Map of the Hawai'i-Emperor hotspot trace. Sinking and erosion causes the volcanoes to become smaller the farther they are from the hotspot. The last island where any volcanic rock sticks up above sea level is Gardner pinnacles. From Gardner to Kure the islands are atolls - coral reefs built on top of volcanoes that are now submerged. Beyond Kure even the coral has submerged and there are only seamounts (mountains on the ocean floor that don't make it to sea level). The seamounts at the bend have been dated at ~40 million years, and Meiji seamount is about 70 million years old. The ocean crust itself in the vicinity of Hawaii is about 90 million years old. (From Clague & Dalrymple 1987).