In sailing directions sometimes only a brief, sometimes very detailed (with maps, diagrams, tables) verbal description of the waves is given, giving an idea of ​​the magnitude and nature of the waves by the seasons of the year and in certain areas of the sea.

Atlases of physical and geographical data. They consist of a set of different maps characterizing the waves of a particular basin by months and seasons of the year. On these maps, "roses" in eight points show the frequency of wave and swell in direction and strength in individual squares of the ocean. The length of the rays on the scale determines the percentage of wave direction repeatability, and the numbers in the circles indicate the percentage of the absence of waves. In the lower corner of the square is the number of observations in this square.

Reference books and tables on waves. The manual contains tables of frequency of winds and waves, a table of the dependence of wave elements on wind speed, duration and length of wind acceleration, and also gives the values ​​\u200b\u200bof the greatest heights, lengths and periods of waves. With the help of this table, for areas of the open sea, according to wind speed (in m / s) and the length of the acceleration (in km), one can determine their height, period and duration of growth.

These benefits allow the navigator to correctly assess the conditions of navigation and choose the most profitable and safe navigation routes, taking into account wind and waves.

Wave cards

Wave maps show the positions of synoptic objects

(cyclones, anticyclones with an indication of pressure in the center; atmospheric fronts), a picture of wave fields in the form of isolines of equal wave heights with digitization of their values ​​and an indication of the direction of propagation by a contour arrow, as well as a characteristic of wind and wave conditions at individual points of stations.

12. Causes of sea currents.sea ​​currents called the translational movement of masses of water in the sea under the influence of natural forces. The main characteristics of currents are speed, direction and duration of action.

The main forces (causes) that cause sea currents are divided into external and internal. The external ones include wind, atmospheric pressure, tide-forming forces of the Moon and the Sun, and the internal ones include the forces arising from the uneven horizontal distribution of the density of water masses. Immediately after the onset of the movement of water masses, secondary forces appear: the Coriolis force and the friction force, which slows down any movement. The direction of the current is influenced by the configuration of the banks and the topography of the bottom.

13. Classification of sea currents.

Sea currents are classified:

According to the factors causing them, i.e.

1. By origin: wind, gradient, tidal.

2. By stability: constant, non-periodic, periodic.

3. According to the depth of location: surface, deep, near-bottom.

4. By the nature of the movement: rectilinear, curvilinear.

5. By physical and chemical properties: warm, cold, salty, fresh.

Origin currents are:

1 wind currents occur under the action of frictional force on the water surface. After the beginning of the action of the wind, the current speed increases, and the direction, under the influence of the Coriolis acceleration, deviates by a certain angle (in the northern hemisphere to the right, in the southern hemisphere - to the left).

2. Gradient flows are also non-periodic and caused by a number of natural forces. They are:

3. waste, associated with surge and surge of water. An example of a runoff current is the Florida Current, which is the result of the surge of waters into the Gulf of Mexico by the windy Caribbean Current. The excess waters of the bay rush into the Atlantic Ocean, giving rise to a powerful current. Gulfstream.

4. stock Currents are generated by the flow of river water into the sea. These are the Ob-Yenisei and Lena currents, penetrating hundreds of kilometers into the Arctic Ocean.

5. barometric currents arising due to uneven changes in atmospheric pressure over neighboring areas of the ocean and the associated increase or decrease in water levels.

By sustainability currents are:

1. Permanent - the vector sum of the wind and gradient currents is drift current. Examples of drift currents are the trade winds in the Atlantic and Pacific Oceans and the monsoons in the Indian Ocean. These currents are constant.

1.1. Powerful steady currents with speeds of 2-5 knots. These currents include the Gulf Stream, Kuroshio, Brazilian and Caribbean.

1.2. Constant currents with speeds of 1.2-2.9 knots. These are the North and South trade winds and the equatorial countercurrent.

1.3. Weak constant currents with speeds of 0.5-0.8 knots. These include the Labrador, North Atlantic, Canary, Kamchatka and California currents.

1.4. Local currents with speeds of 0.3-0.5 knots. Such currents for certain areas of the oceans in which there are no clearly defined currents.

2. Periodic flows - These are such currents, the direction and speed of which change at regular intervals and in a certain sequence. An example of such currents are tidal currents.

3. Non-periodic flows are caused by non-periodic action of external forces and, first of all, by the effects of wind and pressure gradient considered above.

By depth currents are:

Surface - currents are observed in the so-called navigation layer (0-15 m), i.e. layer corresponding to the draft of surface vessels.

The main reason for the occurrence superficial The currents in the open ocean is the wind. There is a close relationship between the direction and speed of the currents and the prevailing winds. Steady and continuous winds have a greater influence on the formation of currents than winds of variable directions or local ones.

deep currents observed at a depth between the surface and bottom currents.

bottom currents take place in the layer adjacent to the bottom, where big influence they are subjected to friction on the bottom.

The speed of movement of surface currents is highest in the uppermost layer. Deeper it goes down. Deep waters move much more slowly, and the speed of movement of bottom waters is 3–5 cm/s. The speed of the currents is not the same in different regions of the ocean.

According to the nature of the movement of the current, there are:

According to the nature of the movement, meandering, rectilinear, cyclonic and anticyclonic currents are distinguished. Meandering currents are called currents that do not move in a straight line, but form horizontal undulating bends - meanders. Due to the instability of the flow, meanders can separate from the flow and form independently existing eddies. Rectilinear currents characterized by the movement of water in relatively straight lines. Circular currents form closed circles. If the movement in them is directed counterclockwise, then these are cyclonic currents, and if clockwise, then they are anticyclonic (for the northern hemisphere).

By the nature of physical and chemical properties distinguish between warm, cold, neutral, saline and freshwater currents (the division of currents according to these properties is to a certain extent conditional). To assess the specified characteristic of the current, its temperature (salinity) is compared with the temperature (salinity) of the surrounding waters. Thus, a warm (cold) flow is a water temperature in which the temperature of the surrounding waters is higher (lower).

warm currents are called, in which the temperature is higher than the temperature of the surrounding waters, if it is lower than the current are called cold. In the same way, saline and desalinated currents are determined.

Warm and cold currents . These currents can be divided into two classes. The first class includes currents, the water temperature of which corresponds to the temperature of the surrounding water masses. Examples of such currents are the warm North and South trade winds and the cold current of the West Winds. The second class includes currents, the water temperature of which differs from the temperature of the surrounding water masses. Examples of currents of this class are the warm currents of the Gulf Stream and Kuroshio, which carry warm waters to higher latitudes, as well as the cold East Greenland and Labrador Currents, which carry cold waters of the Arctic Basin to lower latitudes.

Cold currents belonging to the second class, depending on the origin of the cold waters they carry, can be divided: into currents carrying the cold waters of the polar regions to lower latitudes, such as East Greenland, Labrador. the Falklands and Kurils, and lower latitude currents such as the Peruvian and Canary (the low temperature of the waters of these currents is caused by the rise of cold deep waters to the surface; but deep waters are not as cold as the waters of currents going from higher latitudes to low latitudes).

Warm currents carrying warm water masses to higher latitudes act on the western side of the main closed circulations in both hemispheres, while cold currents act on their eastern side.

On the eastern side of the southern Indian Ocean, there is no upwelling of deep waters. The currents on the western side of the oceans, compared with the surrounding waters at the same latitudes, are relatively warmer in winter than in summer. Cold currents coming from higher latitudes are of particular importance for navigation, as they carry ice to lower latitudes and cause in some areas a greater frequency of fog and poor visibility.

In the oceans by nature and speed the following groups can be distinguished. The main characteristics of the sea current: speed and direction. The latter is determined in the reverse way compared to the direction of the wind, i.e., in the case of a current, it indicates where the water flows, while in the case of a wind, it indicates where it blows from. Vertical movements of water masses are usually not taken into account when studying sea currents, since they are not large.

There is not a single area in the World Ocean where the speed of currents would not reach 1 knot. At a speed of 2–3 knots, there are mainly trade winds and warm currents near the eastern coasts of the continents. With such a speed there is an Intertrade countercurrent, currents in the northern part of the Indian Ocean, in the East China and South China Seas.

This I know

2. What are the reasons for the formation of currents?

The main reason for the formation of currents is the wind. In addition, the movement of water is affected by the difference in its temperature, density, salinity.

3. What is the role of ocean currents?

Ocean currents influence climate formation. Currents redistribute heat on the Earth. Due to the currents, planktonic organisms carry out their movements.

4. What are the types of ocean currents and give examples of them?

Currents by origin are windy (the course of Western winds), tidal, density.

Temperature currents are warm (Gulf Stream) and cold (Bengal).

Currents in terms of stability are permanent (Peruvian) and seasonal (currents of the northern part of the Indian Ocean, El Niña)

5. Match the current - warm (cold):

1) the course of the Western winds

2) Gulf Stream

3) Peruvian

4) Californian

5) Kuroshio

6) Benguela

A) warm

B) cold

This I can

6. Give examples of the interaction of the ocean and the atmosphere.

Currents redistribute heat and influence air temperature and precipitation. Sometimes the interaction of currents and the atmosphere leads to the formation of adverse and dangerous weather phenomena.

7. Give a description of the course of the Western winds according to the plan:

1. Geographic location

The current bends between 400 and 500 S. Earth.

2. Type of flow

A) according to the properties of water (cold, warm)

The current is cold.

B) by origin

The course of the Western winds is windy in origin. It is caused by westerly winds in temperate latitudes.

C) stability (permanent, seasonal)

The flow is constant.

D) by location in the water column (surface, deep, bottom)

Surface flow.

8. In ancient times, not knowing the real reasons for the formation of currents in the Ocean, sailors believed that Neptune, the Roman god of the seas, could drag a ship into the ocean depths. Using information from popular science and fiction literature, the Internet, collect materials about ships whose disappearance is associated with currents. Document the materials in the form of drawings, essays, reports.

Secrets of the Bermuda Triangle

The Bermuda Triangle or Atlantis is a place where people disappear, ships and planes disappear, navigation instruments fail, and wrecked almost no one ever finds. This hostile, mystical, ominous country for a person instills such great horror in the hearts of people that they often simply refuse to talk about it.

About the existence of such a mysterious and amazing phenomenon called the Bermuda Triangle a hundred years ago, few people knew. To actively occupy people's minds and force them to put forward various hypotheses and theories, this mystery of the Bermuda Triangle began in the 70s. of the last century, when Charles Berlitz published a book in which he described the stories of the most mysterious and mystical disappearances in this region in an extremely interesting and fascinating way. After that, the journalists picked up the story, developed the theme, and the story of the Bermuda Triangle began. Everyone began to worry about the secrets of the Bermuda Triangle and the place where the Bermuda Triangle or the missing Atlantis is located.

This wonderful place or the missing Atlantis is located in the Atlantic Ocean near the coast North America- between Puerto Rico, Miami and Bermuda. It is located in two climatic zones at once: the upper part, the larger one - in the subtropics, the lower one - in the tropics. If these points are connected with each other by three lines, a large triangular figure will appear on the map, the total area of ​​\u200b\u200bwhich is about 4 million square kilometers. This triangle is rather conditional, since ships also disappear outside its borders - and if you mark on the map all the coordinates of disappearances, flying and floating vehicles, you will most likely get a rhombus.

At knowledgeable people the fact that ships often crash here is not particularly surprising: this region is not easy to navigate - there are many shallows, a huge number of fast water and air currents, cyclones often arise and hurricanes rage.

Water currents. Gulfstream.

Almost the entire western part of the Bermuda Triangle is crossed by the Gulf Stream, so the air temperature here is usually 10 ° C higher than in the rest of this mysterious anomaly. Because of this, in the places of collisions of atmospheric fronts of different temperatures, one can often see fog, which often strikes the mind of overly impressionable travelers. The Gulf Stream itself is a very fast current, the speed of which often reaches ten kilometers per hour (it should be noted that many modern transoceanic ships move slightly faster - from 13 to 30 km / h). An extremely fast flow of water can easily slow down or increase the movement of the ship (it all depends on which direction it is sailing). There is nothing surprising in the fact that ships of weaker power in the old days easily went off course and were swept absolutely in the wrong direction, as a result of which they suffered wrecks and disappeared forever in the oceanic abyss.

In addition to the Gulf Stream, strong but irregular currents constantly arise in the Bermuda Triangle, the appearance or direction of which is almost never predictable. They are formed mainly under the influence of tidal and ebb waves in shallow water and their speed is as high as that of the Gulf Stream - and is about 10 km / h. As a result of their occurrence, whirlpools are often formed, causing trouble for small ships with a weak engine. There is nothing surprising in the fact that if in former times a sailing ship got here, it was not easy for him to get out of the whirlwind, and under especially unfavorable circumstances, one might even say - impossible.

In the east of the Bermuda Triangle, the Sargasso Sea is located - a sea without shores, surrounded on all sides instead of land by the strong currents of the Atlantic Ocean - the Gulf Stream, the North Atlantic, the North Trade Wind and the Canary.

Outwardly, it seems that its waters are motionless, the currents are weak and hardly noticeable, while the water here is constantly moving, since the water flows, pouring into it from all sides, rotate the sea water clockwise. Another remarkable thing about the Sargasso Sea is the huge amount of algae in it (contrary to popular belief, there are also areas with completely clear water). When in former times ships were brought here for some reason, they became entangled in dense marine plants and, falling into a whirlpool, albeit slowly, they were no longer able to get back.

Ocean or sea currents - this is the translational movement of water masses in the oceans and seas, caused by various forces. Although the most significant cause of currents is the wind, they can form and due to unequal salinity of individual parts of the ocean or sea, the difference in water levels, uneven heating of different parts of the water areas. In the depths of the ocean there are eddies created by uneven bottoms, their size often reaches 100-300 km in diameter, they capture layers of water hundreds of meters thick.

If the factors causing the currents are constant, then a constant current is formed, and if they are episodic, then a short-term, random current is formed. According to the prevailing direction, the currents are divided into meridional, carrying their waters to the north or south, and zonal, spreading latitudinally. Currents in which the water temperature is higher than the average temperature for

the same latitudes are called warm, below - cold, and currents having the same temperature as the surrounding waters are called neutral.

Monsoon currents change their direction from season to season, depending on how the coastal monsoon winds blow. Towards the neighboring, more powerful and extended currents in the ocean, countercurrents are moving.

The direction of currents in the World Ocean is influenced by the deflecting force caused by the rotation of the Earth - the Coriolis force. In the Northern Hemisphere, it deflects currents to the right, and in the Southern Hemisphere, to the left. The speed of currents on average does not exceed 10 m/s, and they extend to a depth of no more than 300 m.

In the World Ocean, there are constantly thousands of large and small currents that go around the continents and merge into five giant rings. The system of currents of the World Ocean is called circulation and is connected, first of all, with the general circulation of the atmosphere.

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

Currents of the oceans

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

from the polar regions due to currents gets to the south. Warm currents increase air temperature, while cold currents, on the contrary, decrease it. Territories washed by warm currents are characterized by a warm and humid climate, and those near which cold currents pass are cold and dry.

The most powerful current of the World Ocean is the cold current of the West Winds, also called the Antarctic circumpolar (from lat. cirkum - around). The reason for its formation is strong and stable westerly winds blowing from west to east over vast expanses of

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

The Gulf Stream is one of the largest warm currents in the Northern Hemisphere. It passes through the Gulf of Mexico (eng. Gulf Stream - the Gulf) and carries the warm tropical waters of the Atlantic Ocean to high latitudes. This giant stream of warm water largely determines the climate of Europe, making it soft and warm. Every second, the Gulf Stream carries 75 million tons of water (for comparison: the Amazon, the most full-flowing river in the world, is 220 thousand tons of water). At a depth of about 1 km under the Gulf Stream, a countercurrent is observed.

SEA ICE

When approaching high latitudes, ships encounter floating ice. Sea ice frames Antarctica with a wide border, covers the waters of the Arctic Ocean. Unlike continental ice formed from atmospheric precipitation and covering Antarctica, Greenland, the islands of the polar archipelagos, these ices are frozen sea water. In the polar regions, sea ice 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 with wind waves. It repeatedly freezes into small tiles, splits again until it forms the so-called ice fat - spongy ice floes, which then coalesce with each other. Such ice is called pancake ice for its resemblance to rounded pancakes on the surface of the water. Plots of such ice, freezing, form young ice - nilas. Every year this ice gets stronger and thicker. He can become multi-year ice more than 3 m thick, and may melt if the currents carry the ice floes to warmer waters.

The movement of ice is called drift. Drifting (or pack) ice covered

Ice mountains are melting, acquiring bizarre shapes

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

ICEBERGS

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

Iceberg off the coast of Norway

tic cover. Some icebergs reach gigantic sizes.

When we want to say that some event or phenomenon in our life can have much more serious consequences than it seems, we say "this is just the tip of the iceberg." Why? It turns out that about 1/7 of the entire iceberg is above the water. It is table-shaped, domed or cone-shaped. The base of such a huge piece of a glacier, which is under water, can be much larger in area.

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

of the famous ship "Titanic" in April 1912.

How long does an iceberg live? The ice mountains that have broken away from the icy Antarctica can float in the waters of the Southern Ocean for more than 10 years. Gradually, they collapse, split into smaller pieces, or, by the will of the currents, move to warmer waters and melt.

"FRAM" IN THE ICE

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

The boundary between land and sea is a constantly changing line. The oncoming waves carry the smallest particles of sand suspension, roll over pebbles, grind rocks. Destroying the coast, especially during strong waves or storms, in one place, they are engaged in "building" in another.

The place of action of coastal waves is a narrow border of the coast and its underwater slope. Where there is mainly destruction of the coast, above the water, as

as a rule, rocks hang overhead - cliffs, waves “gnaw out” niches in them, create under them

bizarre grottoes and even underwater caves. This type of coast is called abrasion (from Latin abrasio - scraping). When the sea level changed - and this happened more than once in the recent geological history of our planet - abrasion structures could be under water or, conversely, on land, far from the modern coast. By

to such forms of coastal relief, located on land, scientists restore 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 transferred from the destroyed areas. Beaches are formed here. At high tide, rolling waves move sand and pebbles deep into the coast, creating an extended

nye alongshore swells. During low tide on such shafts you can see the accumulation of shells, seaweed.

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

Nekton (from the Greek nektos - floating) - living organisms that can move independently in the water column.

Plankton (from Greek planktos - wandering) - organisms living in water, carried by waves and currents and not able to move independently in water.

DEEP FLOORS

Giant steps descend from the coast to the underwater abyssal plains of the ocean floor. Each such "underwater floor" has its own life, because the conditions for the existence of living organisms: illumination, water temperature, its saturation with oxygen and other substances, the pressure of the water column - change significantly with depth. Different organisms relate to the amount of sunlight and the transparency of water. For example, plants can only live where the illumination allows the processes of photosynthesis to take place (these are average depths of no more than 100 m).

Littoral - periodically drained at low tide coastal strip. Marine animals come here, taken out of the water by waves, which have adapted to live in two environments at once - aquatic

And air. These are crabs

And crustaceans, sea urchins, mollusks, including mussels. In tropical latitudes in the littoral there is a fringe of mangrove forests, and in temperate zones- "forests" of kelp algae.

Below the littoral there is a sublittoral zone (down to depths of 200-250 m), a coastal strip of life on the continental shelf. Towards the poles sunlight penetrates into the water quite shallow (no more than 20 m). In the tropics and at the equator, the rays fall almost vertically, which allows them to reach depths of up to 250 m. It is to such depths that algae, sponges, mollusks and light-loving animals, as well as coral buildings - reefs, are found in warm seas and oceans. Animals not only attach to the bottom surface, but also move freely in the water column.

The largest mollusk that lives in shallow water is tridacna (its shell valves reach 1 meter). As soon as the victim swims into the open flaps, they slam shut, and the mollusk begins to digest food. Some mollusks live in colonies. Mussels are bivalves that attach their shells to rocks and other objects. Mollusks breathe oxygen

dissolved in water, so they are not found on the deeper floors of the ocean.

Cephalopods - octopuses, octopuses, squids, cuttlefish have several tentacles and move in the water column due to compression

muscles that allow them to push water through a special tube. Among them there are giants with tentacles up to 10-14 meters! Starfish, sea lilies, urchins

attached to the bottom and corals with special suction cups. Similar to outlandish flowers, sea anemones pass their prey between their tentacles - "petals" and swallow it with a mouth opening located in the middle of the "flower".

Millions of fish of all sizes inhabit these waters. Among them are various sharks - one of the largest fish. Moray eels hide in rocks and caves, and stingrays hide at the bottom, the color of which allows them to merge with the surface.

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

Abyssal is an ocean bed. This is the largest space, occupying more than 70% of the underwater bottom. Its most numerous inhabitants are foraminifera and protozoan worms. Deep-sea sea urchins, fish, sponges, starfish - all have adapted to the monstrous pressure and are not like their relatives in shallow water. At depths where the sun's rays do not droop, marine inhabitants have devices for lighting - small luminous organs.

Land waters make up less than 4% of all water on our planet. Approximately half of their amount is contained in glaciers and permanent snow, the rest - in rivers, lakes, swamps, artificial reservoirs, groundwater and underground permafrost ice. Everything natural waters The lands are called water resources.

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

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

Glaciers

- permanent snow

Rivers

lakes

swamps

The groundwater

- underground permafrost ice

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

Groundwater is formed because some rocks allow water to pass through, while others hold it back. Atmospheric precipitation falling on the surface of the Earth seeps through cracks, voids and pores of permeable rocks (peat, sand, gravel, etc.), and water-resistant rocks (clay, marl, granite, etc.) retain water.

There are several classifications of groundwater by origin, condition, chemical composition and occurrence. Waters that, after rains or snow melt, penetrate the soil, wet it and accumulate in the soil layer, are called soil. On the first water-resistant layer from the earth's surface, groundwater occurs. They are replenished by the atmosphere

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

increases during the wet season, when there is a lot of precipitation or snow melt, and decreases during the dry season.

Below groundwater, there may be several layers of deep groundwater, which are held by water-resistant layers. Often, interstratal waters become pressure. This happens when the layers of rocks lie in the form of a bowl and the water enclosed in them is under pressure. Such groundwater, called artesian, rises up the drilled well and gushing. Often artesian aquifers occupy a significant area, and then artesian sources have a high and fairly constant flow of water. Some famous oases in North Africa originated at artesian springs. Through faults in the earth's crust, artesian waters sometimes rise from aquifers, and they often dry up between the rainy seasons.

Groundwater comes to the surface of the Earth in ravines, river valleys in the form sources - springs or keys. They form where an aquifer of rocks comes to the earth's surface. Since the depth of the groundwater varies with the season and rainfall, the springs sometimes suddenly disappear and sometimes swell. The temperature of the water in the springs can be different. Springs are considered cold with water temperatures up to 20 ° C, warm - with temperatures from 20 to 37 ° C, and hot -

Permeable rocks

Impermeable rocks

Groundwater types

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

Mineral underground waters contain many salts and gases and, as a rule, have healing properties.

The value of groundwater is very great, they can be classified as minerals along with coal, oil or iron ore. Groundwater feeds rivers and lakes, thanks to which the rivers do not become shallow in the summer, when there is little rain, and do not dry out under the ice. A person widely uses groundwater: they are pumped out of the ground for water supply to residents of cities and villages, for the needs of industry and for irrigation of agricultural land. Despite the huge reserves, groundwater is slowly regenerating, there is a danger of their depletion and pollution by domestic and industrial wastewater. Excessive water intake from deep horizons reduces the flow of rivers during low water - the period when the water level is at its lowest.

A swamp is a section of the earth's surface with excessive moisture and a stagnant water regime, in which organic matter accumulates in the form of undecomposed vegetation residues. There are swamps in all climatic zones and on almost all continents of the Earth. They contain about 11.5 thousand km3 (or 0.03%) of the fresh waters of the hydrosphere. The most swampy continents are South America and Eurasia.

The swamps can be divided into two large groups - wetlands, where there is no well-defined peat layer, and proper peat bogs, where peat accumulates. Wetlands include swampy tropical forests, salty mangrove swamps, saline swamps of deserts and semi-deserts, grassy swamps of the Arctic tundra, etc. Peat swamps occupy about 2.7 million km, which is 2% of the land area. They are most common in the tundra, forest zone and forest-steppe and, in turn, are divided into lowland, transitional and upland.

Lowland swamps usually have a concave or flat surface, where conditions are created for moisture to stagnate. They often form along the banks of rivers and lakes, sometimes in areas of flooding of reservoirs. In such swamps, groundwater comes close to the surface, supplying the plants growing here with minerals. On the

lowland swamps often grow alder, birch, spruce, sedge, reed, cattail. In these swamps, a layer of peat accumulates slowly (on average 1 mm per year).

Raised bogs with a convex surface and a thick layer of peat are formed mainly on watersheds. They feed mainly on atmospheric precipitation, which is poor in minerals, so less demanding plants settle in these swamps - pine, heather, cotton grass, sphagnum moss.

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

Marshes intensively evaporate moisture: more active than others are swamps of the subtropical climatic zone, swampy tropical forests, and in a temperate climate - sphagnum-sedge and forest marshes. Thus, swamps increase the humidity of the air, change its temperature, softening the climate of the surrounding areas.

Marshes, as a kind of biological filter, purify water from chemical compounds and solid particles dissolved in it. Rivers flowing through swampy areas do not differ in catastrophic

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

Bogs regulate the flow of not only surface water, but also groundwater (especially raised bogs). Therefore, their excessive drainage can harm small rivers, many of which originate in swamps. The swamps are rich hunting grounds: many birds nest here, many game animals live. The swamps are rich in peat, medicinal herbs, mosses and berries. The widespread belief that growing agricultural crops on drained swamps, you can get a rich harvest, is wrong. Only the first few years of drained peat deposits are fertile. Swamp drainage plans require extensive research and economic calculations.

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

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

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

A river is a watercourse of considerable size, flowing along a depression formed by it in the bottom of a river valley - a channel. The river with its tributaries forms a river system. If you look downstream of the river, then all the rivers that flow into it from the right are called right tributaries, and those that flow from the left are called left. The part of the earth's surface and the thickness of soils and soils, from where the river and its tributaries collect water, is called catchment.

A river basin is a part of the land that includes a given river system. There are watersheds between two basins of neighboring rivers,

river basin

The Pakhra River flows through the East European Plain

are usually hills or mountain systems. The basins of rivers flowing into the same body of water are united respectively into the basins of lakes, seas and oceans. Allocate the main watershed of the globe. It separates the basins of the rivers flowing into the Pacific and Indian Oceans on the one hand, and the basins of the rivers flowing into the Atlantic and Arctic Oceans on the other. In addition, there are drainless regions on the globe: the rivers flowing there do not carry water to the World Ocean. Such endorheic areas include, for example, the basins of the Caspian and Aral Seas.

Every river starts from its source. It can be a swamp, a lake, a melting mountain glacier, or an outlet to the surface of groundwater. The place where a river flows into an ocean, sea, lake or other river is called a mouth. The length of a river is the distance along the riverbed between its source and mouth.

Depending on the size of the river, they are divided into large, medium and small. Large river basins are usually located in several geographical areas. The basins of medium and small rivers are located within the same zone. According to the flow conditions, rivers are divided into flat, semi-mountain and mountain. Plain rivers flow smoothly and calmly in wide valleys, and mountain rivers rush rapidly and swiftly through the gorges.

Replenishment of water in rivers is called river feeding. It can be snowy, rainy, glacial and underground. Some rivers, for example, those that flow in the equatorial regions (Congo, Amazon and others), are distinguished by rain feeding, since it rains all year round in these regions of the planet. Most rivers are temperate

In the climatic zone, they have a mixed diet: in summer they are replenished by rains, in spring - by melting snow, and in winter they are not allowed to run out of groundwater.

The nature of the behavior of the river according to the seasons of the year - fluctuations in the water level, the formation and disappearance of ice cover, etc. - is called the regime of the river. Annually recurring significant increase in water

in the river - high water - on the flat rivers of the European territory of Russia is caused by intense snowmelt in the spring. The rivers of Siberia, flowing down from the mountains, are full-flowing in summer during the melting of snow.

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

Floods and high waters can cause severe floods: melt or rain waters overflow channels, and rivers overflow their banks, flooding not only their valley, but also the surrounding area. Water flowing at high speed has tremendous destructive power, it demolishes houses, uproots trees, and washes fertile soil from fields.

Sandy beach on the banks of the Volga

TO THAT LIVES IN RIVERS?

IN rivers live not only fish. The waters, bottom and banks of rivers are the habitat of many living organisms, they are divided into plankton, nekton and benthos. Plankton include, for example, green and blue-green algae, rotifers and lower crustaceans. The river benthos is very diverse - insect larvae, worms, mollusks, crayfish. Plants - pondweed, reeds, reeds, etc. - settle at the bottom and banks of rivers, and algae grow at the bottom. River nekton is represented by fish and some large invertebrates. Among the fish that live in the seas, and enter the rivers only for spawning, are sturgeon (sturgeon, beluga, stellate sturgeon), salmon (salmon, pink salmon, sockeye salmon, chum salmon, etc.). Carp, bream, sterlet, pike, burbot, perch, crucian carp, etc. constantly live in rivers, and grayling and trout live in mountain and semi-mountain rivers. Mammals and large reptiles also live in the rivers.

Rivers usually flow at the bottom of vast relief depressions called river valleys. At the bottom of the valley, the water stream runs along the recess - the channel - developed by it. Water hits one section of the coast, erodes it and carries rock fragments, sand, clay, silt downstream; in those places where the speed of the current decreases, the river deposits (accumulates) the material carried by it. But the river carries not only sediment washed away by the river flow; during heavy rains and snowmelt, water flowing down the earth's surface destroys the soil, loose soil and transfers small particles to streams, which then deliver them to rivers. By destroying and dissolving rocks in one place and depositing them in another, the river gradually creates its own valley. The process of erosion of the earth's surface by water is called erosion. It is stronger where the water flow rate is greater and where the soils are looser. The sediments that make up the bottom of the rivers are called bottom sediments or alluvium.

Wandering channels

In China and Central Asia, there are rivers in which the channel can shift by more than 10 m per day. They, as a rule, flow in easily eroded rocks - loess or sand. In a few hours, the water flow is able to significantly wash away one side of the river, and on the other side, where the current slows down, to deposit washed-away particles. Thus, the channel shifts - “wanders” along the bottom of the valley, for example, on the Amu Darya River in Central Asia, up to 10-15 m per day.

The origin of river valleys can be tectonic, glacial and erosional. Tectonic valleys repeat the direction of deep faults in the earth's crust. Powerful glaciers that covered the northern regions of Eurasia and North America during the global glaciation, moving, plowed out deep hollows, in which river valleys later formed. During the melting of glaciers, water flows spread to the south, forming extensive depressions in the relief. Later, streams rushed into these depressions from the surrounding hills, a large water stream was formed, which built its own valley.

The structure of the plain river valley

Rapids on a mountain river

DRY RIVERS

There are rivers on our planet that fill with water only during rare rains. They are called "wadis" and are found in deserts. Some wadis reach lengths of hundreds of kilometers and flow into the same dry depressions as they are. Gravel and pebbles at the bottom of dried-up channels give reason to believe that during wetter periods, wadis could be full-flowing rivers capable of carrying large sediments. In Australia, dry riverbeds are called screams, in Central Asia - uzboys.

The valley of lowland rivers consists of a floodplain (a part of the valley that is flooded during high water or during significant floods), a channel located on it, as well as slopes of the valley with several floodplain terraces descending steps to the floodplain. River channels can be straight, winding, divided into branches or meandering. In winding channels, bends, or meanders, are distinguished. Washing out the bend at the concave shore, the river usually forms a pool - a deep section of the channel, its shallow sections are called rifts. The strip in the channel with the most favorable depths for navigation is called the fairway. The water flow sometimes deposits a significant amount of sediment, forming islands. On large rivers, the height of the islands can reach 10 m, and the length can be several kilometers.

Sometimes on the way of the river there is a ledge of hard rocks. Water cannot wash it out and falls down, forming a waterfall. In those places where the river crosses hard rocks that are washed out slowly, rapids are formed that block the path of the water flow.

IN mouth water speed slows down significantly,

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

There are many rivers on earth. Some of them flow like small silvery snakes within the same 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 parameters outstanding. For example, the longest river in the world - the Nile is far from the most full-flowing, and the area of ​​\u200b\u200bits basin is small. The Amazon ranks first in the world in terms of water content (its water flow is 220 thousand m3 / s - this is 16.6% of the flow of all rivers) and in terms of basin area, but is inferior to the Nile in length. The largest rivers are in South America, Africa and Asia.

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

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

The largest rivers of the globe (by basin area): Amazon (7180 thousand km2), Congo (Zaire) (3691 thousand km2), Mississippi with a tributary of the Missouri (3268 thousand km2), La Plata with tributaries of the Parana and Uruguay (3100 thousand km2), Ob (2990 thousand km2).

Volga - the largest river of the East European Plain

MYSTERIOUS NILE

The Nile is a great African river, its valley is the cradle of a bright, original culture that influenced the development of human civilization. The mighty Arab conqueror Amir ibn al-Asi said: “There lies the desert, on both sides it rises, and between the heights is the wonderland of Egypt. And all his wealth comes from the blessed river, slowly flowing through the country with the dignity of a caliph. In the middle reaches, the Nile flows through the most severe deserts of Africa - Arabian and Libyan. It would seem that it should become shallow or dry during the hot summer. But at the very height of summer, the water level in the Nile rises, it overflows the banks, flooding the valley, and retreating, leaves a layer of fertile silt on the soil. This is because the Nile is formed from the confluence of two rivers - the White and Blue Nile, the sources of which lie in the subequatorial climatic zone, where the region is established in summer. low pressure and heavy rains fall. The Blue Nile is shorter than the White Nile, so the rainwater that fills it reaches Egypt earlier, followed by the White Nile flood.

Yenisei - the great river of Siberia

AMAZON - THE QUEEN OF RIVERS

The Amazon is the largest river on Earth. It is fed by many tributaries, including 17 large rivers up to 3500 km long, which, by their size, can themselves be classified as

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

but right tributaries, located in the southern hemisphere, are full of water the other part of the year. During sea tides, a water shaft up to 3.54 meters high enters the mouth of the river from the Atlantic side and rushes upstream. The locals call this wave of "spororok" - "destroyer".

MISSISSIPPI - THE GREAT RIVER OF AMERICA

Mighty river in the south North American continent The Indians called Messi Sipi - "Father of the Waters." Its complex river system with many tributaries looks like a giant tree with a densely branched crown. The Mississippi Basin occupies almost half of the territory of the United States of America. Starting in the region of the Great Lakes in the north, the high-water river carries its waters to the 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 discovered the banks of a huge deep river. One of the first colonists, the Jesuit fathers, who spread the influence of their order in the New World, wrote about the Mississippi as follows: “This river is very beautiful, its width is more than one league; everywhere adjoining it are forests full of game, and prairies where there are a lot of bison. Before the arrival of European colonizers, 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 land has been plowed up.

The waters of rivers and streams, choosing their own path, often fall off rocks and ledges. This is how waterfalls form. Sometimes these are very small steps in the channel with insignificant height differences between the upper section, from where the water falls, and the lower one. However, in nature there are absolutely gigantic "steps" and ledges, the height of which reaches many hundreds of meters. Both those and other waterfalls are formed when the water "opens", i.e. destroys, exposes areas with harder rocks, taking away material from more pliable areas. The upper ledge (edge), from which the water falls, is a more durable layer, and downstream, tireless waters destroy less durable rock layers. Such a structure, for example, has the world-famous waterfall on the Niagara River (its name in the Iroquois language means "thundering water"), which connects two of the Great Lakes of North America - Erie and Ontario. Niagara Falls is relatively low - only 51 m (for comparison - co-

Diagram of water flow in Niagara Falls

Cascade of several waterfalls in Norway. 19th century engraving

the Ivan the Great chapel in the Moscow Kremlin has a height of 81 m), but it is famous for more than its tall and full-flowing "brothers". The popularity of the waterfall was brought not only by its location in close proximity to large American and Canadian cities, but also by its good knowledge.

The water flow, falling from any height to the foot of the slope, forms a depression, a niche even in fairly strong rocks. But the upper edge is gradually washed out and destroyed by the action of flowing water. The peaks of the ledge are crumbling, and. the waterfall, as it were, recedes back, “backs up” up the valley. Long-term observations of the Niagara Falls have shown that such a "backward" erosion "eats" the upper ledge of the waterfall by about 1 m in 60 years.

In Scandinavia, glacial landforms are "guilty" of the formation of waterfalls. There, streams from glacier-lined mountain peaks rush down into the fjords from a great height.

Huge waterfalls, which have arisen under the influence of tectonics - the internal forces of the Earth, are very spectacular. The colossal steps of the waterfalls are formed when the riverbed is disturbed by tectonic faults. It happens that not one ledge is formed, but several at once. Such cascades of waterfalls are incredibly beautiful.

The view of any waterfall is mesmerizing. It is no coincidence that these natural phenomena invariably attract the attention of numerous tourists, often becoming " business cards» localities and even countries.

IGUAZU FALLS

Lakes are called hollows filled with water - natural depressions on the surface of the land that have no connection with the sea or ocean. In order for a lake to form, two conditions are necessary: ​​the presence of a natural depression - a closed depression in the earth's surface - and a certain volume of water.

There are many lakes on our planet. Their total area is about 2.7 million km2, that is, approximately 1.8% of the total land area. The main wealth of the lakes is fresh water, which is so necessary for man. The lakes contain about 180 thousand km3 of water, and the 20 largest lakes in the world, taken together, contain the predominant part of all fresh water available to man.

The lakes are located in a variety of natural areas. Most of them are in the northern parts of Europe and the North American continent. There are a lot of lakes in areas where permafrost is widespread, they are also in drainless areas, in floodplains and river deltas.

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

Depending on the size of the lakes, they are divided into very large ones, the area of ​​which exceeds 1,000 km2, large ones with an area of ​​101 to 1000 km2, medium ones, from 10 to 100 km2, and small ones, with an area of ​​less than 10 km2.

According to the nature of water exchange, lakes are divided into waste and non-drainage. Located in cat-

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

Lakes can be divided into fresh, brackish and salty, or mineral. The salinity of water in fresh lakes does not exceed 1% o - such water, for example, in Baikal, Ladoga and Onega lakes. Water brackish lakes have a salinity of 1 to 25% o. For example, the salinity of water in Issyk-Kul is 5-8% o, and in the Caspian Sea - 10-12% o. Salty lakes are called, the water in which has a salinity of 25 to 47% o. Above 47% of salts contain mineral lakes. So, the salinity of the Dead Sea, lakes Elton and Baskunchak is 200-300% o. Salt lakes tend to form in arid regions. In some salt lakes, the water is a solution of salts close to saturation. If such saturation is reached, then salt precipitation occurs and the lake turns into a self-sedating lake.

In addition to dissolved salts, lake water contains organic and inorganic substances and dissolved gases (oxygen, nitrogen, etc.). Oxygen not only enters lakes from the atmosphere, but is also released by plants during photosynthesis. It is necessary for the life and development of aquatic organisms, as well as for the oxidation of organic

Lake in the Swiss Alps

th substance in the reservoir. If an excess of oxygen is formed in the lake, then it leaves the water into the atmosphere.

According to the nutritional conditions of aquatic organisms, lakes are divided into:

- lakes poor in nutrients. These are deep lakes with clear water, which include, for example, Baikal, Lake Teletskoye;

- lakes with high inflow nutrients and rich vegetation. These are, as a rule, shallow and warm lakes;

YOUNG AND OLD LAKES

The life of the lake has a beginning and an end. Once formed, it is gradually filled with sediment from rivers, the remains of dead animals and plants. Every year the amount of precipitation at the bottom increases, the lake becomes shallower, overgrown and turns into a swamp. The greater the initial depth of the lake, the longer its life lasts. In small lakes, precipitation accumulates for many thousands of years, and in deep lakes - for millions of years.

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

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

They contribute to an increase in the amount of precipitation, the number of days with fogs and generally moderate the climate. Lakes raise the water table and affect soils, vegetation and animal world surrounding areas.

Lake in a trough of the earth's crust Lake in a crater

The basin of Lake Kaali in Estonia is of meteorite origin. It is located in a crater formed as a result of the fall of a large meteorite.

Glacial lakes fill the basins that were formed as a result of the activity of the glacier. Moving, the glacier plowed out softer soil, creating depressions in the relief: in some places - long and narrow, and in others - oval. Over time, they filled with water, and glacial lakes appeared. There are a lot of such lakes in the north of the North American continent, in Eurasia on the Scandinavian and Kola Peninsulas, in Finland, Karelia and Taimyr. In mountainous regions, for example, in the Alps and the Caucasus, glacial lakes are located in kars - bowl-shaped depressions in the upper parts of the mountain slopes, in the creation of which small mountain glaciers and snowfields took part. Melting and retreating, the glacier leaves a moraine - an accumulation of sand, clay with inclusions of pebbles, gravel and boulders. If a moraine dams up a river flowing out from under a glacier, a glacial lake is formed, often having a rounded shape.

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

rax, they can be seen in the Crimea, the Caucasus, the Urals and other regions.

IN tundra, and sometimes in the taiga, where permafrost is common, in the warm season the soil thaws and sags. Lakes appear in small depressions, calledthermokarst.

IN river valleys, when the meandering river straightens its course, old lot the riverbed is isolated. This is how oxbow lakes, often horseshoe-shaped.

Dammed, or dammed, lakes arise in the mountains when, as a result of a collapse, a mass of rocks blocks the riverbed. For example,

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

At coasts of the seas, sandy spits can separate the shallow coastal area from the sea, resulting in the formation lagoon lake. If sandy-clay deposits fence off flooded estuaries from the sea, estuaries are formed - shallow bays with very salty water. There are many such lakes on the coast of the Black and Azov Seas.

Formation of a dam or dam lake

Perennial accumulations of ice in the highlands and cold zones of the Earth are called glaciers. All natural ice is combined into the so-called glaciosphere - a part of the hydrosphere that is in a solid state. It includes the ice of cold oceans, and the ice caps of the mountains, and the icebergs that have broken off from the ice sheets. In the mountains, glaciers are formed from snow. First, during the recrystallization of snow as a result of alternating melting and new freezing of water inside the snow layer, firn is formed.

Distribution of ice on Earth during the Ice Age

which then turns into ice. Under the influence of gravity, ice moves in the form of ice flows. The main condition for the existence of glaciers - both small and huge - is constant low temperatures throughout most of the year, in which the accumulation of snow prevails over its melting. Such conditions exist in the cold regions of our planet - the Arctic and Antarctic, as well as in the highlands.

ICE AGES

IN THE HISTORY OF THE EARTH

IN the history of the Earth several times a strong cooling of the climate led to the growth of glaciers

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

ice ages.

IN Pleistocene (epoch of the Quaternary period of the Cenozoic era), the area covered with glaciers exceeded the modern one by almost three times. At that time

in In the mountains and on the plains of polar and temperate latitudes, huge ice sheets arose, which, increasing, covered vast territories in temperate latitudes. You can imagine what the Earth looked like at that time by looking at Antarctica or Greenland.

How do they know about those ancient ice ages? Moving along the surface, the glacier leaves its traces - the material that it took with it when moving. Such material is called moraine. Glaciers mark the stages of their standing

The movement of the earth's crust during the colossal load of the ice sheet (1) and after its removal (2)

lamy terminal moraine. Often, by the name of the place that the glacier reached, they call the glacier. The furthest glacier on the territory of Eastern Europe reached the valley of the Dnieper, and this glacier is called the Dnieper. On the territory of North America, the traces of maximum southward advances of glaciers belong to two glaciations: in the state of Kansas (Kansas glaciation) and Illinois (Illinois glaciation). The last glaciation reached Wisconsin during the Wisconsin Ice Age.

The Earth's climate changed dramatically during the Quaternary, or Anthropogenic, period, which began 1.8 million years ago and continues to this day. What caused such a grandiose cooling is a question that scientists are solving.

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

Glaciers of Svalbard

Moraines of sheet glaciation

The currently existing sheet glaciers are the remnants of huge ice sheets that existed in temperate latitudes during the last ice ages. And although today they are not as large-scale as in the past, their size is still impressive.

One of the most significant is the Antarctic Ice Sheet. The maximum thickness of its ice exceeds 4.5 km, and the distribution area is almost 1.5 times larger than the area of ​​Australia. From several centers of the dome, the ice of many glaciers spreads in different directions. It moves in the form of huge streams at a speed of 300-800 m per year. Occupying the whole of Antarctica, the cover in the form of outlet glaciers flows into the sea, giving life to numerous icebergs. Glaciers lying or, rather, floating in the coastal area are called shelf glaciers, since they are located in the area of ​​\u200b\u200bthe underwater margin of the mainland - the shelf. Such ice shelves exist only in Antarctica. The largest ice shelves are in West Antarctica. Among them is the Ross Ice Shelf, on which the American McMurdo Antarctic Station is located.

Another colossal ice sheet is in Greenland, covering over 80% of it.

foothill glacier

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

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

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

TO the same "half-cover" type of glaciation includesfoothill glaciers. Often a glacier descending from mountains along a valley reaches their foothills and emerges in wide lobes.

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

on the shelf or in lakes (Patagonian type). Piedmont glaciers are one of the most spectacular and beautiful. They are found in Alaska, in the north of North America, in Patagonia, in the extreme south of South America, in Svalbard. The most famous foothill glacier Malaspina in Alaska.

Reticulated glaciation of Svalbard

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

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

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

WHAT ARE GLACIERS

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

Randklufts - lateral cracks separating the glacier from the rocks

Bergschrund - a fissure in the area

supply of the glacier, separating the fixed and mobile

parts of the glacier

Median and lateral moraines

Transverse cracks in the tongue of the glacier

Primary moraine - material under the glacier

behind. The cirque glaciers fill bowl-shaped depressions on the slope - cirques, or cirques. In the lower part, the circus is limited by a transverse ledge - a crossbar, which is a threshold beyond which the glacier has not crossed for many hundreds of years.

Many mountain-valley glaciers, like rivers, merge from several "tributaries" into one large one that fills the glacial valley. Such glaciers of especially large sizes (they are also called dendritic or tree-like) are characteristic of the high mountains of the Pamirs, Karakorum, the Himalayas, and the Andes. For each region, there is a more fractional division of glaciers.

Summit glaciers occur on rounded or leveled mountain surfaces. The Scandinavian mountains have leveled summit surfaces - plateaus, on which this type of glaciers is common. The plateau breaks off in sharp ledges to fjords - ancient glacial valleys that have turned into deep and narrow sea bays.

The uniform movement of ice in the glacier can be replaced by sharp shifts. Then the tongue of the glacier begins to move along the valley at a speed of up to hundreds of meters per day or more. Such glaciers are called pulsating. Their ability to move is due to the accumulated stress

in glacial thickness. As a rule, constant observations of the glacier make it possible to predict the next pulsation. This helps prevent tragedies like the one that occurred in the Karmadon Gorge in 2003, when as a result of the pulsation of the Kolka glacier in the Caucasus, many settlements of the flowering valley were buried under chaotic heaps of ice blocks. Such pulsating glaciers are not uncommon.

in nature. One of them - the Bear Glacier - is located in Tajikistan, in the Pamirs.

Glacial valleys are U-shaped and resemble a trough. Their name is connected with this comparison - a trog (from it. Trog - a trough).

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

Edge of a glacier in the Himalayas

Clastic material on the surface of a glacier in the Alps

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

WARM AND COLD GLACIERS

On the bed of the glacier, i.e. the part that comes into contact with the surface may have a different temperature. In the highlands of temperate latitudes and in some polar glaciers, this temperature is close to the melting point of the ice. It turns out that a layer of melt water is formed between the ice itself and the underlying surface. On it, as on a lubricant, the glacier moves. Such glaciers are called warm, in contrast to cold ones, which are frozen to the bed.

Imagine a snowdrift melting in the spring. As the weather gets warmer, the snow begins to settle, its boundaries shrink, receding from the “winter ones”, streams run from under it... And everything that has accumulated on the snow and in the snow over the long winter months remains on the surface of the earth: all kinds of dirt, fallen branches and leaves, garbage. Now let's try to imagine

imagine that this snowdrift is several million times larger, which means that the heap of "garbage" after it melts will be the size of a mountain! A large glacier during melting, which is also called a retreat, leaves behind even more material - after all, its volume of ice contains much more "garbage". All inclusions left by the glacier after melting on the surface of the earth are called moraine or glacial deposits.

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

The glacier is in constant motion. As a viscoplastic body, it has the ability to flow. Consequently, the fragment that fell on him from the cliff, after a while, may be quite far from this place. These debris are collected (accumulated), as a rule, at the edge of the glacier, where the accumulation of ice gives way to melting. The accumulated material repeats the shape of the tongue of the glacier and looks like a curved embankment, partially blocking the valley. When the glacier retreats, the final moraine remains in its original place, gradually being washed away by melt water. During the retreat of the glacier, several shafts of terminal moraines may accumulate, which will indicate the intermediate positions of its tongue.

The glacier has receded. A moraine shaft remained in front of his front. But the melting continues. And behind the final moraine, melted glaciers begin to accumulate

kovy waters. A glacial lake appears, which is held back by a natural dam. When such a lake breaks, a destructive mudflow, a mudflow, is often formed.

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

The moraines of sheet glaciers are much larger and more diverse, but they are less preserved in the relief.

Sheet ice deposits

After all, as a rule, they are older. And to track their location on the plain is not as easy as in the mountain glacial valley.

In 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 - selgas - formed. There are many of them in Karelia and in Finland.

It was from there that the glacier brought fragments of crystalline rocks - granites. During the long transportation of rocks, the ice abraded the uneven edges of the debris, turning them into boulders. To this day, such granite boulders are found on the surface of the earth in all areas of the Moscow region. Fragments brought from afar are called erratic. From the maximum stage of the last glaciation - the Dnieper, when the end of the glacier reached the valleys of the modern Dnieper and Don, only moraines and glacial boulders have survived.

After melting, the cover glacier left behind a hilly space - a moraine plain. In addition, numerous streams of melted glacial waters burst out from under the edge of the glacier. They eroded the bottom and terminal moraines, carried away fine clay particles and left sandy fields - sands (from the isl. sand - sand) in front of the edge of the glacier. Melt water often washed its tunnels under the melting glaciers that lost their mobility. In these tunnels, and especially at the exit from under the glacier, washed-out moraine material (sand, pebbles, boulders) accumulated. These accumulations have been preserved in the form of long winding shafts - they are called oses.

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

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

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

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

POLYGONAL SOILS

Ice in the ground can form ice veins. Often they occur in places of frost (formed during severe frosts) cracks filled with water. When this water freezes, the soil between the cracks begins to compress, because 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 a short summer comes and the ice veins begin to thaw, whole spaces are formed, similar to a lattice of pieces of land surrounded by water "channels".

Among the polygonal formations, stone polygons and stone rings are widespread. With repeated freezing and thawing of the earth, freezing occurs, ice pushes larger fragments contained in the soil to the surface. In this way, the soil is sorted, since it small particles remain in the center of rings and polygons, while large fragments are displaced towards their edges. As a result, shafts of stones appear, framing the finer material. Mosses sometimes settle on it, and in autumn the stone polygons amaze with unexpected beauty:

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

The freezing of debris from the ground leads to the fact that on the summit surfaces and slopes of mountains and hills in the tundra zone, a chaotic heap of large stones appears, merging into stone “seas” and “rivers”. For them there is a name "kurums".

BULGUNNYAKHI

This Yakut word denotes surprise

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

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 along closed, almost circular orbits.

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

Rice. 1. The main parts of the wave

The main characteristics of waves are height - the difference between the levels of the crest and bottom of the wave; length - the shortest distance between adjacent crests or wave bottoms; 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 (in proportion to the square of the increase in height).

Under the influence of the Coriolis force, on the right downstream, far from the mainland, a water wall appears, and a depression is created near the land.

By origin waves are divided as follows:

• friction waves;
• baric 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 border of air and water. The height of wind waves does not exceed 4 m, but during strong and protracted storms it increases to 10-15 m and higher. The highest waves - up to 25 m - are observed in the westerly winds of the Southern Hemisphere.

Rice. 2. Wind waves and surf waves

Pyramidal, high and steep wind waves are called crowd. These waves are inherent in the central regions of cyclones. When the wind subsides, the excitement takes on character swell, i.e. unrest by inertia.

Primary form of wind waves - ripples. It occurs when the wind speed is 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 water, based on translational movements, is called surf(see Fig. 2).

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

baric wave

baric waves occur due to the rapid change 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, the coasts of China, India, and Japan are most often subjected 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 large. They move at a very high speed. Near the coasts, their length is reduced, and the height increases sharply (on average, from 10 to 50 m). Their appearance entails human casualties. First, the sea retreats several kilometers from the shore, gaining strength for a push, and then the waves splash onto the shore with great speed with an interval of 15-20 minutes (Fig. 3).

Rice. 3. Tsunami transformation

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

The seismic belt of the Pacific Ocean is the main area of ​​tsunami formation.

seiches

seiches- this standing waves that occur in bays and inland seas. They occur by inertia after the termination of the action of external forces - wind, seismic shocks, sudden changes, intense precipitation, etc. At the same time, water rises in one place, and falls in another.

Tidal wave

tidal waves- These are movements made under the influence of the tide-forming forces of the Moon and the Sun. The reverse reaction of sea water to the tide - low tide. The strip drained at low tide is called drying.

There is a close connection between the height of the tides and the tides with the phases of the moon. New moons and full moons have the highest tides and lowest tides. They're called syzygy. At this time, the lunar and solar tides, advancing simultaneously, overlap each other. 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 height of the tide is small - 1.0-2.0 m, and near the dissected coast 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 of 12.9 m was recorded in Shelikhov Bay (Sea of ​​Okhotsk). In inland seas, tides are hardly noticeable, for example, in the Baltic Sea near St. Petersburg, the tide is 4.8 cm, but along 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, there is excitement 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 action 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 wide, hundreds of meters deep. According to the physical and chemical properties of the waters of sea currents, they are different from those around them.

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

• permanent that pass in the same areas of the ocean, have one general direction, more or less constant speed and stable physico-chemical properties of the transported water masses (North and South trade winds, Gulf Stream, etc.);
• periodical, in which the direction, speed, temperature are subject to periodic laws. 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 of about ° 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 environment(e.g. equatorial currents).

According to the depth of 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 - of the order of several centimeters or a few tens of centimeters per second;
• bottom, regulating the exchange of water between the polar - subpolar and equatorial-tropical latitudes.

By origin distinguish the following currents:

• frictional, which can be drift or wind. Drift ones arise under the influence of constant winds, and wind ones are created by seasonal winds;
• gradient gravity, among which are stock, resulting from the slope of the surface caused by excess water due to their inflow from the ocean and heavy rainfall, and compensatory, which arise due to the outflow of water, scarce precipitation;
• inert, which are observed after the termination 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 that continuously stretches from the North Pole to the South, and impose a generalized scheme of atmospheric winds on it, then, taking into account the deflecting Coriolis force, we get 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 scheme, in reality, on the surface of the ocean there is zonal shift large - several thousand kilometers long - not completely enclosed 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 countercurrents.

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

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

The most powerful and deepest of the surface currents play an important role in the global circulation of the oceans. 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 are oriented from east to west. Tropical latitudes are characterized by warm sewage currents, such as the Gulf Stream, Kuroshio, Brazil, etc.

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

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

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

Monsoon circulation in the northern part of the 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 runoff of Siberian rivers, rotational cyclonic movement (counterclockwise) over the Barents and Kara seas.

In addition to circulation macrosystems, there are open ocean eddies. 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 it is in them that at least 90% of the kinetic energy of the ocean is contained. Vortices are observed not only in the open ocean, but also in marine 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 non-freezing port of Murmansk is located beyond the Arctic Circle, and on the east coast of North America, the Gulf of St. Lawrence (48°N). Warm currents contribute to precipitation, cold currents, on the contrary, reduce the possibility of precipitation. Therefore, areas washed by warm currents have a humid climate, and cold ones have a dry one. With the help of sea currents, migration of plants and animals, the transfer of nutrients and gas exchange are carried out. Currents are also taken into account when sailing.

Which moves with a certain cyclicity and frequency. Differs in a constancy of physical and chemical properties and a specific geographical location. It can be cold or warm, depending on belonging to the hemispheres. Each such flow is characterized by increased density and pressure. The flow rate of water masses is measured in sverdrupa, in more than broad sense- in units of volume.

Varieties of currents

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

1. Gradient. Occur when exposed to isobaric layers of water. A gradient ocean current is a flow characterized by horizontal movements of the isopotential surfaces of the water area. According to their initial features, they are divided into density, baric, stock, compensation and seiche. As a result of the runoff flow, precipitation and ice melting are formed.

2. Wind. Determined by the slope of the sea level, the strength of the air flow and fluctuations in mass density. A subspecies is drifting. This is a flow of water caused purely by the action of the wind. Only the surface of the pool is exposed to oscillations.

3. Tidal. They appear most strongly in shallow water, in estuaries and near the coast.

A separate type of flow is inertial. It is caused by the action of several forces at once. According to 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, the circulation of waters in the world's waters is only beginning to be studied in detail. By and large, specific information is known only about surface and shallow currents. The main snag is that the oceanographic system has no clear boundaries and is in constant motion. It is a complex network of flows due to various physical and chemical factors.

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

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

2. Wind exposure. The circulation of water 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 uneven distribution of salinity and temperature of water masses.

atmospheric effect

In the world's waters, this kind of influence is caused by the pressure of heterogeneous masses. Coupled with cosmic 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 prime example is the Gulf Stream. At the beginning of his journey, he is characterized by increased speed.

During the Gulf Stream, it is accelerated simultaneously by opposite and fair winds. This phenomenon forms a cyclic pressure on the layers of the pool, accelerating the flow. From here in a certain period of time there is a significant outflow and inflow a large number water. The lower the atmospheric pressure, the higher the tide.

When the water level drops, the slope of the Florida Strait becomes less. Because of this, the flow rate is significantly reduced. Thus, it can be concluded that high blood pressure reduces the flow.

wind impact

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, navigators have been able to calculate the appropriate ocean current. This became possible thanks to the work of the scientist W. Franklin on the Gulf Stream, dating back to the 18th century. A few decades later, A. Humboldt indicated precisely the wind in the list of the main extraneous forces affecting the 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 wind becomes the main influencing force on the movement. The current velocity in this case decreases in proportion to the depth. The determining condition for the constant circulation of waters is an infinitely long time of action of the wind. The only exceptions are the trade winds of air, which cause the movement of water masses in the equatorial strip 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 expedition Challenger. Subsequently, the work of scientists was confirmed by Scandinavian physicists.

The heterogeneity of the densities of water masses is the result of several factors at once. 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 state of aggregation of water affects the difference in physical indicators. Freezing or evaporation increases density, precipitation decreases it. Affects the strength of the current and salinity of water masses. It depends on the melting of ice, precipitation and the level of evaporation. In terms of density, the World Ocean is quite uneven. This applies to both surface and deep layers of the water area.

Currents of the Pacific Ocean

The general scheme of flows is determined by the circulation of the atmosphere. Thus, the east trade wind contributes to the formation of the North 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 Equatorial Ocean Current of the Pacific Ocean.

The largest currents in the water area are the Kuroshio, Alaska and California currents. The first two are warm. The third stream is the cold ocean current of the Pacific Ocean. The basin of the Southern Hemisphere is formed by the Australian and Tradewind currents. A little to the east of the center of the water area, the Equatorial countercurrent is observed. Off the coast of South America, there is a branch of the cold Peruvian current.

During the summer, the El Niño ocean current operates near the equator. It pushes back 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 Southwest Current dominates, which originates in the Bay of Bengal. A little further south is Western. This ocean current of the Indian Ocean crosses the water area from the coast of Africa to the Nicobar Islands.

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

Arctic ocean circulation

The main reason for the development of the undercurrent in this part of the World Ocean is a powerful influx of water masses from the Atlantic. The fact is that the centuries-old cover of ice does not give the atmosphere and space bodies affect internal circulation.

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

The Transarctic current is responsible for the direction of ice drift. Other major streams include the Yamal, Svalbard, North Cape and Norwegian currents, as well as a branch of the Gulf Stream.

currents of the atlantic basin

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

Here the main ocean current is the Gulf Stream. Thanks to him, the average water temperature is kept at around +17 degrees. This warm ocean warms both hemispheres.

Also the most important streams of the basin are the Canary, Brazilian, Benguela and Tradewind currents.