The heading angle of the wind is called the ship's course relative to the wind. Depending on the magnitude of this angle, the ship's courses relative to the wind received different names (Fig. 47).
If the wind blows to the starboard side, then the ship's course relative to the wind is also called "starboard tack", and when it blows to the left side - "port tack".
When, due to a change in the direction of the wind, its heading angle decreases, they say that the wind is setting, or becoming steeper; if it increases, then the wind moves away, or becomes fuller. When a change in angle is caused by a change in the ship's course, then in the first case they say that the ship is brought to the wind, or lies steeper, and in the second, that it descends, or lies more fully.
Rice. 48
Under the influence of the wind and the waves and currents it causes, a moving ship deviates from its intended course and changes its speed. Let's consider the effect of wind on a moving ship using the following example (Fig. 48). Let us assume that the ship is moving along some course IR with a speed along the log vl and is affected by the observed (apparent) wind Kw with a speed w at an angle q. The resultant wind pressure on the ship, equal to vector A, is applied to the center of the sail of the ship and makes an angle y with its center plane.
Let us decompose the resultant wind pressure A into two components X and Z. The force X is directed along the diametrical plane and is equal to X = A cozy, it affects the speed of the vessel relative to the water (in this case it reduces the speed) vl.
The force Z is directed perpendicular to the center plane, Z = A.siny and causes a lateral displacement - the ship drifts from the course line at a speed V dr.
By geometrically adding the speed of the vessel along the log vl and the drift of the udr, we obtain the vector of the actual speed of the vessel relative to the water v0, in the direction of which the actual movement of the vessel occurs under the action of this wind.
The line of actual movement of the vessel under the influence of wind is called the track line when drifting PU dr, and the angle between the north part of the true meridian and this line is the track angle. The angle a between the true course line and the track line during drift is called the drift angle. When solving problems, the drift angle is assigned a sign: when there is wind on the starboard tack - minus, and on the port tack - plus.
With the same apparent wind strength, but at different heading angles, its influence on a moving ship is different. At heading wind angles equal to 0 or 180°, the drift angle is zero, and at heading angles Kw close to 50-60°, it reaches its maximum value due to the fact that the direction of Kw is the resultant of the speed and direction of the true wind and the speed of the wind itself. vessel. At angles Kw ~ 50 / 60°, the angle between the direction of the true wind and the center plane of the vessel will be approximately 90°.
Rice. 49
The drift angle increases with a decrease in the vessel's speed and with an increase in its sail area (in the case of a decrease in the vessel's draft). Practice shows that ships with straight stems have less drift than those with inclined stems, and that ships with sharp lines have less drift than ships with full stems. The wind, creating waves, causes the vessel to roll, worsens controllability, and the vessel becomes less stable on course (the vessel develops yaw).
With prolonged exposure to wind in one direction, a surface current is created, which also causes the ship to drift off the true course line.
Thus, the combined effect of the wind and the waves and currents it causes during navigation must be taken into account by introducing a drift correction equal to the drift angle.
The true heading, the course angle during drift and the drift angle are in the following algebraic relationship (Fig. 49):
It should be remembered that the ship, moving along the track when drifting PU a, maintains the direction of its center plane parallel to the IR line and the latter always lies closer to the wind, and PU a - further from the wind (see Fig. 49).
Drift Angle Determination
At present, there are no instruments for determining the value of the drift angle that are convenient for use on a ship, and only experience and practice enable the navigator to correctly assess the effect of the wind on the ship and its probable drift by wind waves and currents.In navigation practice, the drift angle is determined from direct observations using one of the following methods.
Rice. 50
When sailing within sight of the coast using coastal landmarks. Following the constant course KK1 (Fig. 50), several times (at least three) the ship’s position is determined by coastal landmarks. Then, connecting the resulting points A1 A2 and A3, measure with a protractor the angle between the northern part of the true meridian and the line of actual movement of the vessel - line of route PP1. The drift angle a is obtained as the difference between PU and IR, i.e. a = PU - IR. This value of the drift angle is taken into account in the future. However, it should be borne in mind that such a determination can be made when there is no constant current in the area.
By direction finding of the wake jet (used as an approximate method). The wake jet is the wake of a moving vessel due to disturbance by the rotation of the propellers of the mass of water. When there is wind, the direction of the wake jet almost does not shift. Therefore, to obtain the drift angle, you can measure the angle between the directions of the ship's center plane and the wake jet. Bearings are taken along the compass closest to the stern, setting the sighting plane of the direction finder parallel to the wake. If the reading is noticed on the azimuth circle of the compass, then
A = KU - 180°,
And if OKP is removed, then a = OKP - KK.
The value of the drift angle, determined by all available methods, and the conditions under which it was determined (ship's course relative to the wind, ship's speed, wind strength, ship's condition in terms of loading, draft, etc.), must be recorded in a special notebook so that under similar conditions, it was possible to take into account the drift in advance, i.e., when laying, take into account the correction for the wind.
Dead reckoning of a ship while drifting
When conducting graphical dead reckoning taking into account the drift angle, in addition to the true course line, a track line is laid when the PU a is drifting along a given or calculated drift angle a and above it, in addition to the compass course and compass correction, the value of the drift angle is indicated with the corresponding sign. The distance traveled by the vessel (taking into account the correction or lag coefficient) is always taken into account along the PU track.The distance traveled along the log (except for the outboard one) at drift angles of more than 8° is calculated with the introduction of a correction for the drift angle according to the formula
If the distance traveled is determined by the speed of the propellers (according to the table of speed corresponding to the speed of the propellers), then no corrections are introduced.
When conducting graphical dead reckoning taking into account drift, the position of the vessel at the moment of abeam of the landmark should be plotted on the map; calculate the moment the vessel arrives abeam the landmark; determine the shortest distance to a landmark when following a given course and the moment of opening or hiding the landmark.
To plot the ship's position on the map at the moment of abeam of the landmark, the reverse true bearing is calculated using the following formulas. When observing a landmark: on the right
left
The OIP is laid from the landmark to the PUa, and point A (the intersection of the OIP with the PUa) will be the ship’s location on the map at the time of traverse (Fig. 51). In order to determine when the ship will actually come abeam the landmark, it is necessary shortly before this to set the compass direction finder to the pre-calculated OKP = CC ±90° (+90° - landmark on the left, -90° - on the right) and observe. As soon as the direction to the landmark coincides with the sighting plane of the direction finder, this moment will be the moment of traverse.
This problem often has to be solved when determining the turning point to a new course.
Rice. 51
In order to calculate in advance the moment the vessel arrives abeam the landmark, measure on the map along the track the distance S from the last observed point B to point A (see Fig. 51), obtained by crossing the OIP line with the line PUa, and dividing it by the speed of the vessel along lag, a time period corresponding to the duration of the ship’s passage from point B to point A is obtained.
By adding T to the moment of time T1 (observation at point B), we obtain the moment T2 of the vessel arriving abeam, i.e. T2 = T1 + T. To speed up the calculation of the value of T, use the table. 27-b “Time by distance and speed” (MT-63).
To calculate in advance the log reading at the moment the vessel arrives abeam (at point A), using the distance S, determine the role according to the table. 28-a or 28-6 (MT-63) depending on the Al sign or the formula roll = S/Cl. Then, during determination by reference (at point B), the found roll is added to the lag count and we get ol2 = ol1 + roll.
On this day, May 21, 1937 - 79 years ago, the expedition of I. Papanin, E. Krenkel, P. Shirshov, E. Fedorov landed on the ice of the Arctic Ocean in the area of the North Pole and deployed the first polar station “North Pole-1”.
For decades, thousands of desperate travelers and explorers of the North sought to get to the North Pole, trying at all costs to plant the flag of their country there, marking the victory of their people over the harsh and powerful forces of nature.
With the advent of aviation, new opportunities arose to reach the North Pole. Such as the flights of R. Amundsen and R. Bird on airplanes and the flights of the airships “Norway” and “Italy”. But for serious scientific research in the Arctic, these expeditions were short-term and not very significant. A real breakthrough was the successful completion of the first high-latitude airborne Soviet expedition and the landing on drifting ice in 1937 of the heroic “four” under the leadership of I. D. Papanin.
So, O.Yu. Schmidt headed the air part of the transfer to the Pole, and I. D. Papanin was responsible for its sea part and wintering at the drifting station "SP-1". The expedition's plans included a landing in the North Pole region for a year, during which it was planned to collect a huge amount of various scientific data on meteorology, geophysics, and hydrobiology. Five planes took off from Moscow on March 22. The flight ended on May 21, 1937.
At 11:35 a.m. the flagship aircraft, under the control of the flight detachment commander, Hero of the Soviet Union M.V. Vodopyanova landed on the ice, flying 20 km beyond the North Pole. And the last of the planes landed only on June 5, the flight and landing conditions were so difficult. On June 6, the USSR flag was raised over the North Pole, and the planes set off on their return journey.
Four brave researchers remained on the ice floe with a tent for living and working, two radio stations connected by an antenna, a workshop, a meteorological booth, a theodolite for measuring the height of the sun and warehouses built from ice. The expedition included: P.P. Shirshov - hydrobiologist, glaciologist; E.K. Fedorov - meteorologist-geophysicist; THIS. Krenkel - radio operator and I.D. Papanin is the station manager. Months of exhausting work and a difficult life lay ahead. But it was a time of mass heroism, high spirituality and impatient striving forward.
Every day at the North Pole brought new discoveries to the researchers, and the first of them was the depth of water under the ice at 4290 meters. Every day, at certain observation periods, soil samples were taken, depths and drift speed were measured, coordinates were determined, magnetic measurements, hydrological and meteorological observations were carried out.
Soon the drift of the ice floe on which the researchers' camp was located was discovered. Its wanderings began in the area of the North Pole, then the ice floe rushed south at a speed of 20 km per day.
A month after the Papaninites landed on the ice floe (as the brave four were dubbed throughout the world), when a ceremonial meeting of the participants of the world’s first air expedition to the North Pole took place in the Kremlin, a decree was read out on the award of O.Yu. Schmidt and I.D. Papanin was awarded the title of Hero of the Soviet Union, the rest of the drift participants were awarded the Order of Lenin. The ice floe on which the Papanin camp was located, after 274 days, turned into a fragment no more than 30 meters wide with several cracks.
A decision was made to evacuate the expedition. Behind us was a journey of 2,500 km across the Arctic Ocean and the Greenland Sea. On February 19, 1938, the polar explorers were removed from the ice floe by the icebreakers Taimyr and Murman. On March 15, the polar explorers were delivered to Leningrad.
The scientific results obtained in the unique drift were presented to the General Meeting of the USSR Academy of Sciences on March 6, 1938 and were highly appreciated by specialists. The scientific staff of the expedition were awarded academic degrees. Ivan Dmitrievich Papanin received the title of Doctor of Geographical Sciences.
With the heroic drift of the Papaninites, the systematic development of the entire Arctic basin began, which made navigation along the Northern Sea Route regular. Despite all the gigantic obstacles and difficulties of fate, the Papaninites, with their personal courage, wrote one of the brightest pages in the history of Arctic exploration.
80 years ago, the icebreaking ships of the Northern Fleet "Murman" and "Taimyr" removed four scientists from the first research station "North Pole" under the leadership of Ivan Papanin from a drifting ice floe.
The expedition landed on the ice floe in May 1937 and in nine months drifted 2.5 thousand km. However, in the Greenland Sea the ice floe almost completely collapsed and the rescue of the Papanins became an epic, watched by the entire Soviet Union.
Unpredictable ice
The Papanin expedition was prepared for about five years. Before them, no one had ever tried to live on a drifting ice floe for a long time, while collecting invaluable material for research. Going to the North Pole, scientists, thanks to the fact that the direction of ice movement could be calculated, imagined how their route would go, but they could not predict how long their journey would last or how it would end.
“Damn it, we only lived on this ice floe for nine months, but we’ve been through so much,” radio operator Ernst Krenkel later wrote in his diary. His memoirs describe in most detail the entire history of the first North Pole research station. In addition to Krenkel and Papanin, the station included meteorologist Evgeny Fedorov and oceanologist Pyotr Shirshov. Another member of the expedition was the dog Vesely, who was taken to warn polar explorers that polar bears were approaching the station.
When preparing the Papanins, the organizers of the expedition tried to provide for everything - from the operating conditions of the most advanced equipment for that time to everyday details. They were provided with substantial supplies of food, a field laboratory and instruments for scientific research, a windmill for generating energy and a radio station for transmitting messages. The main feature of the Papanin expedition was that it was prepared on the basis of theoretical ideas about the conditions of staying at the North Pole, without having any practice, so the most difficult thing was to foresee the main thing: how to get the scientists off the ice floe.
There is food and fuel - float, drift
“Of course, there is always a risk before going to such places, but everything possible was done to minimize it, despite the fact that there was no fundamental knowledge about the high-latitude Arctic at that time, except for the data received by Nansen (Norwegian navigator and traveler, geographer Fridtjof Nansen - approx. TASS) - this was all that could be based on,” said TASS about the 1937–38 expedition, a follower of the Papanins - the famous Russian polar traveler, honorary polar explorer of Russia, Chairman of the Polar Commission of the Russian Geographical Society, Viktor Boyarsky. He wintered at the drifting station "North Pole - 24" in the late 1970s.
“In fact, staying on an ice floe, when there is food and fuel, is not a very risky activity - you float on your own, you drift,” says Boyarsky. The Papaninites had approximately the same impression during the first few months of the drift. Their life on the ice floe can be judged from the exhibition in the Russian State Museum of the Arctic and Antarctic in St. Petersburg. There is a tent in which the expedition members lived, a windmill, a dynamo and other items that served the first polar explorers.
The tent, measuring 4 x 2.5 m, was insulated according to the principle of a down jacket: the frame was covered with three covers - the inner one was made of canvas, then there was a silk cover lined with eider down, the outer shell was made of thin black tarpaulin impregnated with a waterproof compound. Deer skins lay on the floor as insulation. “We had a real tent on display until the early 2000s, but then it was removed due to its disrepair. Special conditions are needed to preserve it, so it is now in the collections,” a specialist from the museum’s scientific and educational department told TASS Ingrid Safronova.
“The Papaninites recalled how cramped it was for them here, but they even managed to set up a laboratory in the tent. They recalled in their diaries how they were afraid of touching something and breaking these “secrets of the ocean.” They needed to have acrobatic qualities in order to move inside the cramped tent , and even in bulky clothes,” said Safronova.
The first concentrated mixtures
“They ate very well. Sausage, lard, butter, cheese. And they had concentrated soup mixtures - the “progenitors” of bouillon cubes, only much more healthy and tasty. These mixtures were specially developed for SP-1 (this abbreviation stuck with time to denote the expedition - TASS note) and after they showed themselves well in this expedition, they were put into production in the Soviet Union. One such pack was enough to cook an excellent rich soup for four,” said a museum employee. Arctic.
Food for the Papanites was packaged in metal cans, each weighing 45 kg. Primus stoves and blowtorches were used for cooking. To save space, all utensils - pots, pans, cups - were made so that one item fits into another - this principle later also became widely used by manufacturers of kitchenware.
All equipment, utensils, and buildings for polar explorers were specially created from lightweight but durable materials so that the ice would not break under their weight. In the place where the polar explorers landed, its thickness was about three meters.
Thin place
The Papaninians initially understood that difficulties awaited them, but they were inspired and ready to take risks, realizing that they were making important discoveries. “I can’t believe that we are at the Pole, I can’t believe that in such a prosaic situation the hundred-year-old dream of progressive humanity has come true,” he wrote in his diary on May 21, 1937, after landing on the ice floe from the ANT-4 plane.
While the station was operating, Petr Shirshov took depth measurements, took soil samples, water samples at different depths, determined its temperature, salinity, and oxygen content in it. The samples were immediately processed in a field hydrochemical laboratory. One of the main tasks of the scientific station was meteorological observations, and Evgeny Fedorov was responsible for them. Scientists measured atmospheric pressure, temperature, relative humidity, and determined wind speed and direction. The data was immediately transmitted via radio to Rudolf Island. Communication sessions were held four times a day.
Difficulties began after the new year, when the ice floe moved south quite quickly and encountered bad weather. “It turned out that for the first station the most “thin spot” was the possibility of filming from an ice floe. This became apparent when the need arose for a fairly urgent evacuation. It’s one thing to land at the North Pole, but when the ice floe went south, active breaking of the ice began, speeches there could be no landing of the plane; the airship, as we know, died tragically... There was no way to quickly respond to the situation. In this, the risk of that first expedition was higher than its modern counterparts,” noted Viktor Boyarsky.
When the ice cracked, they sat down to play chess
The most alarming days for the Papaninites occurred at the end of January - beginning of February. “Evening of January 31. The blizzard was raging for the fifth day. Dmitrich (Ivan Dmitrievich Papanin) and Petya (Shirshov) went to the crack to check the safety of the hydrological system. Just in case, they tied each other with ropes. Halfway up, Petya noticed a thin meander of the crack in the snow. Dmitrich I measured it with a shovel. The shovel fell through. This means that the crack is deep - perhaps the ice floe burst,” it is written in Krenkel’s diary.
The polar explorers tried to remain calm and follow the usual routine. “In the tent, our glorious old living tent, a kettle was boiling, dinner was being prepared. Suddenly, in the midst of pleasant preparations, there was a sharp push and a creaking rustle. It seemed as if silk or linen were being torn somewhere nearby,” Krenkel recalled about how The ice cracked, narrowing the station area.
"Dmitrich could not sleep. He smoked (the first sign of excitement) and tinkered with household chores. Sometimes he looked longingly at the loudspeaker suspended from the ceiling. When jolted, the loudspeaker swayed and rattled slightly. In the morning, Papanin suggested a game of chess. They played thoughtfully, calmly, with full awareness of the importance of the task at hand. And suddenly an unusual noise broke through the roar of the wind. The ice floe shuddered convulsively. We decided not to stop the game,” he wrote about the moment when the ice floe cracked right under the tent.
Even when the elements left the polar explorers a tiny place to exist in the raging cold ocean, they did not panic and refused to send a distress signal. Krenkel then rather casually radioed Papanin’s message: “As a result of a six-day storm at 8 a.m. on February 1, in the area of the station, the field was torn apart by cracks from half a kilometer to five. We are on the wreckage of a field 300 meters long, 200 meters wide. Two bases have been cut off, as well as a technical warehouse with secondary property. Everything valuable has been saved from the fuel and utility storage. There is a crack under the living tent. We will inform you about the coordinates later today; if the connection is lost, please do not worry."
The ships "Taimyr" and "Murman" have already moved towards the polar explorers, but it turned out to be very difficult for them to get to the station. They approached 50–60 km, and at night the polar explorers saw the light of their searchlights, but it was impossible to get closer due to the difficult ice conditions. Plans to send planes for polar explorers did not come true - the site that the polar explorers were preparing for landing the plane on the ice collapsed. One of the planes sent to search for the polar station from the ship got lost, and a rescue operation was required for it itself. The ships were able to make their way to the station when a polynya formed; they suffered significant damage in the ice along the way.
On February 18, 1938, the ships finally appeared. “Dmitrich stood on a high hummock and waved a flag. The smoke of the steamer was clearly visible, then the masts appeared,” Krenkel wrote in his diary.
"Murman" and "Taimyr" moored to the ice field one and a half kilometers from the polar station at 13:40 on February 19. They took on board all the expedition members and their equipment. On February 21, the Papanins transferred to the icebreaker Ermak, which delivered them to Leningrad on March 16.
Experience needs to be accumulated
"Of course, it was most difficult for them: they were the first. Then we had a whole galaxy of wonderful stations, and every year experience accumulated. People found themselves in different situations, and therefore they try to avoid the mistakes of previous ones. Woe awaits those travelers, scientists who did not They use previous experience," Boyarsky said.
The last North Pole station was established in Russia in 2015.
The average unevenness of the lower surface of pack ice is approximately 3 m, which significantly affects the nature of the propagation of sound energy emitted by hydroacoustic devices, making it difficult to detect polynyas. However, for correct orientation in ice conditions, you need to know not only the nature of the ice surface, but also its shape, size and concentration.
In terms of shapes and sizes, a distinction is made between ice fields and broken ice. Ice fields are divided into extensive (more than 10 km in diameter), large (2-10 km, small (0.5-2 km) and fragments (100-500 m). In addition, ice can be coarse (ice floes size 20-100 m), small broken ice (2-20 m), chunks (0.5-2.0 m) and ice porridge, broken ice in holes and leads makes it very difficult to ascend. Therefore, equipment designed to support this maneuver must have high resolution. , which makes it possible to distinguish between small broken ice and even pieces, since they can damage the wheelhouse fencing, retractable devices, rudders and propellers, which, for example, happened to the American submarine Karp.
The possibility of ascent also depends on the concentration (thickness) of the drifting ice. Cohesion is usually called the ratio of the total area of ice, which is illuminated by the sound beam of a hydroacoustic device, to the area of the gaps of clear water between individual ice floes. It should be remembered that drifting ice, as a rule, covers the sea unevenly (especially in summer) and its density in different sectors is not the same.
Icebergs and ice islands pose a great danger when swimming under the ice. Icebergs are found in many areas of the Arctic Ocean. The height of their surface part reaches 50 m, but the draft is several times greater than this value. There are icebergs 2-2.5 km long and up to 1.5 km wide. It is clear that an unexpected encounter with such an underwater obstacle threatens the underwater ship with major troubles. In this case, hydroacoustic technology comes to the aid of submariners - sonars and iceberg gauges, but the difficulties of under-ice navigation still remain quite significant.
Icebergs penetrate into the Central AB mainly from the area of Franz Josef Land and Severnaya Zemlya; there are most of them here. Ice mountains that appear in the regions of Greenland and Spitsbergen almost never reach high latitudes. Polar researchers note that the number of icebergs can change dramatically from year to year.”
At the end of the 40s, Soviet polar pilots discovered drifting ice islands in the Central AB and adjacent Arctic seas. Now about two dozen of them are known. The largest of them (discovered in April 1948 by pilot I.P. Mazuruk) measures 17x18 miles. The thickness of the drifting ice islands ranges from 50 to 70 m, the specific gravity of ice is from 0.87 to 0.92 g/cm 3 , the draft reaches 50 m.
Despite the numerous and obvious difficulties of under-ice voyages to high latitudes, in addition to the nuclear submarines of the Soviet Union, submarines from the United States, England and France have visited the polar ice cap in recent years. They also floated to the surface in areas of clear water or in young thin ice. The correct assessment of the possibility of ascent largely depends on determining the size and nature of such spaces. In this regard, let us consider in more detail the characteristics of such forms as a hole, a clearing, a channel, a crack, a window.
A polynya is a fairly stable expanse of clean water among ice fields. The sizes of wormwood can be very different: from several tens of square meters to tens of square kilometers. Most often they have the shape of a rectangle, square or circle. However, there are giant polynyas that are elongated in length. Their size and location are certainly of great interest, especially since they are detected and recorded in advance by aerial reconnaissance. Thus, from the Soviet aircraft N-169 on March 2-3, 1941, in the area of the “pole of relative inaccessibility”, polynyas up to 500 m wide and up to 18 km long were observed; Occasionally, vast expanses of clear water were encountered, up to 10 km wide and up to 45 km long. In addition, two large open expanses of clean water constantly exist in the Central Arctic Basin: the “Siberian Polynya” north of the New Siberian Islands and Severnaya Zemlya and the “Great Polynya” northeast of Ellesmere Island. Aerial reconnaissance also revealed that the formation of large polynyas occurring at the border of drifting ice and coastal fast ice is mainly associated with wind conditions.
A floodway is a less stable expanse of clear water several tens of meters wide, subject to the action of winds and tidal phenomena. The most characteristic form of the ripples is elongated, up to several kilometers long. Often the leads are curved, which makes it difficult to choose a site for ascent.
A channel is a narrow long strip of water (the length is more than 10 times greater than the width between large ice floes, usually appearing due to the expansion of cracks. As researchers note, channels, as well as ice holes and leads, are found in the central Arctic not only in summer, but also in winter time. Due to their small width, the channels are difficult to detect using echo-ice meters, as noted in his book “Sea Dragon” by the commander of the American nuclear submarine D. Steele during a special flight over the Arctic ice.
A crack is a gap in the ice up to 10 m wide. When diving under the ice, it is useful to mark the location of long cracks on a map, since it is known that in a short time a narrow crack can turn into a fairly wide channel. The cracks can be used for radio communications by releasing special buoy radio antennas into them.
Window is a still unestablished term adopted to designate areas of young ice covering the surface of polynyas, leads and channels. The window is clearly visible through the periscope. It stands out as a bright spot against the darker background of the rest of the surface, covered with thick pack ice.
The formation of young ice in polynyas, leads and channels begins in the first half of September, and sometimes even in the second half of August. The rate of its increase depends primarily on the air temperature. At minus 40 °C, you can expect an increase in ice thickness by an average of 2.5 cm in a few hours, in a week - by 30 cm, in a month - up to 1 m. Echo ice meters, polynya indicators and other devices that provide navigation in winter.
For a successful ascent, it is also important to take into account the current, nature, direction and speed of ice drift in general and individual ice formations in particular. To confirm this, we can cite an example when the submarine “Skate”, in an opening about 100 m wide, was unable to surface the first time due to failure to take into account ice drift. The maneuver was a success only after careful consideration of ice drift and the submarine's ascent speed.
Project 613 submarine in Arctic ice.
What does ice drift depend on and what are its elements? Professor N.N. Zubov gives three most typical cases:
– wind drift of compacted ice, causing even an independent drift subglacial current;
– drift of an individual ice floe under the influence of wind on its upper part and wind current on its lower part;
– wind drift of thin ice, when it turns out that each ice floe (due to differences in shape and size) drifts in its own way, which is especially dangerous when ascending, since the ice situation in such cases changes very quickly.
The direction of ice drift in stable winds differs from the wind direction by approximately 30° to the right, and the dependence of the drift speed on the wind speed is determined in the general case by a wind coefficient equal to 0.32. The direction of the wind current (when there is no ice on the sea surface) deviates from the wind direction by 45° to the right.
The reasons causing the general movement of large masses of ice in the Central AB are mainly constant currents and prevailing winds associated with the distribution of atmospheric pressure. Under the influence of these factors, a significant part of the ice is carried into the passage between Greenland and Spitsbergen. In the sector adjacent to America, the ice drifts clockwise in a vicious circle. These general directions become noticeable only at great distances. When drifting, ice floes usually describe bizarre loops and zigzags and often return to their starting points. Regarding annual fluctuations in ice removal, famous Soviet polar explorers N.A. Volkov and Z.M. Gudkovich note: “The average speed of the surface outflow current also changes noticeably throughout the year. The maximum speed occurs in July–September, and the minimum in October–December.”
Clickable
According to modern plate theories The entire lithosphere is divided into separate blocks by narrow and active zones - deep faults - moving in the plastic layer of the upper mantle relative to each other at a speed of 2-3 cm per year. These blocks are called lithospheric plates.
The first suggestion about the horizontal movement of crustal blocks was made by Alfred Wegener in the 1920s within the framework of the “continental drift” hypothesis, but this hypothesis did not receive support at that time.
Only in the 1960s did studies of the ocean floor provide conclusive evidence of horizontal plate movements and ocean expansion processes due to the formation (spreading) of oceanic crust. The revival of ideas about the predominant role of horizontal movements occurred within the framework of the “mobilistic” trend, the development of which led to the development of the modern theory of plate tectonics. The main principles of plate tectonics were formulated in 1967-68 by a group of American geophysicists - W. J. Morgan, C. Le Pichon, J. Oliver, J. Isaacs, L. Sykes in the development of earlier (1961-62) ideas of American scientists G. Hess and R. Digtsa about the expansion (spreading) of the ocean floor.
It is argued that scientists are not entirely sure what causes these shifts and how the boundaries of tectonic plates are defined. There are countless different theories, but none completely explains all aspects of tectonic activity.
Let's at least find out how they imagine it now.
Wegener wrote: “In 1910, the idea of moving continents first occurred to me ... when I was struck by the similarity of the outlines of the coasts on both sides of the Atlantic Ocean.” He suggested that in the early Paleozoic there were two large continents on Earth - Laurasia and Gondwana.
Laurasia was the northern continent, which included the territories of modern Europe, Asia without India and North America. The southern continent - Gondwana united the modern territories of South America, Africa, Antarctica, Australia and Hindustan.
Between Gondwana and Laurasia there was the first sea - Tethys, like a huge bay. The rest of the Earth's space was occupied by the Panthalassa Ocean.
About 200 million years ago, Gondwana and Laurasia were united into a single continent - Pangea (Pan - universal, Ge - earth)
About 180 million years ago, the continent of Pangea again began to separate into its component parts, which mixed on the surface of our planet. The division occurred as follows: first Laurasia and Gondwana reappeared, then Laurasia split, and then Gondwana split. Due to the split and divergence of parts of Pangea, oceans were formed. The Atlantic and Indian oceans can be considered young oceans; old - Quiet. The Arctic Ocean became isolated as landmass increased in the Northern Hemisphere.
A. Wegener found many confirmations of the existence of a single continent of the Earth. What seemed especially convincing to him was the existence in Africa and South America of the remains of ancient animals - listosaurs. These were reptiles, similar to small hippopotamuses, that lived only in freshwater bodies of water. This means that they could not swim huge distances in salty sea water. He found similar evidence in the plant world.
Interest in the hypothesis of continental movement in the 30s of the 20th century. decreased somewhat, but was revived again in the 60s, when, as a result of studies of the relief and geology of the ocean floor, data were obtained indicating the processes of expansion (spreading) of the oceanic crust and the “diving” of some parts of the crust under others (subduction).
Structure of the continental rift
The upper rocky part of the planet is divided into two shells, significantly different in rheological properties: a rigid and brittle lithosphere and an underlying plastic and mobile asthenosphere.
The base of the lithosphere is an isotherm approximately equal to 1300°C, which corresponds to the melting temperature (solidus) of the mantle material at lithostatic pressure existing at depths of the first hundreds of kilometers. Rocks in the Earth above this isotherm are quite cold and behave like rigid materials, while underlying rocks of the same composition are quite heated and deform relatively easily.
The lithosphere is divided into plates, constantly moving along the surface of the plastic asthenosphere. The lithosphere is divided into 8 large plates, dozens of medium plates and many small ones. Between the large and medium slabs there are belts composed of a mosaic of small crustal slabs.
Plate boundaries are areas of seismic, tectonic, and magmatic activity; the internal regions of the plates are weakly seismic and characterized by weak manifestation of endogenous processes.
More than 90% of the Earth's surface falls on 8 large lithospheric plates:
Some lithospheric plates are composed exclusively of oceanic crust (for example, the Pacific Plate), others include fragments of both oceanic and continental crust.
Rift formation scheme
There are three types of relative movements of plates: divergence (divergence), convergence (convergence) and shear movements.
Divergent boundaries are boundaries along which plates move apart. The geodynamic situation in which the process of horizontal stretching of the earth's crust occurs, accompanied by the appearance of extended linearly elongated slot or ditch-like depressions, is called rifting. These boundaries are confined to continental rifts and mid-ocean ridges in ocean basins. The term "rift" (from the English rift - gap, crack, gap) is applied to large linear structures of deep origin, formed during the stretching of the earth's crust. In terms of structure, they are graben-like structures. Rifts can form on both continental and oceanic crust, forming a single global system oriented relative to the geoid axis. In this case, the evolution of continental rifts can lead to a break in the continuity of the continental crust and the transformation of this rift into an oceanic rift (if the expansion of the rift stops before the stage of rupture of the continental crust, it is filled with sediments, turning into an aulacogen).
The process of plate separation in zones of oceanic rifts (mid-ocean ridges) is accompanied by the formation of new oceanic crust due to magmatic basaltic melt coming from the asthenosphere. This process of formation of new oceanic crust due to the influx of mantle material is called spreading (from the English spread - to spread, unfold).
The structure of the mid-ocean ridge. 1 – asthenosphere, 2 – ultrabasic rocks, 3 – basic rocks (gabbroids), 4 – complex of parallel dikes, 5 – basalts of the ocean floor, 6 – segments of the oceanic crust formed at different times (I-V as they become more ancient), 7 – near-surface igneous chamber (with ultrabasic magma in the lower part and basic magma in the upper), 8 – sediments of the ocean floor (1-3 as they accumulate)
During spreading, each extension pulse is accompanied by the arrival of a new portion of mantle melts, which, when solidified, build up the edges of plates diverging from the MOR axis. It is in these zones that the formation of young oceanic crust occurs.
Collision of continental and oceanic lithospheric plates
Subduction is the process of pushing an oceanic plate under a continental or other oceanic one. Subduction zones are confined to the axial parts of deep-sea trenches associated with island arcs (which are elements of active margins). Subduction boundaries account for about 80% of the length of all convergent boundaries.
When the continental and oceanic plates collide, a natural phenomenon is the displacement of the oceanic (heavier) plate under the edge of the continental one; When two oceans collide, the more ancient (that is, cooler and denser) of them sinks.
Subduction zones have a characteristic structure: their typical elements are a deep-sea trench - a volcanic island arc - a back-arc basin. A deep-sea trench is formed in the zone of bending and underthrusting of the subducting plate. As this plate sinks, it begins to lose water (found in abundance in sediments and minerals), the latter, as is known, significantly reduces the melting temperature of rocks, which leads to the formation of melting centers that feed volcanoes of island arcs. In the rear of a volcanic arc, some stretching usually occurs, which determines the formation of a back-arc basin. In the back-arc basin zone, stretching can be so significant that it leads to rupture of the plate crust and the opening of a basin with oceanic crust (the so-called back-arc spreading process).
The volume of oceanic crust absorbed in subduction zones is equal to the volume of crust emerging in spreading zones. This position emphasizes the idea that the volume of the Earth is constant. But this opinion is not the only and definitively proven one. It is possible that the volume of the plane changes pulsatingly, or that it decreases due to cooling.
The immersion of the subducting plate into the mantle is traced by the foci of earthquakes that occur at the contact of the plates and inside the subducting plate (colder and, therefore, more fragile than the surrounding mantle rocks). This seismofocal zone is called the Benioff-Zavaritsky zone. In subduction zones, the process of formation of new continental crust begins. A much rarer process of interaction between the continental and oceanic plates is the process of obduction - the pushing of part of the oceanic lithosphere onto the edge of the continental plate. It should be emphasized that during this process, the ocean plate is separated, and only its upper part - the crust and several kilometers of the upper mantle - moves forward.
Collision of continental plates
When continental plates collide, the crust of which is lighter than the mantle material and, as a result, is not able to sink into it, a collision process occurs. During the collision, the edges of colliding continental plates are crushed, crushed, and systems of large thrusts are formed, which leads to the growth of mountain structures with a complex fold-thrust structure. A classic example of such a process is the collision of the Hindustan plate with the Eurasian plate, accompanied by the growth of the grandiose mountain systems of the Himalayas and Tibet. The collision process replaces the subduction process, completing the closure of the ocean basin. Moreover, at the beginning of the collision process, when the edges of the continents have already moved closer together, the collision is combined with the process of subduction (the remnants of the oceanic crust continue to sink under the edge of the continent). Large-scale regional metamorphism and intrusive granitoid magmatism are typical for collision processes. These processes lead to the creation of a new continental crust (with its typical granite-gneiss layer).
The main reason for plate movement is mantle convection, caused by mantle thermogravitational currents.
The source of energy for these currents is the difference in temperature between the central regions of the Earth and the temperature of its near-surface parts. In this case, the main part of the endogenous heat is released at the boundary of the core and the mantle during the process of deep differentiation, which determines the disintegration of the primary chondritic substance, during which the metal part rushes to the center, building up the core of the planet, and the silicate part is concentrated in the mantle, where it further undergoes differentiation.
Rocks heated in the central zones of the Earth expand, their density decreases, and they float up, giving way to sinking colder and therefore heavier masses that have already given up some of the heat in the near-surface zones. This process of heat transfer occurs continuously, resulting in the formation of ordered closed convective cells. In this case, in the upper part of the cell, the flow of matter occurs almost in a horizontal plane, and it is this part of the flow that determines the horizontal movement of the matter of the asthenosphere and the plates located on it. In general, the ascending branches of convective cells are located under the zones of divergent boundaries (MOR and continental rifts), while the descending branches are located under the zones of convergent boundaries. Thus, the main reason for the movement of lithospheric plates is “dragging” by convective currents. In addition, a number of other factors act on the slabs. In particular, the surface of the asthenosphere turns out to be somewhat elevated above the zones of ascending branches and more depressed in the zones of subsidence, which determines the gravitational “sliding” of the lithospheric plate located on an inclined plastic surface. Additionally, there are processes of drawing heavy cold oceanic lithosphere in subduction zones into the hot, and as a consequence less dense, asthenosphere, as well as hydraulic wedging by basalts in the MOR zones.
The main driving forces of plate tectonics are applied to the base of the intraplate parts of the lithosphere - the mantle drag forces FDO under the oceans and FDC under the continents, the magnitude of which depends primarily on the speed of the asthenospheric flow, and the latter is determined by the viscosity and thickness of the asthenospheric layer. Since the thickness of the asthenosphere under the continents is much less, and the viscosity is much greater than under the oceans, the magnitude of the FDC force is almost an order of magnitude lower than the FDO value. Under the continents, especially their ancient parts (continental shields), the asthenosphere almost pinches out, so the continents seem to be “stranded.” Since most lithospheric plates of the modern Earth include both oceanic and continental parts, it should be expected that the presence of a continent in the plate should, in general, “slow down” the movement of the entire plate. This is how it actually happens (the fastest moving almost purely oceanic plates are the Pacific, Cocos and Nazca; the slowest are the Eurasian, North American, South American, Antarctic and African plates, a significant part of whose area is occupied by continents). Finally, at convergent plate boundaries, where the heavy and cold edges of lithospheric plates (slabs) sink into the mantle, their negative buoyancy creates the FNB force (an index in the designation of force - from the English negative buoyance). The action of the latter leads to the fact that the subducting part of the plate sinks in the asthenosphere and pulls the entire plate along with it, thereby increasing the speed of its movement. Obviously, the FNB force acts sporadically and only in certain geodynamic settings, for example in the cases of slab failure across the 670 km divide described above.
Thus, the mechanisms that set lithospheric plates in motion can be conditionally classified into the following two groups: 1) associated with the forces of mantle drag mechanism applied to any points of the base of the plates, in the figure - forces FDO and FDC; 2) associated with forces applied to the edges of the slabs (edge-force mechanism), in the figure - FRP and FNB forces. The role of one or another driving mechanism, as well as certain forces, is assessed individually for each lithospheric plate.
The combination of these processes reflects the general geodynamic process, covering areas from the surface to the deep zones of the Earth. Currently, two-cell mantle convection with closed cells is developing in the Earth's mantle (according to the model of through-mantle convection) or separate convection in the upper and lower mantle with the accumulation of slabs under subduction zones (according to the two-tier model). The probable poles of the rise of mantle material are located in northeastern Africa (approximately under the junction zone of the African, Somali and Arabian plates) and in the Easter Island region (under the middle ridge of the Pacific Ocean - the East Pacific Rise). The equator of subsidence of mantle matter passes approximately along a continuous chain of convergent plate boundaries along the periphery of the Pacific and eastern Indian Oceans. The modern regime of mantle convection, which began approximately 200 million years ago with the collapse of Pangea and gave rise to modern oceans, will in the future be replaced by a single-cell regime (according to the model of through-mantle convection) or (according to an alternative model) convection will become through the mantle due to the collapse of slabs through the 670 km section. This may lead to a collision of continents and the formation of a new supercontinent, the fifth in the history of the Earth.
Plate movements obey the laws of spherical geometry and can be described based on Euler's theorem. Euler's rotation theorem states that any rotation of three-dimensional space has an axis. Thus, rotation can be described by three parameters: the coordinates of the rotation axis (for example, its latitude and longitude) and the rotation angle. Based on this position, the position of the continents in past geological eras can be reconstructed. An analysis of the movements of the continents led to the conclusion that every 400-600 million years they unite into a single supercontinent, which subsequently undergoes disintegration. As a result of the split of such a supercontinent Pangea, which occurred 200-150 million years ago, modern continents were formed.
Plate tectonics was the first general geological concept that could be tested. Such a check was carried out. In the 70s a deep-sea drilling program was organized. As part of this program, several hundred wells were drilled by the Glomar Challenger drilling vessel, which showed good agreement between ages estimated from magnetic anomalies and ages determined from basalts or sedimentary horizons. The distribution diagram of sections of the oceanic crust of different ages is shown in Fig.:
Age of the ocean crust based on magnetic anomalies (Kennet, 1987): 1 - areas of lack of data and land; 2–8 - age: 2 - Holocene, Pleistocene, Pliocene (0–5 million years); 3 - Miocene (5–23 million years); 4 - Oligocene (23–38 million years); 5 - Eocene (38–53 million years); 6 - Paleocene (53–65 million years) 7 - Cretaceous (65–135 million years) 8 - Jurassic (135–190 million years)
At the end of the 80s. Another experiment to test the movement of lithospheric plates was completed. It was based on measuring baselines relative to distant quasars. Points were selected on two plates at which, using modern radio telescopes, the distance to the quasars and their declination angle were determined, and, accordingly, the distances between the points on the two plates were calculated, i.e., the base line was determined. The accuracy of the determination was a few centimeters. After several years, the measurements were repeated. A very good agreement was obtained between the results calculated from magnetic anomalies and the data determined from the baselines
Diagram illustrating the results of measurements of the mutual movement of lithospheric plates obtained by the very long baseline interferometry method - ISDB (Carter, Robertson, 1987). The movement of the plates changes the length of the baseline between radio telescopes located on different plates. The map of the Northern Hemisphere shows baselines from which sufficient data have been obtained using the ISDB method to make a reliable estimate of the rate of change in their length (in centimeters per year). The numbers in parentheses indicate the amount of plate displacement calculated from the theoretical model. In almost all cases the calculated and measured values are very close
Thus, plate tectonics has been tested over the years by a number of independent methods. It is recognized by the world scientific community as the paradigm of geology at the present time.
Knowing the position of the poles and the speed of modern movement of lithospheric plates, the speed of spreading and absorption of the ocean floor, it is possible to outline the path of movement of the continents in the future and imagine their position for a certain period of time.
This forecast was made by American geologists R. Dietz and J. Holden. In 50 million years, according to their assumptions, the Atlantic and Indian oceans will expand at the expense of the Pacific, Africa will shift to the north and thanks to this the Mediterranean Sea will gradually be eliminated. The Strait of Gibraltar will disappear, and a “turned” Spain will close the Bay of Biscay. Africa will be split by the great African faults and its eastern part will shift to the northeast. The Red Sea will expand so much that it will separate the Sinai Peninsula from Africa, Arabia will move to the northeast and close the Persian Gulf. India will increasingly move towards Asia, which means the Himalayan mountains will grow. California will separate from North America along the San Andreas Fault, and a new ocean basin will begin to form in this place. Significant changes will occur in the southern hemisphere. Australia will cross the equator and come into contact with Eurasia. This forecast requires significant clarification. Much here still remains debatable and unclear.
sources
http://www.pegmatite.ru/My_Collection/mineralogy/6tr.htm
http://www.grandars.ru/shkola/geografiya/dvizhenie-litosfernyh-plit.html
http://kafgeo.igpu.ru/web-text-books/geology/platehistory.htm
http://stepnoy-sledopyt.narod.ru/geologia/dvizh/dvizh.htm
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