Hawaii hotspot created at least 129 volcanoes, more than 123 of which are extinct volcanoes, seamounts, and atolls, four of which are active volcanoes, and two of which are dormant volcanoes. They can be organized into three general categories: the Hawaiian archipelago, which comprises most of the U.S. state of Hawaii and is the location of all modern volcanic activity; the Northwestern Hawaiian Islands, which consist of coral atolls, extinct islands, and atoll islands; and the Emperor Seamounts, all of which have since eroded and subsided to the sea and become seamounts and guyots (flat-topped seamounts). Hawaiian volcanoes are characterized by frequent
Extinct radionuclide Extinct radionuclide An extinct radionuclide is a radionuclide that was formed by nucleosynthesis before the formation of the Solar System, about 4.6 billion years ago, and incorporated into it, but has since decayed to virtually zero abundance, due to having a half-life shorter than about 100 million years. Short-lived radioisotopes that are found in nature are continuously generated or replenished by natural processes, such as cosmic rays (cosmogenic nuclides), background radiation, or the decay chain or spontaneous fission of very long-lived isotopes such as uranium or thorium. Short-lived isotopes that are not generated or replenished by natural processes are not