Reservoirs on the planet have a different origin. Water, glaciers, the earth's crust and wind are involved in their creation. Signs of a lake that appeared in this way may be different.
What is a lake
What is a lake, what are its signs? The answer to this question is contained in textbooks on geography. Lake - a depression in the earth's crust with water, the renewal of which occurs slowly. Ditches are formed under the influence of natural elements. They eventually fill with surface or groundwater. Thus, a new body of water is obtained.
Scientists-geographers have developed different classifications of lakes according to the presence of flora and fauna, salinity and the method of formation. The school studies in detail the signs of the lake (grade 2).
Lifeless lakes tend to have a high level of mineralization. The main number of reservoirs is formed by tectonic and volcanic processes. Some of the deepenings under the lakes were formed by glaciers during their retreat. More and more reservoirs are created by man for various needs. Least of all lakes have occurred as a result of their separation from the ocean.
Dam lakes
Signs of the lakedam type: the presence of a valley blocked by a glacier, a landslide, a collapse of rocks, etc. Varieties of these reservoirs:
- River. Occur during the summer low water on individual streams, the level of which in some places drops below the surface of the channel. The river turns into a chain of lakes separated by dry patches.
- Floodplain. Their other name is old people. If the river makes a shorter path for itself, then a lake will form in the place of the former channel.
- Valley. Appear in mountain gorges in which there are watercourses. As a result of the massive fall of stones, the channel is blocked by a natural dam. It turns out a new lake.
- Coastal: lagoons and estuaries. The first are bays of shallow depth, which were fenced off from the sea by a sandy spit or sediments of rivers. The second are river mouths flooded with the sea.
Moraine lakes
Morainic include lakes that were formed as a result of the movement of the glacier. Most of them appeared in the Quaternary period. During the retreat, the glacier leaves behind a trail consisting of a large number of debris (sand, crushed stone, clay, rocks, etc.). The moraine does not remain an even layer, but creates hills and depressions. Once filled with water, the latter become lakes.
What are the most noticeable signs of this type of lake? As a rule, the depth of the reservoir does not exceed 10 m, and the banks have a rugged contour. Most of them have a small area, but there are also large lakes (Seliger, Ilmen, Chudsko-Pskovskoye).
Car Lakes
These lakes also owe their origin to the glacier. The impact of the ice cover, firn and weathering led to the appearance of depressions, which subsequently filled with water. You can meet such reservoirs high in the mountains. Signs of a lake (karovoy): round or oval shape, small area, even border, steep banks, gently sloping bottom.
The place of their formation is depressions on mountain slopes. Snow and ice accumulate in them, which, as a result of repeated melting and freezing, deepen the car.
Karst lakes
Karst lakes are called, which have arisen under the influence of surface and groundwater. Voids underground are formed as a result of the processes of dissolution and removal of the smallest particles of clay. After some time, the ground above this place will fail and a funnel will appear.
Signs of this type of lake: sinkhole filled with water. They also include those that were formed in permafrost regions. For these lakes, a special term has been coined - thermokarst.
Deflationary, tectonic and volcanic lakes
Deflationary lakes (their second name is eolian) are water-filled gaps between dunes. Weathering processes sometimes form depressions that become the basis of a reservoir. They are also classified as eolian. This name has ancient Greek roots: Eol is the god of the wind.
Tectonic lakes originated inthe result of active processes in the earth's crust. Usually they are gigantic. Baikal is a typical representative of tectonic lakes.
Volcanic lakes can be found in craters and depressions on the surface of cooled lava.
Lake Baikal
Baikal is the most famous lake in the Russian Federation. It is located not far from the center of Asia, and its fame has spread far beyond the mainland. This is one of the oldest lakes on the planet, it is about 25 million years old. During the specified period of time, the distance between the banks increased by 2 cm per year. In millions of years, the reservoir will become much larger.
The most famous signs of Lake Baikal:
- The greatest depth is 1.62 km.
- Area - 31.5 thousand km2.
- Contains one fifth of the planet's fresh water. It would take the Amazon 4 years to fill the empty bed of Lake Baikal.
- 336 rivers flow into the lake, the largest of which is the Selenga. It accounts for half of the amount of water applied.
- Angara is the only river flowing from Lake Baikal. The Irkutsk hydroelectric power station was built on it and the Bratsk reservoir, the largest on Earth, was created.
The water in the lake has a rich blue color, and its purity is impressive. In June, the transparency of the water is maximum, so you can easily see what is at a depth of 40 m. The s alt content in the lake is so low that the rivers flowing into it have a greater mineralization. This phenomenon has no scientific explanation yet. There is a hypothesis thatBaikal at great depths has a powerful source of almost distilled water.
The signs of Lake Baikal are being studied at school classes in natural science (Grade 2). All students know about the exceptional purity of water. When studying this issue, one cannot fail to mention one living creature, thanks to which the water from the lake is suitable for drinking without prior purification. This is a small crustacean epishura, which lives exclusively in Baikal. He is constantly filtering water by passing it through his body. This crustacean is not the only endemic. This group includes ⅔ representatives of the flora and fauna of Baikal. Approximately 2.6 thousand species of living organisms are found in the lake.
In the last century, the lake began to be subjected to strong anthropogenic impact. A pulp and paper mill was built on the shores of Lake Baikal, and a central mill was built on the Selenga River. There were many opponents of their commissioning, but the need for these plants was stronger. The effluents of enterprises have a detrimental effect on the flora and fauna of the lake. By the 21st century, potent chemicals have poisoned about 10 km2 of the coastal zone. Baikal's ability to self-cleanse is not unlimited. If a tipping point occurs, it will be impossible to save the lake.
