The Society Islands of the South Pacific mirror the Hawaiian Chain, 2700 miles to their north. They too are a linear archipelago that formed (and continue to form) above a mantle plume, commonly known as a hotspot. As the Pacific Plate moves to the northwest, a volcanic ridge forms above the hotspot and the islands represent high points along that ridge; there are 14 named islands in the Society Islands chain.
The youngest of the Society Islands, Mehetia, ESE of Tahiti, began to form about 500,000 years ago and continues to enlarge. Tahiti, composed of two shield volcanoes, formed about 1 million years ago while Maupiti, the oldest of the eight primary islands (and thus at the northwest end of the chain) is about 4.6 million years old. By comparison, the primary chain of the Hawaiian Ridge has been forming for almost 40 million years; in addition, the Hawaiian hotspot is much larger, igniting volcanism above the surface over a span of 2-3 million years (e.g. Maui, 2 million years old, is still at risk for volcanic activity while Tahiti, 1 million years old, is safely out of range of its parent hotspot). Finally, the Hawaiian hotspot has been active for at least 80 million years while the Society Islands plume apparently formed about 5 million years ago.
As tropical volcanic oceanic islands age, the central cone(s) erode and eventually disappear beneath the sea, leaving only the coral reef that encircled the island. Known as atolls, they are found at the leading edge of the volcanic chain (far from the hotspot); they too will disappear over time, leaving the remnant neck of the volcano, known as a seamount, far below the surface of the sea.
