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ON THE COVER C’est si bon! Halau Mele chanter Marques Hanalei Marzan with Paris’ most famous landmark—la Tour Eiffel—in the background. Photo by Kevin German
Vol.17, no.6
December 2014 / January 2015


The Hidden Giant 
Story By: Dave Choo
Photos By: Elyse Butler 

Kaneana has many stories to tell. According to legend, the 100-foot-tall, 450-foot-deep sea cave named for Kane, the Hawaiian god of creation, is where humankind first emerged from the womb of the earth goddess Haumea. Later, Nanaue, a half-shark, half-human shapeshifter, lured his victims into Kaneana, where he would devour them in the cave’s deepest, darkest corners. The demigod Maui is said to have resided there along with his grandmother. Another part-time resident of the cave was Haumea’s hotheaded daughter, the fire goddess Pele. But Kaneana has another story to tell, this one encoded in its rocks and being slowly retold not in the language of myth and legend but of science.

On a humid, windless September morning, I take the hour-long drive from Honolulu to Kaneana, which sits just off Farrington Highway a few miles from Ka‘ena Point, O‘ahu’s northwestern tip. Waiting for me are John Sinton and Deborah Eason, whose research is telling Kaneana’s geological story. We stand in the cave’s sun-filled entrance while Sinton points to a foot-wide vein of dense, dark-colored rock running up the cave wall. There are dozens of these lines, which vary in width but not in orientation. They run parallel up the wall and eventually disappear into the mountain. These lines are the exposed edges of sheets of rock called dikes—dense, hard lava rock that work like a volcano’s plumbing system through which magma flows on its way to the surface. Hundreds of thousands of years of pounding surf carved Kaneana out of the mountainside, exposing the dike rock for scientists to read. 

Sinton says that Kaneana’s dike complex indicates that this area was once a major eruption center for the Wai‘anae volcano, which rose from the ocean about four million years ago and stretched from Kaneana to Kapolei nearly twenty miles away. “What’s unusual about Kaneana is that its dikes run so parallel to one another,” says Sinton. What’s also unusual is that the pattern seems isolated: “Further south in Nanakuli,” which was another eruption center, “the dikes have a radial orientation; they run all over the place. For twenty-five years we’ve wondered, Why is Wai‘anae volcano so different from one end to the other?”

To understand why that question is important, you need to know a little bit about how the Hawaiian Islands—and O‘ahu in particular—formed. All of Hawai‘i’s islands were born from the same “hot spot,” a place where magma rises from the core to the surface of the Earth. As the Earth’s crust moves—in the case of Hawai‘i, the Pacific Plate, which is drifting to the northwest at a rate of five to ten centimeters a year—new volcanoes punch through the crust and create islands. Volcanic activity ebbs the farther an island drifts from the hot spot. Once extinct the volcano erodes, with parts of it falling into the sea. The farther southeast along the Hawaiian chain one goes, the younger the volcanoes are. The Hawaiian hot spot forms shield volcanoes, which have gently sloping flanks like those you can see on Mauna Kea and Mauna Loa on the Big Island today. At one point in history, it was believed, O‘ahu had two such shield volcanoes: the Wai‘anae (three to four million years old) and the Ko‘olau (two to three million years old). Today the remnants of those volcanoes can be seen in the jagged profiles of the Wai‘anae and Ko‘olau mountains, with the broad saddle of Wahiawa between them. 

That seems like a fairly straightforward creation story: Two volcanoes formed one after the other as the plate moved over the hot spot and remained connected. But as the features in Kaneana suggest, the story couldn’t be that straightforward. Sinton, who has been studying Wai‘anae volcano since 1979, was baffled by several nagging mysteries surrounding the leeward coast’s geology. In 2010, for example, researchers found rocks in Wai‘anae valley that had a different chemical composition from the stones around them. They seemed to have come from nowhere, as if dropped from the sky or spit up from a deeper region of the Earth. Another mystery: Kaneana was believed to be the Wai‘anae volcano’s westernmost eruption center—if so, then how did Ka‘ena Point form? Five miles away and sloping to the northeast, Ka‘ena is too distant and lying in the wrong orientation to be a remnant of the Wai‘anae volcano. Then there’s the question of leeward O‘ahu’s puzzling topography: The dry leeward side is where you find O‘ahu’s largest valleys, but this is an anomaly, says Sinton. Big valleys usually result from erosion, and in Hawai‘i they are usually found on the windward sides of islands, where rain falls, water flows and winds rage. Scientists had long surmised that leeward O‘ahu’s expansive valleys, such as those found in Wai‘anae and Nanakuli, were the result of catastrophic landslides. But what could have caused them? Sinton had a theory but no proof.