Abstract

The seven volcanoes comprising the island of Hawaii and its submarine base are, in order of growth, Mahukona, Kohala, Mauna Kea, Hualalai, Mauna Loa, Kilauea, and Loihi. The first four have completed their shield-building stage, and the timing of this event can be determined from the depth of the slope break associated with the end of shield building, calibrated using the ages and depths of a series of dated submerged coral reefs off northwest Hawaii. The composition of lavas collected adjacent to these reefs helps to define the eruptive history of the various volcanic centers. The island of Hawaii has grown at an average rate of about 0.02 km2/yr for the past 600 k.y. and presently is close to its maximum size. Mahukona completed shield building about 465 ka; Kohala, 245 ka; Mauna Kea, 130 ka; and Hualalai, 130 ka. On each volcano, the transition from eruption of tholeiitic to alkalic lava occurs near the end of shield building. The larger volcanic systems (which stood more than 4 km above their shoreline at the end of shield building) change in composition before the end of shield building, and the smaller volcanoes change near or after the end of shield building, or never make the change to eruption of alkalic lava.

The rate of southeastern (south 40° east) progression of the end of shield building (and hence the postulated movement rate of the Pacific plate over the Hawaiian hotspot) in the interval from Haleakala to Hualalai is about 13 cm/yr. Based on this rate and an average spacing of volcanoes on each loci line of 40-60 km, the volcanoes require about 600 thousand years to grow from the ocean floor (generally from a point on the southeastern submarine flank of the next older volcano of the same loci line) to the time of the end of shield building. They arrive at the ocean surface about midway through this period.

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