A towering wall of water, potentially reaching 1,000 feet high, could race across the ocean at hundreds of miles per hour and devastate coastal areas. According to Dailymail UK, These mega-tsunamis differ from ordinary tsunamis caused by earthquakes, as they usually result from massive landslides or collapsing volcanoes. In the United States, Alaska, Hawaii, and the West Coast face such threats due to their proximity to unstable geological formations and active seismic zones.
One of the most discussed scenarios involves the Cumbre Vieja volcano on the Canary Island of La Palma. A study from 2001 by Dr. Simon Day and Steven Ward warned that a collapse of the volcano’s west flank could send up to 120 cubic miles of rock into the Atlantic Ocean. This event could produce a mega-tsunami starting 2,000 feet high near the volcano and still towering 150 feet upon reaching the Americas. This scenario was dramatized in the Netflix series La Palma, depicting the risk to US East Coast communities.
Alaska: Site of the Tallest Recorded Mega-Tsunami and Increasing Risks
On July 9, 1958, Alaska’s Lituya Bay witnessed the tallest tsunami ever recorded. An earthquake triggered a massive landslide at Gilbert Inlet, where approximately 90 million tons of rock, measuring roughly 2,400 feet by 3,000 feet, crashed into the water. According to NASA, this was equivalent to eight million dump truck loads falling simultaneously, generating a 1,719-foot wave.
Eyewitnesses described a loud “boom” and saw ice-filled waves sweep away lighthouses and strip forests bare. One fisherman’s boat was lifted so high he could look down on treetops, while a couple disappeared during the event. The event was caused by an earthquake shaking loose massive rock from steep cliffs, which displaced the water and created the enormous wave.
Alaska’s rugged terrain and frequent earthquakes continue to make it prone to landslides. Climate change worsens this threat by melting glaciers, destabilizing slopes further. In 2020, fourteen scientists warned that the retreat of Barry Glacier could soon cause a rockslide into Harriman Fiord, potentially triggering a tsunami as large as the 1958 event. Steve Masterman, director of Alaska’s Division of Geological Surveys, emphasized that “these events are becoming increasingly likely as temperatures warm.”
Hawaii’s Volcanic Islands and History of Mega-Tsunamis
Hawaii’s volcanic landscape has a history of massive waves caused by volcanic collapses. About 105,000 years ago, a 1,000-foot wave struck the island of Lanai, leaving marine fossils high on mountain slopes. Researchers attribute this to a huge volcanic landslide, similar to the Cumbre Vieja scenario.
Another example is the 20-mile-long Nu’uanu slide, which sent enormous volumes of rock into the ocean, creating waves up to 300 feet high and reshaping coastlines. The islands’ steep volcanic slopes are prone to collapse during eruptions or earthquakes. The ongoing volcanic activity, including recent eruptions from Kīlauea—which was actively erupting for months before its last eruption ended on May 6—adds to the risk.
Researchers from Penn State warn that these unstable slopes could collapse again, unleashing massive waves. Residents and visitors are urged to stay prepared for sudden tsunami warnings and evacuation orders due to the region’s constant geological activity.
The West Coast and the Threat From the Cascadia Subduction Zone
On January 26, 1700, a magnitude 9 earthquake along the Cascadia Subduction Zone generated a mega-tsunami that destroyed the village of Pachena Bay on the US West Coast. Waves up to 100 feet high struck just 30 minutes after the quake, leaving no survivors. Huu-ay-aht Chief Louis Clamhouse recounted, “The land shook at night… they had no time to escape. All drowned.” The earthquake also lowered coastal forests into the tidal zone, creating “ghost forests” of dead tree stumps that are still visible today. A mysterious tsunami recorded in Japan was later linked to this event.
Unlike landslide-driven tsunamis, the Cascadia mega-tsunami resulted from one tectonic plate sliding beneath another, displacing vast amounts of ocean water. This event demonstrated how far-reaching such waves can be. The US Geological Survey and FEMA estimate a 37 percent chance of another magnitude 8 to 9 earthquake in the Cascadia zone within the next 50 years. Similar events could cause waves resembling Japan’s 2011 Tohoku tsunami, which claimed nearly 16,000 lives. Coastal towns such as Tillamook, Astoria, and Newport could be submerged, with some areas sinking permanently.
The active geology and environmental changes in Alaska, Hawaii, and along the West Coast make these regions vulnerable to future mega-tsunamis. Ongoing monitoring and improved emergency preparedness aim to reduce impacts, but the threat posed by landslides, volcanic collapses, and massive earthquakes remains.
