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 unevenly distributed. The total area of the Earth's lakes is about 2.7 million km 2 , or about 1.8% of the land surface.
Lakes among themselves have a number of differences both in external parameters and in the composition of the water structure, origin, etc.
Classification of lakes by origin
Glacial ponds were formed due to the melting of glaciers. This happened during periods of severe cooling, which have fettered the continents more than once over the past 2 million years. The result of the ice ages was modern lakes located in North America and Europe, namely in Canada, Baffin Island, Scandinavia, Karelia, the Baltic States, the Urals and other places.
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 spread tectonic plates. In these pits and faults, after the melting of the ice, water bodies formed. One of the representatives of glacial lakes can be called Lake. Arbersee.
The reason for the emergence of tectonic lakes was the movement of lithospheric plates, as a result of which faults formed in the earth's crust. They began to fill with water from melting glaciers, which led to the appearance of this type of reservoir. The clearest example is Lake Baikal.
River lakes appear when some sections of flowing rivers dry out. In this case, there is the formation of chain reservoirs arising from one river. The second option of river formations are floodplain lakes, which appear due to water barriers that interrupt the water channel.
Seaside lakes are called estuaries. They appear during the flooding of lowland rivers with the waters of the seas or as a result of the sinking 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 that emerged from the confluence of the river and the sea, the water has a slightly salty taste.
Karst lakes are earth pits that are filled with the waters of underground rivers. Excavations are dips in the lithosphere, which is composed of limestone rocks. Due to the failure, limestone rocks line the bottom of the reservoir, which affects the transparency of the waters it fills: they are crystal clear.
Karst lakes have one distinctive feature - they are periodic in their appearance. That is, they can disappear and form again. This phenomenon depends on the level of underground rivers.
Mountain lakes are located in mountain basins. They are formed in several ways. Due to mountain collapses that block the river flow and thereby form lakes. The second way of formation is the slow gathering of huge blocks of ice, which leave behind them deep dips of land - hollows that are filled with water from melted ice.
Volcanic lakes appear in the craters of dormant volcanoes. Such craters have a significant depth and high edges, which prevents runoff and inflow of river waters. This makes the volcanic lake virtually isolated. Craters are filled with rainwater. The specific location of such objects is often reflected in the composition of their waters. The increased carbon dioxide content makes them dead, unsuitable for life.
Artificial lakes are reservoirs and ponds. They are created intentionally for the industrial purposes of settlements. Also, artificial lakes can be the result of earthworks, when the remaining earth pits are filled with rainwater.
The classification of lakes according to origin was compiled above.
Types of Lakes by Position
The classification of lakes depending on the position in relation to the land can be done as follows:
- Ground lakes are located directly on the land surface. These water bodies participate in the constant circulation of water.
- Underground lakes are located in underground mountain caves.
Mineral Classification
The classification of lakes by the number of salts is as follows:
- Fresh lakes are formed from rainwater, melting glaciers, groundwater. The waters of such natural objects do not contain salts. In addition, fresh lakes are the result of overlapping riverbeds. The largest fresh lake is Baikal.
- Salt water bodies are divided into brackish and saline.
Brackish lakes are common in arid areas: steppes and deserts.
Salt lakes in terms of salt content in the thickness of their waters resemble oceans. Sometimes the salt concentration of the lakes is slightly higher than in the seas and oceans.
Chemical classification
The chemical composition of the Earth's lakes is different, it depends on the amount of impurities in the water. Lakes are named based on this:
- In carbonate lakes, an increased concentration of Na and Ca. From the bowels of such reservoirs, soda is being extracted.
- Sulphate lakes are considered medicinal due to the content of Na and Mg in them. In addition, sulfate lakes are the place where glauber salt is mined.
- Chloride - these are salt lakes, which are the place of extraction of common table salt.
Water Balance Classification
- Sewage lakes are endowed with river runoff, 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 the resulting one is always the same. An excellent example is the large lakes - Baikal and Teletskoye. The water of the sewage lakes is fresh.
- Drainage-free - these are salt lakes, since the water flow in them is more active than its flow. They are located in desert zones and steppes. Sometimes in them on an industrial scale is the extraction of salt and soda.
Nutrient classification
- Oligotrophic lakes contain a relatively small amount of nutrients. The features are transparency and purity of water, color from blue to green, the depth of the lakes is significant - from medium to deep, a decrease in oxygen concentration closer to the bottom of the lake.
- Eutrophic saturated with a high concentration of nutrients. The following phenomena are peculiarities of such lakes: the amount of oxygen decreases abruptly to the bottom, mineral salts are abundant, the color of water is from dark green to brown, which is why water transparency is low.
- Dystrophic lakes are extremely poor in minerals. There is little oxygen, transparency is low, the color of the water may be yellow or dark red.
Conclusion
The Earth's water basin consists of: rivers, seas, oceans, glaciers of the oceans, lakes. There are several types of lake classifications. They were considered in this article.
Lakes, like other water bodies, are the most important natural resources that are actively used by man in various fields.