Ocean floor

When we explore an ocean floor, we meet huge and long underwater mountain chains, where earthquakes occur and which are characterized by an intense volcanic activity. These long mountain chains (ocean ridges) stretch without interruptions all along the Atlantic, Indian, Antarctic and Pacific ocean, for a total length of 80,000 km. They are very big and fragmented mountains, with an approximate height of 3 km from the ocean floor and an approximate width of 1500 km. The highest part is called the rift valley. It is formed of a deep cut (like a long and narrow trench), surrounded by mountains and plateaux. This valley is a volcano that has a very intense activity and the rocks that originated from the lava solidification form the ocean crust. The new ocean crust forms the new ocean floor and the ocean becomes bigger. In some cases the new ocean ridge emerges from the ocean surface and forms volcanic islands like, for example, Iceland and the Azores.
The earth does not increase its volume since the ocean crust, that forms on the ridges, is consumed in another area. This is typical of oceans. This area is called ocean trench. Here the ocean crust submerges under the continental crust, as it happens near the Andean Cordillera and volcanic arches.

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From the Multimedia section

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