Many tourists who vacationed in the resorts of Thailand or Vietnam, faced with such natural phenomena as the ebb and flow of the sea. At a certain hour, the water suddenly recedes from the usual edge, exposing the bottom. This pleases the local residents: women and children come ashore to collect crustaceans and crabs who did not have time to evacuate along with the ebb wave. And at other times, the sea begins to advance, and after about six hours, a deck chair standing at a distance ends up in the water. Why is this happening? What is the reason for this? Why, for example, do we not observe tides in the Black or Azov Seas, while daily fluctuations in the water level near Murmansk are significant? Let's unravel these mysteries of the ocean.
Physics of a natural phenomenon
Paradoxical as it may seem, but the cause of the ebb and flow on the planet Earth is its satellite. It would seem thatdoes the bottomless depth of the seas have in common with a celestial body? The fact is that not only the Earth keeps the Moon in orbit with its attraction. This process is mutual. The moon also has weight (and not small), and therefore the forces of gravity also act on our planet. The Moon does not lift stones, but it can lift such light matter as water. The World Ocean seems to be arching towards the Moon. And since the Earth's satellite moves in its orbit (for us - in the sky), then high water moves behind it. Invisible in the open ocean, the wave manifests itself along the coast, in narrow bays and in shallow water, causing the tide to rise and fall. The sun also influences the force of gravity of huge masses of water. This luminary has a mass much greater than that of the Moon, but it is also four hundred times farther from the Earth than our satellite. Therefore, the solar tides are twice weaker than the lunar ones.
Frequency of high and low tides
According to the logic of things, the highest water level should be observed at the moment when the Moon is at its zenith. When the month is in the nadir, we can expect a low, outgoing wave. But the strange thing is that high and low tide are observed twice a day. And the second time is exactly when the Moon is in the nadir (the point opposite to the zenith). This is because the satellite still attracts water, even through the entire thickness of the globe. Thus, the level of the World Ocean can be compared to an ellipse, the elongated ends of which lie on the same axis as the Moon, while the flattened ends are perpendicular to it. In addition, one should not discount such an important factor as one's ownrotation of the earth around its axis. Huge masses of water under the action of centripetal force form two waves at mutually opposite points of the planet.
Why the strength of this phenomenon is not uniform at different points of the Earth
In theory, on all coasts, we should observe the same strength of the tides. Murmansk, however, can boast that the water rises four meters along its embankments, while in the Gulf of Finland off the coast of St. Petersburg this natural phenomenon is barely noticeable, and even then only in shallow water. The main factor that enhances the manifestation of the tide is the connection of the water area with the World Ocean. In the inland seas - the Black, B altic, Marmara, Mediterranean, and even more so the Azov - this phenomenon is almost not felt. The water level can rise by 5-10 centimeters, no more.
Another factor that can increase the ebb and flow of the tide is the ruggedness of the coast. In narrow bays with a shallow bottom, these phenomena are expressed more powerfully. If the mouth of the river has an easterly direction (opposite to the passage of the Moon), then the tidal wave drives the water upstream, sometimes several tens of kilometers from the sea. This is especially true in the Amazon. The water rises up to four meters. The wave moves deep into the mainland at a speed of 25 km/h.
What affects the intensity of the phenomenon
Staying on the same beach for a long time, we notice that on different days the tide has unequal strength. At one time, the sea comes ashore very intensively, and justfar away from him. And a week later, the ebb and flow are no longer so strong. The reason lies in the action of the Sun. We have already noted that the luminary also attracts the water column, although not as strongly as the Moon. Therefore, in geography, two types of tides are distinguished - syzygy and quadrature. It all depends on the relative position of the Moon and the Sun in relation to the Earth. If the luminary and the satellite of our planet are on the same axis (this is called syzygy), the tides increase. When the Sun and Moon are at right angles (square), their effect on the attraction of water is reduced. Then the smallest tide occurs.
Record breakers
Where do the highest tides occur? The first place was shared by two geographical points. Both are in Canada. These are the Ungava Bay north of Quebec and the Bay of Fundy between Nova Scotia and New Brunswick. Here the spring tide reaches eighteen meters! But even when the Sun and Moon are in this area, the level of water rise is serious - fifteen and a half meters. In Europe, the highest tide is observed near the city of Saint-Malo, in the French province of Brittany. Due to the peculiarities of the coastline and the current of the English Channel, the natural phenomenon intensifies and the water height reaches 13.5 m.
The third place in terms of the height of the tide (almost thirteen meters) is occupied by the Penzhinskaya Bay in the Sea of Okhotsk. This place is also a record holder on the entire Pacific coast. The mouths of the rivers and the prevailing winds also make their own adjustments to the tides. Arkhangelsk,located at the confluence of the Northern Dvina into the sea, knows such a phenomenon as maniha. It's nothing but a tide. He drives river waters upstream.
Ebb and flow in Murmansk
The Mezen Bay of the White Sea also boasts a serious arrival of water - as much as ten meters! However, in the Murmansk port itself, the difference between high and low water (the height of the end of high and low tide) is not so significant - only four meters. But since the coast here is shallow, the entrance to the sea is gentle, a large territory is exposed. Tourists specially go to watch the ebb. Where the waves raged a few hours ago, birds roam, looking for mollusks and crustaceans in the pits. And so that ships do not run aground when leaving the bay, the port authority has a special table where it is calculated when the tide begins on a particular day.
Kola Bay
This is an amazing place in the Murmansk region. It is washed by the North Cape Current, which is an offshoot of the Gulf Stream. Thanks to the huge masses of warm water, the sea does not freeze here, although frosts on the coast can reach temperatures of -24, and in the depths of the mainland and all -34 degrees. In fact, the Kola Bay is a fjord that cuts into the land for 60 kilometers. In it, the tides are amplified by the force of the wind, which drives the sea towards the shores. The sea level at high water rises by four meters.
