Figure 12.26The movement of a plate over a hot spot generates a trail of progressively older volcanoes. (a) The volcanoes of the Hawaiian island chain and its extension into the northwestern Pacific (the Emperor seamounts) show a northwestward trend toward progressively older ages. (b) A chain of progressively older calderas marks the movement of the North American Plate over a continental hot spot during the past 16 million years. (Ma, million years ago.)