§ 63. Internal waters of Eurasia
Distribution of inland waters. Eurasia is rich in inland waters. Many of the world's major rivers flow through it. The lakes of Eurasia stand out for their size and depth. Since the relief and climate of different parts of Eurasia are not the same, rivers and lakes are distributed very unevenly across the mainland.
Flowing down from the mountains and hills located inside the mainland, the rivers direct their course towards the oceans. The territories from which the rivers flow into each of the oceans are approximately the same. The densest river network is along the outskirts of the mainland, and only in the southwest it is much rarer. At the same time, vast inland regions do not have a runoff to the World Ocean. About 1/3 of the mainland falls on the territory of internal flow.
Valuable natural wealth is groundwater. Their reserves are especially large under the West Siberian Plain. They not only replenish rivers and lakes, but are also used by the population.
Considerable reserves of valuable fresh water on Earth are contained by the deepest lake in the world - Baikal. An important custodian of fresh water is continental ice.
The Amur, Huang He, Yangtze flow into the Pacific Ocean. The Yangtze is the longest river in Eurasia (5800 m). It overflows during the monsoon rains. As it flows into the sea, the Yangtze forms a large delta. For a considerable distance, the Yangtze is a navigable river. In the lower reaches, even ocean-going vessels can rise along it. The waters of the river and its tributaries are used for irrigation. A quarter of China's population lives in its basin.
The Ganges also flows through an area with a monsoonal climate. In terms of the amount of water, the Ganges is second only to the Amazon and the Congo. It originates in the Himalayas and flows through the most humid territory of the mainland. Like the Yangtze, the Ganges floods in the summer. The muddy yellow waters of the river bring a huge mass of solid particles from the mountains; when it flows into the Bay of Bengal, the Ganges forms a vast delta.
The Indus is fed by water from the melting of snow and ice in the Himalayas and from the monsoon rains that fall there, but is inferior to the Ganges in terms of high water.
One of the largest Siberian rivers is the Lena, and the most abundant is the Yenisei.
Territories of internal flow. A significant part of the mainland does not have a runoff into the ocean. The largest of the rivers in this region is the Volga. Together with its tributaries, it collects water from a significant part of the East European Plain. The temperate continental climate of the plain determines the regime of the Volga. (Remember its features.) Thanks to the reservoirs, the river remains full-flowing and navigable all summer.
Rice. 96. Change in water level in the Yangtze River during the year
Dry and waterless Central and Central Asia is almost devoid of rivers. They start high in the mountains, descending to the plain. These few rivers flow into endorheic lakes. Water gives life to desert lands, so the population of oases uses this water for irrigation. High rises of water occur in summer, when snow and ice melt in the mountains under the hot rays of the sun. The largest river in this part of Asia is the Amu Darya.
- Describe on the maps and plan (see appendix) one of the rivers of the mainland of your choice. Determine the features of this river associated with relief and climate.
- Indicate the source of food and the features of the regime of the rivers of the western part of Eurasia. How do these features affect the economic use of rivers?
- Find on the map the rivers Think, Rhine, Elbe, Oder, Vistula. How do the feeding and regime of these rivers change in a temperate continental climate?
The regime of the rivers flowing into the Mediterranean Sea is notable for its inconstancy. Winter rains flood the rivers with water. In the summer, during dry times, they become noticeably shallow, and some even dry up.
Rice. 97. Lake in the Alps
In contrast to them, on rivers with a monsoonal precipitation regime, the water level rises sharply in summer (Fig. 96). At the same time, snow and ice in the mountains melt. A stormy flood begins, rivers overflow their banks and cause severe flooding. The population builds dams, but river waters sometimes break through them and bring great trouble. In winter, the water level drops greatly, and in the monsoon climate of the temperate zone, rivers even freeze, for example, the Amur.
In the Greater Sunda Islands, where the climate is equatorial, the rivers are fed by rain and are always full of water.
Many rivers of Eurasia are glacially fed. These include rivers of internal flow flowing from the high mountains of Central Asia. They overflow in late spring and early summer, when mountain snows and glaciers melt. One of these rivers is the Amu Darya.
The lakes of Eurasia are numerous and diverse in origin, size and water regime. Like rivers, they are distributed unevenly across the mainland. The number of lakes in the north-west of Eurasia is especially large. The largest of them are Ladoga and Onega. Their basins, formed as a result of the slow subsidence of the earth's crust, were subsequently processed by glaciers and have significant depths. Their water is fresh.
Where the climate is dry and hot, lakes are usually few and have salty water. These are the lakes of the territory of internal flow. A number of lakes in the mountains are located in the faults of the earth's crust. Lake Baikal lies in the deepest fault. In the Alps is Lake Geneva, famous for its beauty.
The remains of the ancient sea basin, once connected to the World Ocean, are the Caspian and Aral sea-lakes. Lake Balkhash is located in the southeast of Kazakhstan, and in the Tien Shan mountains is the ice-free lake Issyk-Kul (which means "warm lake").
The economic importance of the lakes is great. Many of them - Baikal, Ladoga, Onega and others - contain large reserves of clean fresh water and are convenient for navigation.
modern glaciation. Significant areas of Eurasia are covered with modern glaciers. They are found on many northern islands - in Iceland, Spitsbergen, Novaya Zemlya, etc., as well as in the highest mountains - in the Alps, the Himalayas, the Tien Shan and the Pamirs. Sliding down, mountain glaciers give rise to numerous rivers. In countries with a hot and dry climate, their water is used for irrigation, without which it is impossible to grow crops. The waters of the Huang He, Yangtze, Indus, Ganges, and Amu Darya are especially widely used.
Permafrost. Permafrost is widespread over a large area of Northern Eurasia. It is also called "eternal". It covers almost 1/3 of the territory of the Asian part of the mainland. The frozen rock layer contains ice and ranges in thickness from a few meters on the Kola Peninsula to 1,500 m on the Taimyr Peninsula. In summer, the frozen layer thaws to a depth of 40-150 cm.
The reason for the formation of permafrost, according to scientists, is cold winters with little snow and average annual temperatures below 0°C. At the same time, the large thickness of the permafrost layer is evidence of its great antiquity.
Rivers flowing through a layer of frozen soil flood widely in the spring, forming numerous swamps, since the water cannot seep into the depths and stagnates. Permafrost hinders the construction of roads, housing, and the development of agriculture.
- Why are large areas covered by modern glaciers in Eurasia?
- Compare the Lena and Huang He rivers according to the regime and type of food. How to explain the difference between them?
- Write on the contour map the rivers and lakes highlighted in the text.
