influenced by the process of supply of alluvial sediments brought by rivers flowing into the lake. Surface watercourses flowing into the lake erode soils along their route and carry erosion products into the lake.

In addition to mineral sediments that fall into the lake bed as a result of waves or brought by river flows, the lake basin is also filled with silt deposits of organic origin. This silt is a product of processes occurring in the lake itself, and is formed as a result of the death and subsequent deposition to the bottom of microscopic animals and plant organisms suspended in the water (the so-called plankton), as well as as a result of the death of coastal vegetation, which disintegrates into tiny particles after rotting, easily carried away by currents to the middle of the lake. The intensive development of these organisms during the warm period of the year, and their death during the cold season, causes layer-by-layer deposition of these silts on the bottom of the lake, which makes it possible to determine the age of the lake by layers.

Overgrowing of lakes. The amount of mineral sediments and organic silt at the bottom of the lake increases every year, as a result of which the bottom gradually rises.

In lakes with gently sloping shores, wetland plants move onto the lake from the shores, bordering the water surface with a wide green ring.

For shallow lakes with flat shores, a number of belts can be distinguished, regularly changing from the shores to the center of the lake (Fig. 2).

Rice. 2. Scheme of overgrowing of shallow lakes.

1 - sedge peat, 2 - reed and reed peat, 3 - sapropel peat, 4 - sapropelite.

Sometimes on shallow lakes you can observe alloys - islands of vegetation isolated from the shores or directly adjacent to the mineral shore (Fig. 3). At first, these rafts form small areas, then, as the lake further shallows, they grow, connect with others and cover the lake with a continuous cover of marsh vegetation from grass and moss tiers. These formations are known as muddy.

Rice. 3. Overgrowth pattern deep lake through the formation of alloys.

1 - rafting peat; 2 - mutta, or pelogen; 3 - sapropel peat; 4 - sapropelite.

Geographical location of the lake. Morphometric characteristics. An important characteristic of the lake is its geographical location (latitude, longitude) and altitude above sea level.

These data already allow us to form a general idea of ​​the main features of the lake’s regime. The geographical position of the lake to a certain extent reflects the general climatic characteristics of the area, and the altitude position also determines the local influence of climatic and other factors on the processes occurring in the lake.

When studying lakes and lake basins, it is important to establish not only the conditions of their formation, but also to determine a number of numerical characteristics that give quantitative ideas about the main elements of the lake and lake basin. These characteristics are called morphometric.

Lake area ω, m2, is calculated in two ways: either together with the area of ​​the islands, or separately the area of ​​the water surface. Since the shores of lakes are not vertical, the area of ​​the water surface (lake surface) changes as the lake level changes.

Lake length -L, m - the shortest distance between the two most distant points located on the shores of a lake, measured along the surface of the lake.

Thus, this line will be straight only in the case of relatively simple lake outlines; for a winding lake, this line, obviously, may not be straight, but consist of separate segments of straight and curved lines.

Lake width– distinguish:

Largest width - V, m , defined as the largest diameter (perpendicular) to the length line of the lake,

Average width – On Wednesday , m , representing the area ratio ω lake to its length L

Tortuosity coefficientT - degree of coastline development - ratio of coastline length s to the circumference of a circle having an area equal to the area of ​​the lake,

The coastline tortuosity ratio can also be expressed as the ratio of the coastline length S to the perimeter of the broken line S" , outlining the contour of the lake:

m = S/ S"

In this case, a more correct idea of ​​the ruggedness of the coastline is obtained.

It is widely used in assessing lake water reserves. curve of changes in lake area with depth , which is a graph of the relationship between the areas of horizontal sections of the lake and the corresponding depths, and lake volume change curve depending on its depth.

Rice. 4. Curves of areas and volumes of Lake Onega

In Fig. Figure 4 shows curves of changes in the area and volume of Lake Onega with depth. Such curves make it possible to determine the surface area of ​​the lake and the volume of water for any level. These values ​​must be known for all calculations.

Volume of water in the lake W , m 3 can be determined from an isobath map using the “prism method”. Isobath surfaces divide the volume of the lake into a number of layers, each of which can be considered approximately as a prism, the bases of which will be the areas limited by adjacent isobaths, and the height is equal to the section between them. Having designated the areas limited by individual isobaths through ω 0 , ω 1 , ω 2 , ω 3 … ω n , and their section through h , the volume of water in the lake is determined by the formula

W =
+
+
+…+
+ ∆ W =

=
∆ W,

Where ∆ W – the volume enclosed between the area of ​​the last deepest isobath and the point of the lake bottom with the maximum depth, determined by the formula:

∆W=
,

Where h poppy With - maximum depth lakes in meters; h n – depth corresponding to the greatest isobath, ω n – area of ​​the last (deepest) isobath.

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 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 (waste or not), salinity parameters (fresh or not), its chemical composition etc.

In addition, the following parameters need to be accurately determined: the total area of ​​the water surface, 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 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 closed depression of land that collects and stores surface and underground water. Unlike rivers, these are reservoirs of slow water exchange. total area of all lakes on Earth is 2.7 million square kilometers. They occupy about 1.8% of the land surface.

Lakes are always and everywhere formed according to one scenario - a depression, lowland or fault is formed in the area for various reasons - a basin. If it is subsequently filled with water, it will form a lake. Everything else is not significant. The location and origin of lakes is associated with the climate of the area, which determines their nutrition and evaporation, as well as with factors contributing to the formation of lake depressions. Where the climate is humid, the lakes are deep, fresh and numerous. For the most part they are flowing here. In arid areas, lakes are shallow, often salty and drainless. Thus, the hydrochemical features of lakes are determined by their geographical location.

Lakes are usually classified according to four characteristics: the origin of lake basins; the origin of the water mass; water regime and mineral composition (salinity).

Origin of lake basins

Based on their origin, there are 5 groups of lake basins. Tectonic lake basins - are formed as a result of cracks, faults and subsidence of the earth's crust. Such lakes are distinguished by their steep slopes and depth. As an example - Lake Baikal, the Dead Sea, Chad, Titicaca.

Volcanic lake basins - formed in the craters of volcanoes or in the lowlands of lava fields. As an example, we can note Lake Kuril in Kamchatka, lakes in Java and New Zealand. In the photo - lakes in the craters of the Kelimutu volcano.

Glacial (moraine) lake basins are dug by moving glaciers with subsequent erosion and accumulation of water in front of glacial landforms. When a glacier melts, the material it brings is deposited in the form of hills, ridges, hills and depressions. Such lakes are usually narrow and long, stretched along the melting line of the glacier - lakes in Finland, Karelia, the Alps, the Urals, and the Caucasus.

Karst lake basins - they arose as a result of failures, soil sedimentation and erosion of soft rocks - limestone, gypsum, dolomite. As a result, small but deep lake basins are formed.

Dammed (dammed or dammed) lake basins - arise as a result of blocking the river bed by rock falls. This is how Lake Sevan and a number of lakes in the Alps, Himalayas and the Caucasus were formed.

But depressions suitable for filling with water can appear in other ways. Here everything depends on the location and climate - the proximity of the sea, rivers, strong winds, groundwater, layers of permafrost in the soil. The result is still the same - the formation of a basin and filling it with water.

Other types of lakes

Estuary lakes are located along the shores of the seas. They are coastal areas of the sea, separated from it by coastal spits.

Organogenic lakes appear over time among swamps and coral reefs. Floodplain lakes are associated with changes in the river bed - lakes of the Kuban floodplains, ilmen of the Volga delta. Such lakes have a characteristic horseshoe shape.

The wind creates aeolian lakes that form in blowing basins - Lake Teke, Lake Selecty in Kazakhstan and a number of others arose in this way.

Suffosion lakes appear where groundwater actively washes away small pieces of rock, causing the ground to settle. Such lakes are typical for the south of Western Siberia.

Thermokarst sinkhole lakes (pictured) appear when areas of permafrost melt. Dips form in the ground and fill with melt water. There are many such lakes in the Kolyma Lowland - the most lake region of Russia.

Based on the origin of water masses, lakes are divided into two types - atmospheric and relict. Atmospheric lakes have never been part of the oceans. There are the majority of such lakes on Earth. Relict (or residual) lakes appeared on the site of the retreated seas - the Caspian, Aral, Ladoga, Onega, Ilmen and others.

According to the water regime, there are two types of lakes - drainage and drainless. Sewage lakes are lakes in which water exchange occurs, rivers flow into them and flow out of them. They are usually fresh. Such lakes are often located in areas of excess moisture.

Mineral Lakes

Endorheic lakes have inflowing rivers, but no outflowing ones. The water consumption of such lakes is dominated by evaporation and all minerals remain in the reservoir. Most of them are salty. Such lakes are located in areas of insufficient moisture.

Based on salinity, lakes are divided into four types - fresh, salt, brackish and mineral. Fresh lakes - if the salinity does not exceed 1 ppm. Salt lakes - if the content of soluble substances in them is within the range of 24.7 - 47 ppm. Brackish - salinity up to 24 ppm. Mineral - 47 ppm. These can be soda, sulfate, chloride lakes. In mineral lakes, salts can precipitate, for example lakes Elton and Baskunchak, which are a source of salt production. On the picture - salt Lake in Kenya.

Lakes play an important role in the planet's ecosystem. They create a special microclimate favorable for different forms of life. Even when salted, they attract many different organisms. And freshwater forms its own balanced and surprisingly rich ecosystems. Geological forces tend to level the surface of the continent through erosion, and the accumulation of sediment leads to a decrease in the depth of the lake and its gradual disappearance. Biological and chemical reactions occur in lake waters, as a result of which some elements pass into bottom sediments or, conversely, dissolve in water. Bottom sediments change the topography of the lake bottom and, under certain conditions, can be transformed into rocks of organic origin. Overgrowing of lakes creates new forms of relief.

Most lakes are relatively young formations. One of the most ancient is Baikal. Its age is 25 - 30 million years. The largest of the lakes is the Caspian. Its area is about 368 thousand square kilometers. The deepest is Baikal - 1620 meters. I would like to hope that these amazing natural formations will remain in their pristine state for a long time.

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