The Hawaiian-Emperor volcanic chain is made up of at least 107 indentifiable shield volcanoes (Chase and others, 1970; Bargar and Jackson, 1974; Clague and others, 1980) and is the longest linear island and seamount chain in the Pacific (Fig. 1). Beginning at the active volcanoes Kilauea and Mauna Loa on the island of Hawaii, this chain of volcanoes extends west-northwestward along the Hawaiian Ridge for a distance of 3,500 km, where it turns northward and continues another 2,300 km as the Emperor Seamounts, ending near the intersection of the Aleutian and Kurile Trenches.
It is now thought that the Hawaiian-Emperor chain was formed as the Pacific lithospheric plate moved first northward and then northwestward relative to the Hawaiian hot spot, a more or less stable melting anomaly in the asthenosphere, and that the bend in the chain reflects a major change in Pacific plate motion. Several mechanisms have been proposed to explain the Hawaiian (and other) hot spots, including a propagating fracture (Betz and Hess, 1942; Jackson and Wright, 1970); diapiric upwelling along a line of structural weakness (Green, 1971; McDougall, 1971); thermal (Morgan, 1972a, 1972b) or chemical (Anderson, 1975) plumes of gravitationally unstable material rising from the deep mantle; shear melting coupled with thermal feedback (Shaw, 1973) and geographically stabilized by gravitational sinking of refractory residua (Shaw and Jackson, 1973); and extrusion induced by lateral motion along plate boundaries (Handschumacher, 1973). Despite the variety of dynamic models proposed, there has yet to be devised a definitive experiment to test any of them. All these mechanisms are, however, encompassed by the general (or kinematic) hot spot hypothesis, which, when used in the broadest sense, implies neither mechanism nor excess heat.