| The Ocean Floor
Important features of the ocean floor near the continents are the continental shelf, the continental slope, and the continental rise. These areas are covered with thick layers of sediments (sand, mud, rocks). The depth of the ocean varies. Ocean trenches are very deep, and the continental shelf is relatively shallow.
The continental shelf is an area around the edges of the continents. The continental shelf extends about 80 kilometers (50 miles) from the shoreline, and is no more than 140 meters deep. This is the part of the beach that you go to during the summer! Beyond this is a continental slope that steeply drops to about 3,000 meters deep. The continental rise is the lower portion of the continental slope extending to the ocean floor. These three parts of the ocean floor are similar to the design of a slide on a playground. The flattest parts of the ocean are the abyssal plains. They are covered by a thick layer of ooze made up of mud, sand, and decaying organic materials.
Parts of the abyssal plains have ridges, volcanoes, and trenches. A ridge of mountains (such as the Mid-Atlantic Ridge) rises about 1 to 3 kilometers in the center of the Atlantic, Pacific, and Indian Oceans. Volcanoes also rise from the abyssal plain. The tops of some of these are above the ocean’s surface, creating islands. Often near these islands are deep spots in the oceans known as trenches. Trenches are similar to canyons founds on Earth’s surface.
As the depth of ocean water increases, the temperature decreases, the pressure increases, and the amount of light decreases.
Feature
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Definition
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Illustration
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Coastline
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Sandy, outer land part that people lay out on while enjoying the beach
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Continental Shelf
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Shallow part of the ocean that meets the coastline. When you walk out into the water you are standing on the continental shelf. Composed of sediment or sedimentary rock.
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Continental Slope
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Drop off point from the continental shelf. Steeply sloping portion of continental crust found between continental shelf and continental rise.
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Continental Rise
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Area connecting the continental slope to the abyssal plain
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Abyssal Plain
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Flattest part of the ocean floor
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Seamount
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Underwater active volcano found on an ocean basin.
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Guyot
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Extinct volcano that is flat on top
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Mid-Ocean Ridge
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Series of underwater mountain chain
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Island
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A piece of land that is surrounded by water on all sides. The land is most likely created by seamounts.
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Trench
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Valley and rift in ocean floor creates a pocket: deepest part of the ocean
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Volcanic Island Arc
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An elevated area of the ocean floor created from the release of lava from a volcanic vent.
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