Third Underwater Volcano Discovered that Restructures Formation of O'ahu Island

The discovery of a new underwater volcano reveals that the Hawaiian Island of O'ahu was formed not by two but three major shield volcanoes. 

A team of international scientists found that O'ahu actually has three Hawaiian shield volcanoes.  Till date it was believed that only two volcanoes, Wai'anae and Ko'olau formed the island. It was said that O'ahu was a remnant of these two volcanoes.

But the latest finding reveals the presence of a large region and shallow swath of submerged rock that extends nearly 100 km WNW from Ka'ena Point, and is called the submarine Ka'ena Ridge.  That region of Ka'ena ridge has been identified as the precursor volcano and researchers say that the Wai'anae and Ko'olau volcanoes were formed on its flanks.

Before the finding of the Ka'ena volcano, the Wai'anae volcano was thought to be massive.

 "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," said John Sinton, lead author of the study and Emeritus Professor of Geology and Geophysics at the UHM School of Ocean and Earth Science and Technology (SOEST).

In 2010, the team discovered unusual lavas from Wai'anae.  It was initially though that they were formed by the fractional meeting of the crust below Wai'anae, but the researchers failed to understand the presence of an isotopic composition.

This new finding solves the mystery as the researchers realized that the deep crust that melted beneath Waianae was basically a portion of the earlier Ka'ena volcano.

Mapping of the seafloor revealed that the Ka'ena Ridge had an unusual structure, different from the submarine rift zone extensions of on-land volcanoes. 

Analyzing the geochemical and age data along with the geological and geophysical data, the researchers confirmed that Ka'ena did not belong to Waianae and was actually a previous volcanic structure. And Wai'ana was built on the flanks of Ka'ena.

"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," said Sinton.

The newly discovered precursor volcano is still being investigated by 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.