What is the tectonic origin of the lake. Lakes of tectonic origin. Let's take a closer look at the main types of lakes

A lake is a body of water with slow water exchange. Lakes are classified according to various criteria: in origin (tectonic, volcanic, dammed, glacial, sinkhole, karst, etc.); by salinity (fresh, brackish, saline, brine, etc.); by trophicity (oligotrophic, mesotrophic, eutrophic, etc.); by position in the landscape (lowland, floodplain, highland, etc.); by depth (shallow, deep, super-deep); by morphology (rounded, elongated, ribbon-shaped, crescent-shaped, bead-shaped, etc.); by flow (non-drainage, low-flow, periodically flow-through, temporary, relict); by types of use (fishery, for water supply, for the extraction of salt, sapropel ore, therapeutic mud and so on.); according to condition (clean, polluted, overgrown, etc.).

How long do lakes live?

Most often, it is relatively short - a few thousand or tens of thousands of years. This applies primarily to glacial and oxbow lakes. Karst, volcanic and especially tectonic lakes can exist for millions and tens of millions of years. For example, one of the lakes in Australia was formed about 700 million years ago.

How many lakes are on earth?

An exact count has not yet been made. Probably about 2 million lakes in Canada and Alaska, about 100 thousand in Finland and Scandinavian peninsulas. About 100 thousand in Great Britain and Ireland as well as Denmark, Belgium, Holland and France. Hydrologists believe that there are about 5 million lakes on the earth.

Tectonic lakes.

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

bottom profile tectonic lakes sharply outlined, has the form 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 stone rocks that are weakly susceptible to erosion, which is one of the reasons for the weak process of sedimentation. These lakes belong to the group of lakes of normal depth (a=2-4) and deep (a=4-10). The deep-water zone (more than 10 m) of the total volume of the lake is 60-70%, shallow water (0-5m) 15-20%. The waters of the lakes are thermally heterogeneous: during the period of the greatest warming surface water low bottom temperatures are maintained, which is facilitated by stable thermal stratification. Aquatic vegetation is rare, only in a narrow strip along the shores of closed bays. Typical lakes in the river basin. The suns are large and medium-sized: Palye, Sundozero, Sandal, as well as very small lakes Salvilambi and Randozero, located on private watersheds of lakes Palye and Sandal.

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

There are many lakes in the forest-steppe Trans-Urals. Here are such large reservoirs as Uelgi, Shablish, Argayash, B. Kuyash, Kaldy, Sugoyak, Tishki, etc. The depths of the lakes on the Trans-Ural Plain noticeably decrease and do not exceed 8-10 m. By origin, these lakes belong to the erosion-tectonic type. Tectonic depressions were modified as a result of the impact of erosion processes. Many lakes of the Trans-Urals are confined to ancient hollows of river flow (Etkul, Peschanoe, Alakul, Kamyshnoe, etc.).

Lake Baikal. General information

Lake Baikal

Baikal - freshwater lake on South Eastern Siberia, it stretched from 53 to 56°N. and from 104 to 109°30’ E Its length is 636 km and the coastline is 2100 km. The width of the lake varies from 25 to 79 km. The total area of ​​the lake (mirror area) is 31,500 sq. km.

Baikal is the deepest lake in the world (1620 m). It contains the largest fresh water reserves on earth - 23 thousand cubic km, which is 1/10 of the world's reserve fresh water. A complete change of such a huge amount of water in Baikal takes 332 years.

This is one of the oldest lakes, its age is 15 - 20 million years.

336 rivers flow into the lake, including the Selenga, Barguzin, Upper Angara, and only one Angara flows out. Baikal has 27 islands, the largest of which is Olkhon. The lake freezes in January, opens in May.

Baikal lies in a deep tectonic depression and is surrounded by taiga-covered mountain ranges; the area around the lake has a complex, deeply dissected relief. Near Baikal, the band of mountains expands noticeably. mountain ranges stretch here parallel to one another in the direction from the northwest to the southeast and are separated by basin-like depressions, along the bottom of which rivers flow and lakes are located in some places. The height of most of the ranges of Transbaikalia rarely exceeds 1300 - 1800, but most high ridges reach high values. For example, xr. Khamar-Daban (Sokhor peak) - 2304 m, and Barguzinsky ridge. about 3000 m.

Tectonic movements continue here even now. This is evidenced by frequent earthquakes in the region of the basin, outcrops of hot springs, and, finally, subsidence of significant sections of the coast.

The waters of Lake Baikal have a blue-green color, are distinguished by exceptional purity and transparency, often even greater than in the ocean: you can clearly see stones lying at a depth of 10-15 m and thickets of greenish algae, and a white disk lowered into the water is visible at a depth of 40 m.

Baikal lies in the temperate zone.

Geography of Lake Baikal

Lake Baikal is located in the south of Eastern Siberia. In the form of a crescent being born, Baikal stretched from southwest to northeast between 55°47" and 51°28" north latitude and 103°43" and 109°58" east longitude. The length of the lake is 636 km, the maximum width in the central part is 81 km, the minimum width opposite the Selenga delta is 27 km. Baikal is located at an altitude of 455 m above sea level. Length coastline about 2000 km. The area of ​​the water mirror, determined at the water's edge of 454 m above sea level, is 31,470 square kilometers. The maximum depth of the lake is 1637 m, average depth- 730 m. 336 permanent rivers and streams flow into Baikal, while half of the volume of water entering the lake comes from the Selenga. flows out of Baikal the only river- Angara. However, the question of the number of rivers flowing into Baikal is rather controversial, most likely there are fewer than 336. There is no doubt that Baikal is the deepest lake in the world, the closest contender for this title, African lake Tanganyika, lags behind by as much as 200 meters. There are 22 islands on Baikal, although, as mentioned above, there is no unanimity on this issue. Most large island- Olkhon.

Age of Lake Baikal

The age of the lake is usually given in the literature as 20-25 million years. In fact, the question of the age of Baikal should be considered open, since the use of various methods for determining the age gives values ​​from 20-30 million to several tens of thousands of years. Apparently, the first estimate is closer to the truth - Baikal is really very ancient lake.

It is believed that Baikal arose as a result of the action of tectonic forces. Tectonic processes are still going on, which is manifested in the increased seismicity of the Baikal region. If we assume that the age of Baikal is indeed several tens of millions of years, then this is the oldest lake on Earth.

origin of name

Numerous scientific studies have been devoted to the problem of the origin of the word "Baikal", which indicates a lack of clarity in this matter. There are about a dozen possible explanations for the origin of the name. Among them, the most probable is the version of the origin of the name of the lake from the Turkic-speaking Bai-Kul - a rich lake. Of the other versions, two more can be noted: from the Mongolian Baigal - a rich fire and Baigal Dalai - big lake. The peoples who lived on the shores of the lake called Baikal in their own way. Evenks, for example, - Lamu, Buryats - Baigal-Nuur, even the Chinese had a name for Baikal - Beihai - the North Sea.

The Evenk name Lamu - the Sea was used for several years by the first Russian explorers in the 17th century, then they switched to the Buryat Baigal, slightly softening the letter "g" by phonetic replacement. Quite often, Baikal is called the sea, simply out of respect, for its violent temper, for the fact that the far opposite shore is often hidden somewhere in the haze... At the same time, the Small Sea and the Big Sea are distinguished. Small Sea - what is located between north coast Olkhon and the mainland, everything else is the Big Sea.

Baikal water

Baikal water is unique and amazing, like Baikal itself. It is unusually transparent, pure and saturated with oxygen. In not so ancient times, it was considered healing, with its help, diseases were treated. In spring, the transparency of Baikal water, measured using the Secchi disk (a white disk with a diameter of 30 cm), is 40 m (for comparison, in the Sargasso Sea, which is considered the standard of transparency, this value is 65 m). Later, when a massive algae bloom begins, the transparency of the water decreases, but in calm weather, the bottom can be seen from a boat at a fairly decent depth. This high transparency is due to the fact that Baikal water, due to the activity of living organisms living in it, is very weakly mineralized and close to distilled. The volume of water in Baikal is about 23 thousand cubic kilometers, which is 20% of the world's fresh water reserves.

A lake is a closed depression of land filled with water. It has a slow water exchange, unlike rivers, and does not flow into the waters of the oceans, unlike the seas. These reservoirs on our planet are distributed unevenly. total area lakes of the Earth is about 2.7 million km 2, or about 1.8% of the land surface.

The lakes have a number of differences among themselves both in external parameters and in the composition of the water structure, origin, etc.

Classification of lakes by origin

Glacial reservoirs were formed due to the melting of glaciers. This happened during periods of severe cooling, which fettered the continents repeatedly over the past 2 million years. result ice ages become modern lakes located on the territory North America and Europe, namely in Canada, Baffin Island, Scandinavia, Karelia, the Baltic States, the Urals and other areas.

Huge blocks of ice, under the weight of their weight, and also because of their movements, formed considerable pits in the thickness of the earth's surface, sometimes even pushed apart tectonic plates. In these pits and faults, after the melting of ice, reservoirs were formed. One of the representatives glacial lakes can be called a lake. Arbersee.

The cause of the occurrence was the movement of lithospheric plates, as a result of which faults were formed in the earth's crust. They began to fill with water from melting glaciers, which led to the emergence of this type of reservoir. The brightest example is Lake Baikal.

River lakes appear when some sections of flowing rivers dry up. In this case, the formation of chain reservoirs arising from one river takes place. The second variant of river formations are floodplain lakes, which appear due to water barriers that interrupt the water channel.

Seaside lakes are called estuaries. They appear when lowland rivers are flooded by the waters of the seas or as a result of the lowering of sea coasts. In the latter case, a strip of land or shallow water appears between the newly formed bay and the sea. In estuaries, which appeared from the confluence of the river and the sea, the water has a slightly salty taste.

Karst lakes are earthen pits that are filled with water underground rivers. Pit pits are failures of the lithosphere, consisting of limestone rocks. Due to the failure, limestone rocks line the bottom of the reservoir, which affects the transparency of its filled waters: they are crystal clear.

Karst lakes have one distinguishing feature- they are periodic in their appearance. That is, they can disappear and form again. This phenomenon depends on the level of underground rivers.

They are located in mountain valleys. They are formed in several ways. Due to mountain landslides that block the river flow and thereby form lakes. The second way of formation is the slow descent of huge blocks of ice, which leave behind deep land failures - basins that are filled with water from melted ice.

Volcanic-type lakes appear in the craters of dormant volcanoes. Such craters are of significant depth and high edges, which prevents flows and inflows river waters. It does volcanic lake practically isolated. Craters fill with rainwater. The specific location of such objects is often reflected in the composition of their waters. Increased content carbon dioxide make them dead, uninhabitable.

These are reservoirs and ponds. They are created intentionally for industrial purposes. settlements. Also, artificial lakes can be the result of earthworks, when the remaining earthen pits are filled with rainwater.

Above was a classification of lakes depending on the origin.

Types of lakes by position

It is possible to make a classification of lakes depending on their position in relation to the earth as follows:

1. Terrestrial lakes are located directly on the surface of the land. These are involved in the constant water cycle.
2. Underground lakes are located in underground mountain caves.

Mineralization classification

You can classify lakes by the amount of salts as follows:

1. Fresh lakes formed from rainwater, melting glaciers, groundwater. The waters of such natural objects do not contain salts. In addition, fresh lakes are a consequence of the overlapping of river beds. The largest fresh lake is Baikal.
2. Salt water bodies are divided into brackish and saline.

Brackish lakes are common in arid areas: steppes and deserts.

Salt lakes in terms of the content of salts in the thickness of their waters resemble oceans. Sometimes the salt concentration of lakes is somewhat higher than in the seas and oceans.

Classification by chemical composition

The chemical composition of the lakes of the Earth is different, it depends on the amount of impurities in the water. Lakes are named based on this:

1. In carbonate lakes, there is an increased concentration of Na and Ca. Soda is mined from the depths of such reservoirs.
2. Sulfate lakes are considered curative due to the content of Na and Mg in them. In addition, sulfate lakes are a place for the extraction of Glauber's salt.
3. Chloride lakes are salt lakes, which are the place where common table salt is mined.

Water balance classification

1. Waste lakes are endowed with the help of which a certain amount of water is discharged. As a rule, such reservoirs have several rivers flowing into their basin, but there is always one flowing one. An excellent example is the large lakes - Baikal and Teletskoye. The water of sewage lakes is fresh.
2. Endorheic lakes are saline lakes, since the flow of water in them is more active than its inflow. They are located in the desert and steppe zones. Sometimes they produce salt and soda on an industrial scale.

Classification according to the amount of nutrients

1. Oligotrophic lakes contain a relatively small amount of nutrients. The peculiarities are the transparency and purity of the waters, the color from blue to green, the depth of the lakes is significant - from medium to deep, the decrease in oxygen concentration closer to the bottom of the lake.
2. Eutrophic plants are saturated with a high concentration of nutrients. The peculiarities of such lakes are the following phenomena: the amount of oxygen sharply decreases to the bottom, there is an excess of mineral salts, the color of the water is from dark green to brown, which is why the transparency of the water is low.
3. Dystrophic lakes are extremely poor in minerals. There is little oxygen, the transparency is low, the color of the waters can be yellow or dark red.

Conclusion

The water basin of the Earth is made up of: rivers, seas, oceans, glaciers of the oceans, lakes. There are several types of lake classifications. They have been reviewed in this article.

Lakes, like other bodies of water, are the most important Natural resources which are actively used by man in various fields.

Topic 7. Hydrology of lakes

Origin, types and morphology of lake basins

lakes called hollows or hollows the earth's surface, filled with water and not having a direct connection to the sea.

The sizes of lakes fluctuate in 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 terrain, which are formed, for example, during the spring snowmelt.

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

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

Reservoir -And man-made lake .

Pond -small reservoir .

Pond - natural lakes, on the area of ​​​​which aquatic vegetation is common.

Types of lakes according to the nature of the basins. Despite big variety lakes occurring in nature, among them certain types can be distinguished that have similarities in a number of ways.

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

According to the nature of the basins, which served as the basis for the formation of the lake, can be distinguished:

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

Among the dam lakes, one can distinguish

- river - may occur as temporary formations as a result of sharp decline runoff of individual rivers during the dry season; in this case, the rivers often turn into a chain of lakes lying in the 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 sediments and the formation of a new channel by the river.

- valley - arise in the mountains from rubble. Lakes of landslide 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 in the case when shallow bays, or bays, are separated from the sea by alluvial sandy-argillaceous shafts, or spits.

Estuaries represent the mouth part 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 expanses under them. After the retreat (melting) and disappearance of such an ice sheet, detrital material remained in its place, which carried the glacier with it: clay, sand, crushed stone, large blocks of rocks, etc.

A large accumulation of this material (moraines) in some places and insignificant in others creates a relief characterized by hilly, continuous and frequent alternation of elevations 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 conditions of a moraine landscape, there are many lakes that also belong to the dam type.

3. Karovye lakes occupy depressions worked out during the ice age by the joint work of ice, firn and frosty weathering.

4. Karst lakes are the result of the chemical (dissolving) 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 funnels on the surface of the earth; if these funnels are filled with water, karst lakes will appear in their place.

A peculiar kind of karst type of lakes are thermokarst lakes , resulting from 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 ice lenses. The melting of this ice not only contributes to the formation of a lake basin, but also supplies water to a large extent to fill the basin.

5. deflationary lakes are located in hollows created as a result of the blowing process, and in depressions between dunes 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. Lakes Issyk-Kul, Baikal, Sevan and others can serve as examples.

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 drain, mainly in the form of a river);

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

By chemical composition The waters of the lake 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 regularly constructed relief that distinguishes it from depressions not occupied by water.

The initial shape of the basins changes under the action of erosion both by surface runoff into the lake and by waves: the slopes of the basin flatten out, the irregularities of the bottom topography are smoothed out, filled with sediments, and the slopes of the coast acquire a stable profile.

The section of lake science, which deals with the patterns that are manifested in the formation of the relief of lake basins, is called lake morphology .

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

The root bank ends edge, or line of conjugation of slopes with the surface of the adjacent terrain.

The part of the basin filled with water up to the height of the maximum level rise 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 three zones are distinguished:

1) coastal slopes (yar)- a part of the lake slope that surrounds the lake from all sides and is not affected by the wave surf;

2) coast - includes dry part , which is exposed to water only during strong waves and especially when the water is high, flooded , which is covered with water periodically - during the rise in the water level of the lake, and underwater , which usually lies below the surface of the water and, in contrast to the deeper parts of the coastal area, is exposed to waves during waves;

3) coastal shoal - 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 shoal corresponds to the lower boundary of the impact on the coastal area of ​​the wave surf.

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

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

The coast and coastal shallows are combined into one zone - coastal or littoral. Its lower limit is determined by the depth of the wave, sometimes by the depth of penetration of the sun's rays. Deep part of the lake profundal. Between the littoral and the profundal sublittoral.

Formation of the lake bed under the influence of waves and sedimentation. Excitement, depending on the strength of the wind, the depth and size of the lake, affects the coastal area of ​​the lake basin for a long period, destroys its components rocks and carries the eroded material down the slopes and to the bottom of the lake. As a result of this, the sizes of the coast and erosion shoals increase, at the same time, the area of ​​alluvium increases and decreases due to the deep region of the lake.

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

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

In addition to roughness, the shape of the lake bed is significantly affected by the process of alluvial sediment inflow brought by the rivers flowing into the lake. The surface streams flowing into the lake erode the soil along the way and carry the erosion products into the lake.

In addition to mineral sediments falling into the lake bed as a result of waves or carried by rivers, 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 sedimentation of microscopic animal and plant organisms suspended in the water (the so-called plankton), as well as the death of coastal vegetation, which decays after decay into the smallest particles, easily carried by currents to the middle of the lake. The intensive development of these organisms during the warm period of the year, and the death during the cold period, determines the 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.

Overgrowth of lakes. The amount of mineral precipitation 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 approach the lake from the shores, edging the water surface with a wide green ring.

For shallow lakes with gently sloping 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 one can observe alloys - islands of vegetation detached from the coast or directly adjacent to the mineral coast (Fig. 3). At first, these quays form small areas, then, as the lake becomes shallower, they grow, join with others, and cover the lake with a continuous cover of bog vegetation from grass and moss layers. These formations are known as quicksand.

Rice. 3. Scheme of overgrowing deep lake by the formation of alloys.

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

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

These data already make it possible to form a general idea of ​​the main features of the lake regime. The geographical position of the lake to a certain extent reflects the general climatic features of the area, and the altitude 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 for 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, calculated in two ways: either together with the area of ​​the islands, or separately the area of ​​the water surface. Since the shores of the lakes are not sheer, the area of ​​the water surface (mirror of the lake) changes when the level of the lake changes.

The length of the lakeL, 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 outlines of the lake; for a meandering lake, this line, obviously, may not be straight, but may consist of separate segments of straight and curved lines.

Lake width– distinguish:

Greatest 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 lakes to its length L

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

The tortuosity coefficient of a shoreline can also be expressed as the ratio of the length of a shoreline S to the perimeter of the broken line S" , circling the contour of the lake:

m = S/ S"

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

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

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

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

The volume of water in the lake W , m 3 can be determined from the 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 bounded by adjacent isobaths, and the height is equal to the cross section between them. Denoting the areas bounded by individual isobaths, through ω 0 , ω 1 , ω 2 , ω 3 … ω n , and cutting them 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 is the depth corresponding to the largest isobath, ω n – the area of ​​the last (deepest) isobath.

The maximum depth of the lake ish Max , m.

WITH
average lake depth - h Wed , m - the ratio of the volume of water in a lake to the area of ​​its surface.

Average bottom slope between isobaths is determined by the formula:

Where l 1 , l 2 are the lengths of the isobaths between which the slope is determined; h isobath section, ω is the area of ​​the ring between the isobaths.

Average slope of the lake I is determined by the formula:

Where n is the number of isobaths.

Knowledge of the elements that characterize the shape of the lake basin is necessary not only to understand the basic laws of the lake regime, but also to solve a number of economic problems directly related to the exploitation of the lake. For example, when using a lake for transport purposes, it is necessary to know the distribution of depths within the entire water area and, in particular, in the coastal shallow zone. When regulating the flow of rivers flowing from the lake, it is necessary to have curves of the dependence of the volume of water and the areas of the lake on the height of the level. To calculate wave elements, it is important to know the distribution of depths and widths of the lake in different directions, etc.

Level regime of lakes.

The level regime of lakes is determined by a complex of the following natural conditions:

a) the ratio between the incoming (precipitation on the lake surface, surface inflow, underground inflow) and the outgoing part of the lake's water balance (evaporation, surface and underground runoff from the lake);

b) morphometric characteristics of the lake bowl and the lake basin (the ratio between the height of the water in the lake and the area of ​​its water surface);

c) the size of the lake, its shape, the nature of the shores, the nature of wind activity, which determines the size of waves, surges and surges.

Lake level fluctuations can be reduced to the following three main types: seasonal , annual And short-term .

Sometimes fluctuations in the level in the annual (seasonal) and long-term period, reflecting the regime of inflow and loss of water in the lake, are called absolute fluctuations , and short-term, which occur simultaneously with absolute changes in the level, are called relative fluctuations . Due to the fact that relative fluctuations occur simultaneously with absolute fluctuations, they additionally increase or decrease the amplitude of the absolute fluctuation of the lake level at its individual points.

Seasonal fluctuations that occur during the year are due to different in different months, but more or less correctly, annually recurring ratios between the incoming and outgoing parts of the water balance.

Amplitude of annual level fluctuations water in different lakes is different and depends on a number of factors: climatic conditions, the nature of nutrition, the size of the catchment area, the size of the lake, the geological conditions of the lake bed, etc.

The absolute values ​​of the amplitude of fluctuations in the levels of natural lakes vary over a fairly wide range - from tens of centimeters to 2-4 m and more, depending on the combination of the above conditions.

After a number of high-water years, when the inflow exceeds the water discharge from the lake, there is a higher level standing than after low-water periods. Due to the fact that on large (especially drainless) lakes the level of each given year is a consequence of the nature of the water content of a number of previous years, a low level can also occur in a high-water year if this year is included in the cycle of years of a low-water period, and a high level can occur in a low-water period if this a dry year is observed within a high-water period.

In addition to the mentioned cause, which takes place on each lake, sometimes there are so-called secular fluctuations , caused by geological factors (uplift, lowering of the lake basin and its individual parts).

Short-term, or relative, fluctuations in water levels in the lake are the result of waves, wind surges, and seiches.

Dynamic phenomena in lakes

Permanent and temporary movements of water masses. The movements of the water mass that occur in lakes can be divided into permanent and temporary.

Constant movements The waters in the lake in the form of currents are caused by a river flowing into or out of the lake (sewage streams). The intensity of such currents is determined by the ratio of the volume of the lake and the flow rate of the inflowing or outflowing river. If the volume of water in a flowing lake is small compared to the volume of water flowing into the lake, then a current is established in the lake similar to that in a river, only with correspondingly lower velocities. Such flowing lake can in some sense be considered as an extreme case of a significant expansion of the riverbed.

If, on the contrary, the volume of the lake is very large in comparison with the volume of water flowing in and out of it, then, although in this case it is also called flowing, in many respects, in terms of the nature of the processes occurring in it, it is closer to a drainless lake. A current of this type is observed in the lake. Baikal, the volume of which is extremely large compared to the volume of the flow of the rivers Selenga, Upper Angara, etc. flowing into it, and the river flowing from it. Hangars.

Temporary movements The water mass of the lake can manifest itself in the form of currents and waves.

Among the temporary currents, first of all, one should single out those that arise under the influence of the wind and as a result of uneven heating and cooling of the lake water.

Wind (drift) currents have a particularly significant effect on the nature of physical processes in lakes with large area, flat shape of the lake bed and shallow depths.

The uneven cooling and heating of the water masses of the lake primarily causes vertical, so-called convection currents , to some extent affecting the horizontal movement of water masses.

Among the temporary movements of the water masses of the lake, the most important are wind waves Andseiches.

Wind waves. Research has shown; that if two media of different density are located one above the other, but only in a state of rest of one medium relative to the other, the surface separating them will be a plane. If one of them moves relative to the other, then the surface separating them takes on a wave-like character, and the size of the waves depends on the speed of movement, the difference in densities and depths of both media.

When air moves over the water surface, as a result of friction, an unstable equilibrium is created on the surface of their separation, which, inevitably, being disturbed, naturally passes into a wave form that is stable under these conditions with an increase in the separation plane against the initial level line in some places and with a decrease in others.

Waves are characterized by the following elements (Fig. 5):

- vertex , or crest , waves - the highest point of a wave A;

- sole , or hollow - the lowest point of the wave IN;- height waves - the difference between the marks of the ridge and sole;

- length - distance between two peaks or two soles;

- steepness waves ( A ) at a given point - the tangent of the angle that is tangent to the wave profile with a horizontal line. Often in the calculated dependences, the steepness of a wave is understood not as the steepness at a given point, but as the ratio of the wavelength to the wave height;

- period waves - the period of time during which the wave runs a distance equal to its length;

- speed wave propagation - the distance traveled by any point of the wave (for example, a crest) per unit time.

According to the external form, they distinguish:

a) correct - two-dimensional - excitement, when one system of waves propagating in one direction and having the same shape and size is observed;

b) irregular - three-dimensional - excitement, consisting of randomly moving waves, the crests and hollows of which are divided into separate hillocks and depressions.

Rice. 5. Scheme of the wind wave

As applied to the case of regular two-dimensional waves, there is a theory of waves, known as the theory trochoidal waves . This theory establishes the external form of the wave and the laws of motion of water particles.

The waveform, according to the theory under consideration, is trochoid, i.e., a curve described by some point inside a circle rolling (without slipping) along a straight line, while a point on the circle of such a circle describes a curve called cycloid (Fig. 6).

Rice. 6. Trochoid (1) and cycloid (2).

seiches. Sometimes in the lake there is an oscillation of the entire mass of water, and no wave propagates over its surface. This oscillatory movement is called seiches . During seiches, the surface of the lake acquires a slope to one side or the other. The fixed axis around which the mirror of the lake oscillates is called node . Studies show that seiches are more stable in deep waters than in shallow waters.

Characteristics of the process of heating and cooling water in lakes.

Heating and cooling changes non-simultaneously throughout the water column. The most dramatic changes in temperature are observed on the surface of the reservoir, from where, under the influence of dynamic and convective mixing, currents and waves, they propagate throughout the entire water column.

How many closed depressions are there on land in which water accumulates. When water does not have time to evaporate, it forms lakes. That's what a lake is!

Definition of "lake"

A lake is an accumulation of water in a natural depression on land. It consists of a lake bowl or a bed filled with water to the brim. This body of water is not connected to the sea and ocean. Knowing what a lake is, it is easier to understand its origin. And it differs significantly. There is a lake: tectonic, glacial, river, seaside. There are also failure, mountain, crater and artificial.

Lake Features

What is a lake, what are its features? First, unlike rivers, lakes do not have currents and are not part of the oceans. Secondly, lakes have different mineralization of water. The deepest and freshest lake is Baikal. And the largest lake, and, in terms of salt composition, similar to ocean water, is the Caspian. Once it was the sea, as it was connected to the ocean.

There is also a division of lakes according to their position, according to the water balance, according to the chemical composition of the water and according to the nutritional value of the substances contained in the lake.

There are really a lot of features. There are lakes of different shapes, sizes, bottom topography. So, small lakes are called lagoons, and larger ones are called "seas". They receive water not only from rain, but also from underground rivers. Such close "cooperation" allows the rivers not to dry up. Often lakes even give life to new rivers.

A lake is a closed depression of land filled with water and not directly connected to the ocean. Unlike lakes, these are reservoirs of slow water exchange. The total area of ​​the Earth's lakes is about 2.7 million km2, or about 1.8% of the land surface. Lakes are ubiquitous, but uneven. On the geographical location of the lakes big influence the climate that determines their nutrition and evaporation, as well as factors contributing to the formation of lake basins. There are many lakes in the regions, they are full-flowing, fresh and mostly flowing. In areas with a dry climate, ceteris paribus, there are fewer lakes, often they are shallow, more often drainless, and therefore often saline. Thus, the distribution of lakes and their features are determined geographically.

4. Karst lakes, the basins of which arose as a result of sinkholes, soil subsidence and erosion (limestone, gypsum, dolomite). The dissolution of these rocks with water leads to the formation of deep, but insignificant lake basins.

5. Damped (dammed, or dammed) lakes arise as a result of blocking the channel (valley) of the river with blocks of rocks during landslides in the mountains (Sevan, Tana, many lakes of the Alps, and other mountainous ones). From a large mountain collapse in 1911, Sarez Lake was formed with a depth of 505 m.

A number of lakes are formed by other reasons:

• estuary lakes are common on the shores of the seas - these are coastal areas of the sea, separated from it by means of coastal spits;
• oxbow lakes - lakes that have arisen in old riverbeds.

According to the origin of the water mass, lakes are of two types.

1. Fresh lakes - the salinity of which does not exceed 1‰ (one ppm).

2. Brackish - the salinity of such lakes is up to 24‰.

3. Salty - with a content of dissolved substances in the range of 24.7-47‰.

4. Mineral (47‰). These lakes are soda, sulfate, chloride. In mineral lakes, salts can precipitate. For example, self-sustaining lakes Elton and Baskunchak, where salt is mined.

Usually sewage lakes are fresh, as the water in them is constantly updated. endorheic lakes more often they are salty, because evaporation prevails in their water consumption, and all minerals remain in the reservoir.

Lakes, like rivers, are the most important natural resources; are used by man for navigation, water supply, fishing, obtaining mineral salts and chemical elements. In separate places small lakes often artificially created by man. Then they are also called.