HONOLULU (KHON2) — If there’s one thing Hawai’i knows, it’s the sheer strength of the ocean. Most folks are quick to recognize tsunamis as massive waves from distant earthquakes, but few are aware that the islands themselves have been responsible for some of the biggest tsunamis in Earth’s history.
Recently, a couple of major underwater landslides, one near O’ahu and another off Moloka’i, generated tsunamis of monumental size, reshaping shorelines and leaving long-lasting impact that can still be seen today.
Nū‘anu and Wailau Landslides Explained
The Nū‘anu landslide on O’ahu and its counterpart, the Wailau landslide on Moloka’i, combine to create one of the planet’s largest landslide systems. Researchers have found that the rapid growth of these volcanic terrains led to structural instability, resulting in a breakdown that sent vast amounts of materials sprawling across the ocean floor.
This geologic phenomenon not only altered the islands’ shapes but also sparked significant earthquakes, shifted coastlines dramatically, and unleashed massive tsunamis.
The Unseen Forces of Hawai’i
Historically, these islands have unleashed two of the most powerful tsunamis recorded. Unlike those caused by seismic activities, these waves stemmed from colossal landslides that transformed the geological layout, sending waves racing across the Pacific ocean toward the east and west.
Going back around 1.5 million years, two huge sections from different volcanoes fell apart. On O’ahu, the Koʻolau Volcano gave way in an event now known as the Nū‘anu Slide.
The eastern edge became what is now Kāʻneʻohe Bay, while the western side morphed into the Koʻolau Range—home to the stunning Nū‘anu Pali lookout. This event flung debris across a 140-mile expanse of seabed northeast of the island.
Meanwhile, on Moloka’i, the northern section of East Moloka’i Volcano crumbled during the Wailau Slide, leaving behind an immense amphitheater-like cavity that dominates the eastern part of the island today.
It’s essential to highlight that both of these landslides rank among Earth’s most massive.
Gigantic Waves on the Horizon
As sections of these volcanoes plunged into the ocean, they displaced vast amounts of water, resulting in gigantic tsunamis.
Research indicates that these waves might have soared hundreds of feet high, and in instances could have reached astonishing heights of up to 2,000 feet. They crashed onto nearby shores and traversed the ocean to reach as far as Asia and Turtle Island (now North America).
Physical Traces of the Past
Scientists have been scrutinizing the ocean floor where they have tracked the remains of these cataclysmic landslides. The seabed displays thick accumulations of volcanic rock that unfurl in fields extending for hundreds of kilometers.
On land, disorganized layers of rocks and sands convey where titanic waves once surged, a stark difference to the usual storm layering, marking the fierce tsunamis that are much larger than any seen in today’s Hawaiian records.
A Beautiful Place with a Monumental History
Today, Hawai’i is regarded as a gorgeous paradise, renowned for adventure and beauty. Yet, its landscape carries a profound narrative of earth-shattering geological events.
The Nū‘anu and Wailau Slides serve as potent reminders of the unstable nature of volcanic islands. The monstrous waves they created not only transformed coasts but proved that the natural bounty we now cherish boasts a turbulent history etched in the very rocks and waters.
Another History-making Incident
Research unveils another significant natural event faced by Hawai’i about 500 years ago, when a 9.0 magnitude earthquake originating from the Aleutian Islands, Alaska, sent tsunami waves reaching heights of 30 feet crashing against Kaua’i.
In the Makauwahi sinkhole, scientists unearthed layers containing coral chunks, shells, and sand, illustrating the tsunami’s immense power. The volume of these deposits was equal to that of multiple shipping containers.
This analysis pinpointed the tsunami as being at least three times stronger than the destructive wave of 1946, marking the worst such tsunami in recent Hawaiian history. The unique shape of the Aleutian trench served to redirect much of its force right toward Hawai’i.
Valuable Lessons from History
In light of these findings, city planners in Honolulu are updating evacuation routes to accommodate potential huge waves, including an expanded range of areas falling under evacuation risks. Although such extreme tsunamis are quite rare, there’s no denying the historical evidence that Hawai’i has withstood waves far more powerful than anything recorded in modern times.
For those curious about tsunami research, feel free to explore more here, here, here, here, here, here, here, here and here.
