The Ocean Floor 

Background Information

The land is dotted with plains, mountains, and deep canyons.  The area seven miles below the surface of the sea is very similar to the topography of the continental United States. The sea bottom is divided into three areas: the continental shelf, the continental slope, and the ocean floor.

We have learned about the ocean floor thanks to the introduction of the echo sounder. The echo sounder calculates water depth by measuring time between emission of a sound signal directed toward the ocean floor and the return echo. From echo-sounder data and bottom samples, marine geologists have gathered information to produce charts of the ocean bottom features.

Terms used to describe the ocean floor are very similar to terms used to describe features on the land.

Ocean Ridges are like mountain ranges.

Ocean Trenches are the Grand Canyons of the sea.

The continental shelf has numerous hills, ridges, terraces, and canyons. Its average width is 30 miles, but it can extend several miles from shore. 

All oceans except the North Pacific are divided by mountain systems - several of which are higher than Mt. Everest. 

The largest mountain chain is the Mid-Atlantic Ridge.

Much of the deep ocean floor, especially in the Pacific, is covered with basins, and somewhat resembles the surface of the moon.

Another prominent feature of the deep ocean floor is the deep ocean trenches which are found in areas of volcanic activity. Narrow, often arc-shaped, these depressions are 50-60 miles wide, as much as 1,000 feet long, and up to 36,000 feet deep. 

The largest, the Tonga-Kermadec Trench in the Western Pacific, is spacious enough to contain six Grand Canyons.

Movement in the trenches can displace the ocean surface leading to the formation of dreaded tsunami waves, often erroneously called tidal waves.

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