How Kapolei’s Landscape Was Formed, According To Science

There’s a fire spout in the Earth that’s been making land—including the land Kapolei sits on—for 85 million years.

As the Pacific continental plate passes over the spout, it fires lava up through the ocean, eventually creating land.

Waiʻanae Volcano Begins to Erupt

About 4 million years ago, around the same time a strange new ape species began walking on two legs in East Africa, land formed by a volcano later named Waiaʻnae surfaced in the Pacific Ocean.

Had modern geologists existed at the time, they would have classified Waiʻanae as a “seamount,” same as Lōʻihi, off the southern coast of Big Island, is today.

At the time, Waiʻanae was the southeastern-most island in the Hawaiian chain. Maui, Lānaʻi, Molokaʻi, and Big Island did not yet exist.

Waiʻanae continued to grow over the next million years or so, spouting lava from what today is the Lualualei valley.

Waiʻanae Erodes — And Koʻolau Grows

When Waiʻanae volcano began to die out, about 3 million years ago, it would’ve looked similar to Big Island does now. But, as the lava flows slowed down the land began to erode.

Streams carved great valleys on the southwest side of the mountain, where the land was older and rocks weaker. We call these valleys: Nānākuli, Lualualei, Waiʻanae, and Mākaha.

Then, over the next million years, while the descendents of those walking apes first began traveling to Europe and Asia, a new volcano rose just to the east of Waiʻanae. Koʻolau Volcano was now over the fire spout. It grew and grew.

Waiʻanae’s Last Gasp: Puʻuokapolei

Waiʻanae wasn’t completely finished.

One of its final eruptions gave us Puʻuokapolei. The hill bordered by Ft. Barrette Rd. and Kapolei Regional Park — and former heiau — is a late-stage volcanic cone.

Puʻuokapolei erupted between 2.5 million to 3 million years ago — while Koʻolau volcano was also erupting above sea level. So, much like Mauna Loa and Kilauea today, there was overlap between the eruptions of Waiʻanae and Koʻolau.

As you’re driving on the H1 through Kapolei, the surface of everything mauka is lava flow. Everything makai is something else — either ancient sea bed or eroded rock. The one exception is Puʻuokapolei. It’s the last remnant of Waiʻanae lava in the lowlands.

Koʻolau Saves The West Side

By about 2 million years ago, Koʻolau was tall enough that it shielded the older Waiʻanae land.

If not for Koʻolau popping up in the perfect spot, it’s possible that the rain and wind would have washed Waiʻanae into the ocean.

Instead, the winds and rain didn’t happen so often, and erosion slowed. Also, flow from Koʻolau piled atop the final lava eruptions of Waiʻanae to form what we now call the ʻEwa plain.

Rising and Falling Seas Build The Land Beneath Us

Fire was done shaping the west side. Now, water would take over completely.

Over the next two million years, cyclic changes in Earth’s orbit caused the climate to warm and cool. In warm periods, the sea level rose. So, for tens of thousands of years, the ʻEwa plain was a sea bed — decomposing marine life accumulated on the surface.

Then, the Earth cooled again. Northern waters became trapped in ice and the seas receded, by as much as 350 feet. On this rich land, and thanks to cooler worldwide temperatures, the ʻEwa plain became a forest for thousands of years.

A vast underground forest, covered by ash from the Salt Lake eruption, lies beneath our feet — bores for wells have found it.

About 11,000 years ago, not long after the walking primates made their way to the Americas over the Bering land bridge, the Earth warmed up again. The seas rose again, and West Oʻahu’s coast reached its current level.

The topography of Kapolei and the west side hasn’t changed much since.

Dr. Ken Rubin, a professor in the Dept. of Earth Sciences at UH-Mānoa, was kind enough to review this article and make suggestions. Still, any errors or inaccuracies are the fault of the writer, not Dr. Rubin.

Coming soon: Our next installment — what science says about the west side before people.

Photo of lava spilling into the Pacific Ocean from Kilauea in 2018, by National Park Service. The 2018 eruptions created 875 acres of new land.


Geology of the State of Hawaiʻi, by Harold T Stearns.
The Formation of the Hawaiian Islands, Ken Rubin, Hawaiʻi Center for Volcanology
Roadside Geology of Hawaiʻi, by Richard W. Hazlett and Donald W Hyndman.