What is the ebb and flow. High tides in Murmansk and Arkhangelsk

Many tourists who vacationed in the resorts of Thailand or Vietnam, faced with such phenomena of nature as the tide and ebb of the sea. At a certain hour, water suddenly recedes from the usual edge, exposing the bottom. This pleases the local residents: women and children go ashore to collect not having time to evacuate along with the sheer wave of crustaceans and crabs. And at another time the sea begins to attack, and about six hours later the chaise longue is in the water. Why is this happening? What is the cause? Why, for example, on the Black Sea or the Sea of Azov we do not observe tides, and near Murmansk, the daily fluctuations in the water level are significant? Let's look at these riddles of the ocean.

Physics of the natural phenomenon

Paradoxically, the cause of tides on planet Earth is its satellite. It would seem that the common in the bottomless depth of the seas with the heavenly body? The fact is that not only the Earth keeps the Moon in orbit by its attraction. This process is mutual. The moon also has a weight (and not a small one), and therefore the forces of gravity act on our planet. A month does not raise stones, but such an easy matter, like water, can. The World Ocean seems to bend to the Moon to meet. And as the satellite of the Earth moves in its orbit (for us - over the sky), then the high water moves behind it. Unseen in the open ocean, the wave shows itself off the coast, in narrow bays and in shallow water, causing a rush. The sun also affects the force of gravity of huge masses of water. This luminous mass is much larger than that of the Month, but it is located four hundred times farther from Earth than our companion. Therefore, the solar tides are twice as weak as the lunar tides.

Tidal frequency

Logically, the highest water level should be observed at a time when the Moon is at its zenith. When the month is in the nadir, we can expect a low, outgoing wave. But a strange thing: the ebb and flow are observed twice a day. And the second time is precisely when the moon is in the nadir (a 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 with an ellipse, the elongated ends of which lie on the same axis with the Moon, and the flattened perpendicular to it. In addition, we should not discount such an important factor as the Earth's own rotation around its axis. Huge masses of water under the action of centripetal force form two waves at mutually opposite points of the planet.

Why is the power of this phenomenon heterogeneous in different points of the Earth

In theory, on all coasts, we must observe the same force of ebb and flow. Murmansk, however, can boast of the fact that its quays water rises by four meters, 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 between the water area and the World Ocean. In the inland seas - Black, Baltic, Marble, Mediterranean and even more Azov - this phenomenon is almost not felt. The water level can rise by 5-10 centimeters, no more.

Another factor that can increase tide and 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 eastern direction (opposite to the passage of the Moon), then a tidal wave drives the water upstream, sometimes several dozen kilometers from the sea. This is especially pronounced in the Amazon. The water rises to four meters. The wave moves deeper into the mainland at a speed of 25 km / h.

What affects the intensity of the phenomenon

Staying long on the same beach, we notice that on different days the tide has an unequal power. At one time the sea comes to the shore very intensely, and just as far away from it. And a week later, the tide and ebb do not differ by such force. The reason lies in the action of the Sun. We have already noted that the star also attracts the water column, although not as much as the Moon. Therefore, geography distinguishes two types of tides - syzygy and quadrature. Everything depends on the relative location of the Moon and the Sun in relation to the Earth. If the light and the satellite of our planet are on the same axis (this is called syzygy), the tides increase. When the Sun and the Moon are at right angles (quadrature), their effect on the attraction of water decreases. Then the smallest tide occurs.

Records

Where does the greatest ebb and flow occur? The first place was divided into two geographical points. Both of them are in Canada. This is the Ungava Bay north of Quebec and the Bay of Fundy, which is between Nova Scotia and New Brunswick. Here the syzygy tide reaches a mark of eighteen meters! But when the Sun and the Moon are in this area, the level of water raising is serious - fifteen and a half meters. In Europe, the largest tide is observed near the city of Saint-Malo, in the French province of Brittany. Because of the features of the coastline and the course of the English Channel, the natural phenomenon is intensified and the water reaches a height of 13.5 m.

Third place in the height of the tide (almost thirteen meters) is occupied by the Penzhinskaya Bay in the Sea of Okhotsk. This place is also the champion on the entire Pacific coast. The mouths of rivers and the prevailing winds also make their corrections to the ebb and flow. Arkhangelsk, located at the confluence of the Northern Dvina Sea, knows such a phenomenon as the Manicha. This is nothing but a tide. He drives the river waters upstream.

High tides in Murmansk

Mezensky Bay of the White Sea, too, can boast of the serious arrival of water - as much as ten meters! However, in the Murmansk port, the difference between full and low water (the height of the high tide and low tide) is not so significant - only four meters. But since the coast is shallow, the entrance to the sea is flat, then a large area is exposed. Tourists specially go to observe the ebb. Where the waves raged a few hours ago, birds are wandering about, looking for mollusks and crustaceans in pits. And in order for ships not to run aground when leaving the bay, there is a special table in the port administration, where it is calculated when a tide begins on this or that day.

Kola Bay

This is an amazing place in the Murmansk region. It is washed by the Nordkapp current, which is a branch of the Gulf Stream. Due to the huge mass of warm water, the sea does not freeze here, although the frosts on the coast can reach -24 degrees, and in the interior of the continent and all -34 degrees. In fact, the Kola Bay is a fjord, crashing into the land for 60 kilometers. In it the ebbs and ebbs are intensified by the force of the wind, which drives the sea towards the shores. The sea level at high water rises by four meters.