§ 26. Bevel the bottom of the oceans (textbook)

§ 26. Bevel the bottom of the oceans


Remember what type of oceanic crust different from the mainland.


Relief Ocean Floor. Bevel the bottom of the oceans is buried under thickness water. Distinctions inequality it can be depth. Measure their echo-sounder. This device sends a ship in water sounds. They reach the bottom of it and bounce back back. Researchers record the time that the sound went to the bottom and back. Knowing the speed of sound in water (1 500 m / s), you can determine the depth Ocean. Now come to the aid of space and underwater vehicles capable of photograph ocean floor.

This helped to map the seabed topography and Oceans. They make it possible to see that relief ocean floor not less complicated than on land. Each physical map, along with the scale heights accommodate the scale and depth. Using it, you can determine the depth of the seas and Oceans. It turned out that at the bottom, as on land, major landforms are underwater mountains and plains. In addition, clearly defined parts of the ocean bottom: pidvodna margin,bed and the Mid-ocean ridges.


Fig. Relief of the ocean floor


Margin. Boundary between mainlands and oceans is no coastline, and under water. Part of continental crust continues under the ocean. Therefore this part of the floor and was named continental margin. Along the stretches of continents шelf (shelf). This plot really shallow: up to 200 m deep. Underwater shelf is slightly inclined plain. Its width varies. The shelf is covered with loose sedimentary rocks, brought by rivers from land.

Deeper, 3000 m, is located Mainland slope. It's quite a steep escarpment. In many places, it cut deep valleys. The bottom part looks like a slope inclined wavy plain.

Where marginal goes to bed Ocean, located deep sea. From the ocean to frame chains of islands. These islands are vast underwater ridges and peaks that rise above the water. To islands adjacent deep gutters. This long and narrow hollows with steep slopes that have considerable depth (more than 6 000 m). A striking example of this combination is Sea of Okhotsk, Kuril Islands і Kuril-Kamchatka gutter. Transitional zones are zones of high seismicity. There is often there are earthquakes and volcanic eruptions. And just for the groove starts bed Ocean.

Bed Ocean.Sea floor - is the central most part of the bottom of the oceans. Its depth reaches 4 000-6 000 m. couch has an oceanic earth crust type.

Relief bed is a combination of huge plains - depression. In their central parts of the sediment layer is very thin. It is formed volcanic dust, skeletons of marine organisms. Piled it very slowly: 1 mm per thousand years. Sometimes in the cavity rises cones submarine volcanoes. Active - spew lava that accumulates at the bottom. Extinct volcano have flat tops, their smooth sea currents. Basin separated mountain ranges. For example, at the bottom of the Arctic Ocean rise ranges Lomonosov і Mendeleev.

Mid-ocean ridges. Almost in the middle of oceans pass valopodibni rise of oceanic crust. They are called Mid-ocean ridges. This immense mountain building. They continuous wide strip stretch bottom all oceans, forming a chain length of about 70 000 km. Height ranges relative to the bottom than 3 000 м. Seredynnoatlantychnyy spine shares bed of the Atlantic Ocean into two parts.

Mid-ocean dissected ridges along the deep canyon. It cracked across the bottom of which poured lava. On the slopes accumulate volcanoes. Top volcanic mountains sometimes reach ocean surface and form islands of frozen lava (eg, Fr. Iceland). Цis evidence that Mid-ocean ridges are zones of volcanism and earthquakes.

Changes in ocean floor relief. Bevel the bottom of the oceans as land, form the internal and external processes. Internal processes form submarine ranges, volcanoes, deep grooves. Major changes associated with the bottom surface earthquakes and volcanic eruptions.

External processes provide demolition and accumulation of sediment on the bottom. It leads to equalization of underwater topography. Most sedimentary rocks piled up near the continental slope. In the central parts of the ocean they accumulated very slowly: a layer of 1 mm - a thousand years.

FAQ task

1. How can inequality ocean floor?

2. What divided the bottom of the oceans?

3. What are the main  landforms ocean floor.

4. What are the similarities plains upland and bottom of the World Ocean?

5. Tell us about the Mid-ocean ridges.

6. Speed of sound in water is about 1 500 m per second. Determine the depth bottom, when the sound went sounders  the bottom of 2.5 seconds.

7. Describe the relief on the bottom of the Indian Ocean 200 AP. sh.

8. Check that planetary (major) form relief of the earth's crust meet the mainland, and which - like the ocean.

9. What are the major landforms land meet stable areas of the earth's crust - a platform, and what - moving seismic belt?

10. What part of Ocean Floor coincide with moving seismic zone?