The dots mark the youngest islands of some hot spot island chains. Think about the different Hawaiian islands you have visited. Of the islands we can visit, Kauai has the deepest eroded valleys and the most coral reefs, which are indicative of age in the process of island formation and degradation. The extinct volcano underlying the coral atoll of Midway is 26 million years old. The Society Islands follow the same pattern as Hawaii, with the youngest volcano at the southeast end of the island group and the oldest volcano at the northwest end.
Volcanoes form on the plate above the hot spot.
As the plate moves over the hot spot, new volcanoes form, and the old ones, which no longer overlie the hot spot, become extinct. In Hawaii, the hot spot is currently under the active volcanoes of Mauna Loa, Kilauea, and Loihi, a submarine volcano southeast of the Big Island. From the geometry of the islands and submarine ridges on the Pacific Plate, we know that the Pacific Plate has been moving west-northwest for the last 43 million years. The Pacific Plate moved directly northward from about 43 to 80 million years ago. A hot spot volcano making news recently is Fogo in the Cape Verde Islands off of the west coast of Africa.