Geology and Volcanology of the Hawaiian Islands

This article summarizes the present state of knowledge of the geology of Hawaii. It tends to concentrate on aspects not usually covered by review articles. Current ideas on hotspots and mantle plumes are applied to the specific example of Hawaii, the eight volcanic systems currently nourished by the hotspot are identified, and gross differences in magma-supply rate are related to position of these systems on the hotspot. The important role played by level of neutral buoyancy in distributing incoming magma between magma chambers, rift zones, intrusions, and surface flows is discussed. This is important because volcanic edifices may expand nearly as much by growth of subsurface intrusions as by surface lava outpourings. Recent discoveries, however, show how strongly volcano growth is countered by subsidence and major collapses. A brief description is given of styles of volcanism in Hawaii, and recent ideas on how formation of aa and pahoehoe depends on eruption discharge rate are discussed . A brief summary description pointing to highlights of each volcano is then presented. Finally, I indulge in speculations regarding geographical distribution of the volcanoes and show how, by postulating that a considerable strike-slip motion has occurred on two faults, a much more orderly arrangement of volcano and rift-zone alignments appears, leading to a dynamic model of island-chain growth that is simpler then current models . Proceeding from Kaua'i toward the southeast, an alternating sequence of southeast and west-southwest alignments is revealed. These alignments may be related, respectively, to fractures propagated against the plate motion direction (because ofextensional stresses resulting from diverging flow in the mantle plume) and along faults of the Moloka'i fracture