§ 46. Work rivers
Remember, any work performed and temporary constant flow of water.
Work river.You already know that the river is a powerful external force that turns the surface. First carry out the River destructive work. For centuries, rivers, rivulets and rivers blur, sharpen, drill mountain breed until they work out their way to the sea. This way - the river valley. But and after a water stops. It vhryzayetsya ledges in banks, extends and deepens the valley. Destructive work called River river erosion.
Destroyed crushed rock (sand, clay, pebble) River transfer down flow. Gradually they lay and keeping them in the mouth. In keeping with rivers sediment formed beaches, spits and islands. At the mouth of the river rocks brought deposited on the bottom. Every year at the mouth of the river becomes milkishoyu. There have small islands, composed of silt brought. Over time an island connected and form the plain - delta. Delta is constantly growing and slides into the sea. Yes delta River Mississippi nominated annually in the Gulf of Mexico 100 of Delta is covered by vegetation and numerous cut sleeves and ducts. At Delta settled people. But the river continues to breed and form carry the all-new and new islands, new areas of land. One of largest deltas - In the Amazon. The width of the delta is 335 km. Among hundreds of islands of the delta is quite large. Yes, the island Marazhohas the same area as the European country Switzerland.
Why do not disappear continents?
Each year selected rivers in the continents 12 km3 solid substances and carry them into the sea. For land enough in 1910 millionyears for all its surface zmylasya, dissolved and floated along with the river with water in the ocean.
The nature of the flow of rivers. Direction, character and ability of rivers produce a valley depend primarily on relief. Direction of flow river is determined by the general inclination of the surface, which it flows. Yes, the territory, which runs the Dnieper, tilted to the south, so river flows southward.
What greater slope, the more it breaks down the river, the river is deeper Valley. Mountain River flow in the mountains area where a large hill. Therefore, they have great speed and turbulent flow. Such character of the flow causes the formation of deep and narrow river valleys. Hundreds of thousands of years go on that river cut through the mountains valley. Flowing river flow plains. The plains have little slope. Therefore, the current flat rate of small rivers - About 1 m / sec. They flow slowly and quietly. Without power, sufficient to pave a direct path, flowing river and avoids obstacles manufactures a wide but shallow valley, which meanders down her bed. Yes Dniprocircumflex below Kyiv forced speech Dnieper Upland. So he deviates to the southeast, and only after Dnepropetrovsk again returns to south. Flowing river is also Volga, Amazon et al.
In nature of many rivers that begin in the mountains and have the mountain. But then they enter the valley and become flat. These are, for example Danube Yangtze.
Thresholds and waterfalls. The bottom of rivers compiled by various hardness rocks. Softer breed easily washed downstream harder - much slower. Hard rock (granite, shale) as huge stone blocks protrude from the water, forming Thresholds. They have Ik on the mountain, and on lowland rivers. Thresholds dramatically change the character of flow. Breaking Through them, the river sparkle, sparks fly up high, there are whirlpools. In such places plain similar to mountain rivers. Once thresholds were on Dnipro. They performed with water from Dnipropetrovsk to Zaporizhzhya, where the Dnieper crosses hard crystalline rocks. This area of 80 km was impassable for vehicles. After constructing the dam at Zaporozhye formed large reservoir that is buried deep under water rapids. Now they do not interfere with navigation.
If River is a high rocky ledge, the water falls from it, forming waterfall. River seemed to make the jump from a height. Highest waterfall on Earth - Angel in South America in the Orinoco River basin. The water there falls from a height of 1054 m bottom of deep gorges. One of the best known and most powerful in the world is Niagara waterfall in North America. Water that falls from a ledge, 50 meters in height creates such a noise that he heard at a distance of 25 km. No wonder the word "Niagara" Indian means "booming water. Stone, which is running in swirls, drilled under bahatometrovyy pit falls. In Ukraine there are small waterfalls on mountain rivers of the Carpathians and Crimea.
Fig. Niagara waterfall
Using rivers.Rivers in nature are important. They are part of the world water cycle. Cycling of water in them occurs every 12 days.
Rivers and for people to do a great job. Primarily they are a major source Freshwater. This most vital substance for human and all living. So people always settled near the rivers. It is near major rivers there were great civilizations of the ancient world.
Long ago River served connections. They facilitate people's access to the sea. River transport is about 3 times cheaper than rail. Out river water irrigated land in arid areas. Energy flowing water is widely used for hydropower (HPP) for relatively cheap electricity. Many of the river water is using factories. Water is also needed for domestic purposes rights. Water heated our house. Water acts as a nurse. Majority people resting near rivers, where you can angle, boating, swimming.
Requirements in the water are increasing. Therefore exacerbated the shortage of fresh water and rivers from pollution waste management business. Therefore, residents should take care of our planet preservation of the Blue Treasure, because there is nothing more valuable in the world ordinary clean water.
Fig. Rivers - ancient human connections
Questions and Tasks
1. What job do the rivers in nature?
2. What is a river delta?
3. In the delta of the river where there was one of the oldest countries in the world - Egypt?
4. What is different from the flowing river mountain?
5. Consider a geographic information embedded in the name of Zaporozhye?
6. How people use the river for their needs?
7. Why rivers need to carefully protect and use their water?