Mention Hawaii and most of us think of a handful of Pacific Islands known for their fabulous weather, lush vegetation, big waves and volcanoes. In fact, these are the eastern end of a chain of 137 islands, islets and atolls that stretch for almost 2000 miles across the ocean. Trending southeast to northwest, they represent the summits of an underwater, volcanic range, a 40 million year product of the Hawaiian hotspot, now located under the Big Island.
The hotspot has remained nearly stationary for the last 80 million years as the Pacific Plate has moved over it. Initially, the plate moved northward, producing a volcanic range that has since eroded into the Emperor Seamounts, now stretching north from the west end of the Hawaiian chain. About 43 million years ago, the Pacific plate changed to a northwest heading and, in concert with the hotspot, produced the Hawaiian Ridge, composed of numerous volcanoes. Midway, 27.7 million years old, is a summit near the west end of the ridge while the Big Island, only 500,000 years old, anchors the eastern end. Kauai developed 5 million years ago, Oahu 4 million and Maui about 2 million years ago; the latter island, composed of 7 volcanoes, was once larger that the Big Island, which is a composite of 5 volcanoes. Loihi, now forming on the ocean floor, 20 miles southwest of the Big Island, will emerge from the sea in 100,000 years or so, welding itself to its much larger neighbor.
Mauna Loa, which last erupted in 1984, occupies most of the Big Island and is the largest volcano on Earth; indeed, from sea floor to summit, it is taller than Mt. Everest. Kilauea, forming the southeast corner of the Island, has been erupting since 1983, making it one of the most active volcanoes on the planet. Geologists believe that, based on the speed of the Pacific plate, most of the Hawaiian Ridge volcanoes developed peak activity within 500,000 years and became dormant within 2-3 million years; if so, the Maui volcanoes are still potentially active.