Geology of the Hawaiian Islands

Abstract

Long known as the island chain farthest from any continental landmass, the Hawaiian Islands are the subaerial expression of volcanism above the relatively fixed Hawaiian hot spot as the Pacific plate drifts northwest above it. Each island is built by one or several overlapping shield volcanoes, some of the most voluminous on Earth. Plate translation creates the well-known age-progressive sequence of shield volcanoes from northwest to southeast. Total volume of magma produced along the Hawaiian chain has been irregular but generally increasing for the past 50 million years, a trend that has peaked in the last 3 million years. Hawaiian volcanoes grow through stages that have geologic expression and geochemical differences that reflect position relative to the underlying hot spot. Of these stages, the shield stage is the most productive when an estimated 80–95% of a volcano's ultimate volume is emplaced. The shield stage endures for about 1 million years. The burden of shield volcanoes depresses the ocean crust near the hot spot, creating the Hawaiian Moat. Greatest rate of subsidence today occurs at the Island of Hawai‘i, 2–3 mm per year along its coast. Flexural rebound occurs as volcanoes move away from the hot spot; the Island of O‘ahu shows the greatest uplift. Slow subsidence resumes downstream from the flexure, leading ultimately to submergence of each island in the chain. Large landslides, albeit infrequent, can occur at any stage of island evolution. Ground water is the principal source of potable and agricultural water on all islands; its distribution both reflects and influences island geology.