Surface currents of the world's oceans. Water circulation

4. Ocean currents.

© Vladimir Kalanov,
"Knowledge is power".

The constant and continuous movement of water masses is the eternal dynamic state of the ocean. If rivers on Earth flow to the sea along their inclined channels under the influence of gravity, then currents in the ocean are caused by various reasons. The main causes of sea currents are: wind (drift currents), unevenness or changes in atmospheric pressure (barogradient), attraction of water masses by the Sun and Moon (tidal), differences in water densities (due to differences in salinity and temperature), differences in levels created by influx of river water from continents (runoff).

Not every movement of ocean water can be called a current. In oceanography, sea currents are the forward movement of water masses in the oceans and seas..

Two physical forces cause currents - friction and gravity. Excited by these forces currents are called frictional And gravitational.

Currents in the World Ocean are usually caused by several reasons. For example, the mighty Gulf Stream is formed by the merger of density, wind and discharge currents.

The initial direction of any current soon changes under the influence of the Earth's rotation, frictional forces, and the configuration of the coastline and bottom.

According to the degree of stability, currents are distinguished sustainable(for example, North and South trade wind currents), temporary(surface currents of the North Indian Ocean caused by monsoons) and periodic(tidal).

Based on their position in the ocean water column, currents can be superficial, subsurface, intermediate, deep And bottom. Moreover, the definition of “surface current” sometimes refers to a fairly thick layer of water. For example, the thickness of inter-trade wind countercurrents in the equatorial latitudes of the oceans can be 300 m, and the thickness of the Somali Current in the northwestern part of the Indian Ocean reaches 1000 meters. It is noted that deep currents are most often directed in the opposite direction compared to the surface waters moving above them.

Currents are also divided into warm and cold. Warm currents move water masses from low latitudes to higher ones, and cold- in the opposite direction. This division of currents is relative: it characterizes only the surface temperature of moving waters in comparison with the surrounding water masses. For example, in the warm North Cape Current (Barents Sea) the temperature of the surface layers is 2–5 °C in winter and 5–8 °C in summer, and in the cold Peruvian Current (Pacific Ocean) - all year round from 15 to 20 °C, in the cold Canary Current (Atlantic) – from 12 to 26 °C.

The main source of data is ARGO buoys. The fields were obtained using optimal analysis.

Some ocean currents combine with other currents to form a basin-wide gyre.

In general, the constant movement of water masses in the oceans is a complex system of cold and warm currents and countercurrents, both surface and deep.

The most famous for residents of America and Europe is, of course, the Gulf Stream. Translated from English, this name means Current from the Bay. Previously, it was believed that this current begins in the Gulf of Mexico, from where it rushes through the Strait of Florida into the Atlantic. Then it turned out that the Gulf Stream carries only a small fraction of its flow from this bay. Having reached the latitude of Cape Hatteras on the Atlantic coast of the United States, the current receives a powerful influx of water from the Sargasso Sea. This is where the Gulf Stream itself begins. A peculiarity of the Gulf Stream is that when it enters the ocean, this current deviates to the left, whereas under the influence of the Earth’s rotation it should deviate to the right.

The parameters of this powerful current are very impressive. The surface speed of water in the Gulf Stream reaches 2.0–2.6 meters per second. Even at a depth of 2 km, the speed of the water layers is 10–20 cm/s. When leaving the Strait of Florida, the current carries out 25 million cubic meters of water per second, which is 20 times more than the total flow of all the rivers of our planet. But after adding the flow of water from the Sargasso Sea (Antilles Current), the power of the Gulf Stream already reaches 106 million cubic meters of water per second. This powerful stream moves northeast to the Great Newfoundland Bank, and from here it turns south and, together with the Slope Current that separated from it, is included in the North Atlantic water cycle. The depth of the Gulf Stream is 700–800 meters, and its width reaches 110–120 km. The average temperature of the surface layers of the current is 25–26 °C, and at depths of about 400 m it is only 10–12 °C. Therefore, the idea of ​​the Gulf Stream as a warm current is created precisely by the surface layers of this stream.

Let us note another current in the Atlantic – the North Atlantic. It runs across the ocean to the east, towards Europe. The North Atlantic Current is less powerful than the Gulf Stream. The water flow here is from 20 to 40 million cubic meters per second, and the speed is from 0.5 to 1.8 km/h, depending on the location. However, the influence of the North Atlantic Current on the climate of Europe is very noticeable. Together with the Gulf Stream and other currents (Norwegian, North Cape, Murmansk), the North Atlantic Current softens the climate of Europe and the temperature regime of the seas washing it. The warm Gulf Stream current alone cannot have such an impact on the climate of Europe: after all, the existence of this current ends thousands of kilometers from the shores of Europe.

Now let's return to the equatorial zone. Here the air heats up much more than in other areas of the globe. The heated air rises, reaches the upper layers of the troposphere and begins to spread towards the poles. Approximately in the area of ​​28-30° northern and southern latitudes, the cooled air begins to descend. More and more new air masses flowing from the equator region create excess pressure in subtropical latitudes, while above the equator itself, due to the outflow of heated air masses, the pressure is constantly reduced. From areas of high pressure, air rushes to areas of low pressure, that is, to the equator. The rotation of the Earth around its axis deflects the air from the direct meridional direction to the west. This creates two powerful flows of warm air, called trade winds. In the tropics of the Northern Hemisphere, trade winds blow from the northeast, and in the tropics of the Southern Hemisphere - from the southeast.

For simplicity of presentation, we do not mention the influence of cyclones and anticyclones in the temperate latitudes of both hemispheres. It is important to emphasize that the trade winds are the most stable winds on Earth; they blow constantly and cause warm equatorial currents that move huge masses of ocean water from east to west.

Equatorial currents benefit navigation by helping ships cross the ocean from east to west more quickly. At one time, H. Columbus, without knowing anything in advance about the trade winds and equatorial currents, felt their powerful effect during his sea voyages.

Based on the constancy of equatorial currents, the Norwegian ethnographer and archaeologist Thor Heyerdahl put forward a theory about the initial settlement of the Polynesian islands by the ancient inhabitants of South America. To prove the possibility of sailing on primitive ships, he built a raft, which, in his opinion, was similar to the watercraft that the ancient inhabitants of South America could use when crossing the Pacific Ocean. On this raft, called Kon-tiki, Heyerdahl, along with five other daredevils, made a perilous voyage from the coast of Peru to the Tuamotu archipelago in Polynesia in 1947. In 101 days, he swam a distance of about 8 thousand kilometers along one of the branches of the southern equatorial current. The brave men underestimated the power of the wind and waves and almost paid for it with their lives. Up close, the warm equatorial current, driven by the trade winds, is not at all gentle as one might think.

Let us briefly look at the characteristics of other currents in the Pacific Ocean. Part of the waters of the North Equatorial Current in the area of ​​the Philippine Islands turns north, forming the warm Kuroshio Current (in Japanese, “Dark Water”), which in a powerful stream flows past Taiwan and the southern Japanese islands to the northeast. The width of Kuroshio is about 170 km, and the penetration depth reaches 700 m, but in general, in terms of fashionability, this current is inferior to the Gulf Stream. About 36°N Kuroshio turns into the ocean, moving into the warm North Pacific Current. Its waters flow east, cross the ocean approximately at the 40th parallel and warm the coast of North America all the way to Alaska.

The turn of Kuroshio from the coast was noticeably influenced by the influence of the cold Kuril Current, approaching from the north. This current is called Oyashio (“Blue Water”) in Japanese.

There is another remarkable current in the Pacific Ocean - El Niño (Spanish for “The Baby”). This name was given because the El Niño current approaches the shores of Ecuador and Peru before Christmas, when the arrival of the baby Christ into the world is celebrated. This current does not occur every year, but when it nevertheless approaches the shores of the mentioned countries, it is not perceived as anything other than a natural disaster. The fact is that too warm El Niño waters have a detrimental effect on plankton and fish fry. As a result, the catches of local fishermen are reduced tenfold.

Scientists believe that this treacherous current can also cause hurricanes, rainstorms and other natural disasters.

In the Indian Ocean, waters move along an equally complex system of warm currents, which are constantly influenced by monsoons - winds that blow from the ocean to the continent in summer, and in the opposite direction in winter.

In the strip of forties latitudes of the Southern Hemisphere in the World Ocean, winds constantly blow in the direction from west to east, which gives rise to cold surface currents. The largest of these currents, with almost constant waves, is the Western Wind Current, which circulates in a direction from west to east. It is no coincidence that sailors call the strip of these latitudes from 40° to 50° on both sides of the equator the “Roaring Forties”.

The Arctic Ocean is mostly covered with ice, but this does not make its waters at all motionless. The currents here are directly observed by scientists and specialists from drifting polar stations. Over the course of several months of drift, the ice floe on which the polar station is located sometimes travels many hundreds of kilometers.

The largest cold current in the Arctic is the East Greenland Current, which carries the waters of the Arctic Ocean into the Atlantic.

In areas where warm and cold currents meet, phenomenon of rising deep waters (upwelling), in which vertical water flows bring deep water to the ocean surface. Together with them, nutrients that are contained in the lower water horizons rise.

In the open ocean, upwelling occurs in areas where currents diverge. In such places, the ocean level drops and deep water inflows. This process develops slowly - a few millimeters per minute. The most intense rise of deep waters is observed in coastal areas (10 - 30 km from the coastline). There are several permanent upwelling areas in the World Ocean that affect the overall dynamics of the oceans and affect fishing conditions, for example: the Canary and Guinea upwellings in the Atlantic, the Peruvian and California upwellings in the Pacific Ocean, and the Beaufort Sea upwelling in the Arctic Ocean.

Deep currents and rises of deep waters are reflected in the nature of surface currents. Even such powerful currents as the Gulf Stream and Kuroshio sometimes wax and wane. The temperature of the water changes in them and deviations from a constant direction and huge eddies are formed. Such changes in sea currents affect the climate of the corresponding land regions, as well as the direction and distance of migration of some species of fish and other animal organisms.

Despite the apparent chaos and fragmentation of sea currents, in fact they represent a certain system. Currents ensure that they have the same salt composition and unite all waters into a single World Ocean.

© Vladimir Kalanov,
"Knowledge is power"

Excitement is the oscillatory movement of water. It is perceived by the observer as the movement of waves on the surface of the water. In fact, the water surface oscillates up and down from the average level of the equilibrium position. The shape of waves during waves is constantly changing due to the movement of particles in closed, almost circular orbits.

Each wave is a smooth combination of elevations and depressions. The main parts of the wave are: crest- the highest part; sole - lowest part; slope - profile between the crest and trough of a wave. The line along the crest of the wave is called wave front(Fig. 1).

Rice. 1. Main parts of the wave

The main characteristics of waves are height - the difference in the levels of the wave crest and wave bottom; length - the shortest distance between adjacent wave crests or troughs; steepness - the angle between the wave slope and the horizontal plane (Fig. 1).

Rice. 1. Main characteristics of the wave

Waves have very high kinetic energy. The higher the wave, the more kinetic energy it contains (proportional to the square of the increase in height).

Under the influence of the Coriolis force, a water swell appears on the right side of the current, away from the mainland, and a depression is created near the land.

By origin waves are divided as follows:

• friction waves;
• pressure waves;
• seismic waves or tsunamis;
• seiches;
• tidal waves.

Friction waves

Friction waves, in turn, can be wind(Fig. 2) or deep. Wind waves arise as a result of wind waves, friction at the boundary of air and water. The height of wind waves does not exceed 4 m, but during strong and prolonged storms it increases to 10-15 m and higher. The highest waves - up to 25 m - are observed in the westerly wind zone of the Southern Hemisphere.

Rice. 2. Wind waves and surf waves

Pyramidal, high and steep wind waves are called crowding. These waves are inherent in the central regions of cyclones. When the wind subsides, the excitement takes on a character swell, i.e., disturbances due to inertia.

The primary form of wind waves is ripple It occurs at a wind speed of less than 1 m/s, and at a speed greater than 1 m/s, first small and then larger waves are formed.

A wave near the coast, mainly in shallow waters, based on forward movements, is called surf(see Fig. 2).

Deep waves arise at the boundary of two layers of water with different properties. They often occur in straits with two levels of current, near river mouths, at the edge of melting ice. These waves mix up the sea water and are very dangerous for sailors.

Pressure wave

Pressure waves arise due to rapid changes in atmospheric pressure in the places of origin of cyclones, especially tropical ones. Usually these waves are single and do not cause much harm. The exception is when they coincide with high tide. The Antilles, the Florida Peninsula, and the coasts of China, India, and Japan are most often exposed to such disasters.

Tsunami

Seismic waves occur under the influence of underwater tremors and coastal earthquakes. These are very long and low waves in the open ocean, but the force of their propagation is quite strong. They move at very high speed. Along the coasts, their length decreases and their height increases sharply (on average from 10 to 50 m). Their appearance entails human casualties. First, the sea water retreats several kilometers from the shore, gaining strength to push, and then the waves splash onto the shore with great speed at intervals of 15-20 minutes (Fig. 3).

Rice. 3. Tsunami transformation

The Japanese named seismic waves tsunami, and this term is used all over the world.

The seismic belt of the Pacific Ocean is the main area for tsunami generation.

Seiches

Seiches are standing waves that occur in bays and inland seas. They occur by inertia after the cessation of external forces - wind, seismic shocks, sudden changes, intense precipitation, etc. In this case, in one place the water rises and in another it falls.

Tidal wave

Tidal waves- these are movements made under the influence of the tidal forces of the Moon and the Sun. Reverse reaction of sea water to the tide - low tide. The strip that drains during low tide is called drying.

There is a close connection between the height of the tides and the phases of the moon. New and full moons have the highest tides and lowest tides. They're called Syzygy. At this time, the lunar and solar tides, occurring simultaneously, overlap each other. In the intervals between them, on the first and last Thursdays of the Moon phases, the lowest, quadrature tides.

As already mentioned in the second section, in the open ocean the tide height is low - 1.0-2.0 m, but near dissected coasts it increases sharply. The tide reaches its maximum value on the Atlantic coast of North America, in the Bay of Fundy (up to 18 m). In Russia, the maximum tide - 12.9 m - was recorded in Shelikhov Bay (Sea of ​​Okhotsk). In inland seas, the tides are little noticeable, for example, in the Baltic Sea near St. Petersburg the tide is 4.8 cm, but in some rivers the tide can be traced hundreds and even thousands of kilometers from the mouth, for example, in the Amazon - up to 1400 cm.

A steep tidal wave rising up a river is called boron In the Amazon, boron reaches a height of 5 m and is felt at a distance of 1400 km from the mouth of the river.

Even with a calm surface, disturbances occur in the thickness of the ocean waters. These are the so-called internal waves - slow, but very significant in scope, sometimes reaching hundreds of meters. They arise as a result of external influence on a vertically heterogeneous mass of water. In addition, since the temperature, salinity and density of ocean water do not change gradually with depth, but abruptly from one layer to another, specific internal waves arise at the boundary between these layers.

Sea currents

Sea currents- these are horizontal translational movements of water masses in the oceans and seas, characterized by a certain direction and speed. They reach several thousand kilometers in length, tens to hundreds of kilometers in width, and hundreds of meters in depth. In terms of physical and chemical properties, the waters of sea currents are different from those around them.

By duration of existence (sustainability) sea ​​currents are divided as follows:

• permanent, which pass in the same areas of the ocean, have the same general direction, more or less constant speed and stable physical and chemical properties of the transported water masses (North and South trade winds, Gulf Stream, etc.);
• periodic, in which direction, speed, temperature are subject to periodic patterns. They occur at regular intervals in a certain sequence (summer and winter monsoon currents in the northern part of the Indian Ocean, tidal currents);
• temporary, most often caused by winds.

By temperature sign sea ​​currents are:

• warm which have a temperature higher than the surrounding water (for example, the Murmansk Current with a temperature of 2-3 ° C among waters O ° C); they have a direction from the equator to the poles;
• cold, the temperature of which is lower than the surrounding water (for example, the Canary Current with a temperature of 15-16 ° C among waters with a temperature of about 20 ° C); these currents are directed from the poles to the equator;
• neutral, which have a temperature close to the environment (for example, equatorial currents).

Based on the depth of their location in the water column, currents are distinguished:

• superficial(up to 200 m depth);
• subsurface, having a direction opposite to the surface;
• deep, the movement of which is very slow - on the order of several centimeters or a few tens of centimeters per second;
• bottom regulating the exchange of water between polar - subpolar and equatorial-tropical latitudes.

By origin The following currents are distinguished:

• friction, which can be drift or wind. Drift ones arise under the influence of constant winds, and wind ones are created by seasonal winds;
• gradient-gravitational, among which are stock, formed as a result of the slope of the surface caused by excess water due to its influx from the ocean and heavy rainfall, and compensatory, which arise due to the outflow of water, scanty precipitation;
• inert, which are observed after the cessation of the action of the factors that excite them (for example, tidal currents).

The system of ocean currents is determined by the general circulation of the atmosphere.

If we imagine a hypothetical ocean extending continuously from the North Pole to the South Pole, and superimpose on it a generalized scheme of atmospheric winds, then, taking into account the deflecting Coriolis force, we obtain six closed rings -
gyres of sea currents: Northern and Southern equatorial, Northern and Southern subtropical, Subarctic and Subantarctic (Fig. 4).

Rice. 4. Cycles of sea currents

Deviations from the ideal scheme are caused by the presence of continents and the peculiarities of their distribution over the Earth's surface. However, as in the ideal diagram, in reality there is zonal change large - several thousand kilometers long - not completely closed circulation systems: it is equatorial anticyclonic; tropical cyclonic, northern and southern; subtropical anticyclonic, northern and southern; Antarctic circumpolar; high-latitude cyclonic; Arctic anticyclonic system.

In the Northern Hemisphere they move clockwise, in the Southern Hemisphere they move counterclockwise. Directed from west to east equatorial inter-trade wind countercurrents.

In the temperate subpolar latitudes of the Northern Hemisphere there are small current rings around baric minimums. The movement of water in them is directed counterclockwise, and in the Southern Hemisphere - from west to east around Antarctica.

Currents in zonal circulation systems are quite well traced down to a depth of 200 m. With depth, they change direction, weaken and turn into weak vortices. Instead, meridional currents intensify at depth.

The most powerful and deepest surface currents play a critical role in the global circulation of the World Ocean. The most stable surface currents are the North and South Trade Winds of the Pacific and Atlantic Oceans and the South Trade Winds of the Indian Ocean. They have a direction from east to west. Tropical latitudes are characterized by warm waste currents, for example the Gulf Stream, Kuroshio, Brazilian, etc.

Under the influence of constant westerly winds in temperate latitudes there are warm North Atlantic and North-

The Pacific Current in the Northern Hemisphere and the cold (neutral) current of the Western Winds in the Southern Hemisphere. The latter forms a ring in the three oceans around Antarctica. The large gyres in the Northern Hemisphere are closed by cold compensatory currents: along the western coasts in tropical latitudes there are the Californian and Canary currents, and in the Southern Hemisphere there are the Peruvian, Bengal, and Western Australian currents.

The most famous currents are also the warm Norwegian Current in the Arctic, the cold Labrador Current in the Atlantic, the warm Alaskan Current and the cold Kuril-Kamchatka Current in the Pacific Ocean.

The monsoon circulation in the northern Indian Ocean generates seasonal wind currents: winter - from east to west and summer - from west to east.

In the Arctic Ocean, the direction of movement of water and ice occurs from east to west (Transatlantic Current). Its reasons are the abundant river flow of the rivers of Siberia, the rotational cyclonic movement (counterclockwise) over the Barents and Kara seas.

In addition to circulation macrosystems, there are eddies of the open ocean. Their size is 100-150 km, and the speed of movement of water masses around the center is 10-20 cm/s. These mesosystems are called synoptic vortices. It is believed that they contain at least 90% of the kinetic energy of the ocean. Eddies are observed not only in the open ocean, but also in sea currents such as the Gulf Stream. Here they rotate at an even higher speed than in the open ocean, their ring system is better expressed, which is why they are called rings.

For the climate and nature of the Earth, especially coastal areas, the importance of sea currents is great. Warm and cold currents maintain the temperature difference between the western and eastern coasts of the continents, disrupting its zonal distribution. Thus, the ice-free port of Murmansk is located above the Arctic Circle, and on the east coast of North America the Gulf of St. Lawrence (48° N). Warm currents promote precipitation, while cold currents, on the contrary, reduce the possibility of precipitation. Therefore, areas washed by warm currents have a humid climate, while areas washed by cold currents have a dry climate. With the help of sea currents, the migration of plants and animals, the transfer of nutrients and gas exchange are carried out. Currents are also taken into account when sailing.

Lookup table ocean currents contains information on the sea currents of the world's oceans, warm, cold, current speed, temperature, salinity, in which ocean they flow. The information contained in the table can be used in the independent work of students of geographers and ecologists, when writing coursework and preparing manuals for each continent and part of the world.

Map of world ocean currents

World ocean currents warm and cold table

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A source of information: Reference book “Physical geography of continents and oceans.” - Rostov-on-Don, 2004

Which moves with a certain cyclicity and frequency. It is distinguished by the constancy of its physical and chemical properties and its specific geographical location. It can be cold or warm depending on the hemisphere. Each such flow is characterized by increased density and pressure. The consumption of water masses is measured in sverdrup, in a broader sense - in units of volume.

Types of currents

First of all, cyclically directed water flows are characterized by such characteristics as stability, speed of movement, depth and width, chemical properties, influencing forces, etc. Based on the international classification, currents come in three categories:

1. Gradient. Occur when exposed to isobaric layers of water. A gradient ocean current is a flow that is characterized by horizontal movements of isopotential surfaces of the water area. Based on their initial characteristics, they are divided into density, pressure, drain, compensation and seiche. As a result of the waste flow, sediments and ice melt occur.

2. Wind. They are determined by the slope of sea level, the strength of air flow and fluctuations in mass density. A subspecies is drift. This is a flow of water caused purely by the action of the wind. Only the surface of the pool is subject to vibrations.

3. Tidal. They appear most strongly in shallow waters, at river mouths and near the coast.

A separate type of flow is inertial. It is caused by the action of several forces at once. Based on the variability of movement, constant, periodic, monsoon and trade wind flows are distinguished. The last two are determined by direction and speed seasonally.

Causes of ocean currents

At the moment, water circulation in the world's waters is just beginning to be studied in detail. By and large, specific information is known only about surface and shallow currents. The main problem is that the oceanographic system has no clear boundaries and is in constant motion. It is a complex network of flows caused by various physical and chemical factors.

Nevertheless, the following causes of ocean currents are known today:

1. Cosmic influence. This is the most interesting and at the same time difficult process to study. In this case, the flow is determined by the rotation of the Earth, the impact of cosmic bodies on the atmosphere and hydrological system of the planet, etc. A striking example is the tides.

2. Exposure to wind. Water circulation depends on the strength and direction of air masses. In rare cases, we can talk about deep currents.

3. Density difference. Streams are formed due to the uneven distribution of salinity and temperature of water masses.

Atmospheric exposure

In the world's waters, this kind of influence is caused by the pressure of heterogeneous masses. Coupled with space anomalies, water flows in the oceans and smaller basins change not only their direction, but also their power. This is especially noticeable in the seas and straits. A striking example is the Gulf Stream. At the beginning of its journey, it is characterized by increased speed.

The Gulf Stream is accelerated by both contrary and favorable winds. This phenomenon forms a cyclic pressure on the layers of the pool, accelerating the flow. From here, at a certain period of time, there is a significant outflow and influx of large amounts of water. The weaker the atmospheric pressure, the higher the tide.

As water levels drop, the slope of the Straits of Florida becomes smaller. Because of this, the flow speed is significantly reduced. Thus, we can conclude that increased pressure reduces the flow force.

Exposure to wind

The connection between the flows of air and water is so strong and at the same time simple that it is hard not to notice even with the naked eye. Since ancient times, sailors have been able to calculate the appropriate ocean current. This became possible thanks to the work of scientist W. Franklin on the Gulf Stream, dating back to the 18th century. Several decades later, A. Humboldt pointed out precisely the wind in the list of the main extraneous forces affecting water masses.

From a mathematical point of view, the theory was substantiated by the physicist Zeppritz in 1878. He proved that in the World Ocean there is a constant transfer of the surface layer of water to deeper levels. In this case, the main force influencing the movement is the wind. The flow speed in this case decreases in proportion to the depth. The determining condition for constant water circulation is the infinitely long duration of wind action. The only exceptions are trade wind air flows, which cause the movement of water masses in the equatorial zone of the World Ocean seasonally.

Density difference

The impact of this factor on water circulation is the most important cause of currents in the World Ocean. Large-scale studies of the theory were carried out by the international Challenger expedition. Subsequently, the scientists' work was confirmed by Scandinavian physicists.

The heterogeneity of water mass densities is the result of several factors. They have always existed in nature, representing a continuous hydrological system of the planet. Any deviation in water temperature entails a change in its density. In this case, an inversely proportional relationship is always observed. The higher the temperature, the lower the density.

Also, the difference in physical indicators is affected by the state of aggregation of water. Freezing or evaporation increases density, precipitation decreases it. Affects the strength of the current and the salinity of water masses. It depends on melting ice, precipitation and evaporation levels. In terms of density, the World Ocean is quite uneven. This applies to both surface and deep layers of the water area.

Pacific Currents

The general flow pattern is determined by atmospheric circulation. Thus, the eastern trade wind contributes to the formation of the Northern Current. It crosses the waters from the Philippine Islands to the coast of Central America. It has two branches that feed the Indonesian Basin and the Pacific Equatorial Ocean Current.

The largest currents in the water area are the Kuroshio, Alaska and California currents. The first two are warm. The third current is the cold ocean current of the Pacific Ocean. The basin of the Southern Hemisphere is formed by the Australian and Trade Wind currents. The Equatorial Countercurrent is observed just east of the center of the water area. Off the coast of South America there is a branch of the cold Peruvian Current.

In the summer, the El Niño ocean current operates near the equator. It pushes aside the cold masses of water of the Peruvian Stream, forming a favorable climate.

Indian Ocean and its currents

The northern part of the basin is characterized by a seasonal change of warm and cold flows. This constant dynamics is caused by the action of the monsoon circulation.

In winter, the South-Western Current dominates, which originates in the Bay of Bengal. A little further south is Western. This oceanic current of the Indian Ocean crosses the waters from the coast of Africa to the Nicobar Islands.

In summer, the east monsoon contributes to significant changes in surface waters. The equatorial countercurrent shifts to depth and noticeably loses its strength. As a result, its place is taken by powerful warm Somali and Madagascar currents.

Circulation of the Arctic Ocean

The main reason for the development of the underwater current in this part of the World Ocean is the powerful influx of water masses from the Atlantic. The fact is that the centuries-old ice cover does not allow the atmosphere and cosmic bodies to influence the internal circulation.

The most important current in the Arctic Ocean is the North Atlantic. It brings in huge volumes of warm masses, preventing the water temperature from dropping to critical levels.

The Trans-Arctic Current is responsible for the direction of ice drift. Other major flows include the Yamal, Spitsbergen, North Cape and Norwegian currents, as well as a branch of the Gulf Stream.

Atlantic Basin Currents

The salinity of the ocean is extremely high. The zonality of water circulation is the weakest among other basins.

The main ocean current here is the Gulf Stream. Thanks to it, the average water temperature remains at +17 degrees. This oceanic warmth warms both hemispheres.

Also, the most important currents in the basin are the Canary, Brazilian, Benguela and Trade Wind currents.

Oceanic or sea currents - this is the forward movement of water masses in the oceans and seas, caused by various forces. Although the most significant cause of currents is wind, they can also form because of unequal salinity of individual parts of the ocean or sea, differences in water levels, uneven heating of different areas of water areas. In the depths of the ocean there are vortices created by bottom irregularities; their size often reaches 100-300 km in diameter, they capture layers of water hundreds of meters thick.

If the factors causing currents are constant, then a constant current is formed, and if they are episodic in nature, then a short-term, random current is formed. According to the predominant direction, 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, lower ones are called cold, and currents that have the same temperature as the surrounding waters are called neutral.

Monsoon currents change direction from season to season, depending on how the offshore monsoon winds blow. Countercurrents move towards neighboring, more powerful and extended currents in the ocean.

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 their depth extends to no more than 300 m.

In the World Ocean there are constantly thousands of large and small currents that circle the continents and merge into five giant rings. The system of currents in the World Ocean is called circulation and is associated primarily with the general circulation of the atmosphere.

Ocean currents redistribute solar heat absorbed by masses of water. They transport warm water heated by the sun's rays at the equator to high latitudes, and cold water

Currents of the World Ocean

Upwelling - the rise of cold waters from the depths of the ocean

from the polar regions, thanks to currents, it flows to the south. Warm currents contribute to an increase in air temperature, and cold currents, on the contrary, reduce it. Territories washed by warm currents have a warm and humid climate, while those near which cold currents pass have a cold and dry climate.

The most powerful current in the World Ocean is the cold current of the Western Winds, also called the Antarctic Circumpolar Current (from the Latin cirkum - around). The reason for its formation is strong and stable westerly winds blowing from west to east over vast areas.

areas of the Southern Hemisphere from temperate latitudes to the coast of Antarctica. This current covers an area 2500 km wide, extends to a depth of more than 1 km and transports up to 200 million tons of water every second. There are no large land masses along the path of the Western Winds, and it connects the waters of three oceans - the Pacific, Atlantic and Indian - in its circular flow.

The Gulf Stream is one of the largest warm currents in the Northern Hemisphere. It passes through the Gulf Stream and carries the warm tropical waters of the Atlantic Ocean to high latitudes. This gigantic flow 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 deepest river in the world, carries 220 thousand tons of water). At a depth of about 1 km, a countercurrent is observed under the Gulf Stream.

SEA ICE

When approaching high latitudes, ships encounter floating ice. Sea ice frames Antarctica with a wide border and covers the waters of the Arctic Ocean. Unlike continental ice, formed from atmospheric precipitation and covering Antarctica, Greenland, and the islands of the polar archipelagos, this ice is frozen sea water. In polar regions, sea ice is perennial, while in temperate latitudes water freezes only during 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 under wind waves. It repeatedly freezes into small tiles, then splits again until it forms the so-called ice lard - spongy ice floes, which then grow together. This type of ice is called pancake ice for its resemblance to round pancakes on the surface of the water. Areas of such ice, when frozen, form young ice - nilas. Every year this ice gets stronger and thickens. It can become multi-year ice more than 3 m thick, or it can melt if currents carry the ice floes to warmer waters.

The movement of ice is called drift. Covered with drifting (or pack) ice

Ice mountains are melting, taking on bizarre shapes

the space around the Canadian Arctic Archipelago, off the coast of Severnaya and Novaya Zemlya. Arctic ice drifts at speeds of several kilometers per day.

ICEBERGS

Colossal pieces of ice often break off from huge ice sheets and set off on their own voyage. They are called “ice mountains” - icebergs. Without them, the ice sheet in Antarctica would constantly grow. In fact, icebergs compensate for melting and provide a balance to the Antarctic state.

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 approximately 1/7 of the entire iceberg is above water. It can be table-shaped, dome-shaped or cone-shaped. The base of such a huge piece of glacier, located under water, can be much larger in area.

Sea currents carry icebergs far from their birthplaces. A collision with such an iceberg in the Atlantic Ocean caused a

construction of the famous ship Titanic in April 1912.

How long does an iceberg live? Ice mountains that break away from the icy Antarctica can float in the waters of the Southern Ocean for more than 10 years. Gradually they are destroyed, split into smaller parts or, by the will of currents, move to warmer waters and melt.

"FRAM" IN ICE

To find out the path of the drifting ice, the great Norwegian traveler Fridtjof Nansen decided to drift on his ship Fram with them. This bold expedition lasted three whole years (1893-1896). Having allowed the Fram to freeze into the drifting pack ice, Nansen planned to move with it to the North Pole area, and then leave the ship and continue the journey by dog ​​sled and skis. However, the drift went further south than expected, and Nansen's attempt to reach the Pole on skis was unsuccessful. Having traveled more than 3,000 miles from the New Siberian Islands to the western coast of Spitsbergen, the Fram collected unique information about drifting ice and the influence of the Earth's daily rotation on its movement.

The border between land and sea is a line that constantly changes its shape. The oncoming waves carry the smallest particles of suspended sand, roll over pebbles, and grind down rocks. Destroying the coast, especially during strong waves or storms, in one place, they engage in “construction” in another.

The area where coastal waves act is the narrow edge of the shore and its underwater slope. Where the destruction of the coast is mainly taking place, above the water, like

As a rule, there are overhanging rocks - cliffs, the waves “gnaw out” niches in them, creating under them

wonderful grottoes and even underwater caves. This type of shore is called abrasive (from the Latin abrasio - scraping). When sea levels change - and this has happened many times in the recent geological history of our planet - abrasion structures could end up under water or, conversely, on land, far from the modern shore. By

For such forms of coastal relief located on land, scientists reconstruct the history of the formation of ancient coasts.

In areas of a leveled coast with shallow depths and a gentle underwater slope, waves deposit (accumulate) material that was transported from the destroyed areas. Beaches are formed here. At high tide, rolling waves move sand and pebbles deep into the shore, creating a long

ny alongshore levees. During low tide, you can see accumulations of shells and seaweed on such ridges.

Benthos (from the Greek benthos - depth) - living organisms and plants living at depth, at the bottom of oceans and seas.

Nekton (from the Greek nektos - floating) are living organisms capable of independently moving through the water column.

Plankton (from the Greek planktos - wandering) are organisms living in water, transported by waves and currents and unable to move independently in water.

ON THE DEEP FLOORS

The ocean floor descends in giant steps from the coast to the underwater abyssal plains. Each such “underwater floor” has its own life, because the conditions of existence of living organisms: illumination, water temperature, its saturation with oxygen and other substances, the pressure of the water column - change significantly with depth. Organisms react differently to the amount of sunlight and water transparency. For example, plants can live only where illumination allows photosynthesis processes to take place (this is an average depth of no more than 100 m).

The littoral zone is a coastal strip periodically drained at low tide. This includes marine animals carried 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 zone there is a border of mangrove forests, and in temperate zones there are “forests” of kelp algae.

Below the littoral zone is the sublittoral zone (down to depths of 200-250 m), the coastal strip of life on the continental shelf. Towards the poles, sunlight penetrates the water very 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 structures - 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 the tridacna (its shell valves reach 1 meter). As soon as the prey swims into the open doors, they slam shut and the mollusk begins to digest the 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 in 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 also giants with tentacles up to 10-14 meters! Starfish, sea lilies, urchins

They are attached to the bottom and corals with special suction cups. Sea anemones, similar to strange flowers, 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 - some of the largest fish. Moray eels hide in rocks and caves, and stingrays hide at the bottom, the color of which allows them to blend into the surface.

Below the shelf, an underwater slope begins - the bathyal (200 - 3000 m). Living conditions here change with every meter (temperature drops and pressure rises).

Abyssal - ocean bed. This is the most extensive 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 reach, marine inhabitants developed devices for lighting - small luminous organs.

Land waters make up less than 4% of all water found on our planet. About half of their quantity is contained in glaciers and permanent snow, the rest is in rivers, lakes, swamps, artificial reservoirs, groundwater and underground ice of permafrost. All natural waters on Earth are called water resources.

The most valuable reserves for humanity are fresh water reserves. There is a total of 36.7 million km3 of fresh water on the planet. They are concentrated primarily in large lakes and glaciers and are unevenly distributed between continents. Antarctica, North America and Asia have the largest reserves of fresh water, South America and Africa have somewhat smaller reserves, and Europe and Australia are the least rich in fresh water.

Groundwater is the water contained in the earth's crust. They are associated with the atmosphere and surface waters and participate in the water cycle on the globe. Underground

Glaciers

- constant snow

Rivers

Lakes

Swamps

The groundwater

- underground permafrost ice

waters are found not only under continents, but also under oceans and seas.

Groundwater forms because some rocks allow water to pass through while others retain it. Atmospheric precipitation falling on the Earth's surface seeps through cracks, voids and pores of permeable rocks (peat, sand, gravel, etc.), and waterproof rocks (clay, marl, granite, etc.) retain water.

There are several classifications of groundwater based on origin, condition, chemical composition and nature of occurrence. Water that, after rain or melting snow, penetrates the soil, wets it and accumulates in the soil layer is called soil water. Groundwater lies on the first waterproof layer from the surface of the earth. They are replenished due to the atmosphere

spheral precipitation, filtration of water streams and reservoirs and condensation of water vapor. The distance from the earth's surface to the groundwater level is called depth of groundwater. She

increases in the wet season, when there is a lot of rainfall or snow melts, and decreases in the dry season.

Below the groundwater there may be several layers of deep groundwater, which are held by impermeable layers. Often interstratal waters become pressure. This occurs when layers of rock form a bowl and the water contained within is under pressure. Such groundwater, called artesian, rises up the drilled well and gushes out. Often artesian aquifers occupy a significant area, and then artesian springs have a high and fairly constant flow of water. Some famous oases in North Africa arose from artesian springs. Along faults in the earth's crust, artesian waters sometimes rise from aquifers, and between rainy seasons they often dry up.

Groundwater reaches the surface of the Earth in ravines and river valleys in the form sources - springs or springs. They form where a rock aquifer reaches the earth's surface. Because the depth of groundwater varies depending on the season and rainfall, the springs sometimes suddenly disappear, and sometimes they bubble up. The water temperature in the springs may vary. Springs with a water temperature of up to 20 °C are considered cold, warm - with a temperature from 20 to 37 °C, and hot -

Permeable rocks

Waterproof rocks

Types of groundwater

mi, or thermal, - with a temperature above 37 ° C. Most hot springs occur in volcanic areas, where groundwater aquifers are heated by hot rocks and molten magma that comes close to the earth's surface.

Mineral groundwater contains many salts and gases and, as a rule, has healing properties.

The importance of groundwater is very great; it can be classified as a mineral 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 little rain falls, and do not dry up under the ice. Humans widely use groundwater: they are pumped out of the ground to supply water to residents of cities and villages, for industrial needs and to irrigate agricultural land. Despite the huge reserves, groundwater is renewed slowly, and there is a danger of its depletion and contamination by domestic and industrial wastewater. Excessive water intake from deep horizons reduces the flow of rivers during low-water periods - the period when the water level is lowest.

A swamp is an area of ​​the earth's surface with excessive moisture and stagnant water regime, in which organic matter accumulates in the form of undecomposed remains of vegetation. Swamps exist in all climate 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.

Swamps can be divided into two large groups - wetlands, where there is no well-defined peat layer, and peat bogs themselves, where peat accumulates. Wetlands include tropical wetlands, salt mangrove swamps, salt marshes of deserts and semi-deserts, grass 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 for moisture stagnation are created. They often form along the banks of rivers and lakes, sometimes in flood zones of reservoirs. In such swamps, groundwater comes close to the surface, supplying the plants growing here with minerals. On

Alder, birch, spruce, sedge, reed, and cattails often grow in lowland swamps. In these bogs, the peat layer 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 - pine, heather, cotton grass, sphagnum moss - settle in these swamps.

An intermediate position between lowland and upland ones is occupied by transitional swamps with a flat or slightly convex surface.

Swamps evaporate moisture intensively: the most active ones are swamps of the subtropical climate zone, swampy tropical forests, and in temperate climates - sphagnum-sedge and forest swamps. Thus, swamps increase air humidity, change its temperature, softening the climate of the surrounding areas.

Swamps, like a kind of biological filter, purify water from chemical compounds and solid particles dissolved in it. Rivers flowing through swampy areas are no different from catastrophes.

trophic spring floods and floods, since their flow is regulated by swamps, which gradually release moisture.

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. Swamps are rich hunting grounds: many birds nest here and many game animals live. The swamps are rich in peat, medicinal herbs, mosses and berries. The widespread belief that by growing crops in drained swamps one can get a rich harvest is wrong. Only the first few years are drained peat deposits fertile. Plans for draining swamps require comprehensive studies and economic calculations.

The development of a peat bog is the process of accumulation of peat as a result of the growth, death and partial decomposition of vegetation under conditions of excess moisture and lack of oxygen. The entire thickness of peat in a bog is called a peat deposit. It has a multilayer structure and contains from 91 to 97% water. Peat contains valuable organic and inorganic substances, which is why it has long been used in agriculture, energy, chemistry, medicine and other fields. For the first time, Pliny the Elder wrote about peat as “combustible earth” suitable for heating food in the 1st century. AD In Holland and Scotland, peat was used as fuel in the 12th-13th centuries. An industrial accumulation of peat is called a peat deposit. The largest industrial reserves of peat are in Russia, Canada, Finland and the USA.

Fertile river valleys have long been developed by humans. Rivers were the most important transport routes; their waters irrigated fields and gardens. Populous cities arose and developed on the river banks, and borders were established along the rivers. Flowing water turned the wheels of the mills and later provided electrical energy.

Each river is individual. One is always wide and full of water, while the other has a channel that remains dry for most of the year and only fills with water during rare rains.

A river is a watercourse of significant size that flows along a depression formed by itself in the bottom of a river valley - a channel. A river with its tributaries forms a river system. If you look down the river, then all the rivers flowing into it from the right are called right tributaries, and those flowing from the left are called left tributaries. The part of the earth's surface and thickness of soil and ground from which the river and its tributaries collect water is called a catchment area.

A river basin is the portion of 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

These are usually highlands or mountain systems. Basins of rivers flowing into the same body of water are combined, respectively, into basins of lakes, seas and oceans. The main watershed of the globe is identified. 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 drainage areas on the globe: the rivers flowing there do not carry water to the World Ocean. Such drainless areas include, for example, the basins of the Caspian and Aral seas.

Every river begins at its source. This could be a swamp, a lake, a melting mountain glacier, or groundwater coming to the surface. The place where a river flows into an ocean, sea, lake or other river is called an estuary. The length of a river is the distance along the channel between the source and the mouth.

Depending on their size, rivers are divided into large, medium and small. Large river basins are usually located in several geographic 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 violently and rapidly through gorges.

The replenishment of water in rivers is called river recharge. It can be snow, rain, glacial and underground. Some rivers, for example those that flow in equatorial regions (Congo, Amazon and others), are fed by rain, since it rains all year round in these areas of the planet. Most rivers are temperate

climatic zone have a mixed diet: in the summer they are replenished by rain, in the 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 water level, formation and disappearance of ice cover, etc. - is called the river regime. Annually recurring significant increase in water

in the river - flood - on the lowland rivers of the European territory of Russia is caused by intense snow melting in the spring. The rivers of Siberia flowing from the mountains are full of water in the summer when the snow melts

V mountains A short-term rise in water level in a river is called flood It occurs, for example, when heavy rainfall occurs or when snow melts intensively during a thaw in winter. The lowest water level in the river is low water. It is installed in the summer; at this time there is little rain and the river is fed mainly by groundwater. Low water also occurs in winter, during severe frosts.

Floods and floods can cause severe floods: melt or rainwater overwhelms the riverbeds, and rivers overflow their banks, flooding not only their valleys, but also the surrounding area. Water flowing at high speed has enormous destructive power, it demolishes houses, uproots trees, and washes away fertile soil from fields.

Sandy beach on the banks of the Volga

TO DOES IT LIVE IN RIVERS?

IN Not only fish live in rivers. The waters, bottom and banks of rivers are the habitat of many living organisms; they are divided into plankton, nekton and benthos. Plankton includes, for example, green and blue-green algae, rotifers and lower crustaceans. The river benthos is very diverse - insect larvae, worms, mollusks, crayfish. Plants settle on the bottom and banks of rivers - pondweed, reeds, reeds, etc., and algae grow on the bottom. River nekton is represented by fish and some large invertebrates. Among the fish that live in the seas and enter rivers only to spawn 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 rivers.

Rivers usually flow at the bottom of extensive relief depressions called river valleys. At the bottom of the valley, the water flow runs along a depression it has created itself - a channel. Water hits one section of the shore, erodes it and carries rock fragments, sand, clay, and silt downstream; in those places where the flow speed decreases, the river deposits (accumulates) the material it carries. But the river carries not only sediments eroded by the river flow; During stormy rains and melting snow, water flowing over the earth's surface destroys 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 washing away the earth's surface with water is called erosion. It is stronger where the speed of water flow is higher and where the soils are looser. The sediment that makes up the bottom of rivers is called bottom sediments or alluvium.

Wandering channels

In China and Central Asia there are rivers whose bed can shift by more than 10 m in a day. They, as a rule, flow in easily eroded rocks - loess or sand. In a few hours, a water flow can significantly erode one bank of the river, and deposit washed-away particles on the other bank, where the flow slows down. 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 follow the direction of deep faults in the earth's crust. Powerful glaciers that covered the northern regions of Eurasia and North America during the period of global glaciation, moving, plowed 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, forming a large water flow that built its own valley.

Structure of a lowland 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 a length of hundreds of kilometers and flow into dry depressions similar to themselves. Gravel and pebbles at the bottom of dry riverbeds suggest that in wetter periods, wadis could have been full-flowing rivers capable of carrying large sediments. In Australia, dry river beds are called creeks, in Central Asia - uzboi.

The valley of lowland rivers consists of a floodplain (part of the valley that is flooded during high water or during significant floods), a channel located on it, as well as valley slopes with several above the floodplain terraces, descending steps to the floodplain. River channels can be straight, meandering, divided into branches or wandering. Winding channels have bends, or meanders. By eroding the bend near the concave bank, the river usually forms a stretch - a deep section of the channel, its shallow sections are called riffles. The strip in the riverbed with depths most favorable for navigation is called a fairway. The water flow sometimes deposits significant amounts of sediment, forming islands. On large rivers, the height of the islands can reach 10 m and the length can be several kilometers.

Sometimes along the river's path there is a ledge of hard rock. The water cannot wash it away and falls down, forming a waterfall. In those places where the river crosses hard rocks that erode slowly, rapids are formed that block the path of the water flow.

IN estuary the water speed slows down significantly,

And the river deposits most of its sediment. Formed delta is a low-lying plain in the shape of a triangle, here the channel is divided into many branches and channels. River mouths flooded by the sea are called estuaries.

There are a great many rivers on Earth. Some of them flow like small silvery snakes within one forest area 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 outstanding parameters. For example, the longest river in the world, the Nile, is far from the deepest, and its basin area 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 in length to the Nile. The largest rivers are in South America, Africa and Asia.

The longest rivers in the world: Amazon (over 7 thousand km from the source of the Ucayali River), Nile (6671 km), Mississippi with the Missouri tributary (6420 km), Yangtze (5800 km), La Plata with the Parana and Uruguay tributaries (3700 km).

The deepest rivers (having maximum values ​​of average annual water flow): Amazon (6930 km3), Congo (Zaire) (1414 km3), Ganges (1230 km3), Yangtze (995 km3), Orinoco (914 km3).

The largest rivers on the globe (by basin area): Amazon (7,180 thousand km2), Congo (Zaire) (3,691 thousand km2), Mississippi with its tributary of the Missouri (3,268 thousand km2), La Plata with tributaries of the Parana and Uruguay (3,100 thousand km2), Ob (2990 thousand km2).

Volga is the largest river of the East European Plain

MYSTERIOUS NILE

The Nile is a great African river, its valley is the cradle of a vibrant, original culture that influenced the development of human civilization. The powerful Arab conqueror Amir ibn al-Asi said: “There lies a desert, on both sides it rises, and between the heights is the wonderland of Egypt. And all his wealth comes from the blessed river, flowing slowly through the country with the dignity of a caliph.” In its middle course, the Nile flows through the harshest deserts in Africa - the Arabian and Libyan. It would seem that it should become shallow or dry out during the hot summer. But at the height of summer, the water level in the Nile rises, it overflows its banks, flooding the valley, and as it recedes, it 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, the sources of which lie in the subequatorial climate zone, where an area of ​​​​low pressure is established in the summer and heavy rainfall occurs. 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 - 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 considered

to the great rivers of the world. The source of the Amazon lies in the rocky Andes, where its main tributary, the Marañon, flows from the mountain lake Patarcocha. When the Marañon merges with the Ucayali, the river takes on the name Amazon. The lowland through which this majestic river flows is a country of jungle and swamps. On their way to the east, tributaries continually replenish the Amazon. It is full of water throughout the year, because its left tributaries, located in the northern hemisphere, are full of water from March to September,

A the right tributaries, located in the southern hemisphere, are full 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 and rushes upstream. Locals call this wave “pororoka” - “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 Waters.” Its complex river system with many tributaries looks like a giant tree with a densely branched crown. The Mississippi Basin occupies almost half the territory of the United States of America. Beginning 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 the Russian Volga River 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 he 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: “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 many bison.” Before the arrival of European colonialists, vast areas in the river basin were occupied by virgin forests and prairies, but now they can only be seen in national parks, most of the land is plowed.

The waters of rivers and streams, choosing their path, often fall off cliffs and ledges. This is how waterfalls are formed. Sometimes these are very small steps in the riverbed with minor differences in height between the upper section, from where the water falls, and the lower one. However, in nature there are also absolutely gigantic “steps” and ledges, the height of which reaches many hundreds of meters. Both waterfalls are formed when the water “opens up”, i.e. destroys, exposes areas with harder rocks, carrying 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 -

Diagram of water movement in Niagara Falls

Cascade of several waterfalls in Norway. 19th century engraving

The Ivan the Great bell tower in the Moscow Kremlin has a height of 81 m), but is more famous than its tall and full-flowing “brothers”. The waterfall became famous not only because of its location in close proximity to large American and Canadian cities, but also because it was well studied.

A water stream, falling from any height to the foot of the slope, forms a depression, a niche, even in fairly strong rocks. But the upper edge is gradually eroded and destroyed by the action of flowing water. The peaks of the ledge collapse, and... The waterfall seems to retreat back, “backing away” up the valley. Long-term observations of Niagara Falls have shown that such “backward” erosion “eats” the upper ledge of the waterfall by about 1 m over 60 years.

In Scandinavia, glacial landforms are to blame for the formation of waterfalls. There, streams from glacier-lined mountain peaks flow from great heights into the fjords.

The huge waterfalls that arose under the influence of tectonics - the internal forces of the Earth - are very impressive. Colossal steps of waterfalls are formed when the river bed is disrupted by tectonic faults. It happens that not one ledge is formed, but several at once. These 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.

IGUAZU FALLS

Lakes are hollows filled with water - natural depressions on the surface of the land that have no connection with the sea or ocean. 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. Their total area is about 2.7 million km2, that is, approximately 1.8% of the total land area. The main wealth of lakes is fresh water, which is so necessary for humans. The lakes contain about 180 thousand km3 of water, and the 20 largest lakes in the world combined contain the majority of all fresh water available to humans.

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 common; there are also lakes in drainless areas, in floodplains and river deltas.

Some lakes are filled only during the wet seasons and remain dry the rest of the year - these are temporary lakes. But most lakes are constantly filled with water.

Depending on their size, lakes are divided into very large, with an area exceeding 1,000 km2, large - with an area from 101 to 1,000 km2, medium - from 10 to 100 km2 and small - with an area of ​​less than 10 km2.

Based on the nature of water exchange, lakes are divided into drainage and drainless. Located in the cat

In the valley, lakes collect water from the surrounding areas, streams and rivers flow into them, while at least one river flows out of drainage lakes, and not a single one flows out of drainage lakes. Drainage lakes include Baikal, Ladoga and Onega lakes, and drainage lakes include Lake Balkhash, Chad, Issyk-Kul, and the Dead Sea. The Aral and Caspian Seas are also closed lakes, but due to their large size and regime similar to the sea, these reservoirs are conventionally considered seas. There are so-called blind lakes, for example, formed in the craters of volcanoes. Rivers do not flow into them or flow out of them.

Lakes can be divided into fresh, brackish and saline, or mineral. The salinity of water in fresh lakes does not exceed 1% - such water, for example, in Lake Baikal, Lake Ladoga and Lake Onega. The water of brackish lakes has a salinity from 1 to 25%. For example, the salinity of water in Issyk-Kul is 5-8%o, and in the Caspian Sea - 10-12%o. Salty lakes are those lakes whose water has a salinity of 25 to 47%. Mineral lakes contain more than 47% salts. Thus, the salinity of the Dead Sea, lakes Elton and Baskunchak is 200-300%. Salt lakes tend to form in arid areas. In some salt lakes, the water is a solution of salts close to saturation. If such saturation is achieved, then salts precipitate and the lake turns into a self-sediment lake.

In addition to dissolved salts, lake water contains organic and inorganic substances and dissolved gases (oxygen, nitrogen, etc.). Oxygen not only enters the lakes from the atmosphere, but is also released by plants during the process of 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

of the substance found in the reservoir. If excess oxygen forms in the lake, 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 with 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 a lake has a beginning and an end. Once formed, it is gradually filled with river sediments and the remains of dead animals and plants. Every year the amount of precipitation at the bottom increases, the lake becomes shallow, overgrown and turns into a swamp. The greater the initial depth of the lake, the longer its life continues. In small lakes, sediment accumulates over many thousands of years, and in deep lakes, over millions of years.

Lakes with an excess amount of organic substances, the oxidation products of which are harmful to living organisms.

Lakes regulate river flow and have a significant impact on the climate of the surrounding areas.

They contribute to an increase in precipitation, the number of days with fogs and generally soften the climate. Lakes raise groundwater levels and affect the soils, vegetation and wildlife of surrounding areas.

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 basins that were formed as a result of glacier activity. As it moved, the glacier plowed up softer soil, creating depressions in the relief: long and narrow in some places, and oval in others. 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 the Caucasus, glacial lakes are located in karas - bowl-shaped depressions in the upper parts of 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 a river flowing from under a glacier, a glacial lake is formed, often having a round shape.

In areas composed of limestone, dolomite and gypsum, karst lake basins arise as a result of the chemical dissolution of these rocks by surface and groundwater. Thicknesses of sand and clay lying above karst rocks fall into underground voids, forming depressions on the earth's surface, which over time fill with water and become lakes. Karst lakes are also found in caves

rah, they can be seen in the Crimea, the Caucasus, the Urals and other areas.

IN In the tundra, and sometimes in the taiga, where permafrost is widespread, the soil thaws and subsides during the warm season. Lakes appear in small depressions calledthermokarst.

IN in river valleys, when a meandering river straightens its channel, the old section of the channel becomes isolated. This is how they are formed 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 river bed. For example,

V In 1911, during an earthquake in the Pamirs, a gigantic mountain collapse occurred, it dammed the Murghab River, and Lake Sarez was formed. Lake Tana in Africa, Sevan in Transcaucasia and many other mountain lakes are dammed.

U on the coast of the seas, sand spits can separate the shallow coastal area from the sea area, resulting in the formation lake-lagoon. If sandy-clay deposits fence off flooded river mouths 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 dammed or dammed lake

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 - the part of the hydrosphere that is in a solid state. It includes the ice of cold oceans, the ice caps of mountains, and icebergs that have broken off ice mountains from ice sheets. In the mountains, glaciers are formed from snow. First, when snow recrystallizes as a result of alternating melting and new freezing of water inside the snow column, 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 streams. The main condition for the existence of glaciers - both small and large - is constant low temperatures during most of the year, at 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

IN Several times in the history of the Earth, severe climate cooling led to the growth of glaciers

And the formation of one or more ice sheets. This time is called glacial or

ice ages.

IN During the Pleistocene (the era of the Quaternary period of the Cenozoic era), the area covered by glaciers was almost three times larger than the modern one. At that time

V Huge ice sheets arose in the mountains and plains of polar and temperate latitudes, which, growing, 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 learn about those ancient ice ages? Moving along the surface, the glacier leaves its traces - the material that it took with it as it moved. Such material is called moraine. The stages of their standing glaciers mark their

Movement of the earth's crust under the colossal load of the ice sheet (1) and after its removal (2)

lami of the terminal moraine. Often, by the name of the place that the glacier reached, it is called a glacial area. The furthest glacier on the territory of Eastern Europe reached the Dnieper valley, and this glacier is called the Dnieper. In North America, traces of 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 Anthropocene, period, which began 1.8 million years ago and continues to this day. What caused this enormous cooling is a question that scientists are trying to solve.

Dozens of hypotheses try to explain the appearance of huge glaciers by a variety of terrestrial and cosmic causes - the fall of giant meteorites, catastrophic volcanic eruptions, changes in the direction of ocean currents. The hypothesis of the Serbian scientist Milankovic, proposed in the last century, was very popular, who explained climate change by periodic fluctuations in the inclination of the planet’s rotation axis and the distance of the Earth from the Sun.

Glaciers of Spitsbergen

Glaciation moraines

The ice sheets that currently exist are the remnants of huge ice sheets that existed in temperate latitudes during the last glacial periods. And although today they are not as large 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 its 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 entire 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 area of ​​the coastline are called shelf glaciers, since they are located in the area of ​​the underwater edge of the continent - 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 Antarctic station McMurdo is located.

Another colossal ice sheet is in Greenland, occupying more than 80% of it

Foothill Glacier

the largest island in the world. Greenland's ice accounts for about 10% of all ice on Earth. The speed of ice flow here is much less than

V Antarctica. But Greenland also has its own record holder - a glacier that moves at a very high speed - 7 km per year!

Reticulate glaciation characteristic of the polar archipelagos - Franz Josef Land, Spitsbergen, and the Canadian Arctic Archipelago. This type of glaciation is transitional between cover and mountain. In plan, these glaciers resemble a honeycomb grid, hence the name. Peaks, pointed peaks, rocks, and areas of land protrude from under the ice in many places, like islands in the ocean. They are called nunataks. "Nunatak" is an Eskimo word. This word came into scientific literature thanks to the famous Swedish polar explorer Nils Nordenskiöld.

TO The same “half-cover” type of glaciation also includesfoothill glaciers. Often a glacier descending from the mountains along a valley reaches their foot and emerges with wide blades

V melting zone (ablation) to the plain (this type of glaciers is also called Alaskan) or even

on the shelf or in lakes (Patagonian type). Foothill glaciers are among the most spectacular and beautiful. They are found in Alaska, northern North America, Patagonia, the extreme south of South America, and Spitsbergen. The most famous is the Malaspina foothill glacier in Alaska.

Reticulate glaciation of Svalbard

Where latitude and altitude above sea level do not allow snow to melt during the year, glaciers appear - accumulations of ice on mountain slopes and peaks, in saddles, depressions and niches on the slopes. Over time, the snow becomes

spins into firn and then into ice. Ice has the properties of a viscoplastic body and is capable of flow. At the same time he grinds and plows

the surface on which it moves. In the structure of a glacier, a zone of accumulation, or accumulation, of snow and a zone of ablation, or melting, are distinguished. These zones are separated by a food boundary. Sometimes it coincides with the snow line, above which there is snow throughout the year. The properties and behavior of glaciers are studied by glaciologists.

WHAT ARE THERE ARE GLACIERS

Small hanging glaciers lie in depressions on the slopes and often extend beyond the snow line. These are many glaciers of the Alps and Caucasus -

Randklufts - side cracks separating the glacier from the rocks

Bergschrund - crack in the area

glacier supply, separating the stationary and mobile

glacier parts

Median and lateral moraines

Transverse cracks on the glacier tongue

Basic moraine - material beneath a glacier

behind. Tar glaciers fill cup-shaped depressions on the slope - cirques, or cirques. In the lower part, the cirque 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 of especially large size (they are also called dendritic or tree-like) are characteristic of the highlands of the Pamirs, Karakoram, Himalayas, and Andes. For each region, there are also more detailed divisions 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 plateaus break off with sharp ledges towards the fjords - ancient glacial valleys that have turned into deep and narrow sea bays.

The uniform movement of ice in a glacier can give way to sudden movements. Then the glacier tongue 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 accumulated tension

V glacial thicker. As a rule, constant observations of a glacier allow one 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 populated areas of the flowering valley were buried under chaotic piles of ice blocks. Pulsating glaciers like these are not that uncommon.

V 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 - trog (from German Trog - trough).

When a mountain peak is covered on all sides by glaciers, gradually destroying the slopes, sharp pyramidal peaks are formed - carlings. Over time, neighboring circuses may merge.

Edge of a glacier in the Himalayas

Debris on the surface of a glacier in the Alps

Rivers fed by glaciers, i.e. flowing out from under the glaciers, very muddy and stormy during the melting period in the warm season and, on the contrary, become clean and transparent in winter and autumn. The terminal moraine ridge is sometimes a natural dam for a glacial lake. During rapid melting, the lake can erode the shaft, and then a mudflow is formed - a mud-stone flow.

WARM AND COLD GLACIERS

On the glacier bed, 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 ice. It turns out that a layer of melt water forms between the ice itself and the underlying surface. The glacier moves along it, like lubricant. Such glaciers are called warm, in contrast to cold ones, which are frozen to the bed.

Let’s imagine a snowdrift melting in the spring. As it gets warmer, the snow begins to settle, its boundaries decrease, retreating from the “winter” ones, streams run from under it... And on the surface of the earth, everything that has accumulated on and in the snow over the long winter months remains: 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 pile of “garbage” after it melts will be the size of a mountain! When a large glacier melts, which is also called retreat, it leaves behind even more material - because its ice volume contains much more “garbage”. All inclusions left by a glacier after melting on the surface of the earth are called moraine or glacial deposits.

dynamic. After melting, such moraines look like long mounds stretching along the slopes down the valley.

The glacier is in constant motion. As a viscoplastic body, it has the ability to flow. Consequently, the fragment that fell on him from the cliff, after some time, may turn out to be quite far from this place. These fragments are collected (accumulated), as a rule, at the edge of the glacier, where the accumulation of ice gives way to melting. The accumulated material follows the contours of the glacier tongue and has the appearance of a curved embankment, partially blocking the valley. When the glacier retreats, the terminal moraine remains in its original place, gradually being eroded by meltwater. When a glacier retreats, several ridges of terminal moraines may accumulate, which will indicate intermediate positions of its tongue.

The glacier has retreated. A moraine swell remained in front of its front. But the melting continues. And behind the final moraine, melted ice begins to accumulate

rocky waters. A glacial lake appears, which is held back by a natural dam. When such a lake breaks through, a destructive mud-stone flow - a mudflow - often forms.

As the glacier moves down the valley, it destroys its base. Often this process, which is called "exaration", occurs unevenly. And then steps are formed in the glacier bed - crossbars (from German Riegel - barrier).

The moraines of cover glaciers are much more extensive and diverse, but they are less well preserved in the relief.

Glacier deposits

After all, as a rule, they are more ancient. And tracing their location on the plain is not as easy as in a mountain glacial valley.

During the last ice age, a huge glacier moved from the region of the Baltic crystalline shield, from the Scandinavian and Kola peninsulas. Where the glacier plowed out the crystalline bed, elongated lakes and long ridges - selgi - formed. There are many of them in Karelia and Finland.

It was from there that the glacier brought fragments of crystalline rocks - granites. During the long transportation of rocks, ice abraded the uneven edges of the fragments, 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 been preserved.

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 thin clay particles and left sandy fields in front of the edge of the glacier - outwash (from the Il. sand - sand). Melt water often washed tunnels under melting glaciers that had lost their mobility. In these tunnels, and especially when exiting from under the glacier, washed-up moraine material (sand, pebbles, boulders) accumulated. These accumulations are preserved in the form of long winding shafts - they are called eskers.

IN In cold climates, water in the depths and on the surface freezes to a depth of 500 m or more. Over 25% of the Earth's entire land surface is occupied by permafrost.

IN our country has more than 60% of such territory, because almost all of Siberia lies in its distribution zone.

This phenomenon is called perennial or permafrost. However, the climate can change toward warming over time, so the term "perennial" is more appropriate for this phenomenon.

IN 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 be either under this frozen layer, or remain in a liquid state between permafrost layers (it forms water lenses - taliks) or above the frozen layer. The top layer that is subject to freezing and thawing is calledactive layer.

POLYGONAL SOILS

Ice in the ground can form ice veins. They often appear in places where frost cracks (formed during severe frosts) are filled with water. When this water freezes, the soil between the cracks begins to compress, because ice occupies a larger area than water. A slightly convex surface is formed, framed by depressions. Such polygonal soils cover a significant part of the tundra surface. When the short summer arrives and the ice veins begin to thaw, entire spaces are formed that look like 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 ground, freezing occurs, pushing larger fragments contained in the soil to the surface by ice. In this way, soil is sorted, since its small particles remain in the center of the rings and polygons, and large fragments are shifted to their edges. As a result, shafts of stones appear, framing smaller material. Mosses sometimes settle on it, and in the fall the stone polygons amaze with their unexpected beauty:

bright mosses, sometimes with cloudberry or lingonberry bushes, surrounded on all sides by gray stones, looking like specially made garden beds. In diameter, such polygons can reach 1-2 m. If the surface is not flat, but inclined, then the polygons turn into stone strips.

The freezing of debris from the ground leads to the formation of a chaotic accumulation of large stones on the top surfaces and slopes of mountains and hills in the tundra zone, merging into stone “seas” and “rivers.” There is a name for them “kurums”.

BULGUNNYAKHI

This Yakut word denotes amazing

On the surface of the planet, not only belts of continuous permafrost stand out in cold natural zones. There are areas with so-called island permafrost. It exists, as a rule, in the highlands, in harsh places with low temperatures, for example in Yakutia, and is the remnants - “islands” - of the former, more extensive permafrost belt, preserved since the last ice age