In the northwest Society Islands, the grouping of Motu Iti Atoll, Bora-Bora, Tahaa, and Raiatea islands depicts the last two stages of coral atoll development, as the growing reefs respond to the sinking of the island masses into the ocean's crust. The sister islands of Tahaa and Raiatea are enclosed by a barrier reef in the same stage of development as that around Yap Island. To the west, Bora-Bora is surrounded by a mature barrier reef with only one navigable entrance and a few overflow channels.
Farther to the northwest, Motu Iti Atoll represents the final stage in the sequence from fringing reef to atoll. This mature atoll has only three passes through the reef into the lagoon, and none are deep, navigable channels.