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. The total area of the Earth's lakes is about 2.7 million km2, 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 as a result of the melting of glaciers. This happened during periods of severe cooling, which fettered the continents repeatedly over the past 2 million years. The ice ages resulted in modern lakes located in North America and Europe, namely in Canada, Baffin Island, Scandinavia, Karelia, the B altic states, the Urals and in 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 tectonicplates. In these pits and faults, after the melting of ice, reservoirs were 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 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 clearest 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 option for 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. The estuaries, formed from the confluence of the river and the sea, have a slightly s alty taste of water.
Karst lakes are earth pits that are filled with the waters of 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 onea distinctive feature is that 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 hollows. 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 sinkholes of land - hollows that are filled with water from melted ice.
Lakes of volcanic type appear in the craters of dormant volcanoes. Such craters have a significant depth and high edges, which prevents the runoff and inflow of river waters. This makes the volcanic lake practically isolated. Craters fill with rainwater. The specific location of such objects is often reflected in the composition of their waters. High levels of carbon dioxide make them dead, uninhabitable.
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 earthen pits are filled with rainwater.
Above, a classification of lakes was compiled depending on their origin.
Types of lakes by position
Create a classification of lakes depending on the position in relation to the earth, as follows:
- Land lakes are located directly on the land surface. These water bodies participate in the constant water cycle.
- Underground lakes are located in underground mountain caves.
Classification by mineralization
You can classify lakes by the amount of s alts as follows:
- Fresh lakes are formed from rainwater, melting glaciers, groundwater. The waters of such natural objects do not contain s alts. In addition, fresh lakes are a consequence of the overlapping of river beds. The largest fresh lake is Baikal.
- Saline water bodies are divided into brackish and s alty.
Brackish lakes are common in arid areas: steppes and deserts.
S alt lakes in terms of s alt content in the thickness of their waters resemble oceans. Sometimes the s alt concentration of lakes is slightly higher than in the seas and oceans.
Classification by chemical composition
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 there is an increased concentration of Na and Ca. Soda is mined from the depths of such reservoirs.
- Sulfate lakes are considered curative due to their content of Na and Mg. In addition, sulfate lakes are the place where Glauber's s alt is mined.
- Chloride lakes are s alt lakes, which are the place where common table s alt is mined.
Classification by water balance
- Waste lakes are endowed with river runoff, which is used to dischargesome amount of water. 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. Waste lake water is fresh.
- Drainless lakes are saline lakes, since water consumption in them is more active than its flow. They are located in the desert and steppe zones. Sometimes they produce s alt and soda on an industrial scale.
Nutrient classification
- Oligotrophic lakes contain relatively few 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.
- Eutrophic are saturated with a high concentration of nutrients. The peculiarities of such lakes are the following phenomena: the amount of oxygen sharply decreases towards the bottom, there is an excess of mineral s alts, the color of the water is from dark green to brown, hence the low transparency of the water.
- Dystrophic lakes are extremely poor in minerals. There is little oxygen, transparency is low, the color of the water can be yellow or dark red.
Conclusion
The water basin of the Earth consists 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 that are actively used by humans in various fields.
