How are freshwater lakes formed? How freshwater lakes are formed

Lakes are formed by water accumulation in land depressions, and they are relatively wide and have slow flow changes. Under the geological actions such as crustal tectonic movements, glaciation, and river scouring and silting, many depressions are formed on the surface of the earth, and water accumulates into lakes. Unlike rivers, lakes have unusually slow flow and different from seas in that they do not have direct contact with the ocean.

Under the influence of the natural geographical conditions of the river basin. The lake's basin, lake water and water matter interact with each other and constrain each other, causing the lake to evolve. For example, according to the discharge conditions of the lake, it is divided into outflow lakes and inland lakes.

According to the genesis of the lake basin, the lakes can be divided into tectonic lakes, crater lakes, glacial lakes and dammed lakes.

Wait. According to the thermal conditions of the lake, it is divided into tropical lake, temperate lake and cold lake. According to the nutrients in the lake water, it is divided into eutrophic lakes, mesotrophic lakes and poor nutrient lakes. Freshwater lakes are classified according to the salinity of the water.

The salinity is below the limit; Brackish water lake with salinity. Between; Saltwater lake with a salinity of 244% to 3Between 5% of the salt water lake, the salinity is greater than.

The primary condition for the development of lakes is the lake basin, that is, the basin where water is collected and stored, and the second is that there is water. There are many reasons for the formation of lake basins. Tectonic lake basins are commonly found in fault zones or rift zones on the surface, such as lake basins developed along the rift valley in East Africa, the Caspian Sea and Lake Baikal in Russia.

Wait. China's Yunnan Province has developed two basin groups near Kunming and Dali, including Dianchi Lake.

and Erhai Lake are both tectonic lake basins. The river basin is a lake basin caused by the bending and diversion of the river and the silting up of both ends of the waste channel.

Volcanism creates crater lake basins, which are of two broad categories. One is the crater lake, that is, after the volcanic eruption stops, the crater accumulates water into a lake, such as Changbai Mountain in Jilin.

The main peak is Mt. Baekdu.

of the Heavenly Pond; Second, volcanic eruptions dam river valleys into lakes, such as Jingpo Lake in Heilongjiang Province. Glacial lake basins are formed by the erosion of glaciers. In the mountain glacial area, the original cirque depression area can accumulate water into a small cirque lake; The continental glacial zone forms a long, narrow basin of different depths arranged in the direction of the ice flow.

Rivers can also be blocked by glaciers or ice breaks, such as Tianchi in the Tianshan Mountains in Xinjiang. The Haicheng Lake Basin is formed by the crust of the adjacent areas and the isolation of the sea itself, such as the Black Sea in Europe, which was once the Mediterranean.

a bay.

The West Lake in Hangzhou was originally Hangzhou Bay.

Part of it, belongs to Haicheng Lake, and the current lake water is ** rainwater, so it is a freshwater lake. The wind into the lake basin is related to the wind, the wind can blow the wind and sand at the same time, can not only dig into the lake, but also pile up sand into a lake. The basin of the lake is round or oval in shape and extends downwindward. Northwest and Inner Mongolia Huda.

Most of them belong to this, such as Juyanhai.

Rob Nol in the Turpan Basin. There is also a kind of lake basin caused by a meteorite, that is, an extraterrestrial object strikes to form a nearly circular crater, and the water in the pit is a lake. <>

There are many reasons for the formation of lakes, such as the movement of the earth's crust, natural erosion, accumulation and man-made forces, which can cause the surface to form a depression and become a lake. Generally speaking, the genesis of lakes can be divided into several types: (1) tectonic lakes:

In the surface of alpine plateaus, hills and plains, there are fractures and depressions, and the depressions gradually store water to form lakes, such as Sun Moon Lake is Yushan Mountain, Alishan is an alpine tectonic lake turned into a mountain tectonic lake due to water accumulation in the intermountain fault basin. (2) Crater Lake: After the eruption of the volcano, a huge crater will be left at the top of the volcano, and the crater will gradually store water to form a lake, for example, there is also a volcano and a crater lake on Guishan Island outside the Yilan Plain.

3) Rivers become lakes: Some rivers located in plain areas will form lakes on the river due to the migration and swing of the river channel, the silting of the river channel, etc., and such lakes will expand in the wet season and shrink in the dry season due to the influence of river water injection; When the water volume is relatively balanced, the river lake morphology is more stable, but when the water volume changes greatly, the change of river lake morphology also increases. (4) Oxbow Lake:

In the plains, the rivers will be more and more curved due to the erosion and erosion of the river channel by the current, and finally the river will naturally bend and straighten, and the original curved river channel will be abandoned, forming the so-called oxbow lake. For example, near Erren Creek, there is a oxbow lake formed by the action of the river. (5) Dammed Lake:

A dammed lake is a lake formed by a landslide caused by geological changes, such as volcanic lava flows, ** activity, etc., which causes the blockage of a river valley or riverbed, and then stores water. If a dammed lake is formed due to volcanic lava blockage, it is called a lava dammed lake, such as Bamboo Lake and Caoling Lake are typical dammed lakes. (6) Glacial Lake:

Glacial lakes are mostly distributed in high mountains and glaciers, when the glaciers melt, they will become lakes because of the craters dug by the glaciers, and the water from the melting of the icebergs is blocked and accumulated, and the glacial lakes in Taiwan are mostly distributed in high-altitude areas, such as the Snow Mountain Range. (7) Artificial lakes - reservoirs and ponds: Lakes formed by human beings building dikes in river valleys for irrigation and drinking to intercept water in the river, and reservoirs can store reservoirs and collect more water resources, such as Shimen Reservoir, Mingde Reservoir and Baoshan Reservoir.

A lake is a continuum of a basin, its water, and the substances contained in it – minerals, dissolved matter, organic matter, and aquatic organisms. Lakes can be formed in many forms, such as crustal movements, natural erosion, accumulation, and man-made forces, all of which turn the surface of the earth into a depression. However, no matter how a lake is formed, it must meet two basic conditions:

One is the depression, that is, the lake basin, and the other is the water body accumulated in the lake basin.

Therefore, in geography, the genesis of lake basins is usually used as the main basis for lake classification. In recent years, the dominant factor in the classification of lakes has taken into account the accumulation of water in the lake basin, because only the depression where water accumulates is called a lake.

Freshwater Lake.

Closed freshwater lakes are mostly located high in the mountains or rather inland, with no significant river inflow and outflow. The open ones can be quite large, with islands and multiple rivers flowing in and out. Freshwater lakes are generally outflow lakes because the water source can be replenished by renewal, and the water in freshwater lakes is very low in salinity.

According to the salinity of lake water, it can be divided into four categories: freshwater lakes, brackish water lakes, saltwater lakes and salt water lakes. The salinity of the freshwater lake is less than 1 gram liter; The salinity of brackish lakes ranges from 1 to 24 grams; The salinity of the saltwater lake is between 24 and 35 grams; The salinity of the lagoon is greater than 35 grams. Most of the outflow lakes are freshwater lakes, while most of the inland lakes are saltwater lakes and saltwater lakes.

Salt content between 1 35g liters is called pure consumption is called saltwater lake, and more than 35g is saltwater lake. )

China actually has five major freshwater lakes

Freshwater lakes are lakes with low salt content. China's freshwater lakes are mainly distributed in the middle and lower reaches of the Yangtze River plain, the lower reaches of the Huai River and the southern part of Shandong, and the lake area in this area accounts for about one-third of the total lake area in the country. China's five major freshwater lakes – Poyang Lake, Dongting Lake, Taihu Lake, Hongze Lake and Chaohu Lake – are located in this area.

Poyang lake. Poyang Lake is located in the northern part of Jiangxi Province, on the south bank of the Yangtze River, and is the largest freshwater lake in China. At the flood level, the lake is kilometers long, the average width is kilometers, the area is 2,933 square kilometers, the maximum water depth meters, the average water depth meters, and the storage capacity is cubic meters.

The water of Poyang Lake mainly depends on surface runoff and lake precipitation, and the main rivers entering the lake include Ganjiang River, Fuhe River, Xinjiang River, Rao River, Xiushui River, etc.

Dongting Lake. Dongting Lake is located south of the middle reaches of the Yangtze River in northern Hunan Province and is the second largest freshwater lake in China. It covers an area of about 3,100 square kilometers during dry seasons and more than 3,900 square kilometers during flood periods, with a total area of 18,000 square kilometers in the lake.

The volume is 120 billion cubic meters. The main rivers entering the lake are Xiangjiang, Zishui, Yuanshui and Lishui.

Taihu Lake. Taihu Lake is located at the junction of Jiangsu and Zhejiang provinces, in the southern part of the Yangtze River Delta. It is the largest lake in the eastern coastal area of China and the third largest freshwater lake in China.

The total area of the lake is about 3,100 square kilometers, and the water area is about 2,420 square kilometers. The rivers that flow into Taihu Lake mainly include Dongru Creek and so on.

Hongze Lake. Located on the alluvial plain of the middle reaches of the Huai River in the western part of Hongze County, Jiangsu Province, Hongze Lake is the fourth largest freshwater lake in China. Hongze Lake is a shallow lake, with a water depth of less than 4 meters and a maximum water depth of one meter.

The total area of the lake area is 2,069 square kilometers. In addition to atmospheric precipitation, the water of the lake mainly depends on the water from the river. The rivers that flow into Hongze Lake include the Huai River, the Sui River, the Bianhe River and the An River.

Chaohu Lake. Chaohu Lake is located in the middle of the Jianghuai hills in Anhui Province and is the fifth largest freshwater lake in China. The total area is 753 square kilometers. Its source originates from Ying, Huo Ershan, and the main rivers entering the lake are Fengle River, Hangbu River, Zhaohe River and so on.

Poyang Lake, Dongting Lake, Taihu Lake, Hongze Lake, Chaohu Lake.