The Hawaiian island of O'ahu has actually formed by three massive shield volcanoes, not two as previously thought, experts report. The discovery of the Ka'ena Volcano, which was primarily an underwater volcano, reveals new clues to how some Hawaiian islands and additional volcanoes were formed.

Nearly 100 km West-North-West from the island of O'ahu is the Ka'ena Ridge, a wide and shallow swath of submerged rock that stretches far out from the island proper. According to the University of Hawaii, past researchers theorized that the volcano Wai'anae made up a significant portion of this ridge, making it an unusually wide and isolated volcano. They theorized that a second volcano, Ko'olau, erupted from the ocean floor and helped Wai'anae create the Island of Oahu we see today.

However, new investigations of the Ka'ena ridge has revealed that the ridge contains a precursor volcano of its own, meaning that Wai'ane is much smaller than previously though and likely rose from the crust of this older and larger sub-surface 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," John Sinton, a lead researcher of Ka'ena, said in a recent University of Hawaii press release.

According to Sinton, many of the shield volcanoes that are known to have formed the Hawaiian Islands quickly rise high above seas levels, as they formed on the flanks of earlier ones. With the discovery of the Ka'ena volcano, researchers have an opportunity to study one of these ancient "submarine" precursor volcanoes.

Sinton and his colleagues from the University of Hawai'i - Mānoa (UHM), the Laboratoire des Sciences du Climat et de L'Environment of France, and the Monterey Bay Aquarium Research Institute, are in the midst of an ongoing investigation of this newly discovered precursor volcano.

A press release from the University of Hawaii was published on May 15 details preliminary findings of this ongoing study.