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http://dailydigestnews.com/2014/05/new- ... in-hawaii/
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According to a statement from the University of Hawaii at Manoa, researchers recently found that Oahu, the third largest of the Hawaiian Islands, actually consists of three major Hawaiian shield volcanoes, not two, as previously believed.
The island of Oahu is the leftovers of two volcanoes, Waianae and Koolau. But stretching out nearly 100 km from the western tip of the island of Oahu is a sizable region of shallow bathymetry (submarine topography or the depths and shapes of underwater terrain), known as the submarine Kaena Ridge, that is the region that has now been identified as a precursor volcano to the island of Oahu.
Previously, the Waianae volcano was assumed to have been unusually big and to have developed an exceptionally great distance from its next oldest neighbor, Kauai. LiveScience notes, for example, that when the U.S. Navy surveyed the seafloor during World War II, scientists believed the ridges were continuations of Waianae.
Both of these assumptions can now be revised: Waianae is not as large as previously thought and Kaena Volcano formed in the region between Kauai and Waianae, explained lead author John Sinton, Emeritus Professor of Geology and Geophysics at the UHM School of Ocean and Earth Science and Technology.
In 2010, researchers made note of the strange chemistry of some odd lavas of Waianae.
We previously knew that they formed by partial melting of the crust beneath Waianae, but we didnt understand why they have the isotopic composition that they do, Sinton posited. Now, we realize that the deep crust that melted under Waianae is actually part of the earlier Kaena Volcano.
New data from the Research Vessel Kilo Moana revealed that Kaena Ridge had a strange morphology, different than that of submarine rift zone extensions of on-land volcanoes. Researchers then started gathering samples from Kaena and Waialu submarine Ridges. The data confirmed that Kaena was not part of Waianae, but was actually a third volcano.
What is particularly interesting is that Kaena appears to have had an unusually prolonged history as a submarine volcano, only breaching the ocean surface very late in its history, noted Sinton.
Oregon State Universitys Volcano World notes that beneath the oceans a worldwide system of mid-ocean ridges generates an estimated 75 percent of the yearly output of magma. In addition, an estimated 0.7 cubic miles of lava is erupted. The magma and lava supply heat and chemicals to some of the planets strangest and rarest ecosystems.
According to researchers, there is still much to be learned about this large volcanic edifice. The latest samples from the Kaena Ridge will likely help them determine the timing of the most recent volcanism on Kaena.
