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USGS CMG InfoBank: Coral Atolls

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Comment: 23:16 - 24:37 (01:21)
Source: Annenberg/CPB Resources - Earth Revealed - 6. Plate Dynamics
Keywords: "Tanya L. Atwater", Hawaii, seamount, guyot, "sea floor", island, erosion, wave, plate, "hot spot", "mid-oceanic ridge", "coral reef", "coral atoll"

Our transcription: As the islands of Hawaii age and weather away they ultimately become flat-topped submerged seamounts or guyots.
Thousands of such seamounts dot the ocean floor.
One thing that's interesting about oceanic islands is that they don't last very long.
The erosive power of the waves is so strong that any island that isn't being continually built will be eroded away in a few million years, planed right down to wave base.
As plate movement carries the islands away from hot spots and mid-ocean ridges, the underlying sea floor cools and subsides.
In lower latitudes coral reefs build up completely capping the remnants of the sinking islands.
Such caps are called "coral atolls."
Ultimately, the atolls themselves may sink from view.
The Big Island of Hawaii is being built right now, and, in fact, there's new land being added out to the ocean.
But even all the other Hawaiian Islands in the chain, even though they're still islands are planed away.
So when you drive up on a ship with a sonar you come up the side, and then there's a big flat surface, and then the island is the last little erosional remnant that hasn't been chewed away by the waves yet.

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