Volcanic Islands and Archipelagos

The Hawaiian Islands owe their existence to a stationary plume of unusually hot mantle material, a hotspot, that has been punching through the Pacific Plate in roughly the same location for at least 80 million years while the plate itself slides steadily northwest above it, at a rate of roughly 7 to 10 centimeters per year. As the plate moves, each volcano is eventually carried off the hotspot and goes extinct, replaced by a new one forming directly above the plume, so that the islands form a long, age-progressive chain: the Big Island of Hawaii, home to the still-active volcanoes Kilauea and Mauna Loa, sits directly over the hotspot today, while Maui, Oahu, and Kauai, each progressively older and more eroded, lie to the northwest, and the chain continues underwater as the Emperor Seamounts, a line of drowned, extinct volcanoes stretching toward the Aleutian Trench. A pronounced bend in this chain, dated by argon-argon radiometric methods to roughly 47 million years ago, marks a documented shift in the direction of Pacific Plate motion, turning the older Emperor Seamounts nearly due north while the younger Hawaiian Ridge trends northwest, giving geologists a natural record of changing plate motion spanning tens of millions of years. Mauna Loa, rising 4,169 meters above sea level, is recognized as the largest active volcano on Earth by both volume, an estimated 75,000 cubic kilometers, and area.