New discovery finds Oahu is made up of three, not two, volcanoes

Pillow lava at Kaena volcano, a type of lava that only forms underwater. Photo courtesy UH/Manoa
Pillow lava at Kaena volcano, a type of lava that only forms underwater. Photo courtesy UH/Manoa

The University of Hawaii has reported that researchers recently discovered that Oahu actually consists of three major Hawaiian shield volcanoes, not two, as previously thought.

This from the combined efforts of scientists from the Manoa campus, Laboratoire des Sciences du Climat et de L’Environment in France and the Monterey Bay Aquarium Research Institute in California.

It’s been commonly thought that the island of Oahu is made up of the remnants of two volcanoes, Waianae and Koolau. But extending almost 62 miles WNW from Kaena Point is a large region called the submarine Kaena Ridge.

It is that region that has now been recognized to represent a precursor volcano to the island of Oahu, and on whose flanks the Waianae and Koolau Volcanoes later formed.

Prior to the recognition of the Kaena volcano, the Waianae volcano was assumed to have been exceptionally large and to have formed an unusually large distance from its next oldest neighbor, Kauai. “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,” 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.

“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,” Sinton said.

Much of our knowledge of Hawaiian volcanoes is based on those that rise high above sea level, and almost all of those formed on the flanks of earlier ones. Kaena represents a chance to study a Hawaiian volcano that formed in isolation on the deep ocean floor.

Courtesy: University of Hawaii
Courtesy: University of Hawaii
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