§ 42. Waves in the Ocean (textbook)

§ 42. Waves in Ocean

 

Did you watch the waves on the surface Sea (lake, reservoir)? Tell us what you think.

 

The emergence of waves. Water World the ocean is constantly moving. Nabihayut it ashore, then vidkochuyutsya wave. Water waves does not move in horizontal direction. This is easy to verify watching the float on the water. With the approaching waves it rises to its crest and then falls on its sole (Fig.). It does not float close to shore and away from it. He just swinging at Waves: up-down. This indicates that water makes waves in vertical movements, called vibrational. Movement water in waves is comparable to the wheat field, which worried the wind. At This same wheat as the field will not move.

Near shelving shore wave "feels" the bottom. From friction him move to the bottom stalled. A wave crest runs, bends forward and spreads. There surf. Ashore nabihaye scummy water shaft. Meet him with water flowing down the coast the previous wave.

The main cause of waves is wind. It seems vdavlyuye water surface and displays her off balance. Even a gentle breeze creates waves. Typically, wave height is exceeding 4 m. The highest waves over 20 m caused by storm winds. The largest of wind waves height of 34 m (a height of 10-storey building) was seen in the central part of the Pacific Ocean in 1933 when the wind is made weak, high waves rippling change - low anxiety. The stronger and wind longer and more water space, the higher the waves. With the depth anxiety is reduced and becomes noticeable.

Waves perform destructive and creative work. In some places they are hitting with power at shore shattering rocks, which he made. On the banks of the Black Sea power shock wave can reach 25 tons per 1 m2. Not every building will stand such pressure. This water rises up to a height of 60 m. During storm waves are able to move stones weighing several tons. To protect coasts and port facilities from destruction, build breakwaters with special reinforced concrete slabs. Creative work of waves - the crushed particles and delay a sandy and pebbly beaches. In addition, the wave mixing water contribute to enriching it with oxygen and heat. It promotes life of organisms in Ocean.

 

Fig. Destructive waves work

 

Fig. Wind waves

 

Tsunami. You already know sometimes cause the formation of waves are underwater earthquakes and eruptions volcanoes. They cause huge waves - tsunamis that spread in all directions the place of occurrence and cover the whole water column from bottom to surface. Tsunami roll through all the ocean at speeds of jet aircraft - more than 700 km / hr. These waves are powerful, that reaches the coast, are reflected from them and they go forward in opposite direction.

Height Tsunami in the open ocean is small - up to 1 m at a wavelength of 200 km. So among the great excitement of water areas and tsunami can not miss. Everything is changing its approach to the shore. Before the tsunami the sea, exposing the bottom, recedes from the shores of hundreds of meters, as if to run. And then rapidly nakochuyetsya wave. Sandwiched in the narrow banks of the harbor, it grows to 20-30 That is why the city literally Japanese word "tsunami" is translated as "wave in the harbor. A wall of water tsunami with all your weight falls on the coast. It overturns the ship, destroying the building, and retreating, the ocean is all that happens on its way. Most tsunamis occur in West Pacific coast. It is impossible to prevent. You can only advance warn of approaching tsunamis.

The flow and ebb. From time immemorial observed that every 6 h water level in the World Ocean it rises, then falls. Water that comes ashore and moving away dry, then refuse it, exposing the bottom. Lift level of the ocean is called influx, and its decline - outflow. On the coast Sea tidal zone width reaches sometimes several kilometers. In the flow there You can float a boat and fish. In the ebb - walk down and collect shells, algae, marine animals.

The flow - It is also a wave. They are caused by gravity of the moon and sun. Together they manage attracted to their side and flowing liquid water oceans on a few meters, creating a tidal wave. Unlike usual, it has vseplanetnyy nature of the action. The huge water space of the oceans is rising, then falls, as if breathing.

Stretching "Spring water" Oceans Month and less sun cause tides and ebb as scheduled - twice a day. The flow and ebb, like day and night, come to our planet with good precision clock. The timing and tidal height is not always the same. In the open ocean to less than 1 m height, because there are not noticeable. High tides occur a few meters in narrow straits and bays, mouths of rivers. Thus, the rise of tide in Black Sea only a few centimeters, and in narrow bays Okhotsk Seareaches 13 m. The highest is in the world ocean tides, which reach 18 m, observed Gulf Fundy off the east coast of North America.

Mariner long were made special table allowing ships to carry view hot or cold wave. These days, computers are replaced by tables. Tidal waves have tremendous energy, which people began to use receive electricity.

 

Fig. Ebbin North Sea

 

 

FAQ task

1. As the wind generated waves in the ocean?

2. What job do the wave?

3. What force causes tides and ebb of the Earth?

4. How long tsunami that occurred off the coast of Chile, could reach Japan?