Somewhere in the realm of one million years ago, disaster struck Hawaii.

The Nu’uanu Slide, as it has come to be known, ripped apart half of modern-day Oahu, sending untold amounts of sediment into the ocean, and creating a massive tsunami.

Still, today, remnants of the ancient landslide are visible today.

Back then, the Hawaiian Islands were one super landmass, which is today referred to as Maui Nui. And a massive landslide – perhaps one of the largest in known history – happened on the windward side of Oahu, splitting the island in two, and creating a mega-tsunami.

In fact, remnants from that landslide are still visible today, as seen in the video above.

“One of the rock chunks that slid down the mountain is over 16 miles wide,” the narrator says in the clip above. “That’s larger than the island of Lanai. Scattered away from it are relatively smaller rock chunks. This pattern shows the dispersion of debris as it landed on the seafloor, just like a snowball crashing into the ground.”

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What caused it?

“Likely a huge earthquake caused by the sudden release of built up pressure from the hotspot below,” the narrator continues. “This earthquake could have literally been off the richter [scale]. But, of course, there’s no way of knowing for sure.”

As for the resulting tsunami wave, while shifting underwater tectonic plates have been known to create catastrophic waves, some of the biggest surges are formed from landslides. Like, for instance, the biggest-ever tsunami on record at 1,720 feet in Lituya Bay, Alaska from 1958. And the size of this million-year-old tsunami. Hard to tell.

In another armchair historian video, they speculate: “The landslide had an estimated volume of 720 cubic miles of material, and created a destructive Pacific-wide tsunami with wave heights likely surpassing 500 feet in certain locations.

And the rocks still visible from the catastrophic landslide? Per the USGS:

“The caldera was bisected by the catastrophic collapse of the Nu'uanu landslide, which deposited numerous blocks on the sea floor as far as 100 miles northeast of the island. The largest of these blocks is about the same size as Manhattan Island.”

Today, we talk about the big one; but the future quake wasn’t the first.

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This story was originally published by Surfer on Apr 5, 2026, where it first appeared in the News section. Add Surfer as a Preferred Source by clicking here.