Or, as it’s actually called, an atoll:
The birth of ring-shaped islands can take thousands of years. NOAA’s National Ocean Service explains (with a handy animation):
Corals … begin to settle and grow around an oceanic island forming a fringing reef. It can take as long as 10,000 years for a fringing reef to form. Over the next 100,000 years, if conditions are favorable, the reef will continue to expand. As the reef expands, the interior island usually begins to subside and the fringing reef turns into a barrier reef. When the island completely subsides beneath the water leaving a ring of growing coral with an open lagoon in its center, it is called an atoll.
Climate change is expected to take a toll on these low-lying islands in the coming years as rising sea levels result in bigger waves and increased flooding. Daily Overview, to commemorate the start of the Paris Climate Conference, also captures an atoll:
The 2015 UN Climate Change Conference kicked off today in Paris. The event will bring together leaders from more than 190 countries with the goal of creating a legally binding and universal climate agreement that will keep global warming below 2°C. Daily Overview is providing imagery for the UN’s #EarthToParis event next week and we’ll be closely following what comes of the discussions at #cop21 in the coming days. At the conference today, Anote Tong, the president of Kiribati — a low-lying island nation in the Central Pacific Ocean —expressed his gratitude to the country of Fiji. The 102,000 residents of Kiribati may be forced to relocate as increased ice melt causes the Pacific Ocean to rise and submerges its islands. Fiji has boldly offered to take in the people of Kiribati if that occurs. Tarawa, an atoll that serves as the capital of the country and is home to half of it’s population, is seen here.