New Hawaiian Volcano Discovered Underwater

Ka'ena pillow lava — Pillow lavas at Ka'ena volcano, a type of lava that only forms underwater.

(Image credit: University of Hawaii at Manoa)

The sprawling chain of Hawaiian volcanoes just added another underwater branch.

The discovery means Oahu once towered above the ocean with three volcanic peaks, the researchers said. Until now, scientists thought Oahu was built by two volcanoes — Wai'anae on the west and Ko'olau on the east.

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The new volcano, named Ka'ena, was born in the deep underwater channel south of Kauai about 5 million years ago, according to the study, published May 2 in the Geological Society of America Bulletin. Sometime later, Wai'anae rose on Ka'ena's flanks and therefore breached the sea first, breaking through the waves 3.9 million years ago. The researchers think Ko'olau surfaced after that, about 3 million years ago. [See Photos of the Newfound Underwater Volcano]

Ka'ena volcano is about 2.5 miles (4 kilometers) high, but only reached about 3,000 feet above sea level, Sinton said. As Oahu's first-born, Ka'ena is the shortest of the three volcanoes because it had to grow farthest from the seafloor to the ocean surface. But the researchers know Ka'ena was once an island peak, because the underwater mountain is capped by lavas with textures that only form in air. With a remotely operated vehicle, the researchers also spied a sandy beach strewn with shark teeth.

Map showing the three volcanoes now thought to make up Oahu, Hawaii. From oldest to youngest these are the Ka‘ena, Wai‘anae, and Ko‘olau Volcanoes. Upper panel: bold dashed lines delineate possible rift zones of the three volcanoes; also shown are the major landslide deposits around O‘ahu. The lower panel shows how the three volcanic edifices overlap.

Becky Oskin covers Earth science, climate change and space, as well as general science topics. Becky was a science reporter at Live Science and The Pasadena Star-News; she has freelanced for New Scientist and the American Institute of Physics. She earned a master's degree in geology from Caltech, a bachelor's degree from Washington State University, and a graduate certificate in science writing from the University of California, Santa Cruz.