6. Sea waves.
© Vladimir Kalanov,
"Knowledge is power".
The surface of the sea is always moving, even with complete calm. But then the wind blew, and ripples immediately appeared on the water, which turned into waves the faster the stronger the wind blew. But no matter how strong the wind is, it cannot cause waves larger than certain maximum sizes.
Waves generated by wind are considered short. Depending on the strength and duration of the wind, their length and height range from several millimeters to tens of meters (in a storm, the length of wind waves reaches 150-250 meters).
Observations of the sea surface show that waves become strong even at wind speeds of more than 10 m/s, while the waves rise to a height of 2.5-3.5 meters, crashing onto the shore with a roar.
But then the wind turns storm, and the waves reach enormous sizes. There are many places on the globe where very strong winds blow. For example, in the northeastern part of the Pacific Ocean east of the Kuril and Commander Islands, as well as east of the main Japanese island of Honshu in December-January maximum speeds winds are 47-48 m/s.
In the South Pacific, maximum wind speeds are observed in May in the area northeast of New Zealand (49 m/s) and near the Antarctic Circle in the area of Balleny and Scott Islands (46 m/s).
We perceive speeds expressed in kilometers per hour better. So the speed of 49 m/s is almost 180 km/h. Already at a wind speed of more than 25 m/s, waves 12-15 meters high rise. This degree of excitement is rated 9–10 points as a severe storm.
Measurements have established that the height of the storm wave in the Pacific Ocean reaches 25 meters. There are reports that waves up to 30 meters high have been observed. True, this assessment was made not on the basis of instrumental measurements, but approximately, by eye.
IN Atlantic Ocean maximum height wind waves reach 25 meters.
The length of storm waves does not exceed 250 meters.
But the storm stopped, the wind died down, but the sea still did not calm down. Like the echo of a storm on the sea arises swell. Swell waves (their length reaches 800 meters or more) move over enormous distances of 4-5 thousand km and approach the shore at a speed of 100 km/h, and sometimes higher. In the open sea, low and long swell waves are invisible. When approaching the shore, the speed of the wave decreases due to friction with the bottom, but the height increases, the front slope of the wave becomes steeper, foam appears at the top, and the crest of the wave crashes onto the shore with a roar - this is how the surf appears - a phenomenon equally colorful and majestic, as dangerous as it is. The force of the surf can be colossal.
When faced with an obstacle, the water rises to a great height and damages lighthouses, port cranes, breakwaters and other structures. Throwing stones from the bottom, the surf can damage even the highest and most distant parts of lighthouses and buildings. There was a case when the surf tore a bell from one of the English lighthouses from a height of 30.5 meters above sea level. The surf on our Lake Baikal sometimes in stormy weather throws stones weighing up to a ton at a distance of 20-25 meters from the shore.
During storms in the Gagra region, the Black Sea eroded and swallowed up a 20-meter-wide coastal strip over 10 years. When approaching the shore, the waves begin their destructive work from a depth equal to half their length in the open sea. Thus, with a storm wave length of 50 meters, characteristic of seas such as the Black or Baltic, the impact of waves on the underwater coastal slope begins at a depth of 25 m, and with a wave length of 150 m, characteristic of the open ocean, such impact begins already at a depth of 75 m.
Current directions affect the size and strength of sea waves. With countercurrents, the waves are shorter but higher, and with countercurrents, on the contrary, the height of the waves decreases.
Near the boundaries of sea currents, waves of unusual shapes, resembling a pyramid, and dangerous whirlpools often appear, which suddenly appear and just as suddenly disappear. In such places, navigation becomes especially dangerous.
Modern ships have high seaworthiness. But it happens that, having traveled many miles across the stormy ocean, the ships find themselves still in greater danger than at sea when they come to their native bay. The powerful surf, breaking the multi-ton reinforced concrete breakwaters of the dam, is capable of turning even a large ship into a pile of metal. In a storm, it is better to wait until entering the port.
To combat the surf, specialists in some ports tried to use air. Steel pipe with numerous small holes was laid on the bottom of the sea at the entrance to the bay. Air under high pressure was supplied into the pipe. Escaping from the holes, streams of air bubbles rose to the surface and destroyed the wave. This method has not yet found widespread use due to insufficient efficiency. Rain, hail, ice and thickets of marine plants are known to calm waves and surf.
Sailors have long noticed that fat poured overboard smoothes the waves and reduces their height. Animal fat, such as whale blubber, works best. The effect of vegetable and mineral oils is much weaker. Experience has shown that 50 cm 3 of oil is enough to reduce disturbances over an area of 15 thousand square meters, that is, 1.5 hectares. Even a thin layer of oil film noticeably absorbs the energy of vibrational movements of water particles.
Yes, that's all true. But, God forbid, we under no circumstances recommend that captains of sea vessels stock up on fish or whale oil before a voyage in order to then pour these fats into the waves to calm the ocean. After all, things can reach such an absurdity that someone starts dumping oil, fuel oil, and diesel fuel to calm the waves.
It seems to us that The best way combating waves consists of a well-organized weather service that notifies ships in advance about the expected place and time of the storm and its expected strength, good navigational and pilot training of sailors and coastal personnel, as well as constant improvement of the design of ships in order to improve their seaworthiness and technical capabilities. reliability.
For scientific and practical purposes, you need to know the full characteristics of the waves: their height and length, the speed and range of their movement, the power of an individual water shaft and the wave energy in a particular area.
The first measurements of waves were made in 1725 by the Italian scientist Luigi Marsigli. At the end of the 18th – beginning of the 19th centuries, regular observations of waves and their measurements were carried out by Russian navigators I. Kruzenshtern, O. Kotzebue and V. Golovin during their voyages across the World Ocean. The technical basis for measurements in those days was very weak; of course, there were no special instruments for measuring waves on the sailing ships of that time.
Currently, for these purposes, there are very complex and precise instruments that are equipped with research vessels that carry out not only measurements of wave parameters in the ocean, but also much more complex scientific work. The ocean still holds many secrets, the disclosure of which could bring significant benefits to all of humanity.
When they talk about the speed of movement of waves, that waves run up and roll onto the shore, you need to understand that it is not the water mass itself that moves. The water particles that make up the wave forward movement practically do not do it. Only the wave form moves in space, and water particles in a rough sea perform oscillatory movements in the vertical and, to a lesser extent, in the horizontal plane. The combination of both oscillatory movements leads to the fact that the water particles in the waves actually move in circular orbits, the diameter of which is equal to the height of the wave. The oscillatory movements of water particles quickly decrease with depth. Precise instruments show, for example, that with a wave height of 5 meters (storm wave) and a length of 100 meters, at a depth of 12 meters the diameter of the wave orbit of water particles is already 2.5 meters, and at a depth of 100 meters - only 2 centimeters.
Long waves, unlike short and steep ones, transmit their motion to great depths. In some photographs of the ocean floor down to a depth of 180 meters, researchers noted the presence of sand ripples formed under the influence of oscillatory movements of the bottom layer of water. This means that even at such a depth, the surface waves of the ocean make themselves felt.
Is it necessary to prove what danger a storm wave poses to ships?
In the history of navigation, there are countless tragic incidents at sea. Small longboats and high-speed sailing ships, along with their crews, perished. Modern ocean liners are not immune to the insidious elements.
On modern ocean-going ships, among other devices and instruments that ensure safe navigation, pitch stabilizers are used, which prevent the ship from getting an unacceptably large roll on board. In some cases, powerful gyroscopes are used for this, in others, retractable hydrofoils are used to level the position of the ship’s hull. Computer systems on ships are in constant communication with meteorological satellites and other spacecraft, which tell navigators not only the location and strength of storms, but also the most favorable course in the ocean.
In addition to surface waves, there are also internal waves in the ocean. They form at the interface between two layers of water of different densities. These waves travel slower than surface waves, but can have greater amplitude. Internal waves are detected by rhythmic changes in temperature at different depths of the ocean. The phenomenon of internal waves has not yet been sufficiently studied. It has only been established that waves arise at the boundary between layers with lower and higher densities. The situation may look like this: there is complete calm on the surface of the ocean, but at some depth a storm is raging; along the length, internal waves are divided, like ordinary surface ones, into short and long. Short waves have a much longer length less depth, and for long ones, on the contrary, the length exceeds the depth.
There are many reasons for the appearance of internal waves in the ocean. The interface between layers with different densities can be thrown out of balance by a moving large vessel, surface waves, or sea currents.
Long internal waves manifest themselves, for example, in this way: a layer of water, which is a watershed between more dense (“heavy”) and less dense (“light”) water, first rises slowly, for hours, and then suddenly falls by almost 100 meters. This wave is very dangerous for submarines. After all, if a submarine sank to a certain depth, it means it was balanced by a layer of water of a certain density. And suddenly, unexpectedly, a layer of less dense water appears under the hull of the boat! The boat immediately falls into this layer and sinks to the depth where the less dense water can balance it. But the depth may be such that the water pressure exceeds the strength of the hull of the submarine, and it will be crushed in a matter of minutes.
By conclusion American specialists, who were investigating the causes of the sinking of the nuclear submarine Thresher in 1963 in the Atlantic Ocean, this submarine found itself in exactly this situation and was crushed by enormous hydrostatic pressure. Naturally, there were no witnesses to the tragedy, but the version of the cause of the disaster is confirmed by the results of observations carried out by research ships in the area where the submarine sank. And these observations showed that internal waves with a height of more than 100 meters often arise here.
A special type are waves that occur at sea when atmospheric pressure changes. They're called seiches And microseiches. Oceanology studies them.
So, we talked about both short and long waves at sea, both surface and internal. Now let us remember that long waves arise in the ocean not only from winds and cyclones, but also from processes occurring in the earth’s crust and even in the deeper regions of the “interior” of our planet. The length of such waves is many times greater than the longest ocean swell waves. These waves are called tsunami. The height of tsunami waves is not much higher than large storm waves, but their length reaches hundreds of kilometers. The Japanese word "tsunami" roughly translates to "harbour wave" or "coastal wave" . To some extent, this name conveys the essence of the phenomenon. The point is that in open ocean a tsunami poses no danger. At a sufficient distance from the coast, the tsunami does not rage, does not cause destruction, and cannot even be noticed or felt. All tsunami disasters occur on the shore, in ports and harbors.
Tsunamis occur most often from earthquakes caused by the movement of tectonic plates earth's crust, as well as from strong volcanic eruptions.
The mechanism for the formation of a tsunami is most often as follows: as a result of the displacement or rupture of a section of the earth's crust, a sudden rise or fall of a significant section of the seabed occurs. As a result, a rapid change in the volume of the water space occurs, and elastic waves appear in the water, propagating at a speed of about one and a half kilometers per second. These powerful elastic waves generate tsunamis on the ocean surface.
Having arisen on the surface, tsunami waves scatter in circles from the epicenter. At the point of origin, the height of the tsunami wave is small: from 1 centimeter to two meters (sometimes up to 4-5 meters), but more often in the range from 0.3 to 0.5 meters, and the wave length is huge: 100-200 kilometers. Invisible in the ocean, these waves, approaching the shore, like wind waves, become steeper and higher, sometimes reaching a height of 10-30 and even 40 meters. Having hit the shore, tsunamis destroy and destroy everything in their path and, worst of all, bring death to thousands, and sometimes tens and even hundreds of thousands of people.
The speed of tsunami propagation can be from 50 to 1000 kilometers per hour. Measurements show that the speed of a tsunami wave varies proportionally square root from the depths of the sea. On average, a tsunami rushes across the open ocean at a speed of 700-800 kilometers per hour.
Tsunamis are not regular events, but they are no longer rare.
In Japan, tsunami waves have been recorded for more than 1,300 years. Average per Country rising sun destructive tsunamis struck every 15 years (small tsunamis that did not have serious consequences are not taken into account).
Most tsunamis occur in the Pacific Ocean. Tsunamis raged in the Kuril, Aleutian, Hawaiian, and Philippine islands. They also attacked the coasts of India, Indonesia, Northern and South America, as well as to European countries located on Atlantic coast and in the Mediterranean.
The last most destructive tsunami attack was the terrible flood of 2004 with enormous destruction and loss of life, which had seismic causes and originated in the center of the Indian Ocean.
In order to have an idea of the specific manifestations of a tsunami, you can refer to numerous materials that describe this phenomenon.
We will give just a few examples. This is how the results of the earthquake that occurred in the Atlantic Ocean not far from the Iberian Peninsula on November 1, 1755 were described in the press. It caused terrible destruction in the capital of Portugal, Lisbon. The ruins of the once majestic building still tower in the city center convent Karmo that was never restored. These ruins remind the people of Lisbon of the tragedy that struck the city on November 1, 1755. Shortly after the earthquake, the sea receded, and then a wave 26 meters high hit the city. Many residents, fleeing the falling debris of buildings, left the narrow streets of the city and gathered on the wide embankment. The surging wave washed away 60 thousand people into the sea. Lisbon was not completely flooded because it is located on several high hills, but in low-lying areas the sea flooded the land up to 15 kilometers from the coast.
On August 27, 1883, there was a powerful eruption of the Kratau volcano, located in the Sunda Strait of the Indonesian archipelago. Clouds of ash rose into the sky, a strong earthquake arose, generating a wave 30-40 meters high. In a few minutes, this wave washed away all the villages located on the low shores of western Java and southern Sumatra into the sea, killing 35 thousand people. At a speed of 560 kilometers per hour, tsunami waves swept through the Indian and Pacific Oceans, reaching the shores of Africa, Australia and America. Even in the Atlantic Ocean, despite its isolation and remoteness, in some places (France, Panama) a certain rise in water was noted.
On June 15, 1896, the incoming tsunami waves destroyed the east coast Japanese island Honshu 10 thousand houses. As a result, 27 thousand inhabitants died.
It is impossible to fight a tsunami. But it is possible and necessary to minimize the damage they cause to people. Therefore, now in all seismically active areas where there is a threat of tsunami waves, special services warnings equipped with the necessary equipment that receives signals about changes in the seismic situation from sensitive seismographs located in different places on the coast. The population of such areas is regularly instructed on the rules of behavior in the event of a threat of tsunami waves. Tsunami warning services in Japan and Hawaiian Islands More than once they have given timely warning signals about the approaching tsunami, thereby saving more than one thousand human lives.
All types of currents and waves are characterized by the fact that they carry colossal energy - thermal and mechanical. But humanity is not able to use this energy, unless, of course, we count attempts to use the energy of ebbs and flows. One of the scientists, probably a lover of statistics, calculated that the power of sea tides exceeds 1000000000 kilowatts, and all rivers globe– 850000000 kilowatts. The energy of one square kilometer of a stormy sea is estimated at billions of kilowatts. What does this mean for us? Only that a person cannot use even a millionth part of the energy of tides and storms. To some extent, people use wind energy to generate electricity and other purposes. But that, as they say, is another story.
© Vladimir Kalanov,
"Knowledge is power"
People take many natural phenomena for granted. We are accustomed to summer, autumn, winter, rain, snow, waves and do not think about the reasons. And yet, why do waves form in the sea? Why do ripples appear on the surface of the water even in complete calm?
Origin
There are several theories explaining the occurrence of sea and ocean waves. They are formed due to:
- changes in atmospheric pressure;
- ebbs and flows;
- underwater earthquakes and volcanic eruptions;
- ship movements;
- strong wind.
To understand the mechanism of formation, you need to remember that water is agitated and vibrates forcibly - as a result of physical impact. A pebble, a boat, or a hand touching it set the liquid mass in motion, creating vibrations of varying strengths.
Characteristics
Waves are also the movement of water on the surface of a reservoir. They are the result of the adhesion of air particles and liquid. At first, the water-air symbiosis causes ripples on the surface of the water, and then causes the water column to move.
Size, length and strength vary depending on the strength of the wind. During a storm, powerful pillars rise 8 meters and stretch almost a quarter of a kilometer in length.
Sometimes the force is so destructive that it hits the coastal strip, uproots umbrellas, showers and other beach buildings, and demolishes everything in its path. And this despite the fact that oscillations are formed several thousand kilometers from the coast.
All waves can be divided into 2 categories:
- wind;
- standing.
Wind
Wind ones, as the name suggests, are formed under the influence of wind. Its gusts sweep tangentially, pumping the water and forcing it to move. The wind pushes the liquid mass forward in front of it, but gravity slows down the process, pushing it back. Movements on the surface resulting from the influence of two forces resemble ascents and descents. Their peaks are called ridges, and their bases are called soles.
Having found out why waves form on the sea, the question remains open: why do they make oscillatory movements up and down? The explanation is simple - the variability of the wind. It flies in quickly and impetuously, then subsides. The height of the ridge and the frequency of oscillations directly depend on its strength and power. If the speed of movement and the strength of air currents exceed the norm, a storm arises. Another reason is renewable energy.
Renewable Energy
Sometimes the sea is completely calm, but waves form. Why? Oceanographers and geographers attribute this phenomenon to renewable energy. Water vibrations are its source and ways to maintain the potential for a long time.
In life it looks something like this. The wind creates a certain amount of vibrations in a body of water. The energy of these vibrations will last for several hours. During this time, liquid formations cover distances of tens of kilometers and “moor” in areas where it is sunny, there is no wind, and the body of water is calm.
standing
Standing or single waves arise due to tremors on the ocean floor, characteristic of earthquakes, volcanic eruptions, and also due to a sharp change in atmospheric pressure.
This phenomenon is called seiche, which translates from French like "swinging". Seiches are typical for bays, bays and some seas; they pose a danger to beaches, structures in the coastal strip, ships moored at the pier and people on board.
Constructive and destructive
Formations that travel long distances without changing shape or losing energy hit the shore and break. Moreover, each surge has a different effect on the coastal strip. If it washes the shore, it is classified as constructive.
The destructive surge of water hits the coast with its might, destroying it, gradually washing away sand and pebbles from the beach strip. In this case a natural phenomenon classified as destructive.
Destruction comes in different destructive powers. Sometimes it is so powerful that it collapses slopes, splits cliffs, and separates rocks. Over time, even the hardest rocks erode. America's largest lighthouse was built at Cape Hatteras in 1870. Since then, the sea has moved almost 430 meters into the coast, washing away the coastal strip and beaches. This is just one of dozens of facts.
Tsunami is a type of destructive water formations characterized by large destructive force. Their speed reaches up to 1000 km/h. This is higher than jet plane. At depth, the height of the tsunami crest is small, but near the shore they slow down, but increase in height to 20 meters.
In 80% of cases, tsunamis are the result of underwater earthquakes, in the remaining 20% - volcanic eruptions and landslides. As a result of earthquakes, the bottom shifts vertically: one part of it goes down, and the other part rises in parallel. Vibrations of varying strengths are formed on the surface of the reservoir.
Abnormal killers
They are also known as wanderers, monsters, anomalous and more common in the oceans.
Even 30-40 years ago, sailors’ stories about abnormal water fluctuations were considered fables, because in the existing scientific theories and the calculations of the eyewitness accounts did not fit. A height of 21 meters was considered the limit for oceanic and sea fluctuations.
The first written mention of monsters dates back to 1826. And in 1933 the ship US Navy, caught in a prolonged storm, collided with giant wave. The crew miraculously survived - eyewitnesses confirmed the fact. Similar cases were recorded subsequently.
January 1, 1995, when the devices installed on oil platform, for the first time an anomalous 25.6-meter column of water was officially recorded, scientists began to study the phenomenon. Over the next 3 weeks of the study, 10 more similar events occurred in different corners planets.
The reasons for the formation of extreme waves are not fully understood; they exist at the level of hypotheses. One theory explains the phenomenon by nonlinearity effects, as a result of which small groups of waves are formed and travel long distances without changing the original structure.
In other words, under the influence internal factors a 20-meter block of water formed and traveled tens of kilometers without changing its original shape. But, again, this is one theory. There is no explanation confirmed by facts yet, but the fact of the phenomenon has already been scientifically confirmed and is not disputed.
Why are there waves on the sea?
5 (100%) 1 votedSea waves
Sea waves
periodic oscillations of the surface of the sea or ocean caused by back-and-forth or circular movements of water. Depending on the reasons causing the movement, wind waves, tidal waves ( tides And low tides), pressure (seiches) and seismic ( tsunami). The waves are characterized height, equal to the vertical distance between the crest and the bottom of the wave, length– horizontal distance between two adjacent ridges, speed of spread And period. For wind waves it lasts approx. 30 s, for pressure and seismic - from several minutes to several hours, for tidal it is measured in hours.
Most common in reservoirs wind waves. They are formed and developed thanks to wind energy, transferred water due to friction and by the pressure of the air flow on the slopes of wave crests. They always exist in the open ocean and can have a wide variety of sizes, reaching lengths. up to 400 m, altitude 12–13 m and propagation speed 14–15 m/s. Max. registered high wind waves are 25–26 m, and more is possible high waves. In the initial stage of development, wind waves run in parallel rows, which then break up into separate crests. In deep water, the size and nature of the waves are determined by the speed of the wind, the duration of its action and the distance from the leeward space; shallow depths limit wave growth. If the wind that caused the disturbance subsides, then the wind waves turn into the so-called. swell. It is often observed simultaneously with wind waves, although not always coinciding with them in direction and height. 
In the surf zone, so-called surf beats– periodic rises in water level when a group of high waves approaches. High the rise can be from 10 cm to 2 m, rarely up to 2.5 m. Seiches are usually observed in limited bodies of water (seas, bays, straits, lakes) and are standing waves, most often caused by a rapid change in the atmosphere. pressure, less often due to other reasons (sudden influx of flood waters, heavy rains etc.). Once caused, the deformation of the water level leads to gradually damped oscillations in it. At the same time, at some points the water level remains constant - this is the so-called. nodes standing wave. High Such waves are insignificant - usually a few tens of centimeters, rarely up to 1–2 m.
Geography. Modern illustrated encyclopedia. - M.: Rosman. Edited by prof. A. P. Gorkina. 2006 .
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The formation of waves on the surface of water is called disturbance.
Waves observed on the surface of water are divided into:
- Friction waves:
- wind, formed as a result of the action of wind
- deep
- Tidal waves.
- Gravitational waves:
- gravitational waves in shallow water
- gravitational waves in deep water
- seismic waves (tsunamis) that arise in the oceans as a result of an earthquake (or volcanic activity) and reach a height of 10-30 m off the coast.
- ship waves
IN coastal areas In the sea, only wind waves (friction waves) are significant.
Wind waves arise with the wind; when the wind stops, these waves in the form of a dead swell, gradually fading, continue to move in the same direction. Wind waves depend on the size of the water space open for wave acceleration, wind speed and time of action in one direction, as well as depth. As the depth decreases, the wave becomes steeper.
Wind waves are asymmetrical, their windward slope is gentle, their leeward slope is steep. Since the wind acts more strongly on the upper part of the wave than on the lower part, the wave crest crumbles, forming “lambs”. In the open sea, "lamblets" are formed in a wind that is called "fresh" (wind force 5 and a speed of 8.0-10.7 m/s, or 33 km/h).
Swell- excitement that continues after the wind has already died down, weakened or changed direction. A disturbance that spreads by inertia in complete calm is called a dead swell.
When waves from different directions meet in a certain area, a crush. The chaotic accumulation of waves formed when direct waves meet reflected ones is also crush.
When waves pass over banks, reefs and rocks, breakers.
The approach of waves onto the shore with an increase in height and steepness and subsequent capsizing is called surf.
The surf gets different character depending on which shore: shallow (having small angles of inclination and greater width underwater slope) or deep (having significant slopes of the underwater slope).
The overturning of the crest of a moving wave onto a steep bank forms reverse faults having great destructive power.
© Yuri Danilevsky: November storm. Sevastopol
When the surf occurs near a deep shore that rises steeply from the water, the wave breaks up only when it hits the shore. This creates reverse wave, meeting the next one and reducing its impact force, and then a new wave comes and hits the shore again.
Such wave impacts in the case of a large swell or strong waves are often accompanied by surges of waves to a considerable height.
© Storm in Sevastopol, November 11, 2007
On the shores of the Black Sea, the wave impact force can reach 25 tons per 1 m 2.
When upturning, the wave gains enormous force. On the Shetland Islands, north of Scotland, there are fragments of gneiss rocks weighing up to 6-13 tons, thrown by the surf to a height of 20 m above sea level.
The rapid movement of waves and swell onto the shore is called roll forward.
Waves are regular when their crests are clearly visible, and irregular when the waves do not have clearly defined crests and are formed without any visible pattern.
Wave crests perpendicular to the wind direction in the open sea, lake, reservoir, but near the shore they take a position parallel to the coastline, running onto the banks.
The direction of wave propagation in the open sea is indicated on the surface of the water by a family of parallel stripes of foam - the traces of collapsing wave crests.
How are waves formed? Surf condition reports and wave formation forecasts are compiled based on the results scientific research and weather modeling. In order to find out what waves will be formed in soon, it is important to understand how they are formed.
The main cause of wave formation is wind. waves, the best way suitable for surfing, are formed as a result of the interaction of winds above the surface of the ocean, away from the coast. The action of wind is the first stage of wave formation.
Winds blowing offshore in a particular area can also cause waves, but they can also lead to deterioration in the quality of breaking waves.
It has been found that winds blowing from the sea tend to produce unstable and uneven waves as they affect the direction of wave travel. The winds blowing from the coast serve, in a certain sense, as a kind of balancing force. The wave travels many kilometers from the depths of the ocean to the shore, and the wind from land has a “braking” effect on the face of the wave, allowing it to avoid breaking longer.
Low pressure areas = good waves for surfing
Theoretically, areas low pressure contribute to the formation of good, powerful waves. In the depths of such areas, wind speeds are higher and wind gusts form more waves. The friction created by these winds helps create powerful waves that travel thousands of kilometers until they hit their final obstacles, the coastal areas where people live.
If winds generated in areas of low pressure continue to blow on the ocean surface for a long time, the waves become more intense as energy accumulates in all the resulting waves. In addition, if winds from areas of low pressure affect a very large area of the ocean, then all the resulting waves concentrate even more energy and power, which leads to the formation of even larger waves.
From ocean waves to surf waves: the seabed and other obstacles
We have already analyzed how disturbances in the sea and the waves generated by them are formed, but after “birth” such waves still have to travel a huge distance to the shore. Waves originating in the ocean have a long journey to travel before they reach land.
During their journey, before surfers even get on them, these waves will have to overcome other obstacles. The height of the emerging wave does not match the height of the waves the surfers are riding.
As waves move through the ocean, they are exposed to irregularities in the seabed. When gigantic moving masses of water overcome heights of seabed, total the energy concentrated in the waves changes.
For example, continental shelves far from the coast offer resistance to moving waves due to the force of friction, and by the time the waves reach coastal waters, where the depth is shallow, they have already lost their energy, strength and power.
When waves move through deep-sea waters without encountering obstacles on their way, they usually crash into coastline with great strength. Depths ocean floor and their changes over time are studied through bathymetric studies.
Using the depth map, it is easy to find the deepest and shallowest waters of the oceans of our planet. Studying the topography of the seabed has great importance to prevent shipwrecks and cruise liners.
In addition, studying the structure of the bottom can provide valuable information for predicting the surf at a particular surf spot. When waves reach shallow water, their speed usually decreases. Despite this, the wavelength shortens and the crest increases, resulting in an increase in wave height.
Sandbanks and wave crest increase
Sandbanks, for example, always change the nature of beach breaks. This is why the quality of waves changes over time, for better or worse. Sandy irregularities on the ocean floor allow the formation of distinct, concentrated wave crests from which surfers can begin their slide.
When a wave encounters a new sandbar, it will typically form a new crest, since such an obstacle causes the crest to rise, that is, the formation of a wave suitable for surfing. Other obstacles to waves include groins, sunken vessels, or simply natural or artificial reefs.
Waves are generated by the wind and, as they move, are influenced by the topography of the seabed, precipitation, tides, rip currents off the coasts, local winds and bottom irregularities. All these weather and geological factors contribute to the formation of waves suitable for surfing, kitesurfing, windsurfing and boogie surfing.
Wave forecasting: theoretical foundations
- Waves with long period, as a rule, larger and more powerful.
- Waves with short period, as a rule, smaller and weaker.
- The wave period is the time between the formation of two clearly defined crests.
- Wave frequency is the number of waves passing through a certain point in a certain time.
- Big waves move fast.
- Small waves move slowly.
- Intense waves form in areas of low pressure.
- Low pressure areas are characterized by rainy and cloudy weather.
- For regions high pressure characteristic warm weather and clear skies.
- Larger waves form in deep coastal areas.
- Tsunamis are not suitable for surfing.
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