Navigators learned about the presence of ocean currents almost immediately, as soon as they began to surf the waters of the oceans. True, the public paid attention to them only when, thanks to the movement of ocean waters, many great geographical discoveries, for example, Christopher Columbus sailed to America thanks to the North Equatorial Current. After that, not only sailors, but also scientists began to pay close attention to ocean currents and strive to explore them as best and as deeply as possible.
Already in the second half of the XVIII century. sailors studied the Gulf Stream quite well and successfully applied their knowledge in practice: they went with the flow from America to Great Britain, and kept a certain distance in the opposite direction. This allowed them to be two weeks ahead of ships whose captains were not familiar with the terrain.
Oceanic or sea currents are large-scale movements of the water masses of the World Ocean at a speed of 1 to 9 km / h. These streams do not move randomly, but in a certain channel and direction, which is the main reason why they are sometimes called the rivers of the oceans: the width of the largest currents can be several hundred kilometers, and the length can reach more than one thousand.
It has been established that water flows do not move straight, but deviating slightly to the side, they obey the Coriolis force. In the Northern Hemisphere they almost always move clockwise, in the Southern Hemisphere it is vice versa.. At the same time, currents located in tropical latitudes (they are called equatorial or trade winds) move mainly from east to west. The strongest currents were recorded along the eastern coasts of the continents.
Water flows do not circulate by themselves, but they are set in motion by a sufficient number of factors - the wind, the rotation of the planet around its axis, gravitational fields The Earth and the Moon, the bottom topography, the outlines of the continents and islands, the difference in temperature indicators of water, its density, depth in different parts of the ocean, and even its physical and chemical composition.
Of all the types of water flows, the most pronounced are the surface currents of the World Ocean, the depth of which is often several hundred meters. Their occurrence was influenced by trade winds, constantly moving in tropical latitudes in the western eastbound. These trade winds form huge streams of the North and South Equatorial currents near the equator. Smaller part of these flows returns to the east, forming a countercurrent (when the movement of water occurs in the opposite direction from the movement of air masses). Most, colliding with the continents and islands, turns to the north or south.
Warm and cold water streams
It must be taken into account that the concepts of "cold" or "warm" currents are conditional definitions. So, despite the fact that the temperature indicators of the water flows of the Benguela Current, which flows along the cape Good Hope, are 20 ° C, it is considered cold. But the North Cape Current, which is one of the branches of the Gulf Stream, with temperatures ranging from 4 to 6 ° C, is warm.
This happens because the cold, warm and neutral currents got their names based on a comparison of the temperature of their water with the temperature indicators of the ocean surrounding them:
- If the temperature indicators of the water flow coincide with the temperature of the waters surrounding it, such a flow is called neutral;
- If the temperature of the currents is lower than the surrounding water, they are called cold. They usually flow from high latitudes to low latitudes (for example, the Labrador Current), or from areas where, due to the large flow of rivers, ocean water has a reduced salinity of surface waters;
- If the temperature of the currents is warmer than the surrounding water, then they are called warm. They move from the tropics to subpolar latitudes, such as the Gulf Stream.
Main water flows
At the moment, scientists have recorded about fifteen major oceanic water flows in the Pacific, fourteen in the Atlantic, seven in the Indian and four in the Arctic Ocean.
It is interesting that all the currents of the Arctic Ocean move at the same speed - 50 cm / s, three of them, namely the West Greenland, West Svalbard and Norwegian, are warm, and only the East Greenland belongs to the cold current.
But almost all the oceanic currents of the Indian Ocean are warm or neutral, while the Monsoon, Somali, West Australian and the Cape of Needles (cold) move at a speed of 70 cm / s, the speed of the rest varies from 25 to 75 cm / s. The water flows of this ocean are interesting because, along with the seasonal monsoon winds, which change their direction twice a year, ocean rivers also change their course: in winter they mainly flow west, in summer - east (a phenomenon characteristic only of the Indian Ocean). ).
Since the Atlantic Ocean stretches from north to south, its currents also have a meridional direction. Water streams located in the north move clockwise, in the south - against it.
A striking example of the flow of the Atlantic Ocean is the Gulf Stream, which, starting in the Caribbean Sea, carries warm waters to the north, breaking up into several side streams along the way. When the waters of the Gulf Stream end up in the Barents Sea, they enter the Arctic Ocean, where they cool and turn south in the form of a cold Greenland current, after which at some stage they deviate to the west and again adjoin the Gulf Stream, forming a vicious circle.
The currents of the Pacific Ocean are mainly latitudinal and form two huge circles: northern and southern. Since the Pacific Ocean is extremely large, it is not surprising that its water flows have a significant impact on most of our planet.
For example, trade winds move warm water from the western tropical coasts to the eastern ones, which is why the western part of the Pacific Ocean in the tropical zone is much warmer than the opposite side. But in the temperate latitudes of the Pacific Ocean, on the contrary, the temperature is higher in the east.
deep currents
For quite a long time, scientists believed that deep ocean waters almost motionless. But soon, special underwater vehicles discovered both slow and fast-flowing water flows at great depths.
For example, under the Equatorial Pacific Ocean at a depth of about one hundred meters, scientists have identified the Cromwell underwater stream, moving eastward at a speed of 112 km / day.
A similar movement of water flows, but already in the Atlantic Ocean, was found by Soviet scientists: the width of the Lomonosov current is about 322 km, and maximum speed at 90 km / day was recorded at a depth of about one hundred meters. After that, another underwater stream was discovered in the Indian Ocean, however, its speed turned out to be much lower - about 45 km / day.
The discovery of these currents in the ocean gave rise to new theories and mysteries, the main of which is the question of why they appeared, how they formed, and whether the entire ocean area is covered by currents or there is a point where the water is still.
The influence of the ocean on the life of the planet
The role of ocean currents in the life of our planet cannot be overestimated, since the movement of water flows directly affects the planet's climate, weather, and marine organisms. Many compare the ocean to a huge heat engine powered by solar energy. This machine creates a continuous water exchange between the surface and deep layers of the ocean, providing it with oxygen dissolved in water and affecting the life of marine life.
This process can be traced, for example, by considering the Peruvian Current, which is located in the Pacific Ocean. Thanks to the rise of deep waters, which lift phosphorus and nitrogen upward, animal and plant plankton successfully develop on the ocean surface, as a result of which the food chain is organized. Plankton is eaten by small fish, which, in turn, becomes a victim of larger fish, birds, marine mammals, which, with such food abundance, settle here, making the region one of the most highly productive areas of the World Ocean.
It also happens that a cold current becomes warm: the average ambient temperature rises by several degrees, which causes warm tropical showers to fall on the ground, which, once in the ocean, kill fish accustomed to cold temperatures. The result is deplorable - it turns out in the ocean great amount dead small fish, large fish leave, fishing stops, birds leave their nests. As a result, the local population is deprived of fish, crops that were beaten by downpours, and profits from the sale of guano (bird droppings) as fertilizer. It can often take several years to restore the former ecosystem.
As observations show, the layers of the World Ocean move in the form of huge streams tens and hundreds of kilometers wide and thousands of kilometers long. These flows are called currents. They move at a speed of about 1-3 km/h, sometimes up to 9 km/h.
Currents are caused by the action of the wind on water surface gravity and tidal forces. The flow is influenced by the internal friction of water and the Coriolis force. The first slows down the flow and causes eddies at the boundary of layers with different densities, the second changes its direction.
Classification of currents. According to their origin, they are divided into frictional, gravity-gradient and tidal. In frictional flows, drift, caused by constant or prevailing winds; they are of the greatest importance in the circulation of the waters of the oceans.
Gravity-gradient currents are subdivided into stock(waste) and density. Stock flows occur in the case of a steady rise in the water level caused by its inflow (for example, the inflow of Volga water into the Caspian Sea) and an abundance of precipitation, or in the case of a drop in the level due to the outflow of water and its loss to evaporation (for example, in the Red Sea). Density currents are the result of unequal density of water at the same depth. They arise, for example, in straits connecting seas with different salinities (for example, between the Mediterranean Sea and the Atlantic Ocean).
Tidal currents are created by the horizontal component of the tidal force.
Depending on the location in the water column, currents are distinguished superficial, deep and bottom.
According to the duration of existence, currents can be distinguished permanent, occasional and temporary. Constant currents from year to year retain the direction and speed of the current. They can be caused by constant winds, such as trade winds. The direction and speed of periodic currents change in accordance with the change in the causes that caused them, for example, monsoons, tides. Temporal currents are caused by random causes.
Currents can be warm, cold and neutral. The former are warmer than the water in the region of the ocean through which they pass; the latter are colder than the surrounding water. As a rule, currents moving away from the equator are warm, while currents moving towards the equator are cold. Cold currents are usually less salty than warm ones. This is because they flow from areas with more precipitation and less evaporation, or from areas where the water is freshened by melting ice.
Distribution patterns surface currents. The picture of the surface currents of the World Ocean was established in the main features by XX century. The direction and speed of the current were determined mainly from observations of the movement of natural and artificial floats (fin, bottles, drift of ships and ice floes, etc.) and from the difference in determining the place of the ship by the dead reckoning method and the method of observing heavenly bodies. The modern task of oceanology is the detailed study of currents in the entire thickness ocean water. This is done by various instrumental methods, in particular by radar. The essence of the latter is that a radio wave reflector is lowered into the water, and, fixing its movement on the radar, determine
direction and speed of the current.
The study of drift currents made it possible to derive the following regularities:
1) the speed of the drift current increases with the intensification of the wind that caused it and decreases with increasing latitude according to the formula
where BUT- wind coefficient equal to 0.013, W - wind speed, φ - latitude of the place;
2) the direction of the current does not coincide with the direction of the wind: it obeys the Coriolis force. Given sufficient depth and distance from the coast, the deviation is theoretically 45°, but in practice it is somewhat less.
3) the direction of the current is strongly influenced by the configuration of the banks. The current, heading towards the shore at an angle, bifurcates, and its large branch goes towards an obtuse angle. Where two currents approach the shore, a drain-compensation countercurrent arises between them due to the connection of their branches.
The distribution of surface currents in the World Ocean can be represented as the following schematic diagram (Fig. 42).
On both sides of the equator, trade winds cause north and south trade wind currents that deviate from the direction of the wind under the influence of the Coriolis force and move from east to west. Encountering on its way the eastern coast of the mainland, the trade winds bifurcate. Their branches, heading to the equator, meeting, form a drain-compensation countercurrent, following to the east between the trade wind currents. The branch of the northern trade wind current, deviated to the north, moves along the eastern shores of the mainland, gradually moving away from it under the influence of the Coriolis force. North of 30° N. sh. this current falls under the influence of the westerly winds prevailing here and moves from west to east. At the western coast of the mainland (about 50 ° N. Lat.), this current is divided into two branches, diverging in opposite sides. One branch goes to the equator, compensating for the loss of water caused by the northern trade wind current, and joins it, closing the subtropical ring of currents. The second branch follows north along the coast of the mainland. One part of it penetrates the Arctic Ocean, the other joins the current from the Arctic Ocean, completing another ring of currents. In the southern hemisphere, as well as in the northern one, a subtropical ring of currents arises. The second ring of currents is not formed, but instead of it there is a powerful drift current of westerly winds, connecting the waters of three oceans.
The actual distribution of surface currents in each ocean deviates from the principle scheme, since the outlines of the continents influence the direction of the currents (Fig. 43).
Propagation of ocean currents in depth. The movement of water caused by the wind on the surface is gradually transferred to the underlying layers due to friction. In this case, the flow velocity decreases exponentially, and the direction of the flow, under the influence of the Coriolis force, deviates more and more from the initial one and at a certain depth turns out to be opposite to the surface one (Fig. 44). The depth at which the current turns 180° is called the friction depth. At this depth, the influence of the drift current practically ends. This depth is about 200 m. However, the action of the Coriolis force, which changes the direction of the flow, leads to the fact that, at a certain depth, the water jets either overtake the shores or are driven away from them, and then an angle of the surface of equal pressures arises near the shores, setting the entire water column in motion. This movement extends far from the coast. In connection with different conditions heating of the ocean surface at different latitudes, there is a convection of ocean water. In the equatorial region, an upward movement relative to warmer water dominates, in the polar regions, a downward movement relative to colder water. This should lead to the movement of water in the surface layers from the equator to the poles, and in the bottom layers from the poles to the equator.
In areas of high salinity, water tends to sink, in areas of low salinity, on the contrary, it tends to rise. The lowering and rising of water are also caused by surge and surge of water on the surface (for example, in the area of action of the trade winds).
In deep ocean troughs, the temperature of the water rises by a few tenths of a degree due to the internal heat of the Earth. This results in vertical water currents. At the bottom of the continental slopes, powerful currents are observed with a speed of up to 30 m/s, caused by earthquakes and other causes. They carry a large amount of suspended particles and are called muddy streams.
The existence of systems of surface currents with a general direction of movement towards the center or from the center of the system leads to the fact that in the first case there is a downward movement of water, in the second - upward. An example of such areas can be subtropical ring systems of currents.
Very small changes in salinity with depth and the constancy of salt composition at great depths indicate the mixing of the entire water column of the World Ocean. However, the exact picture
distribution of deep and bottom currents has not yet been established. Thanks to the continuous mixing of water, a constant transfer of not only heat and cold, but also the nutrients necessary for organisms is carried out. In the zones of water subsidence, the deep layers are enriched with oxygen; in the zones of water uplift, biogenic substances (phosphorus and nitrogen salts) are carried from the depths to the surface.
Currents in the seas and straits. Currents in the seas are caused by the same reasons as in the oceans, but the limited size and shallower depths determine the scale of the phenomenon, and local conditions give them peculiar features. Many seas (for example, the Black and Mediterranean) are characterized by a circular current due to the Coriolis force. In some seas (for example, in the White Sea), tidal currents are well expressed. In other seas (for example, in the North and Caribbean), sea currents are an offshoot of ocean currents.
According to the nature of the currents, straits can be divided into flowing and exchange straits. In flowing straits, the current is directed in one direction (for example, in Florida). In exchange straits, water moves in two opposite directions. Multidirectional streams of water can be one above the other (for example, in the Bosphorus and Gibraltar) or can be located next to each other (for example, La Perouse and Davis). In narrow and shallow straits, the direction may change to the opposite depending on the direction of the wind (for example, Kerch).
Geography lesson in 7th grade e
Topic: "Ocean currents"
Target: reveal the causes of the circular motion of surface waters, give an idea of the general scheme of surface currents in the World Ocean.
Tasks:
To form an idea of \u200b\u200bocean currents, the reason for their occurrence, the types of currents and their use.
to identify the general patterns of the currents of the World Ocean
Continue learning to work with contour maps, identify patterns, read atlas maps.
Cultivate an aesthetic perception of geographical objects
Equipment: textbook, atlas, map of the oceans, physical map hemispheres, presentation, geographical simulator, test, portraits of travelers (H. Columbus, T. Heyerdahl).
Main content: ocean currents. Reasons for the formation of ocean currents. Types of ocean currents. The main surface currents of the World Ocean. Importance of ocean currents.
Lesson type:
combined.
DURING THE CLASSES
Organizing time
Good morning, guys! Sit down in your seats, check the readiness for the lesson, whether everything is in place. Today we have not just a lesson - today we have a holiday, because guests came to us - geography teachers from all over our region. We were expecting guests, and today, having discarded all the preparatory worries, let's plunge into the world of the wonderful science of geography.
Checking homework.
In the last lesson, we studied the topic ... climatic zones and areas of the earth. Let's remember what we talked about in the past and previous lessons.
1. For the board to perform an individual task will go
Draw a diagram of atmospheric circulation using colored crayons (Task card, blue, red and green chalk)
2.Individual test of our geographic simulator on the issues will perform on a laptop
3. And let's remember what a climate zone is?
Climatic zone -
What are the climatic zones? (main and transitional)
What prefix do we use to denote the transitional climatic zone (Sub)
How many main belts? (7)
What are the main climatic zones (equatorial, tropical, temperate, arctic, antarctic)
Show the main climatic zones on the map ...
How many transition belts? (6)
Name the transitional climatic zones (2 subequatorial, 2 subtropical, subarctic, subantarctic)
Show on the map the transition zones ...
What is the difference between main and transitional belts.
Do all zones have climatic regions (no)
In which climate zone no climatic regions
Name and show them on the area map temperate zone Eurasia (moderate continental, continental, sharply continental, monsoonal)
4. Let's listen to what you wrote in your home mini-composition “I would like to live in …….belt, because…..
Let's see how I coped with the task ... test passed
Knowledge update
You and I remembered what we studied and it's time for us to turn to new material, but it will not be new for us at all. in the 6th grade we already got acquainted with the peculiarities of the nature of the Earth.
And today we will move from atmospheric processes to water processes.
And what is the name water shell Earth? (hydrosphere)
And this picture will become the symbol of our lesson . It depicts the famous Norwegian traveler Thor Heyerdahl. (photo)
In 1947, he and 5 like-minded people built a raft of 9 balsa wood logs and named it Kon-Tiki. For 101 days a brave navigator crossed over Pacific Ocean.
And in 1969, he undertook a new dangerous expedition to prove the possibility of crossing the Atlantic Ocean by African peoples.
He and six of his followers built a papyrus boat, called it "Ra". Their first trip failed. The following year, they again took to the ocean in a papyrus boat, and this time reached their destination in 57 days.
Let's turn to the map: Thor Heyerdahl made a boat trip from the port of Safi (32 0 with. sh. and 9 0 h. e.) to the island of Barbados (13 0 with. sh. and 59 0 h. d.). Follow his route on a map of the oceans. What helped the traveler along the way?
A good way to get around is to move with the help of ocean currents. And in order to use it, you need to get acquainted with the currents
The topic of our lesson, you guessed it- ocean currents
Let's open notebooks, write down the date and the topic of our lesson.
What do you guys think, what are the questions we face in this topic?
What are ocean currents?
What are the currents?
How are they formed?
How do people use ocean currents?
To get answers to our questions, we need to turn to our main source of knowledge. What is it? Textbook. Let's open the textbook page and find and read what an ocean current is.
ocean current -
People have known about ocean currents for a long time. historical background prepared for us...
(REPORT ON THE HISTORY OF THE DISCOVERY OF OCEANIC CURRENTS)
What is the reason for the formation of ocean currents in the World Ocean?
VIDEO
What reason leads to the formation of currents (due to the influence of constant winds). What do we know about constant winds? (Assignment at the board)But there are several other reasons that affect the direction of currents:
1. Constant winds.2. Outlines of the continents.
3. Bottom relief
4
. Rotation of the Earth around its axis.
Let's turn to another reliable source geographic information- map. How are ocean currents shown on a map? (arrows)
The North Atlantic current off the coast of Scandinavia has a temperature of +10 0
C. What is this current?(
Warm)
And the Peruvian current off the coast of South America has a temperature of +19 0 S, what is it? (Cold).
What is the contradiction? (+10 0 C - warm, + 19 0 C - cold)What is the question?
Which currents are called cold and which are warm?
Let's work and fill in the table that you have on your desk
Let's write down
Current name
Color on the map
Current water temperature
Ocean surface water temperature
Temperature Comparison
Type of flow
North Atlantic
red
warm
Peruvian
blue
cold
Conclusion: A current is cold if its temperature is several degrees lower than the temperature of the surrounding water in the ocean.….
Read the page in the textbook and compare, did we draw the right conclusion?
- warm current A current is a current whose water temperature is several degrees higher than the temperature of the surrounding water.
- cold flow It is a current, the temperature of which is several degrees lower than the surrounding water.
Find on the map and put on the c / c currents: Gulf Stream, Canary, Peruvian, Labrador, West Winds, Kuroshio.
Which ones are warm? Cold? What pattern did you notice in the arrangement of these currents? ( Warm currents move from the equator, cold currents move from the poles, close, flow counterclockwise.)
Look closely at the map. What conclusions can be drawn by analyzing the patterns of currents in the northern and southern hemispheres?
Just the direction of currents clockwise and counterclockwise is influenced by the rotation of the Earth around its axis. To the north of the equator, the currents bend to the right, to the south of the equator to the left. This phenomenon is called the Coriolis effect, named after the French mathematician Gaspard de Coriolis who described it. This is a law of physics and you will study it in high school. Currents travel clockwise in the northern hemisphere and counterclockwise in the southern hemisphere.
Fizminutka
Let's take a break from our studies and warm up. What phenomena can be found in the ocean? Waves, storm, hurricane, tsunami… Let's try to depict these phenomena… wave….higher… storm starts…. A hurricane… during a seaquake, a tsunami is formed… quieter, quieter…. We moor to the shore ... that is, at the desk. We warmed up .. Let's continue.
– Are all currents driven by wind?
If the water flow encounters an obstacle (land or uplift of the bottom topography), it divides, bending around the obstacle from different sides. The current also, if it encounters an obstacle, is most often divided into twosewage currents
– When the West Wind Current, which is a wind current, collides, one sewer current is formed, and the West Wind Current continues to move on. But there are cases when the wind current ceases to exist as a result of a collision with the mainland, and two sewage currents are formed instead. Find examples on the map.(California and Alaska, East Australian and Intertrade, Kuroshio and Intertrade.)
Plot two waste streams on the contour maps with thicker arrows.
From what current is formed ... current
- Find the current of the West Winds on the map of the oceans. What oceans does it cross?
(VIDEO ON THE CURRENT OF THE WESTERN WINDS)
Poem about the Course of the West Winds
Antarctica past Australia, America and Africa
Past all possible islands…
Everyone is sailing, my boats are sailing
Downstream of the West Winds.
I will draw on a worn map
This amazing route
In the blue of the vast expanse
Everyone is sailing, boats are sailing.
Speaking of ocean currents, it seems to me that it will be very useful to know the features of the current of our native sea.
What sea am I talking about? (Black)
Which ocean basin does it belong to (Atlantic)
Learn about the currents of the Black Sea will help us ...
Currents of the Black Sea
The main course of the Black Sea is the Main Black Sea Current. It is directed counterclockwise and forms two noticeable rings (“Knipovich glasses”, such a name is associated with the Russian hydrologist Nikolai Knipovich, who described this current). The flow is very changeable. In the coastal waters of the Black Sea, eddies of the opposite direction are formed - anticyclonic currents.
And who likes to swim in the sea in summer? Why?
Water procedures very useful, but know that the sea is fraught with danger .... You are welcome….
Secrets of the Black Sea
When swimming in the Black Sea, you should be aware of the existence of a local Black Sea current - “ traction». In the world, a similar phenomenon is called RIP.
Most often, this current is formed during a storm near sandy shores. The water running ashore does not return back evenly, but in jets along the channels formed in the sandy bottom.
It is dangerous to get into the jet of a draft: it can be carried away to the open sea. To get out of the drag, you need to swim not directly to the shore, but at an angle to reduce the resistance of receding water.
V. Stage of consolidation of knowledge
You and I are practically done with the material. Let's remember what we wanted to know...
Have we received answers ... But we know far from everything. You can supplement your knowledge by doing your homework, which let's write in a diary.VI. Homework
1. Study &20., describe one of the currents according to the plan p.572.Creativeexerciseprepare a flow reportEl Niño
1. What has the greatest effect on the formation of currents in the ocean
A) persistent winds
B) earthquakes
B) the pull of the moon
2. What are the currents
A) warm
B) cold
B) warm and cold
3. What currents begin at the equator
A) warm
B) cold
B) warm and cold
4. What are the effects of ocean currents
A) on the formation of the climate
B) on the formation of the topography of the ocean floor
B) the rotation of the earth
5. What is the largest cold current
A) Gulf Stream
B) The course of the West winds
B) Peruvian Current
VII. Summing up results lesson a
Did you like the lesson?
What made an impression?
What did you like the most?
And I liked your work in the lesson, and I want to evaluate it
History of the discovery of surface currents
The first mentions of the existence of sea currents are found among ancient Greek scientists; Aristotle in his writings speaks of currents in the Kerch, Bosporus and Dardanelles straits. And the Carthaginians had some idea of the Sargasso Sea.
It is known that in the Middle Ages, the Norwegians discovered the sea route from northern Europe, first to Iceland, and then to Greenland and North America. In these voyages, the Normans got acquainted with the sea currents. This is clear from the names that they gave to prominent places they met along the way, such as: Fr. Currents, Gulf of Currents, Cape Currents.
The Arabs sailed extensively in the Indian Ocean and established maritime communications with China, Mesopotamia and Egypt. They were familiar with the monsoon currents.
The Portuguese, when moving south along the coast of Africa, got acquainted with the Guinean and Bengal currents, and Vasco da Gama at the end of the 15th century, during his first voyage to India, noticed the Mozambique current.
First observations of ocean currents
The first detailed observation of currents in open ocean was made by Christopher Columbus during his first voyage to America, September 13, 1492 in the region of 27 ° N. sh. and 40° W. e. He, by the deviation of the lot, lowered deep into the water, noticed that the ship was carrying the current to the SW. Subsequent voyages of Columbus introduced him even more to the North Equatorial Current and gave him the opportunity to suggest that the waters of the ocean along the equator move "together with the vault of heaven" to the west. On his fourth voyage (1502-1504), Columbus discovered a current that runs along the coast of Honduras.
In the oceans and seas, huge streams of water tens and hundreds of kilometers wide and several hundred meters deep move in certain directions over distances of thousands of kilometers. Such flows - "in the oceans" - are called sea currents. They move at a speed of 1-3 km/h, sometimes up to 9 km/h. There are several reasons for causing currents: for example, heating and cooling of the water surface, and evaporation, differences in the density of water, but the most significant role in the formation of currents is.
The currents along the direction prevailing in them are divided into, going to the west and to the east, and meridional - carrying their waters to the north or south.
In a separate group, currents are distinguished, going towards neighboring, more powerful and extended ones. Such flows are called countercurrents. Those currents that change their strength from season to season, depending on the direction of coastal winds, are called monsoons.
Among the meridional currents, the most famous is the Gulf Stream. It carries on average about 75 million tons of water every second. For comparison, it can be pointed out that the most full-flowing one carries only 220 thousand tons of water every second. The Gulf Stream carries tropical waters to temperate latitudes, largely determining, and hence the life of Europe. It was thanks to this current that it received a mild, warm climate and became the promised land for civilization, despite its northern position. Approaching Europe, the Gulf Stream is no longer the same stream that breaks out of the bay. Therefore, the northern continuation of the current is called. Blue waters are replaced by more and more green ones. Of the zonal currents, the most powerful is the current of the Western winds. In the vast expanse of the Southern Hemisphere, there are no significant land masses near the coast. All this space is dominated by strong and steady westerly winds. They intensively carry the waters of the oceans in an easterly direction, creating the most powerful current of the Western winds in everything. It connects the waters of three oceans in its circular flow and carries about 200 million tons of water every second (almost 3 times more than the Gulf Stream). The speed of this current is low: to bypass Antarctica, its waters need 16 years. The width of the current of the Western winds is about 1300 km.
Depending on the water, the currents can be warm, cold and neutral. The water of the former is warmer than the water in the region of the ocean through which they pass; the second, on the contrary, is colder than the water surrounding them; others do not differ from the temperature of the waters among which they flow. As a rule, currents moving away from the equator are warm; the currents going are cold. They are usually less salty than warm. This is because they flow from areas with more precipitation and less evaporation, or from areas where water has been freshened by melting ice. The cold currents of parts of the oceans are formed due to the rise of cold deep waters.
An important pattern of currents in the open ocean is that their direction does not coincide with the direction of the wind. It deviates to the right in the Northern Hemisphere and to the left in the Southern Hemisphere from the direction of the wind by up to 45°. Observations show that under real conditions the deviation at all latitudes is somewhat less than 45°. Each underlying layer continues to deviate to the right (left) from the direction of motion of the overlying layer. In this case, the flow rate decreases. Numerous measurements have shown that the currents end at depths not exceeding 300 meters. The significance of ocean currents lies primarily in the redistribution of solar heat on Earth: warm currents contribute to an increase in temperature, while cold ones lower it. Currents have a huge impact on the distribution of precipitation on land. Territories washed by warm waters always have a humid climate, and cold ones - dry; in the latter case, the rains do not fall, only have moisturizing value. Living organisms are carried along with currents. This primarily applies to plankton, followed by large animals. When warm currents meet cold currents, ascending currents of water are formed. They raise deep water rich in nutrient salts. This water favors the development of plankton, fish and marine animals. Such places are important fishing grounds.
The study of sea currents is carried out both in the coastal zones of the seas and oceans, and in the open sea by special marine expeditions.
Ocean or sea currents - This forward movement water masses in the oceans and seas, caused by various forces. Although the most significant cause of currents is the wind, they can form and due to unequal salinity separate parts ocean or sea, difference in water levels, uneven heating of different parts of water areas. In the depths of the ocean there are eddies created by uneven bottoms, their size often reaches 100-300 km in diameter, they capture layers of water hundreds of meters thick.
If the factors that cause currents are constant, then a constant current is formed, and if they are episodic, then a short-term, random current is formed. According to the prevailing direction, the currents are divided into meridional, carrying their waters to the north or south, and zonal, spreading latitudinally. Currents in which the water temperature is higher than the average temperature for
the same latitudes are called warm, below - cold, and currents having the same temperature as the surrounding waters are called neutral.
Monsoon currents change their direction from season to season, depending on how the coastal monsoon winds blow. Towards the neighboring, more powerful and extended currents in the ocean, countercurrents are moving.
The direction of currents in the World Ocean is influenced by the deflecting force caused by the rotation of the Earth - the Coriolis force. In the Northern Hemisphere, it deflects currents to the right, and in the Southern Hemisphere, to the left. The speed of currents on average does not exceed 10 m/s, and they extend to a depth of no more than 300 m.
In the World Ocean, there are constantly thousands of large and small currents that go around the continents and merge into five giant rings. The system of currents of the World Ocean is called circulation and is connected, first of all, with the general circulation of the atmosphere.
Ocean currents redistribute solar heat absorbed by masses of water. Warm water, heated by the sun's rays at the equator, they carry to high latitudes, and cold water
Currents of the oceans
Upwelling - the rise of cold waters from the depths of the ocean
UPWELLING | |
In many areas of the World Ocean, | |
given "emergence" of deep waters to the surface | |
sea. This phenomenon is called upwelling | |
gom (from English up - up and well - gush), | |
occurs, for example, if the wind drives away | |
warm surface waters, and in their place | |
rise colder. Temperature | |
water in upwelling areas is lower than the average | |
nyaya at a given latitude, which creates a blessing | |
favorable conditions for the development of plankton, | |
and, consequently, other maritime organizations | |
mov - fish and marine animals that they | |
eat. Upwelling areas are the most important | |
commercial areas of the World Ocean. They are | |
are located on the western coasts of the continents: | |
Peruvian-Chilean - from South America, | |
Californian - off North America, Ben- | |
gelic - u South West Africa, Canary | |
sky - off West Africa. |
from the polar regions due to currents gets to the south. Warm currents increase air temperature, while cold currents, on the contrary, decrease it. Territories washed by warm currents are characterized by a warm and humid climate, and those near which cold currents pass are cold and dry.
The most powerful current of the World Ocean is the cold current of the West Winds, also called the Antarctic circumpolar (from lat. cirkum - around). The reason for its formation is strong and stable westerly winds blowing from west to east over vast expanses of
in the southern hemisphere from temperate latitudes to the coast of Antarctica. This current covers a zone 2500 km wide, extends to a depth of more than 1 km and carries up to 200 million tons of water every second. On the path of the Western Winds there are no large land masses, and it connects in its circular flow the waters of three oceans - the Pacific, Atlantic and Indian.
The Gulf Stream is one of the largest warm currents in the Northern Hemisphere. It goes through Gulf of Mexico(eng. Gulf Stream - the course of the bay) and carries the warm tropical waters of the Atlantic Ocean to high latitudes. This giant stream of warm water largely determines the climate of Europe, making it soft and warm. Every second, the Gulf Stream carries 75 million tons of water (for comparison: the Amazon, the most full-flowing river in the world, is 220 thousand tons of water). At a depth of about 1 km under the Gulf Stream, a countercurrent is observed.
SEA ICE
When approaching high latitudes, ships encounter floating ice. Sea ice frames Antarctica with a wide border, covers the waters of the Arctic Ocean. Unlike continental ice formed from atmospheric precipitation and covering Antarctica, Greenland, the islands of the polar archipelagos, these ices are frozen sea water. In the polar regions sea ice perennial, while in temperate latitudes water freezes only in cold seasons.
How does sea water freeze? When the water temperature drops below zero, a thin layer of ice forms on its surface, which breaks with wind waves. It repeatedly freezes into small tiles, splits again until it forms the so-called ice fat - spongy ice floes, which then coalesce with each other. Such ice is called pancake ice for its resemblance to rounded pancakes on the surface of the water. Plots of such ice, freezing, form young ice - nilas. Every year this ice gets stronger and thicker. It can become multi-year ice more than 3 m thick, or it can melt if the currents carry the ice floes into warmer waters.
The movement of ice is called drift. Drifting (or pack) ice covered
Ice mountains are melting, acquiring bizarre shapes
the space around the Canadian Arctic Archipelago, off the coast of Severnaya and Novaya Zemlya. arctic ice drift at a speed of several kilometers a day.
ICEBERGS
Colossal pieces of ice often break off from huge ice sheets, which set off on their own voyage. They are called "ice mountains" - icebergs. Don't be them ice sheet in Antarctica would constantly grow. In fact, icebergs compensate for melting and provide a balance to the state of Antarctica.
Iceberg off the coast of Norway
tic cover. Some icebergs reach gigantic sizes.
When we want to say that some event or phenomenon in our life can have much more serious consequences than it seems, we say "this is just the tip of the iceberg." Why? It turns out that about 1/7 of the entire iceberg is above the water. It is table-shaped, domed or cone-shaped. The base of such a huge piece of a glacier, which is under water, can be much larger in area.
Sea currents carry icebergs away from their birthplaces. The collision with such an iceberg in the Atlantic Ocean caused a
of the famous ship "Titanic" in April 1912.
How long does an iceberg live? The ice mountains that have broken away from the icy Antarctica can float in the waters of the Southern Ocean for more than 10 years. Gradually, they collapse, split into smaller pieces, or, by the will of the currents, move to warmer waters and melt.
"FRAM" IN THE ICE
To find out the path of drifting ice, the great Norwegian traveler Fridtjof Nansen decided to drift on his ship Fram with them. This bold expedition lasted for three whole years (1893-1896). Having allowed the Fram to freeze into drifting pack ice, Nansen expected to move with him to the North Pole region, and then leave the ship and continue on dog sleds and skis. However, the drift went further south than expected, and Nansen's attempt to reach the Pole on skis was unsuccessful. Traveling over 3,000 miles from the New Siberian Islands to west coast Svalbard, "Fram" collected unique information about drifting ice and the impact on their movement daily rotation Earth.
The boundary between land and sea is a constantly changing line. The oncoming waves carry the smallest particles of sand suspension, roll over pebbles, grind rocks. Destroying the coast, especially during strong waves or storms, in one place, they are engaged in "building" in another.
The place of action of coastal waves is a narrow border of the coast and its underwater slope. Where there is mainly destruction of the coast, above the water, as
as a rule, rocks hang overhead - cliffs, waves “gnaw out” niches in them, create under them
bizarre grottoes and even underwater caves. This type of coast is called abrasion (from Latin abrasio - scraping). When the sea level changes - and this has happened repeatedly in recent geological history of our planet - abrasion buildings could be under water or, conversely, on land, far from the modern coast. By
such forms coastal relief located on land, scientists are restoring the history of the formation of ancient shores.
In areas of a leveled coast with shallow depths and a gentle underwater slope, waves deposit (accumulate) material that was transferred from the destroyed areas. Beaches are formed here. At high tide, rolling waves move sand and pebbles deep into the coast, creating an extended
nye alongshore swells. During low tide on such shafts you can see the accumulation of shells, seaweed.
Ebb and flow are related to attraction | ||||
Moon, the satellite of the Earth, and the Sun - our near | ||||
the greatest star. If the influences of the moon and sun | ||||
add up (i.e. the sun and moon turn out to be | ||||
on one straight line relative to the Earth, which | ||||
comes on the days of the new moon and full moon), then ve- | ||||
The tidal range reaches its maximum. | ||||
Such a tide is called a spring tide. When | ||||
The sun and moon weaken each other's influence, | ||||
minimum tides occur (they are called | ||||
quadrature, they occur between the new moon | ||||
and full moon). | ||||
How deposits are formed | ||||
waves of the sea? When moving towards the shore of the wave | ||||
sorts by size and transfers sand | To combat the erosion of the coast as a result of unrest |
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particles, moving them along the coast. | often on the beaches they build barrier ramparts from blocks |
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COAST TYPES |
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The fjord coast is found in places of flood- | the name of this type of coast). They are educated |
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deep glacial troughs | folded during the flooding of folded structures by the sea |
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valleys. Instead of valleys, winding | ||||
bays with steep walls, which are called | The rias coast is formed by flooding |
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fjords. majestic and beautiful | sea of mouths of river valleys. |
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fjords cut through the coast of Norway (the most | Skerries are small rocky islands |
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the heavy Sognefjord here, its length is 137 km), | shores subjected to glacial processing: |
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coast of Canada, Chile. | sometimes these are flooded "ram's foreheads", hills and |
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Dalmatian | shore. | ridges of the terminal moraine. |
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strands of islands line the coast | Lagoons are shallow parts of the sea separated by |
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Adriatic Sea in the region of Dalmatia (hence | nye from the water area by the coastal bar. |
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Benthos (from the Greek benthos - depth) - living organisms and plants living at a depth, at the bottom of the oceans and seas.
Nekton (from the Greek nektos - floating) - living organisms that can move independently in the water column.
Plankton (from Greek planktos - wandering) - organisms living in water, carried by waves and currents and not able to move independently in water.
DEEP FLOORS
Giant steps descend from the coast to the underwater abyssal plains of the ocean floor. Each such "underwater floor" has its own life, because the conditions for the existence of living organisms: illumination, water temperature, its saturation with oxygen and other substances, the pressure of the water column - change significantly with depth. Different organisms relate to the amount of sunlight and the transparency of water. For example, plants can only live where the illumination allows the processes of photosynthesis to take place (these are average depths of no more than 100 m).
The littoral is a coastal strip periodically drained at low tide. Marine animals come here, taken out of the water by waves, which have adapted to live in two environments at once - aquatic
and air. These are crabs
and crustaceans, sea urchins, mollusks, including mussels. In tropical latitudes in the littoral there is a fringe of mangrove forests, and in temperate zones - "forests" of kelp algae.
Below the littoral there is a sublittoral zone (down to depths of 200-250 m), the coastal strip of life on continental shelf. In the direction of the poles, sunlight penetrates the water quite shallowly (no more than 20 m). In the tropics and at the equator, the rays fall almost vertically, which allows them to reach depths of up to 250 m. It is to such depths that algae, sponges, mollusks and light-loving animals, as well as coral buildings - reefs, are found in warm seas and oceans. Animals not only attach to the bottom surface, but also move freely in the water column.
The largest mollusk that lives in shallow water is tridacna (its shell valves reach 1 meter). As soon as the victim swims into the open flaps, they slam shut, and the mollusk begins to digest food. Some mollusks live in colonies. Mussels are bivalves that attach their shells to rocks and other objects. Mollusks breathe oxygen
dissolved in water, so they are not found on the deeper levels of the ocean.
Cephalopods - octopuses, octopuses, squids, cuttlefish have several tentacles and move in the water column due to compression
muscles that allow them to push water through a special tube. Among them there are giants with tentacles up to 10-14 meters! Starfish, sea lilies, urchins
attached to the bottom and corals with special suction cups. Similar to outlandish flowers, sea anemones pass their prey between their tentacles - "petals" and swallow it with a mouth opening located in the middle of the "flower".
Millions of fish of all sizes inhabit these waters. Among them are various sharks - one of the largest fish. Moray eels hide in rocks and caves, and stingrays hide at the bottom, the color of which allows them to merge with the surface.
Below the shelf begins an underwater slope - bathyal (200 - 3000 m). Living conditions here change with every meter (temperature drops and pressure increases).
Abyssal is an ocean bed. This is the largest space, occupying more than 70% of the underwater bottom. Its most numerous inhabitants are foraminifera and protozoan worms. Deep-sea sea urchins, fish, sponges, starfish - all have adapted to the monstrous pressure and are not like their relatives in shallow water. At depths where the sun's rays do not droop, marine inhabitants have devices for lighting - small luminous organs.
Land waters make up less than 4% of all water on our planet. Approximately half of their amount is contained in glaciers and permanent snow, the rest - in rivers, lakes, swamps, artificial reservoirs, groundwater and underground permafrost ice. All natural waters The lands are called water resources.
Fresh water reserves are the most valuable for humanity. In total, there are 36.7 million km3 of fresh water on the planet. They are concentrated primarily in large lakes and glaciers and are unevenly distributed between the continents. largest reserves Antarctica, North America and Asia have fresh water, South America and Africa are somewhat smaller, and Europe and Australia are the least rich in fresh water.
Underground waters are waters contained in the earth's crust. They are connected with the atmosphere and surface waters and participate in the water cycle on the globe. Underground
Glaciers
- permanent snow
Rivers
lakes
swamps
The groundwater
- underground permafrost ice
waters are not only under the continents, but also under the oceans and seas.
Groundwater is formed because some rocks allow water to pass through, while others hold it back. Atmospheric precipitation falling on the surface of the Earth seeps through cracks, voids and pores of permeable rocks (peat, sand, gravel, etc.), and water-resistant rocks (clay, marl, granite, etc.) retain water.
There are several classifications of groundwater by origin, condition, chemical composition and occurrence. Waters that, after rains or snow melt, penetrate the soil, wet it and accumulate in the soil layer, are called soil. On the first water-resistant layer from the earth's surface, groundwater occurs. They are replenished by the atmosphere
spheral precipitation, water filtration of streams and reservoirs, and condensation of water vapor. The distance from the earth's surface to the groundwater level is called groundwater depth. She is
increases during the wet season, when there is a lot of precipitation or snow melt, and decreases during the dry season.
Below groundwater, there may be several layers of deep groundwater, which are held by water-resistant layers. Often, interstratal waters become pressure. This happens when the layers of rocks lie in the form of a bowl and the water enclosed in them is under pressure. Such groundwater, called artesian, rises up the drilled well and gushing. Often artesian aquifers occupy a significant area, and then artesian sources have a high and fairly constant flow of water. Some famous oases North Africa arose from artesian springs. Through faults in the earth's crust, artesian waters sometimes rise from aquifers, and they often dry up between the rainy seasons.
Groundwater comes to the surface of the Earth in ravines, river valleys in the form sources - springs or keys. They form where an aquifer of rocks comes to the earth's surface. Since the depth of the groundwater varies with the season and rainfall, the springs sometimes suddenly disappear and sometimes swell. The temperature of the water in the springs can be different. Springs are considered cold with water temperatures up to 20 ° C, warm - with temperatures from 20 to 37 ° C, and hot -
Permeable rocks
Impermeable rocks
Groundwater types
mi, or thermal, - with a temperature above 37 ° C. Most hot springs occur in volcanic areas where groundwater levels are heated by hot rocks and molten magma coming close to the earth's surface.
Mineral underground waters contain many salts and gases and, as a rule, have healing properties.
The value of groundwater is very great, they can be classified as minerals along with coal, oil or iron ore. Groundwater feeds rivers and lakes, thanks to which the rivers do not become shallow in the summer, when there is little rain, and do not dry out under the ice. A person widely uses groundwater: they are pumped out of the ground for water supply to residents of cities and villages, for the needs of industry and for irrigation of agricultural land. Despite the huge reserves, groundwater is slowly regenerating, there is a danger of their depletion and pollution by domestic and industrial wastewater. Excessive water intake from deep horizons reduces the flow of rivers during low water - the period when the water level is at its lowest.
A swamp is an area of the earth's surface with excessive moisture and stagnant water regime, in which the accumulation of organic matter in the form of undecomposed remains of vegetation occurs. There are swamps in all climatic zones and on almost all continents of the Earth. They contain about 11.5 thousand km3 (or 0.03%) of the fresh waters of the hydrosphere. The most swampy continents are South America and Eurasia.
The swamps can be divided into two large groups - wetlands, where there is no well-defined peat layer, and proper peat bogs, where peat accumulates. Wetlands include swampy tropical forests, salty mangrove swamps, saline swamps of deserts and semi-deserts, grassy swamps of the Arctic tundra, etc. Peat swamps occupy about 2.7 million km, which is 2% of the land area. They are most common in the tundra, forest zone and forest-steppe and, in turn, are divided into lowland, transitional and upland.
Lowland swamps usually have a concave or flat surface, where conditions are created for moisture to stagnate. They often form along the banks of rivers and lakes, sometimes in areas of flooding of reservoirs. In such swamps, groundwater comes close to the surface, supplying the plants growing here with minerals. On the
lowland swamps often grow alder, birch, spruce, sedge, reed, cattail. In these swamps, a layer of peat accumulates slowly (on average 1 mm per year).
Raised bogs with a convex surface and a thick layer of peat are formed mainly on watersheds. They feed mainly on atmospheric precipitation, which is poor in minerals, so less demanding plants settle in these swamps - pine, heather, cotton grass, sphagnum moss.
An intermediate position between lowland and upland ones is occupied by transitional swamps with a flat or slightly convex surface.
Marshes intensively evaporate moisture: more active than others are swamps of the subtropical climatic zone, swampy tropical forests, and in a temperate climate - sphagnum-sedge and forest marshes. Thus, swamps increase the humidity of the air, change its temperature, softening the climate of the surrounding areas.
Marshes, as a kind of biological filter, purify water from chemical compounds and solid particles dissolved in it. Rivers flowing through swampy areas do not differ in catastrophic
trophic spring floods and floods, since their runoff is regulated by swamps, which release moisture gradually.
Bogs regulate the flow of not only surface water, but also groundwater (especially raised bogs). Therefore, their excessive drainage can harm small rivers, many of which originate in swamps. The swamps are rich hunting grounds: many birds nest here, many game animals live. The swamps are rich in peat, medicinal herbs, mosses and berries. The widespread belief that growing agricultural crops on drained swamps, you can get a rich harvest, is wrong. Only the first few years of drained peat deposits are fertile. Swamp drainage plans require extensive research and economic calculations.
The development of a peat bog is a process of peat accumulation as a result of growth, death and partial decomposition of vegetation in conditions of excess moisture and lack of oxygen. The entire thickness of peat in a swamp is called a peat deposit. It has a multilayer structure and contains from 91 to 97% water. Peat contains valuable organic and inorganic substances, so it has long been used in agriculture, energy, chemistry, medicine and other fields. For the first time, Pliny the Elder wrote about peat as a "combustible earth" suitable for heating food in the 1st century BC. AD In Holland and Scotland, peat was used as a fuel in the 12th-13th centuries. An industrial accumulation of peat is called a peat deposit. The largest industrial reserves peat have Russia, Canada, Finland and the USA.
Fertile river valleys have long been mastered by man. Rivers were the most important transport routes, their waters irrigated fields and gardens. Crowded cities arose and developed on the river banks, and borders were established along the rivers. flowing water turned the wheels of mills, and later gave electrical energy.
Each river is individual. One is always wide and full of water, while the other channel remains dry for most of the year and fills with water only during rare rains.
A river is a watercourse of considerable size, flowing along a depression formed by it in the bottom of a river valley - a channel. The river with its tributaries forms a river system. If you look downstream of the river, then all the rivers that flow into it from the right are called right tributaries, and those that flow from the left are called left. The part of the earth's surface and the thickness of soils and soils, from where the river and its tributaries collect water, is called catchment.
A river basin is a part of the land that includes a given river system. There are watersheds between two basins of neighboring rivers,
river basin
The Pakhra River flows through the East European Plain
usually these are hills or mountain systems. The basins of rivers flowing into the same body of water are united respectively into the basins of lakes, seas and oceans. Allocate the main watershed of the globe. It separates the basins of rivers flowing into the Pacific and Indian Oceans on the one hand, and the basins of rivers flowing into the Atlantic and Arctic Oceans on the other. In addition, there are drainless regions on the globe: the rivers flowing there do not carry water to the World Ocean. Such endorheic areas include, for example, the basins of the Caspian and Aral Seas.
Every river starts from its source. It can be a swamp, a lake, a melting mountain glacier, or an outlet to the surface of groundwater. The place where a river flows into an ocean, sea, lake or other river is called a mouth. The length of a river is the distance along the riverbed between its source and mouth.
Depending on the size of the river, they are divided into large, medium and small. Large river basins are usually located in several geographical areas. The basins of medium and small rivers are located within the same zone. According to the flow conditions, rivers are divided into flat, semi-mountain and mountain. Plain rivers flow smoothly and calmly in wide valleys, and mountain rivers rush rapidly and swiftly through the gorges.
Replenishment of water in rivers is called river feeding. It can be snowy, rainy, glacial and underground. Some rivers, for example, those that flow in the equatorial regions (Congo, Amazon and others), are distinguished by rain feeding, since it rains all year round in these regions of the planet. Most rivers are temperate
In the climatic zone, they have a mixed diet: in summer they are replenished by rains, in spring - by melting snow, and in winter they are not allowed to run out of groundwater.
The nature of the behavior of the river according to the seasons of the year - fluctuations in the water level, the formation and disappearance of ice cover, etc. - is called the regime of the river. Annually recurring significant increase in water
in the river - high water - on the flat rivers of the European territory of Russia is caused by intense snowmelt in the spring. The rivers of Siberia, flowing down from the mountains, are full-flowing in summer during the melting of snow.
in mountains. A short-term rise in the water level in a river is called flood. It occurs, for example, when heavy rains fall or when snow melts intensively during a thaw in winter. Most low level water in the river - low water. It is established in the summer, at this time there is little rain and the river is fed mainly by groundwater. Low water also occurs in winter, in severe frosts.
Floods and high waters can cause severe floods: melt or rain waters overflow channels, and rivers overflow their banks, flooding not only their valley, but also the surrounding area. Water flowing at high speed has tremendous destructive power, it demolishes houses, uproots trees, and washes fertile soil from fields.
Sandy beach on the banks of the Volga
To THAT LIVES IN RIVERS?
AT rivers live not only fish. The waters, bottom and banks of rivers are the habitat of many living organisms, they are divided into plankton, nekton and benthos. Plankton include, for example, green and blue-green algae, rotifers and lower crustaceans. The river benthos is very diverse - insect larvae, worms, mollusks, crayfish. Plants - pondweed, reeds, reeds, etc. - settle at the bottom and banks of rivers, and algae grow at the bottom. River nekton is represented by fish and some large invertebrates. Among the fish that live in the seas, and enter the rivers only for spawning, are sturgeon (sturgeon, beluga, stellate sturgeon), salmon (salmon, pink salmon, sockeye salmon, chum salmon, etc.). Carp, bream, sterlet, pike, burbot, perch, crucian carp, etc. constantly live in rivers, and grayling and trout live in mountain and semi-mountain rivers. Mammals and large reptiles also live in the rivers.
Rivers usually flow at the bottom of vast relief depressions called river valleys. At the bottom of the valley, the water stream runs along the recess - the channel - developed by it. Water hits one section of the coast, erodes it and carries rock fragments, sand, clay, silt downstream; in those places where the speed of the current decreases, the river deposits (accumulates) the material carried by it. But the river carries not only sediment washed away by the river flow; during heavy rains and snowmelt, water flowing down the earth's surface destroys the soil, loose soil and carries small particles into streams, which then deliver them to rivers. By destroying and dissolving rocks in one place and depositing them in another, the river gradually creates its own valley. The process of erosion of the earth's surface by water is called erosion. It is stronger where the water flow rate is greater and where the soils are looser. The sediments that make up the bottom of the rivers are called bottom sediments or alluvium.
Wandering channels
In China and Central Asia, there are rivers in which the channel can shift by more than 10 m per day. They, as a rule, flow in easily eroded rocks - loess or sand. In a few hours, the water flow is able to significantly wash away one side of the river, and on the other side, where the current slows down, to deposit washed-away particles. Thus, the channel shifts - “wanders” along the bottom of the valley, for example, on the Amu Darya River in Central Asia, up to 10-15 m per day.
The origin of river valleys can be tectonic, glacial and erosional. Tectonic valleys repeat the direction of deep faults in the earth's crust. Powerful glaciers that covered the northern regions of Eurasia and North America during the global glaciation, moving, plowed out deep hollows, in which river valleys later formed. During the melting of glaciers, water flows spread to the south, forming extensive depressions in the relief. Later, streams rushed into these depressions from the surrounding hills, a large water stream was formed, which built its own valley.
The structure of the plain river valley
Rapids on a mountain river
DRY RIVERS
There are rivers on our planet that fill with water only during rare rains. They are called "wadis" and are found in deserts. Some wadis reach lengths of hundreds of kilometers and flow into the same dry depressions as they are. Gravel and pebbles at the bottom of dried-up channels give reason to believe that during wetter periods, wadis could be full-flowing rivers capable of carrying large sediments. In Australia, dry riverbeds are called screams, in Central Asia - uzboys.
The valley of lowland rivers consists of a floodplain (a part of the valley that is flooded during high water or during significant floods), a channel located on it, as well as slopes of the valley with several floodplain terraces descending steps to the floodplain. River channels can be straight, winding, divided into branches or meandering. In winding channels, bends, or meanders, are distinguished. Washing out the bend at the concave shore, the river usually forms a pool - a deep section of the channel, its shallow sections are called rifts. The strip in the channel with the most favorable depths for navigation is called the fairway. water flow sometimes deposits a significant amount of sediment, forming islands. On large rivers, the height of the islands can reach 10 m, and the length can be several kilometers.
Sometimes on the way of the river there is a ledge of hard rocks. Water cannot wash it out and falls down, forming a waterfall. In those places where the river crosses hard rocks that are washed out slowly, rapids are formed that block the path of the water flow.
AT mouth water speed slows down significantly,
and the river deposits most of its sediment. Formed delta - a low plain in the shape of a triangle, here the channel is divided into many branches and channels. The mouths of rivers flooded by the sea are called estuaries.
There are many rivers on earth. Some of them flow like small silvery snakes within one woodland and then flow into a larger river. And some are truly huge: descending from the mountains, they cross vast plains and carry their waters to the ocean. Such rivers can flow through the territory of several states and serve as convenient transport routes.
When characterizing a river, take into account its length, average annual water flow and basin area. But not all large rivers have all these parameters outstanding. For example, the longest river in the world - the Nile is far from the most full-flowing, and the area of \u200b\u200bits basin is small. The Amazon ranks first in the world in terms of water content (its water flow is 220 thousand m3 / s - this is 16.6% of the flow of all rivers) and in terms of basin area, but is inferior to the Nile in length. The largest rivers are in South America, Africa and Asia.
The longest rivers in the world: the Amazon (over 7 thousand km from the source of the Ucayali River), the Nile (6671 km), the Mississippi with a tributary of the Missouri (6420 km), the Yangtze (5800 km), La Plata with tributaries of the Parana and Uruguay (3700 km).
Most deep rivers(having maximum values average annual water runoff): Amazon (6930 km3), Congo (Zaire) (1414 km3), Ganges (1230 km3), Yangtze (995 km3), Orinoco (914 km3).
The largest rivers of the globe (by basin area): Amazon (7180 thousand km2), Congo (Zaire) (3691 thousand km2), Mississippi with a tributary of the Missouri (3268 thousand km2), La Plata with tributaries of the Parana and Uruguay (3100 thousand km2), Ob (2990 thousand km2).
Volga - the largest river of the East European Plain
MYSTERIOUS NILE
The Nile is a great African river, its valley is the cradle of a bright, original culture that influenced the development human civilization. The mighty Arab conqueror Amir ibn al-Asi said: “There lies the desert, on both sides it rises, and between the heights is the wonderland of Egypt. And all his wealth comes from the blessed river, slowly flowing through the country with the dignity of a caliph. In the middle reaches, the Nile flows through the most severe deserts of Africa - Arabian and Libyan. It would seem that it should become shallow or dry during the hot summer. But at the very height of summer, the water level in the Nile rises, it overflows the banks, flooding the valley, and retreating, leaves a layer of fertile silt on the soil. This is because the Nile is formed from the confluence of two rivers - the White and Blue Nile, whose sources lie in the subequatorial climatic zone, where a low pressure area is established in summer and heavy rains fall. The Blue Nile is shorter than the White Nile, so the rainwater that fills it reaches Egypt earlier, followed by the White Nile flood.
Yenisei - the great river of Siberia
AMAZON - THE QUEEN OF RIVERS
The Amazon is the largest river on Earth. It is fed by many tributaries, including 17 large rivers up to 3500 km long, which, by their size, can themselves be classified as
to the great rivers of the world. The source of the Amazon lies in the rocky Andes, where its main tributary, the Marañon, flows out of the mountain lake Patarcocha. When the Marañon merges with the Ucayali, the river is named the Amazon. The lowland along which this majestic river flows is a country of jungle and swamps. On the way to the east, tributaries constantly replenish the Amazon. It is full-flowing throughout the year, because its left tributaries, located in the northern hemisphere, are full-flowing from March to September,
a right tributaries, located in the southern hemisphere, are full of water the other part of the year. During sea tides, a water shaft up to 3.54 meters high enters the mouth of the river from the Atlantic side and rushes upstream. The locals call this wave of "spororok" - "destroyer".
MISSISSIPPI - THE GREAT RIVER OF AMERICA
The Indians called the mighty river in the southern part of the North American continent Messi Sipi - "Father of the Waters". Its complex river system with many tributaries looks like a giant tree with a densely branched crown. The Mississippi Basin occupies almost half of the territory of the United States of America. Starting in the Great Lakes region in the north, the high-water river carries its waters south - to the Gulf of Mexico, and its flow is two and a half times more than Russian river Volga brings to the Caspian Sea. The Spanish conquistador de Soto is considered the discoverer of the Mississippi. In search of gold and jewelry, he went deep into the mainland and in the spring of 1541 discovered the banks of a huge deep river. One of the first colonists, the Jesuit fathers, who spread the influence of their order in the New World, wrote about the Mississippi as follows: “This river is very beautiful, its width is more than one league; everywhere adjoining it are forests full of game, and prairies where there are a lot of bison. Before coming European colonizers vast areas in the river basin were occupied by virgin forests and prairies, but now they can be seen only in national parks, most of land has been plowed up.
The waters of rivers and streams, choosing their own path, often fall off rocks and ledges. This is how waterfalls form. Sometimes these are very small steps in the channel with insignificant height differences between the upper section, from where the water falls, and the lower one. However, in nature there are absolutely gigantic "steps" and ledges, the height of which reaches many hundreds of meters. Both those and other waterfalls are formed when the water "opens", i.e. destroys, exposes areas with harder rocks, taking away material from more pliable areas. The upper ledge (edge), from which the water falls, is a more durable layer, and downstream, tireless waters destroy less durable rock layers. Such a structure, for example, has the world-famous waterfall on the Niagara River (its name in the Iroquois language means "thundering water"), which connects two of the Great Lakes of North America - Erie and Ontario. Niagara Falls is relatively low - only 51 m (for comparison - co-
Diagram of water flow in Niagara Falls
Cascade of several waterfalls in Norway. 19th century engraving
the Ivan the Great chapel in the Moscow Kremlin has a height of 81 m), but it is famous for more than its tall and full-flowing "brothers". The popularity of the waterfall was brought not only by its location in close proximity to large American and Canadian cities, but also by its good study.
The water flow, falling from any height to the foot of the slope, forms a depression, a niche even in fairly strong rocks. But the upper brow is also gradually blurred and destroyed by the action flowing water. The peaks of the ledge are crumbling, and. the waterfall, as it were, recedes back, “backs up” up the valley. Long-term observations of the Niagara Falls have shown that such a "backward" erosion "eats" the upper ledge of the waterfall by about 1 m in 60 years.
In Scandinavia, glacial landforms are "guilty" of the formation of waterfalls. There, streams from glacier-lined mountain peaks rush down into the fjords from a great height.
Huge waterfalls, which have arisen under the influence of tectonics - the internal forces of the Earth, are very spectacular. The colossal steps of the waterfalls are formed when the riverbed is disturbed by tectonic faults. It happens that not one ledge is formed, but several at once. Such cascades of waterfalls are incredibly beautiful.
The view of any waterfall is mesmerizing. It is no coincidence that these natural phenomena invariably attract the attention of numerous tourists, often becoming "calling cards" of the area and even the country.
VICTORIA WATERFALL | WATERFALL CHURUN-MERU - |
"SALTO ANGEL" |
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"Smoke that thunders" - so from the language of the locals | |
residents translate the name "mosi-oa tupia", which | The highest waterfall in the world is located in South |
which has long been designated this African water | America, in Venezuela. Durable quartzite |
pad. The first Europeans who saw in 1855 | rocks of the Guiana Highlands, fragmented |
this is an amazing creation of nature on the Zambezi River, | mami, form abysses several kilometers long. |
were members of the expedition of David Livingston, | Falls into one of these abysses from a height of 1054 m |
who gave the name to the waterfall in honor of the then ruling | water flow of the famous Churun Meru waterfall on |
Queen Victoria. "The water seemed to sink into the depths | tributary of the Orinoco. This is his Indian name. |
land, since the other slope of the gorge into which it descends | not as well known as the European Angel |
rolled over, was only 80 feet away from me "- so | or Salto Angel. First saw and flew |
Livingston described his impressions. Narrow (from 40 | near the waterfall, the Venezuelan pilot Angel (in |
up to 100 m) the channel into which the waters of the Zambe rush | translated from Spanish - "angel"). His last name and |
zi, reaches a depth of 119 meters. When all the water of the river | gave a romantic name to the waterfall. Opening |
rushes into the gorge, clouds of water dust, vyryva- | this waterfall in 1935 selected "palm per- |
upward, visible from a distance of 35 km! in splashes | venestia” at the African Victoria Falls, counted |
A rainbow is constantly hanging over the waterfall. | previously the tallest in the world. |
IGUAZU FALLS
One of the most famous and beautiful waterfalls | |
dove in the world is the South American Iguazu, | |
located on the river of the same name, a tributary | |
Paranas. Actually, it's not even one, but more | |
250 waterfalls, the streams and jets of which rush - | |
from several sides into a funnel-shaped canyon. | |
The largest of the Iguazu Falls, 72 m high, | |
called "Devil's Throat"! Origin | |
the pas of the waterfall is associated with the structure of the lava plateau, | |
through which the Iguazu River flows. "Layer Pie" | |
basalt is broken by cracks and is destroyed by unequal | |
numbered, which led to the formation of a peculiar | |
noy ladder, along the steps of which they rush - | |
down the waters of the river. The waterfall is located on the border | |
Argentina and Brazil, so one side of the water | |
pada - Argentinean, along which waterfalls, replacing | |
each other, stretching for more than a kilometer, and the other | |
part of the waterfalls is Brazilian. | Waterfall in the Rocky Mountains |
Lakes are called hollows filled with water - natural depressions on the surface of the land that have no connection with the sea or ocean. In order for a lake to form, two conditions are necessary: the presence of a natural depression - a closed depression in the earth's surface - and a certain volume of water.
There are many lakes on our planet. Them total area is about 2.7 million km2, that is, approximately 1.8% of the total land area. The main wealth of lakes - fresh water so necessary for man. The lakes contain about 180 thousand km3 of water, and the 20 largest lakes in the world, taken together, contain the predominant part of all fresh water available to man.
Lakes are located in a wide variety of natural areas. Most of them are in the northern parts of Europe and the North American continent. There are a lot of lakes in areas where permafrost is widespread, they are also in drainless areas, in floodplains and river deltas.
Some lakes are filled only during the wet seasons, and the rest of the year are dry - these are temporary lakes. But most lakes are constantly filled with water.
Depending on the size of the lakes, they are divided into very large ones, the area of which exceeds 1,000 km2, large ones with an area of 101 to 1000 km2, medium ones, from 10 to 100 km2, and small ones, with an area of less than 10 km2.
According to the nature of water exchange, lakes are divided into waste and non-drainage. Located in cat-
In the valley, the lakes collect water from the surrounding territories, streams and rivers flow into them, while at least one river flows out of the sewage lakes, and not a single one flows out of the endorheic lakes. Waste lakes include Lake Baikal, Ladoga and Onega lakes, and drainless lakes include Lake Balkhash, Chad, Issyk-Kul, and the Dead Sea. Aral and Caspian Sea also drainless lakes, but due to their large size and sea-like regime, these reservoirs are conditionally considered seas. There are so-called deaf lakes, for example, formed in the craters of volcanoes. Rivers do not flow into them and do not flow out of them.
Lakes can be divided into fresh, brackish and salty, or mineral. The salinity of water in fresh lakes does not exceed 1% o - such water, for example, in Baikal, Ladoga and Onega lakes. Water brackish lakes have a salinity of 1 to 25% o. For example, the salinity of water in Issyk-Kul is 5-8% o, and in the Caspian Sea - 10-12% o. Salty lakes are called, the water in which has a salinity of 25 to 47% o. Above 47% of salts contain mineral lakes. So, the salinity of the Dead Sea, lakes Elton and Baskunchak is 200-300% o. Salt lakes tend to form in arid regions. In some salt lakes, the water is a solution of salts close to saturation. If such saturation is reached, then salt precipitation occurs and the lake turns into a self-sedating lake.
In addition to dissolved salts, lake water contains organic and inorganic substances and dissolved gases (oxygen, nitrogen, etc.). Oxygen not only enters lakes from the atmosphere, but is also released by plants during photosynthesis. It is necessary for the life and development of aquatic organisms, as well as for the oxidation of organic
Lake in the Swiss Alps
th substance in the reservoir. If an excess of oxygen is formed in the lake, then it leaves the water into the atmosphere.
According to the nutritional conditions of aquatic organisms, lakes are divided into:
- lakes poor in nutrients. These are deep lakes clear water, which include, for example, Baikal, Lake Teletskoye;
- lakes with a large supply of nutrients and rich vegetation. These are, as a rule, shallow and warm lakes;
YOUNG AND OLD LAKES
The life of the lake has a beginning and an end. Once formed, it is gradually filled with sediment from rivers, the remains of dead animals and plants. Every year the amount of precipitation at the bottom increases, the lake becomes shallower, overgrown and turns into a swamp. The greater the initial depth of the lake, the longer its life lasts. In small lakes, precipitation accumulates for many thousands of years, and in deep lakes - for millions of years.
Lakes with an excessive amount of organic matter, the oxidation products of which are harmful to living organisms.
Lakes regulate river flow and have a significant impact on the climate of adjacent areas.
They contribute to an increase in the amount of precipitation, the number of days with fogs and generally moderate the climate. Lakes raise the water table and affect soils, vegetation and animal world surrounding areas.
Looking at the map, everyone | ||
continents you can see lakes. One of them you- | ||
drawn, others rounded. Some lakes are located | ||
wife in mountainous areas, others - on vast | ||
flat plains, some very deep, and | ||
some are quite small. The shape and depth of the lake | ||
ra depend on the size of the basin, which it | ||
takes. Lake basins are formed according to | ||
Most of the world's major lakes | ||
is of tectonic origin. They dis- | ||
rely in large deflections earth's crust on the | ||
plains (for example, Ladoga and Onega | ||
lakes) or fill deep tectonic | ||
cracks - rifts (Lake Baikal, Tanganyika, | ||
Nyasa and others). | ||
Lake basins can become craters and | ||
calderas extinct volcanoes and sometimes lower | ||
on the surface of lava flows. Such lakes | ||
ra, called volcanic, meet, | ||
for example, in the Kuril and Japanese islands, on | ||
Kamchatka, on the island of Java and in other volcanic | ||
some regions of the Earth. It happens that lava and debris | ||
igneous rocks block up to | ||
the line of the river, in this case, a volcano also appears | Lake Baikal |
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nic lake. |
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TYPES OF LAKE BEANS |
Lake in a trough of the earth's crust Lake in a crater
The basin of Lake Kaali in Estonia is of meteorite origin. It is located in a crater formed as a result of the fall of a large meteorite.
Glacial lakes fill the basins that were formed as a result of the activity of the glacier. Moving, the glacier plowed out softer soil, creating depressions in the relief: in some places - long and narrow, and in others - oval. Over time, they filled with water, and glacial lakes appeared. There are a lot of such lakes in the north of the North American continent, in Eurasia on the Scandinavian and Kola Peninsulas, in Finland, Karelia and Taimyr. In mountainous regions, for example, in the Alps and in the Caucasus, glacial lakes are located in kars - bowl-shaped depressions in upper parts mountain slopes, in the creation of which small mountain glaciers and snowfields took part. Melting and retreating, the glacier leaves a moraine - an accumulation of sand, clay with inclusions of pebbles, gravel and boulders. If a moraine dams up a river flowing out from under a glacier, a glacial lake is formed, often having a rounded shape.
In areas composed of limestone, dolomite, and gypsum, as a result of the chemical dissolution of these rocks by surface and underground waters, karst lake basins arise. Thicknesses of sand and clay lying above karst rocks fall into underground voids, forming depressions on the earth's surface, which eventually fill with water and become lakes. Karst lakes are also found in caves.
rax, they can be seen in the Crimea, the Caucasus, the Urals and other regions.
AT tundra, and sometimes in the taiga, where permafrost is common, in the warm season the soil thaws and sags. Lakes appear in small depressions, calledthermokarst.
AT river valleys, when a meandering river straightens its course, the old section of the channel becomes isolated. This is how oxbow lakes, often horseshoe-shaped.
Dammed, or dammed, lakes arise in the mountains when, as a result of a collapse, a mass of rocks blocks the riverbed. For example,
in In 1911, during an earthquake in the Pamirs, a giant mountain collapse occurred, it dammed the Murgab River, and Sarez Lake was formed. Lake Tana in Africa, Sevan in Transcaucasia and many other mountain lakes are dammed.
At coasts of the seas, sandy spits can separate the shallow coastal area from the sea, resulting in the formation lagoon lake. If sandy-clay deposits fence off flooded estuaries from the sea, estuaries are formed - shallow bays with very salty water. There are many such lakes on the coast of the Black and Azov Seas.
Formation of a dam or dam lake
The largest lakes of the Earth: the Caspian Sea- | |
lake (376 thousand km2), Upper (82.4 thousand km2), Vik- | |
thorium (68 thousand km2), Huron (59.6 thousand km2), Michigan | |
(58 thousand km2). The deepest lake on the planet - | |
Baikal (1620 m), followed by Tanganyika | |
(1470 m), Caspian Sea-Lake (1025 m), Nyasa | |
(706 m) and Issyk-Kul (668 m). | |
The Greatest Lake on Earth - Caspian | |
the sea is located in the hinterland of Eura- | |
zia, it contains 78 thousand km3 of water - more than 40% | |
the total volume of lake waters in the world, and in terms of area | |
the Black Sea rises. Sea Caspian lake | |
called because it has many | |
marine characteristics - a huge area | |
due, large volume of water, severe storms | |
and a special hydrochemical regime. | fish that have remained since the time when the Caspian Sea |
From north to south, the Caspian stretches for almost | was connected to the Black and Mediterranean seas. |
1200 km, and from west to east - 200-450 km. | The water level in the Caspian Sea is below the level |
In origin, it is part of the ancient | oceans and changes periodically; at- |
slightly saline Pontic Lake, which existed | The reasons for these fluctuations are not yet clear enough. Me- |
5-7 million years ago. During the Ice Age | the outlines of the Caspian Sea are also visible. At the beginning of the XX century. |
Arctic seas in the Caspian Sea penetrated the seal, be- | the level of the Caspian Sea was approximately -26 m (according to |
salmon, salmon, small crustaceans; is in this | to the level of the World Ocean), in 1972 |
sea-lake and some mediterranean species | do was recorded the lowest position for |
the last 300 years - -29 m, then the level of the sea-lake- |
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ra began to rise slowly and is now |
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about -27.9 m. The Caspian Sea had about |
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70 names: Hyrkan, Khvalyn, Khazar, |
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Sarai, Derbent and others. Its modern |
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The sea received its new name in honor of the ancient |
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men of the Caspians (horse breeders), who lived in the 1st century BC. on the |
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its northwest coast. |
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The deepest lake on the planet Baikal (1620 m) |
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located in the south of Eastern Siberia. It is located |
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zheno at an altitude of 456 m above sea level, its length |
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636 km, and the greatest width in the central part |
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ti - 81 km. There are several versions of the origin |
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the name of the lake, for example, from the Turkic-speaking Bai- |
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Kul - "rich lake" or from the Mongolian Bai- |
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gal Dalai - "big lake". On Baikal 27 stops |
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ditches, the largest of which is Olkhon. Into the lake |
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about 300 rivers and streams flow in, and only |
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Angara river. Baikal is a very ancient lake, it |
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approximately 20-25 million years. 40% plants and 85% vi- |
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of animals living in Baikal are endemic |
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(that is, they are found only in this lake). Volume |
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water in Baikal is about 23 thousand km3, which is |
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20% of the world and 90% of Russian fresh water reserves |
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water. Baikal water is unique - extraordinary |
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but transparent, clean and oxygenated. |
its history has been changed many times. Se- |
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the faithful shores of the lakes are rocky, steep and very |
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picturesque, and the southern and southeastern |
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significantly low, clayey and sandy. coast |
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The Great Lakes are densely populated, located here |
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powerful industrial regions and the largest cities |
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US family: Chicago, Milwaukee, Buffalo, Cleveland, |
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Detroit, as well as the second largest city in Cana- |
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yea - Toronto. Bypassing the rapids of the rivers, |
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connecting the lakes, canals were built and created |
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continuous waterway sea vessels from the Great |
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lakes in the Atlantic Ocean with an eye- |
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lo 3 thousand km and a depth of at least 8 m, accessible |
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for large ships. | ||||||||
African Lake Tanganyika is the most |
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longest on the planet, it was formed in a tecto- |
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depression in the zone of East African |
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faults. | Max Depth | Tanganyika |
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1470 m, this is the second deepest lake in the world after |
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Baikal. Along the coastline, the length of |
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toroy 1900 km, passes the border of four African |
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Kanan states - Burundi, Zambia, Tanzania |
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58 species of fish live in the lake (omul, whitefish, grayling, | and Democratic Republic Congo. Tanganyika |
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taimen, sturgeon, etc.) and lives a typical marine mammal | a very ancient lake, about 170 en- |
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hoarding - Baikal seal. | demic species of fish. Living organisms inhabit |
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In the eastern part of North America in the basin | lake to a depth of about 200 meters, and lower in the water |
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not the St. Lawrence rivers are great | contained | a large number of | hydrogen sulfide. |
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lakes: Superior, Huron, Michigan, Erie and Ontario. | The rocky shores of Tanganyika are indented by numerous |
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They are located in steps, the difference in height | lazy bays and bays. | |||||||
the first four are not pre- | ||||||||
rises 9 m, and only lower | ||||||||
her, Ontario, is | ||||||||
almost 100 m below Erie. | ||||||||
connected | ||||||||
short | ||||||||
high-water | ||||||||
rivers. On the Niaga River | ||||||||
connecting | ||||||||
formed Niagara | ||||||||
50 m). Great Lakes - | ||||||||
greatest | accumulation | |||||||
(22.7 thousand km3). They form | ||||||||
mingled during melt- | ||||||||
huge | ||||||||
cover in the northern | ||||||||
North American | ||||||||
continent | ||||||||
Perennial accumulations of ice in the highlands and cold zones of the Earth are called glaciers. All natural ice is combined into the so-called glaciosphere - a part of the hydrosphere that is in a solid state. It includes the ice of cold oceans, and the ice caps of the mountains, and the icebergs that have broken off from the ice sheets. In the mountains, glaciers are formed from snow. First, during the recrystallization of snow as a result of alternating melting and new freezing of water inside the snow layer, firn is formed.
Distribution of ice on Earth during the Ice Age
which then turns into ice. Under the influence of gravity, ice moves in the form of ice flows. The main condition for the existence of glaciers - both small and huge - is constant low temperatures throughout most of the year, in which the accumulation of snow prevails over its melting. Such conditions exist in the cold regions of our planet - the Arctic and Antarctic, as well as in the highlands.
ICE AGES
IN THE HISTORY OF THE EARTH
AT the history of the Earth several times a strong cooling of the climate led to the growth of glaciers
and the formation of one or more ice sheets. This time is called glaciers or
ice ages.
AT Pleistocene (epoch of the Quaternary period of the Cenozoic era), the area covered with glaciers exceeded the modern one by almost three times. At that time
in In the mountains and on the plains of polar and temperate latitudes, huge ice sheets arose, which, increasing, covered vast territories in temperate latitudes. You can imagine what the Earth looked like at that time by looking at Antarctica or Greenland.
How do they know about those ancient ice ages? Moving along the surface, the glacier leaves its traces - the material that it took with it when moving. Such material is called moraine. Glaciers mark the stages of their standing
The movement of the earth's crust during the colossal load of the ice sheet (1) and after its removal (2)
lamy terminal moraine. Often, by the name of the place that the glacier reached, they call the glacier. The furthest glacier on the territory of Eastern Europe reached the valley of the Dnieper, and this glacier is called the Dnieper. On the territory of North America, the traces of the maximum southward movement of glaciers belong to two glaciations: in the state of Kansas (Kansas glaciation) and Illinois (Illinois glaciation). The last glaciation reached Wisconsin during the Wisconsin Ice Age.
The Earth's climate changed dramatically during the Quaternary, or Anthropogenic, period, which began 1.8 million years ago and continues to this day. What caused such a grandiose cooling is a question that scientists are solving.
Dozens of hypotheses are trying to explain the appearance of huge glaciers by many terrestrial and cosmic reasons - the fall of giant meteorites, catastrophic eruptions volcanoes, changes in the direction of currents in the ocean. The hypothesis proposed in the last century by the Serbian scientist Milanković, who explained climate change periodic fluctuations in the inclination of the planet's axis of rotation and the distance of the Earth from the Sun.
Glaciers of Svalbard
Moraines of sheet glaciation
The currently existing sheet glaciers are the remnants of huge ice sheets that existed in temperate latitudes during the last ice ages. And although today they are not as large-scale as in the past, their size is still impressive.
One of the most significant is the Antarctic Ice Sheet. The maximum thickness of its ice exceeds 4.5 km, and the distribution area is almost 1.5 times larger than the area of Australia. From several centers of the dome, the ice of many glaciers spreads in different directions. It moves in the form of huge streams at a speed of 300-800 m per year. Occupying the whole of Antarctica, the cover in the form of outlet glaciers flows into the sea, giving life to numerous icebergs. Glaciers lying or, rather, floating in the coastal area are called shelf glaciers, since they are located in the area of \u200b\u200bthe underwater margin of the mainland - the shelf. Such ice shelves exist only in Antarctica. The largest ice shelves are in West Antarctica. Among them is the Ross Ice Shelf, on which the American McMurdo Antarctic Station is located.
Another colossal ice sheet is in Greenland, covering over 80% of it.
foothill glacier
the largest island in the world. Greenland ice accounts for about 10% of all ice on Earth. The speed of ice flow here is much less than
in Antarctica. But Greenland also has its own champion - a glacier that moves at a very high speed - 7 km per year!
Reticulated glaciation characteristic of the polar archipelagos - Franz Josef Land, Svalbard, Canadian Arctic Archipelago. This type of glaciation is transitional between cover and mountain. In plan, these glaciers resemble a cellular grid, hence the name. Peaks, pointed peaks, rocks, land areas protrude from under the ice in many places, like islands in the ocean. They are called nunataki. "Nunatak" is an Eskimo word. This word got into the scientific literature thanks to the famous Swedish polar explorer Niels Nordenskiöld.
To the same "half-cover" type of glaciation includesfoothill glaciers. Often a glacier descending from mountains along a valley reaches their foothills and emerges in wide lobes.
in melting (ablation) zone to the plain (this type of glaciers is also called Alaskan glaciers) or even
on the shelf or in lakes (Patagonian type). Piedmont glaciers are one of the most spectacular and beautiful. They are found in Alaska, in the north of North America, in Patagonia, in the extreme south of South America, in Svalbard. The most famous foothill glacier Malaspina in Alaska.
Reticulated glaciation of Svalbard
Where latitude and height above sea level do not allow snow to melt during the year, glaciers arise - accumulations of ice on mountain slopes and peaks, in saddles, depressions and niches on slopes. Over time, the snow
spins into firn and then into ice. Ice has the properties of a viscoplastic body and is able to flow. At the same time, he grinds and plows
surface on which it moves. In the structure of the glacier, a zone of accumulation, or accumulation, of snow and an ablation zone, or melting, are distinguished. These zones are separated by a food boundary. Sometimes it coincides with the snow line, above which snow lies throughout the year. The properties and behavior of glaciers are studied by glaciologists.
WHAT ARE GLACIERS
Small hanging glaciers lie in depressions on the slopes and often go beyond the snow line. Such are the many glaciers of the Alps and the Caucasus
Randklufts - lateral cracks separating the glacier from the rocks
Bergschrund - a fissure in the area
supply of the glacier, separating the fixed and mobile
parts of the glacier
Median and lateral moraines
Transverse cracks in the tongue of the glacier
Primary moraine - material under the glacier
behind. The cirque glaciers fill bowl-shaped depressions on the slope - cirques, or cirques. In the lower part, the circus is limited by a transverse ledge - a crossbar, which is a threshold beyond which the glacier has not crossed for many hundreds of years.
Many mountain-valley glaciers, like rivers, merge from several "tributaries" into one large one that fills the glacial valley. Such glaciers are especially large sizes(they are also called dendritic or tree-like) are characteristic of the highlands of the Pamirs, Karakoram, Himalayas, Andes. For each region, there is a more fractional division of glaciers.
Summit glaciers occur on rounded or leveled mountain surfaces. The Scandinavian mountains have leveled summit surfaces - plateaus, on which this type of glaciers is common. The plateau breaks off in sharp ledges to fjords - ancient glacial valleys that have turned into deep and narrow sea bays.
The uniform movement of ice in the glacier can be replaced by sharp shifts. Then the tongue of the glacier begins to move along the valley at a speed of up to hundreds of meters per day or more. Such glaciers are called pulsating. Their ability to move is due to the accumulated stress
in glacial thickness. As a rule, constant observations of the glacier make it possible to predict the next pulsation. This helps prevent tragedies like the one that occurred in the Karmadon Gorge in 2003, when as a result of the pulsation of the Kolka glacier in the Caucasus, many settlements of the flowering valley were buried under chaotic heaps of ice blocks. Such pulsating glaciers are not uncommon.
in nature. One of them - the Bear Glacier - is located in Tajikistan, in the Pamirs.
Glacial valleys are U-shaped and resemble a trough. Their name is connected with this comparison - a trog (from it. Trog - a trough).
When a mountain peak is covered on all sides by glaciers that gradually destroy the slopes, sharp pyramidal peaks are formed - carlings. Over time, neighboring circuses may merge.
Edge of a glacier in the Himalayas
Clastic material on the surface of a glacier in the Alps
Rivers fed by glaciers, i.e. flowing from under the glaciers, very muddy and stormy during the melting period in the warm season and, conversely, become clean and transparent in winter and autumn. The shaft of the terminal moraine is sometimes a natural dam for a glacial lake. With rapid melting, the lake can wash out the shaft, and then a mudflow is formed - a mud-stone stream.
WARM AND COLD GLACIERS
On the bed of the glacier, i.e. the part that comes into contact with the surface may have a different temperature. In the highlands of temperate latitudes and in some polar glaciers, this temperature is close to the melting point of the ice. It turns out that a layer of melt water is formed between the ice itself and the underlying surface. On it, as on a lubricant, the glacier moves. Such glaciers are called warm, in contrast to cold ones, which are frozen to the bed.
Imagine a snowdrift melting in the spring. As the weather gets warmer, the snow begins to settle, its boundaries shrink, receding from the “winter” ones, streams run from under it... And everything that has accumulated on the snow and in the snow for long periods remains on the surface of the earth. winter months: all kinds of dirt, fallen branches and leaves, garbage. Now let's try to imagine
imagine that this snowdrift is several million times larger, which means that the heap of "garbage" after it melts will be the size of a mountain! big glacier during melting, which is also called retreat, leaves behind even more material - after all, its volume of ice contains much more "garbage". All inclusions left by the glacier after melting on the surface of the earth are called moraine or glacial deposits.
long. After melting, such moraines look like long mounds stretching along the slopes down the valley.
The glacier is in in constant motion. As a viscoplastic body, it has the ability to flow. Consequently, the fragment that fell on him from the cliff, after a while, may be quite far from this place. These debris are collected (accumulated), as a rule, at the edge of the glacier, where the accumulation of ice gives way to melting. The accumulated material repeats the shape of the tongue of the glacier and looks like a curved embankment, partially blocking the valley. When the glacier retreats, the terminal moraine remains on same place, gradually washed away by melt waters. During the retreat of the glacier, several shafts of terminal moraines may accumulate, which will indicate the intermediate positions of its tongue.
The glacier has receded. A moraine shaft remained in front of his front. But the melting continues. And behind the final moraine, melted glaciers begin to accumulate
kovy waters. A glacial lake appears, which is held back by a natural dam. When such a lake breaks, a destructive mudflow, a mudflow, is often formed.
As the glacier moves down the valley, it destroys its base as well. Often this process, which is called "exaration", occurs unevenly. And then steps are formed in the bed of the glacier - crossbars (from German Riegel - a barrier).
The moraines of sheet glaciers are much larger and more diverse, but they are less preserved in the relief.
Sheet ice deposits
After all, as a rule, they are older. And to track their location on the plain is not as easy as in the mountain glacial valley.
During the last ice age, a huge glacier moved from the Baltic crystal shield, from the Scandinavian and Kola Peninsulas. Where the glacier plowed out the crystalline bed, elongated lakes and long ridges - selgas - formed. There are many of them in Karelia and in Finland.
It was from there that the glacier brought fragments of crystalline rocks - granites. During the long transportation of rocks, the ice abraded the uneven edges of the debris, turning them into boulders. To this day, such granite boulders are found on the surface of the earth in all areas of the Moscow region. Fragments brought from afar are called erratic. From the maximum stage of the last glaciation - the Dnieper, when the end of the glacier reached the valleys of the modern Dnieper and Don, only moraines and glacial boulders have survived.
After melting, the cover glacier left behind a hilly space - a moraine plain. In addition, numerous streams of melted glacial waters burst out from under the edge of the glacier. They eroded the bottom and terminal moraines, carried away fine clay particles and left sandy fields - sands (from the isl. sand - sand) in front of the edge of the glacier. Melt water often washed its tunnels under the melting glaciers that lost their mobility. In these tunnels, and especially at the exit from under the glacier, washed-out moraine material (sand, pebbles, boulders) accumulated. These accumulations have been preserved in the form of long winding shafts - they are called oses.
AT In cold climates, water in the bowels and on the surface freezes to a depth of 500 m or more. Over 25% of the entire land surface of the Earth is occupied by permafrost rocks.
AT our country has more than 60% of such territory, because almost all of Siberia lies in the zone of its distribution.
This phenomenon is called permafrost, or permafrost. However, the climate can change in the direction of warming over time, so the term "perennial" is more appropriate for this phenomenon.
AT summer seasons - and they are very short and fleeting here - the top layer of surface soils can thaw. However, below 4 m there is a layer that never thaws. Groundwater can either be under this frozen layer, or stored in liquid state between permafrost (it forms water lenses - taliks) or above the frozen layer. The top layer, which is subject to freezing and thawing, is calledactive layer.
POLYGONAL SOILS
Ice in the ground can form ice veins. Often they occur in places of frost (formed during severe frosts) cracks filled with water. When this water freezes, the soil between the cracks begins to compress, because the ice occupies large area than water. A slightly convex surface is formed, framed by depressions. Such polygonal soils cover a significant part of the tundra surface. When a short summer comes and the ice veins begin to thaw, whole spaces are formed, similar to a lattice of pieces of land surrounded by water "channels".
Among the polygonal formations, stone polygons and stone rings are widespread. With repeated freezing and thawing of the earth, freezing occurs, the ice pushing larger fragments contained in the soil to the surface. In this way, the soil is sorted, since it small particles remain in the center of rings and polygons, while large fragments are displaced towards their edges. As a result, shafts of stones appear, framing more fine material. Mosses sometimes settle on it, and in autumn the stone polygons amaze with unexpected beauty:
bright mosses, sometimes with bushes of cloudberries or lingonberries, surrounded on all sides gray stones, are similar to specially made garden beds. In diameter, such polygons can reach 1-2 m. If the surface is not even, but inclined, then the polygons turn into stone strips.
The freezing of debris from the ground leads to the fact that on the summit surfaces and slopes of mountains and hills in the tundra zone, a chaotic heap of large stones appears, merging into stone “seas” and “rivers”. For them there is a name "kurums".
BULGUNNYAKHI
This Yakut word denotes surprise
body form of relief - a hill or hillock with a | ||
deep core inside. It is formed due to | ||
an increase in the volume of water when freezing in over- | ||
permafrost layer. As a result, the ice rises | ||
surface thickness of the tundra and a hillock appears. | ||
Large bulgunnyakhs (in Alaska they are called es- | ||
Kimos word "pingo") can reach up to | Formation of polygonal soils |
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30-50 m height. |
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On the surface of the planet, not only continuous belts are distinguished permafrost in cold natural areas. There are areas with the so-called insular permafrost. It exists, as a rule, in the highlands, in harsh places with low temperatures, for example, in Yakutia, and is the remnants - "islets" - of the former, more extensive permafrost belt, preserved since the last ice age
