|Nature Gallery (Plate Tectonics)|
This takes around 6 million years, beginning with the formation of a coral reef around the island between 0 and 200 meters deep (0 to 656 feet). Beyond that depth, the coral does not have enough light to survive. At the same time, the island sinks slowly, or subsides, under its own weight.
Over time, the volcanic mountain disappears completely
As the volcano slides back into the ocean,
constantly eroded by torrential tropical downpours, the coral
proliferates. New coral colonies grow on the skeletons of old, constantly
renewing the calcareous crown on the surface.
|This is the phenomenon
where water rises up from the depths of the ocean and passes through the
porous calcareous crust.
This recent theory seeks to explain the richness of plant and animal life around a lagoon: unlike surface water, which is warmed by the sun to about 200 meters, water from the deep down in the ocean is full of nutritious salts.
Channels in the coral mix lagoon water with the ocean
|An atoll usually remains
open to the ocean thanks to a number of channels known as hoa.
These channels mean that the shallow waters of the lagoon are constantly
mixed with the deeper waters of the ocean.
This mixture of nutrient-rich deep ocean water and the warmer lagoon waters in the isolated atolls provides the Tahitian pearl oyster with an ideal environment to produce the most beautiful pearls in the world.