According to a statement from the University of Hawaii at Manoa, researchers recently found that O‘ahu, the third largest of the Hawaiian Islands, actually consists of three major Hawaiian shield volcanoes, not two, as previously believed.

The island of O‘ahu is the leftovers of two volcanoes, Wai‘anae and Ko‘olau. But stretching out nearly 100 km from the western tip of the island of O‘ahu is a sizable region of shallow bathymetry (“submarine topography” or the depths and shapes of underwater terrain), known as the submarine Ka‘ena Ridge, that is the region that has now been identified as a precursor volcano to the island of O‘ahu.

Previously, the Wai‘anae volcano was assumed to have been unusually big and to have developed an exceptionally great distance from its next oldest neighbor, Kaua‘i. LiveScience notes, for example, that when the U.S. Navy surveyed the seafloor during World War II, scientists believed the ridges were continuations of Wai’anae.

“Both of these assumptions can now be revised: Wai‘anae is not as large as previously thought and Ka‘ena Volcano formed in the region between Kauai and Wai‘anae,” 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 Wai‘anae.

“We previously knew that they formed by partial melting of the crust beneath Wai‘anae, but we didn’t 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 Ka‘ena Volcano.”

New data from the Research Vessel Kilo Moana revealed that Ka‘ena Ridge had a strange morphology, different than that of submarine rift zone extensions of on-land volcanoes. Researchers then started gathering samples from Ka‘ena and Wai‘alu submarine Ridges. The data confirmed that Ka‘ena was not part of Waianae, but was actually a third volcano.

“What is particularly interesting is that Ka‘ena 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 University’s “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 planet’s strangest and rarest ecosystems.

According to researchers, there is still much to be learned about this large volcanic edifice. The latest samples from the Ka‘ena Ridge will likely help them determine the timing of the most recent volcanism on Ka‘ena.