Lakes and their origin. Tectonic, volcanic processes

Experts are sounding the alarm about the catastrophic state of the Volga and many other rivers of the Russian Federation.

Economist Valentin Neverov comments:

The Volga, first of all, as well as many other rivers and reservoirs of the European-Ural and North Caucasian regions of the country are becoming catastrophically shallow and polluted. It comes to the point that many coastal cities and towns are forced ... to bring fresh water from other regions, and tourists accustomed to cruises on Russian rivers change to buses and trains. Freight traffic by waterways is also falling, including along the Eurasian route Neva-Ladoga-Volga-Astrakhan (Volgo-Balt).

This situation was recently voiced by Hydrometeorological Center, Rostourism, Green Patrol of the Volga Basin, and the Volga Department of Roshydromet. Thus, in the second quarter of 2015, the inflow of water into the Volga-Kama HPP cascade is expected to be 15-40% below the norm. The inflow of water into the Ivankovskoye reservoir (one of the largest in the Moscow water supply system) will be only 45% of the required volume. In addition, in the first ten days of June this year. in the largest lakes of the European part of Russia, a water level was recorded that was significantly lower than the standard. For example, in Ladoga this figure was below the norm by 76 cm, in Lake Ilmen (Novgorod Region) - by 42 cm, in Pskov and Peipus Lakes (the largest Estonian-West Russian water basin), respectively - by 30 and 27 cm.

What is happening to our reservoirs? Experts can be said to be in solidarity in assessing the main causes of the situation. First, since the late 1980s. in the Russian Federation there is not, and is not yet expected, a single, efficient system of state management of ecology, forestry and water resources. Secondly, massive and long-term deforestation of coastal forests, as well as the growing scale of coastal landfills and waste dumped into the water, have actually destroyed the sources of water supply and the self-cleaning structure of rivers, lakes, and reservoirs. And as a result - a sharp deterioration in water quality, erosion of coasts, irreparable damage to aquatic biological resources, flora and fauna not only in water basins, but also in nearby areas. Over the past 10 years alone, the total stocks of fish resources in the rivers, lakes, reservoirs of the European, Ural and North Caucasian regions of the country have more than halved.

Thirdly, in the same regions, the consequences of the “record” rates of drainage of swamps and other land reclamation measures carried out in the 1960s-1980s continue to affect. with systematic violations of technological and environmental standards. Finally, fourthly: the cleaning of the bottom, coasts and channels of water spaces has been carried out for several years, at most, at a level of 40% of the required volume. Hence - and such a disastrous result for almost all water arteries and basins of the European-Ural and North Caucasian regions. Which, of course, has a negative impact on the state of agricultural soils and other components of the local biosphere. At the same time, the level of fines for environmental violations, at best, purely symbolically compensates for the damage caused.

In addition, there are many schemes for avoiding the official statement of environmental violations, respectively, from paying fines. First of all, experts propose to return the state to water and forestry, in general - to the sphere of protecting the biosphere. Moreover, with tough measures against violators of technological and environmental standards. But what to do in conditions when the volume of state funding for reforestation, water treatment, waste disposal, reconstruction of reclamation networks, etc. are shrinking? When there is an increasing lack of domestic technologies and personnel? When, finally, there is no state control over the use of money allocated for solving environmental and related tasks?

Today it is also worth remembering that clear-cutting of forests, including coastal ones, as well as soil-protective forest belts, started ... back in the mid-1950s, which even then led to a sharp decrease in soil fertility and shallowing of water areas. Oddly enough, but such consequences were predetermined by the Decree of the Central Committee and the Council of Ministers of the USSR No. 192 of February 7, 1955 “On increasing logging in the central, southern and western regions and improving forest management in the USSR.” The document allowed, for example, "... logging and logging in forests of forbidden and protective strips along rivers, lakes, reservoirs, highways and railways."

By the way, the atmosphere that then developed in society around environmental problems can be evidenced by such an amazing, from our point of view, fact. At the end of August 1954, in the midst of the notorious virgin saga, the Central Committee of the Party received a letter from forestry professors P. Vasiliev, V. Timofeev, corresponding member of the USSR Academy of Sciences N. Baransky and agrarian academician V. Sukhachev with a proposal to convince the outstanding Russian writer Leonid Leonov ... to remake his novel "Russian Forest", published during Stalin's lifetime, in January 1953. And, above all, to remove from the novel "bourgeois theories of a certain" permanence "of the forest ...". Say, "... the author exaggerates, especially in the RSFSR, the consequences of expanding logging."

True, this letter was not given a go. But in the context of the post-Stalinist forestry, water management, environmental, and general economic policy, the case is very remarkable. And how is the situation of those distant years, in fact, very similar to the current one, isn't it?

Special for the Centenary

A few years ago, scientists around the world began to talk about the fact that many water bodies of our planet are losing water volumes. Science has found its own explanation for this - the situation was directly linked to global climate change, and therefore they identified a serious problem for humanity. It lies in the fact that in a few decades more and more countries on Earth will lack not only drinking water.

The lack of life-giving moisture will become an obstacle to unlimited shipping and, in general, the situation will have an extremely negative impact on the ecology of many territories. The journalists of the publication "Ecology of Regions" decided to analyze the theoretical statements of scientists, using open sources, the media, forums and social networks, as well as the opinions of experts who agreed to evaluate what is happening. And it is worth noting that the problem really exists and it had to be solved yesterday. Today, the only area on the planet where the water level is constantly rising is the Arctic. The process of snow melting, which has accelerated in recent years, has led to the fact that scientists are forced to look not for the reasons for what is happening, but for ways to stop the process. In general, every year there are fewer and fewer sources of fresh water on Earth - large and small rivers dry up, lakes dry up, the volume of water in the seas decreases. According to American scientists, over nine hundred thousand small rivers have dried up since 2004. It is no better in Russia: each region is ready to provide its own story about how large rivers become shallow and small ones disappear.

Irkutsk region, Russia. The low water level affects the state of reservoirs. Scientists note that there is less water in the Angara, the Bratsk reservoir, Baikal, where the water level is below the critical level, is of particular concern. Ecologist Ivan Smolensky considers the uncontrolled cutting of green spaces in the region one of the main problems that influenced the development of the situation. “The results of many years of research show how cutting down trees affects the state of reservoirs and their filling. In the Irkutsk region, uncontrolled deforestation has been going on for decades. The sad consequence of this is a sharp decrease in the water level in reservoirs, the drying up of small rivers. And the day will come when not only trees, but also water will not remain in the Irkutsk region.”

Samara region, Russia. About the rapid shallowing of the main tributary of the Volga - the Samara River. In 2013, it was officially announced that Samara entered the top ten cities in the country with an unfavorable environmental background. Naturally, such results were announced not only after studying the state of atmospheric air and soil in the subjects of the federation, but also the state of water bodies. So in Samara, scientists and environmentalists announced that every year small rivers are rapidly dying, the areas on which they ran are swamped, and the chairman of the Samara Regional Green League, Sergey Simak, announced the need to develop and implement a regional comprehensive program to save the region's water bodies . The main reason for what is happening in the Samara region was called active human activity. It is he who pollutes the rivers with industrial waste, brings the coastal zones into disorder and does not care about environmental protection. Today, navigation is threatened in the Samara region, and representatives of shipping companies recall those times when the Volga was a full-flowing river and there was no reason to think that the river would begin to shallow and stop river ships.

Voronezh region, Russia. In 2015, ecologists of the Voronezh region officially announced that more than thirty rivers had disappeared in the region. In this subject of the federation, the vast majority of small rivers, the condition of which has deteriorated sharply over the past decades - they have become shallow and do not receive enough water to recover. In 2010, the government of the region approved a concept for saving small rivers; within its framework, funds are annually allocated for the survey and clearing of river beds. On the whole, however, the situation remains critical.

Tula region, Russia. Local ecologists say about the low water level in the reservoirs of the region - it is observed in summer, and even periods of short-term downpours do not fill the reservoirs with the necessary volume of water. In the region in recent years, large rivers have become very shallow, and several small rivers have dried up. The water resources of small rivers currently amount to 1.3 km3 of water at a 75% supply. Depending on the natural conditions for individual rivers, the distribution of annual runoff has different specific features. Officials see the improvement of the situation in the implementation of measures to save the small rivers of the Tula region, but often the implementation of the planned work rests on the lack of funding.

Rostov region, Russia. Last year, scientists in the Rostov region announced an imminent ecological catastrophe - the Don River, one of the main arteries not only in this region, but throughout the entire Southern Federal District, is becoming shallow. As a result - the shallowing of the Volga, the threat to the existence of the shipping company, the extinction of many types of aquatic biological resources. A clear shallowing of the Don has been observed over the past ten years. Candidate of Biological Sciences Oleg Stepanyan believes that one of the reasons is the increase in dry years in the country. The low water level in the Don is noted not only in summer, but also at other times of the year. The marginal sections of the river delta are dying off. And in parallel with these, catastrophic surges of salt water from the Sea of ​​\u200b\u200bAzov are observed. Low water has already become one of the reasons for the poor quality of drinking water. Scientists believe that the basic water supply has been disrupted due to environmental pressures that have occurred after the mass liquidation of coal mines in the region. The water supply of the region is based on the use of surface and ground waters, which are unevenly distributed. Ecologists make the most unfavorable forecasts for the future.

And, perhaps, the Volga was in the most critical situation. Its shallowing is observed in many regions of Russia. And if ten years ago scientists talked about the need to save the river, today ecologists declare the impossibility of stopping the process of destruction of water resources, which a person began not yesterday, but many years ago, mindlessly using natural resources in his own interests, not thinking about restoring nature after how to use her gifts.

Russia occupies a third of the Eurasian continent, its nature is truly rich. Here are some of the largest reserves of fresh water. Surface water accounts for more than 12% of the area of ​​the entire country. It is known that Russian rivers and lakes annually attract a huge number of tourists, and also supply the population with clean water. Some interesting facts about the rivers and lakes of Russia.

water arteries

The largest country in the world has almost 3 million natural streams, many of which have played a huge role in history. They were the main transport routes, the development and settlement of new territories began with them. Most major cities are built on them. Are you curious to know the most interesting facts about the rivers of Russia?

The Ob is the largest river in Russia and the sixth largest in the world.

1. The Ob is formed by two rivers - Katun and Biya, which have a different color. Therefore, sometimes on the Ob you can see a striped stream of water - the confluence of two rivers.
2. Not far from Novosibirsk there is a dam that forms the Ob Sea. There are recreation centers for those wishing to spend a vacation or a weekend by the water.
3. The geography of the flow is very diverse, as is its temperature. The warmest place is located near Barnaul. Here the water warms up to 28 degrees. In other areas, the temperature, as a rule, does not exceed 23 degrees.
4. From there, gas, peat and oil are extracted.
5. Provides a third of the world market with whitefish.

The Yenisei is the second largest river in Russia.

1. The Yenisei is considered one of the most full-flowing, more than 500 rivers flow into it.
2. The confluence of the Small and Big Yenisei is considered the center of Asia.
3. In the 19th century, an artificial canal was built that connected the Yenisei with the Ob. But today it is no longer used.

The Lena is the largest river entirely within Russia.

1. In spring, its level rises by 10-15 m. And because of the risk of flooding, its banks are practically uninhabited.
2. The only river whose course is in the permafrost region.

The Volga is the longest among European rivers and one of the largest in the world.

1. The construction of reservoirs shortened the length of the Volga by more than one and a half hundred kilometers.
2. It is an important source of electricity. Hydroelectric power plants are located on the river, which provide electricity to nearby cities.
3. In the Volga you can meet pelicans and flamingos.

Other rivers in Russia may be smaller, but no less important.

1. Neva is a small stream on the territory of the Leningrad region with a unique water system. In 1963, an incredible event happened there. Due to problems with the chassis, the Tu-124 passenger liner had to splash down directly on the river. This was one of the few splashdowns where no one was hurt.
2. Piana is considered the most winding in the world. On its banks is located the "Ichkalovsky reserve", which is known for its karst caves.
3. The Irtysh is the main tributary of the Ob. It is one of the cleanest in the world. Representatives of sturgeon, carp, pike and other species of fish live in it.
4. The Ural is interesting in that it divides two parts of the world, since one of its shores belongs to Asia, and the other to Europe. The Ural is infamous for the fact that the notorious Chapaev drowned in it.
5. Vishera is formed by the confluence of two rivers - Bolshaya and Malaya. On their banks there are two villages with the same names. It is curious that the settlement, which bears the name of Malaya Vishera, is many times larger than the Bolshoy.

Many large water arteries of our country are difficult to access, so we can still learn many interesting facts about rivers in the future.

reservoirs

There are almost 3 million lakes in Russia, with a total area of ​​​​more than 400 thousand square kilometers. Almost all are of glacial origin. Most of them have fresh water, but there are also salty reservoirs. Consider some interesting facts about lakes.

1. Baikal is undoubtedly the deepest and cleanest lake. Its crystal clarity allows you to see objects at a depth of forty meters. Its basin holds approximately 19% of the world's fresh water. Due to the size of Baikal, it is often compared to the sea;
2. The Caspian Sea excites the minds of scientists by the fact that its level is constantly fluctuating, and today no one can give an unambiguous answer why this is happening. The Caspian is rich in oil and sturgeon reserves. However, getting one, there is a risk of losing the other. Therefore, today the protection of this reservoir is the main environmental task of the country;
3. We owe the birth of the Russian fleet to the Ladoga reservoir. Moreover, during the Great Patriotic War, a path passed through its ice, along which food supplies were delivered to besieged Leningrad, and about a million people were evacuated;
4. We know that Lake Ilmen began to be settled by the Slavs as early as the 8th century, at the time of the birth of Russia. Unfortunately, today it is referred to as "dying lakes". Slowly but surely, the amount of silt is growing, and the waters are swamping.

Undoubtedly, the rivers and lakes of this great country hide many secrets in their depths. After all, these are not only beautiful geographical objects, but also millennia of history. And, of course, there are more interesting facts that we have to learn.

According to Socrates, the exact word reflects reality. So the common name of these five majestic natural reservoirs confirms this truth. They are given a name - the Great Lakes. They, connecting with each other, formed a unique water system on the border of southern Canada and the northeastern United States.

These Great Lakes of North America have a total water surface area of ​​more than 240,000 square kilometers and a fresh water supply that is 1/5 (21%) of the world's total.

Origin story

During the formation of the North American continent, tectonic processes took place that formed the landscape of the area with uplands and lowlands.

Later, about a million years ago, the territory of the modern north of the United States and Canada was covered by an ice sheet, which was given the name Lavrentite by modern scientists (after the St. Lawrence River). Its height, according to various estimates, at its peak reached one and a half to two kilometers. During the time that it was forming and melting, it significantly influenced the future landscape of the area.

12,000 years ago, the glacier retreated towards the North Pole. Natural pits on the land surface were filled with melted fresh water. Thus, the largest system of lakes in the world was formed. It includes five main lakes, interconnected by streams, rivers, channels and straits, and many medium and smaller reservoirs and marsh formations.

The system and individual islands got their name during the exploration of the central and northeastern parts of the continent by European pioneers. It happened in the XVII-XVIII centuries.

List describing the great lakes of North America

Five pearls from the necklace of the world's most beautiful and largest natural reservoirs of fresh water are located on the northeastern border of the United States and Canada. Regarding their location above sea level, they are divided into upper (Upper - the largest, Huron, Michigan) and lower (Erie and Ontario - the smallest of five). In addition to these large reservoirs, there are a number of medium-sized reservoirs in the system.

These primarily include:

• St. Marys;
• St. Clair;
• Nipigon.

The water basin includes more than a thousand small lakes.

The biggest

Of course, it is the large lakes that are of the greatest interest.

Upper

It got its name due to the fact that it is located at an altitude of 186 meters above the Atlantic Ocean. The top one is the largest and coldest.

The volume of fresh water exceeds 12 thousand km³. In the north, it washes the coast of the Canadian province of Ontario, on the other sides - the coast of the American states of Minnesota, Wisconsin, Michigan. The north coast is mostly mountainous.

The water of the reservoir, even in summer, does not warm up above 5º C. But thanks to this fact, it is the cleanest of all reservoirs in the basin. In winter, only the coastal line freezes. The rest of the surface of the reservoir is exposed to seasonal northwesterly winds, which cause constantly raging storms. Sometimes waves reach a height of 10-12 meters.

The St. Marys River, flowing from it, flows into Lake Huron, lower in the cascade.

Huron

Its wide spatial arrangement allowed it to have a variety of natural areas along the coastline.

Its waters also wash the shores of the two countries. The same Canadian province and two states: Illinois and Michigan. On the eastern side of the lake is largest lake island in the world Manitoulin.

Michigan

The name comes from the Indian word Mishegani, which means Big Water. Wide Strait of Michigan like brother with brother - hand in hand - connects with Huron . This is the only lake of the five located entirely within the United States.

Their common ecosystem is in constant interaction and exchange. Therefore, their average annual water temperatures and climate are approximately the same. The total supply of drinking water of the two reservoirs is 8.4 thousand km ³.

Lake Michigan has an elongated shape and 2.5 thousand kilometers of coastline. Spread on the shore, for a hundred kilometers each, are the two largest port cities of the Great Lakes - Milwaukee and Chicago.

Erie

Further down the cascade is Lake Erie. Its area is 25,600 km². Its natural feature among the brothers was expressed in the smallest depth - it is just over 60 meters. Accordingly, it warms up well, which makes it in demand as a resort place.

The plateau slopes towards the ocean, and the water flowing from Erie many millennia ago has found its way to the east. Its stream turned into a short, but famous for its unique waterfall river - the Niagara. After 56 kilometers, it flows into the smallest of the Great Lakes - Ontario.

Ontario

The Huron tribal name means "Lake of Shining Waters".

The location and presence of a warmer climate has turned this lake into a tourist paradise. It has a large number of fish of different species.

Around:

• agriculture is widely developed;
• selected varieties of grapes are grown;
• elite wines are produced.

Saint Lawrence River, flowing from Ontario, is the only natural spillway of the system to the Atlantic.

The smallest

There are thousands of small lakes around the Great ones. Most of them are located in Canada. They are evenly dispersed between Lakes Superior, Huron, and the St. Lawrence River.

Among them are noted:

• Barque;
• Skugog;
• Dumoine;
• Kuerk.

Some of them are so small that it is difficult to find these lakes on the map.

Meaning

The existence of such a water system in the region is of great importance. Its presence is a fundamental factor in active life in the northeastern United States and southern Canada. Its main reason is the total supply of drinking water.

The fresh water of this system provides a population of 40 million people. A unique ecosystem has developed around it, which not only accepts the existing climate and weather, but itself influences and shapes them. In the basin of the entire water area, 25% of the agricultural production of Canada and 7% of the United States is concentrated. Electricity generation by the GRES network on the waterway of the entire system is 50 billion kilowatts per year.

Shipping

The use of lakes as a transport highway began from the time of their discovery. Since ancient times, the Indians have been actively moving to these parts on their famous pirogues and canoes. Taking into account the land inaccessibility of many areas in the vicinity of the lakes, from the second half of the 17th century, passenger and merchant shipping began to actively develop.

At present, a 3,000-kilometer-long waterway, reconstructed in 1959, is used to transport a variety of industrial and agricultural goods and raw materials. There are about 65 ports on the Great Lakes, 15 of them are international.

Tourism

The natural diversity of the entire basin and the vicinity of the lakes created excellent conditions for the development of almost all types of tourism.

The main ones are:

1. Fishing. Individual tours are especially popular. All fishermen note the richness and diversity of local fish species. The main ones are perch, coho salmon, smelt, chinook, quistivomer char, trout, herring whitefish, pike, trout, salmon, crappie and about 120 more species.
2. Water tourism on small row boats(canoes, kayaks, kayaks). Many routes have been laid with equipped places of rest and lodging for the night. Those who wish can go to completely wild corners of the lakes. Due to the presence of channels, canals and rivers, travelers can get from anywhere to anywhere in the Great Lakes basin.
3. Beach holidays and spa treatments. Basically, for these types of recreation, people go to Ontario and Erie.

According to official statistics, 70 million people annually visit the majestic lakes for tourism purposes.

The uniqueness and diversity of the local ecosystem: sandy beaches and rocks, wild steep banks and coastal dunes, deciduous relict forests and prairies, pine and cedar groves - this is not a complete list of the natural forms of the region.

Uniqueness

The climate in the water area of ​​the system is humid, temperate continental. Often there is a change of weather, a significant influence is exerted by various cyclones. Average air temperatures in January range from -8°C in the northern part to -3 ° С on the southern shores. Average in summer - 18-21° C.

The water of the lakes is one of the cleanest among all lakes in the world. It has low mineralization (from 0.06 to 0.13 g/l). This is due to the implementation of large preventive and cleaning measures in recent decades (before that, the situation was much worse). Its average transparency (viewability in depth) is 15 meters. Slightly cloudy in windy conditions.

The system is replenished with water through:

• runoff water;
• precipitation;
• underwater sources.

Drinking water from the lakes is consumed by 40 million people. Thirty - in the US and Canada; and is also exported to 50 countries of the world. The total water consumption is over 20 km³/year. The cleanest water in the northern Upper Lake, the least - in southern Erie.

In the table - the main characteristics.

Environmental problems

The presence on the coast of large industrialized cities and entire conglomerations at one time led to severe pollution of water resources. Discharges of waste technical water and waste from factories in the 18th-19th centuries had no treatment. Only in the 20th century did they begin to seriously deal with environmental issues in the water area of ​​the system.

By the 1970s, the issue had become so urgent that the governments of two countries, the United States and Canada, began to discuss it at the state level. So, in 1972, they signed the “Agreement on the quality of water in the Great Lakes”. These measures have received the widest response from all stakeholders and the public. We began to carry out systematic work aimed at improving the environmental situation in the region. Many national reserves and parks have been created. This, in turn, gives more opportunities to preserve the pristine nature in this area.

By the beginning of the 21st century, scientists carried out a number of observational activities that confirmed the positive results of timely measures taken. The water quality has improved significantly.

There are a great many of those in the history of the discovery, settlement and exploration of North America.

Here are just a few of them:

1. The discovery of unique lakes was accompanied by the following factor: the French pioneers, referring to the stories of local Indians from the outskirts of Quebec, went to look not for lakes, but for Mishigani (in Indian language - “big water”). Which, they said, was west of the headwaters of the St. Lawrence River. The French "forest vagabonds" (as their contemporaries called them) assumed that this water would be the Pacific Ocean, and through it a direct road to India would be opened to them.
2. For a long time, scientists could not give an unambiguous answer to the cause of the origin of the lakes. Initially, variants of volcanic processes or water erosion of the land surface were considered as factors in the formation of lake basins. But only by the end of the 20th century it was definitely found out that a large lake system was formed as a result of the “work” of the Lavrentin glacier. This went on for a million years. And only by the XII century BC, it melted and receded so much that the recesses made by it could be filled with fresh water.
3. The pits of the lakes were formed due to primary tectonic processes and the long-term impact of the glacier. It created pressure from above with huge masses of ice (their height reached 1.5-2 km) and interspersed with fragments of soil, rocks, pumice, etc. When it moved along the surface, the future bottom of the lake system was “grinded”. At the same time, under the weight of the glacier, the surface of the earth was pressed inward. Therefore, under the influence of inertial forces, the reverse process is now taking place - the raising of the concave surface (the bottom of the lakes) at a rate of 2.5 mm per year.
4. The location of Niagara Falls, which is known and accessible for inspection now, was much lower downstream. For several thousand years, it has significantly "raised" up (approximately 10-11 kilometers). This happened due to the gradual hydroerosion of the soil of the channel. Little by little water destroys the slopes of rocks, microparticles are washed downstream, and the ledge of the waterfall recedes back. Now this process is significantly “slowed down” due to the work of bypass channels.
5. The Upper Lake, being the largest of the freshwater lakes, is second in size to the salty Caspian. It, although it is written on the maps "Caspian Sea", is actually a lake. Its area is more than 370,000 km2.
6. The lake system of North America is unique and diverse. In addition to the presence of huge reservoirs and their combinations, there is also the smallest lake in the world on its territory. It is called Sarasota, and it is located in the southern state of Florida. Its diameter is only 120-130 meters.

Video

A lake is a closed depression of land filled with water and not directly connected to the ocean. Unlike rivers, lakes are reservoirs of slow water exchange. The total area of ​​the Earth's lakes is about 2.7 million km 2, or about 1.8% of the land surface. Lakes are ubiquitous, but uneven. The geographic location of lakes is greatly influenced by the climate, which determines their nutrition and evaporation, as well as factors that contribute to the formation of lake basins. In areas with a humid climate, there are many lakes, they are full-flowing, fresh and mostly flowing. In regions with a dry climate, ceteris paribus, there are fewer lakes, they are often shallow in water, more often drainless, and therefore often saline.

In this way, the distribution of lakes and their hydrochemical features are determined by geographical zonality.

The largest lake is the Caspian (area 368 thousand km 2). The largest are also lakes Superior, Huron and Michigan (North America), Victoria (Africa), Aral (Eurasia). The deepest are Baikal (Eurasia) - 1620 m and Tanganyika (Africa) - 1470 m.

Lakes are usually classified according to four criteria:

- origin of lake basins;
- the origin of the water mass;
- water regime;
- salinity (amount of dissolved substances).

According to the origin of lake basins, lakes are divided into five groups.

1 . Tectonic lake basins are formed as a result of the formation of cracks, faults and subsidence of the earth's crust. They are distinguished by great depth and steep slopes (Baikal, the Great North American and African lakes, Winnipeg, the Great Slave, the Dead Sea, Chad, Air, Titicaca, Poopo, etc.).

2 . Volcanic, which are formed in the craters of volcanoes or in the depressions of lava fields (Kuril and Kronotskoe in Kamchatka, many lakes on the island of Java and New Zealand).

3 . Glacial lake basins are formed in connection with the plowing activity of glaciers (erosion) and the accumulation of water in front of glacial landforms, when the glacier, during melting, deposited transported material, forming hills, ridges, uplands and depressions - the site. These lakes are usually narrow and long, oriented along the lines of glacier melting (lakes in Finland, Karelia, the Alps, the Urals, the Caucasus, etc.).

4 . Karst lakes, the basins of which arose as a result of failures, soil subsidence and erosion of rocks (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, the Himalayas and other mountainous countries). From a large mountain collapse in the Pamirs in 1911, Sarez Lake was formed with a depth of 505 m.

A number of lakes are formed by other reasons:

- firth 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 . atmospheric. These are lakes that have never been part of the oceans. Such lakes predominate on Earth.
2 . relic, or residual, lakes that appeared on the site of the retreating seas (Caspian, Aral, Ladoga, Onega, Ilmen, etc.). In the recent past, the Caspian Sea was connected with the Azov Strait, which existed on the site of the current valley of the Manych River.

By water regime also distinguish two types of lakes - waste and closed.

1 . Waste lakes are lakes into which rivers flow and flow out (lakes have a drain). These lakes are most often located in the zone of excessive moisture.
2 . Endorheic - into which rivers flow, but none flows out (lakes do not have a drain). Such lakes are located mainly in the zone of insufficient moisture.

By the amount of dissolved substances There are four types of lakes: fresh, salty, brackish and mineral.

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 are more often saline, because evaporation prevails in their water flow, and all mineral substances remain in the reservoir.

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