Charles Darwin provided one of the first explanations for how atolls form.
An atoll is one of the beautiful yet mysterious land formations found in remote places in warm tropical waters like the Pacific Ocean. Formed more than 30 million years ago, an atoll is home to up to 300 species of coral and a wealth of marine life. Seen from above, it looks like a flat ring of sandy land with a pond in the center. An atoll should not be confused with an island, since its geographical formation is significantly different.
Coral reefs are a key element in the formation of atolls.
Charles Darwin provided an explanation for the formation of an atoll in 1842 that is still widely accepted today. Based on his crude observations of the South Pacific atolls, Darwin concluded that these unique terrestrial creations were the result of two factors occurring simultaneously: coral reef growth and the gradual sinking of an oceanic island.
The atoll formation process takes up to 30 million years. It begins with a new tropical oceanic island, which exists due to tectonic plate collisions or plate movements over oceanic hotspots of volcanic activity. Most of the atolls, especially those located in the Pacific Ocean, are the product of previous volcanic islands. These newly formed volcanic islands will have no sign of any life forms, either on land or in the water. This is because tropical waters are relatively warm and lack enough nutrients to support marine life.
The central lagoons of the atolls are formed by coral growth and volcanic activity.
One hundred thousand years later, a coral reef surrounds the shores of the volcanic island. Coral reefs are made up of hermatypic corals, organisms that thrive in warm surface waters. These organisms multiply and reproduce corals along the coast of the island. New corals grow on top of old or dead ones, and the process continues as the volcanic island begins to sink. This is the second stage in the formation of the atoll.
Waves cause erosion.
Over the next 25 million years, fringing coral reefs transform into barrier reefs. Barrier reefs form when the island sinks almost to sea level while corals continue to grow. These geographical movements in opposite directions result in the development of lagoons between the sinking island and the growing coral reef.
An atoll is born five million years after that, when the island sinks completely below sea level and the coral reef continues its growth towards and above the surface of the water. The lagoon that was produced in the previous stage now dominates the center of the atoll. Eventually, due to wind and wave erosion, the corals break into pieces and become sandy, creating a land surface called an islet.
The process of atoll formation begins with a new tropical ocean island, which exists due to tectonic plate movements.
The atolls are known for their beautiful coral reefs and colorful marine life. Many are attractive tourist spots, especially for lovers of diving and snorkeling. Famous atolls around the world include those of the Tuamotu Archipelago, the Coral Sea Islands, and the Caroline Islands in the Pacific Ocean, as well as the Chagos Archipelago and the Maldives in the Indian Ocean.