The Tuamotu Atolls
Between the Marquesan high islands and the Society Islands with their fringing reefs, lie an area of ring-like atolls. These were notoriously dangerous to shipping in the past as they are so low-lying, but now with GPS it is easier to visit these islands.
An atoll is the remains of a long-gone volcano. The original volcano would have sunk below the ocean surface as the tectonic plate below it moved deeper below a neighbouring plate. However the coral growing around the original perimeter of the volcano would have grown upwards to keep contact with the water surface. Consequently the volcano shrank in height and diameter, with a fringing coral reef of the original size around it, such as may be seen in the Society Islands. Later the volcano completely sinks, leaving only the ring of coral reef. On some atolls the complete ring is a little above sea level and is covered with coconut palms. On other atolls the coral reefs are just awash and practically invisible. On some atolls there are breaks in the coral ring big enough to let boats through inside the lagoon, these are called passes. Some atolls have no such access. The pieces of coral ring are called motus.
We chose to visit two atolls at the northern end of the Tuamotus, in the straightest line between Nuku Hiva and Tahiti. These northern atolls are most frequently visited by yachts and so good information is available for a safe first visit.
We chose to visit Ahé because it is small enough to see the entire atoll at once, and because it is not touristy and has just a small village.
The second atoll was Rangiroa, a much larger and more touristy atoll, with dive schools, hotels and shops. Rangiroa is in fact the largest atoll in the Tuamotus and the second-largest in the Pacific, encircling some 1,000 sq km of lagoon.