That's because, as the Pacific Plate drifts northwestward, each volcano, in turn, is rafted away from the hotspot and dies. The hotspot that fueled the Marquesas has since closed up shop, but the one beneath the Society Islands is still in business. Mehetia, the easternmost island in the Society group, experienced a seismic swarm in 1981 that was probably generated by an undersea eruption on the southeast flank of the island. Castle-like pinnacles are typical of eroded volcanic islands in the tropics. Deep river valleys converge in the interior of the island, separated by knife-edged ridges.
Some ridges become so narrow that great natural windows open within the valley walls.
The crew paid a visit to the small community composed mostly of descendants of the HMS Bounty's mutineers and their Tahitian wives. As a measure of how isolated this island is, the crew noted that the Pitcairners ran out of chocolate three months ago. Pitcairn is an extinct, but young, volcano. Since the 1970s, geologists had suspected that this volcano was at the active end of a hotspot chain that included the Gambier and Duke of Gloucester Islands to the northwest. From Pitcairn the canoe sailed to Mangareva, where the crew is currently preparing for the long crossing to Rapu Nui.