The islands and coral atolls of French Polynesia, located in the southern Pacific Ocean, epitomize the idea of tropical paradise: white sandy beaches, turquoise lagoons, and palm trees. Even from the distance of space, the view of these atolls is beautiful. This image from the Advanced Land Imager on NASA’s Earth Observing-1 (EO-1) satellite shows the southern part of Tikehau Atoll, one of the 78 coral atolls that make up the Tuamotu Archipelago. Patches of coral make star-like spots across the turquoise expanse of the lagoon. A line of tree-covered islets encircles the lagoon. At the southernmost tip of the atoll, a large islet accommodates a small village and an air strip.
NASA image created by Jesse Allen, using EO-1 ALI data provided courtesy of the NASA EO-1 Team. Caption by Rebecca Lindsey.
These two images of the Tuamotu Archipelago, French Polynesia, illustrate diversity in the morphology of atolls, one of the major types of coral reef formations. A typical atoll structure is a lagoon surrounded by a closed rim of cays and shallow spillways that control the exchange of water between the ocean and the lagoon. However, like human beings, this general scheme may vary according to the history of each individual atoll, resulting in a high diversity of morphology, especially for small atolls. The two neighboring atolls shown here have some unique features. What was a lagoon on Nukutavake (19°17′ S 138°48′ W, 6.2 km²) is now dry and completely covered by vegetation. Pinaki (3.54 km²) has a drying shallow lagoon still connected to the ocean via a single narrow spillway. The variation of morphology implies that each atoll may have a different equilibrium between ocean, lagoon, and land ecosystems.