In 1963, Canadian geophysicist J. Tuzo Wilson proposed an idea that would reshape the understanding of volcanic island chains. Most volcanoes form at the boundaries of tectonic plates, where plates collide, separate, or grind past each other. Hawaii sits in the middle of the Pacific Plate, thousands of miles from the nearest boundary. Wilson suggested that a fixed source of heat deep in the mantle -- a hotspot -- was responsible, and that the Pacific Plate was drifting over it like a conveyor belt. Each volcano, fed by the plume while directly above it, would be carried northwest by plate motion, cut off from its magma supply, and gradually die. A new volcano would then begin forming in its place. The result, over tens of millions of years, is a chain of volcanoes arranged by age, youngest to oldest, in the direction of plate motion.

Hawaiian volcanoes follow a remarkably consistent life cycle. Each begins as a submarine seamount, fed by the hotspot plume. Lava output gradually increases until the volcano breaches the ocean surface, becoming an island. Height and eruptive activity peak when the volcano is around 500,000 years old, then decline rapidly. The volcano goes dormant, then extinct. Weathering and erosion strip away the summit, wave action carves sea cliffs, and the island's own weight causes it to subside into the ocean floor. Eventually all that remains is a coral atoll, and then nothing visible at all -- just a submerged seamount being carried toward the Aleutian Trench, where it will be recycled back into the mantle. The Big Island, home to four active volcanoes including Kilauea and Mauna Loa, is in the growth phase. Kauai, 100 miles to the northwest, is already deeply eroded. Midway Atoll, 1,500 miles further, is barely above sea level.

The Hawaiian-Emperor seamount chain does not run in a straight line. About 47 million years ago, the chain makes a sharp bend, shifting from a nearly due-north trend to the northwest orientation visible today. This bend was long interpreted as evidence of a major change in the direction of Pacific Plate motion. More recent research has complicated that picture, suggesting that the hotspot itself may have drifted southward during the earlier period, and that the bend reflects a combination of hotspot motion and plate reorganization. The debate matters because the hotspot's supposed fixity was a cornerstone of Wilson's original theory, and evidence that the plume has moved challenges the simplest version of the model. Still, whether the hotspot is perfectly stationary or merely slow-moving relative to the plate, the basic mechanism -- a deep mantle plume punching through a moving plate -- remains the best explanation for the chain's existence.

The hotspot is not finished. Kamaʻehuakanaloa Seamount, formerly known as Loihi, is the newest volcano in the chain. It sits about 20 miles off the southeast coast of the Big Island, its summit still roughly 3,000 feet below the ocean surface. Geologists estimate it will breach the surface in 10,000 to 100,000 years, eventually merging with the Big Island or forming a new one. Meanwhile, the four currently active volcanoes on the Big Island -- Kilauea, Mauna Loa, Hualalai, and Mauna Kea (considered dormant but not extinct) -- continue to grow. The hotspot produces volcanoes that are among the largest on Earth by volume: Mauna Loa, measured from its base on the ocean floor, rises more than 30,000 feet, making it taller than Mount Everest. The plume that built it has been operating for longer than the Rocky Mountains have existed.