| Volume & rate calculations for the young end of the Hawaiian chain U.S. Geological Survey Summary Recent, high-resolution bathymetric data collected around the Hawaiian Islands, derived from hull-mounted multibeam sonars, along with geophysical studies on loading-induced subsidence of the islands [Moore, 1987; Watts & ten Brink, 1989], allows us to update the volume estimates for the islands (first calculated by Bargar & Jackson [1974]). The volume of material erupted to build the big island of Hawai'i is nearly twice the initial Bargar & Jackson [1974] estimate and significantly greater than the other young islands. A proxy eruption-rate curve derived from parallel, vertical slices across the island chain shows that eruption rates have increased roughly two-fold from Oahu to Hawai'i (0.085 to 0.155 km3/yr peak rates) with a 5-Myr average of 0.096 km3/yr, comparable to modern Kilauea (Pu'u 'O'o) eruption rates of 0.113 km3/yr. An apparent acceleration in the propagation rate of Hawaiian volcanism [Clague & Dalrymple, 1987] is coeval with the observed increase in eruption rates and suggests shared causality. Estimates of the volumes of individual islands, in thousands of km3 are:
|
||||||||||||
|
Discussion Members of the audience provided additional information regarding variations in magmatic rate with time. Longer wavelength variations occur all along the Emperor-Hawaiian chain, and the rate varies from close to zero to the very high present rate, which is the greatest that has ever occurred along the chain. There is evidence that high volume rates occur when the propagation rate is high, and vice versa, though the difficulty of accurately measuring the propagation rate renders this association tentative. If correct, this is the opposite of what is expected if a mantle plume causes Hawaiian volcanism. There are apparently no corresponding variations in geochemistry observed. There seems to be no ready explanation for the variations in volume rate - it is a mystery. |