The density of the island of Hawaii, and density distribution in the earth's crust

Abstract

Goranson examines isostatic gravity anomalies from the conterminous United States and Hawaii as background for an attempt to determine the density of Hawaii. He discusses the computation of the theoretical value of gravity and of isostatic compensation. Based on gravity measurements by the U.S. Coast and Geodetic Survey, the upper part of Mauna Kea has a density of 2.12, and Mauna Loa 2.52. He disputes Preston9s (1894) calculated density for Hawaii (3.26) as being larger than the rock density (2.96) calculated by Washington (1923e). Goranson correctly concludes that the Hawaiian gravity anomalies suggest an Airy-type compensation model but that the island of Hawaii is isostatically uncompensated, constituting a load upon the suboceanic crust. Hawaii, therefore, must either be supported by the strength of the crust, or be slowly sinking. He calculates limits on the sinking, noting that if the crust had zero strength, the island should sink 3,100 m, but as the crust must have some rigidity, the actual sinking would be less. He considers this hypothesis also to be a simpler explanation for drowned coral reefs.