JUNEAU, Alaska — A catastrophic wave that swept through a remote Alaskan inlet last autumn has been confirmed as the second largest megatsunami ever recorded in scientific history, reaching a maximum run-up height of 304 meters — nearly 1,000 feet — according to a peer-reviewed study published Tuesday in the journal Geophysical Research Letters.
The event occurred in October in Taan Fjord, a narrow glacial channel cutting through Wrangell-St. Elias National Park in the southeastern corner of the state. Researchers determined that a massive section of an unstable mountainside, weakened over many years by the progressive retreat of an adjacent glacier, broke free in a single catastrophic failure and plummeted into the fjord below. The displaced material struck the water with sufficient force to set approximately 100 million cubic meters of seawater into violent motion within seconds. The resulting wave stripped vegetation and soil from the surrounding slopes to the recorded height, leaving a pale scar on the valley walls that remains visible in commercial satellite imagery months after the event.
Megatsunamis differ fundamentally from seismically generated ocean tsunamis of the kind produced by subduction-zone earthquakes. Rather than being triggered by broad seafloor movement that sends energy propagating across an ocean basin, megatsunamis result from a sudden and extreme mass displacement — a landslide, rockfall, volcanic collapse, or glacier calving event — into a confined body of water. The energy generated concentrates in a geographically limited zone, producing wave heights that far exceed anything physically possible in open-ocean settings but that attenuate rapidly beyond the immediate basin and fjord system.
The only confirmed megatsunami with a greater run-up height on record was the 1958 Lituya Bay event, also in Alaska, which reached 524 meters following a major rockslide triggered by a magnitude 7.8 earthquake along a nearby fault. That event, which killed two fishermen aboard a vessel anchored in the bay, remains the tallest wave in recorded human history. The newly published study positions the Taan Fjord event in second place globally, surpassing a 1936 fjord wave in Norway that previously held the second-highest rank on the scientific record.
The research team, drawn from geologists and oceanographers at three North American universities, reconstructed the October event using multiple independent data streams. They analysed satellite radar imagery captured both before and after the failure, took direct field measurements during a subsequent research expedition into the fjord, and ran the resulting dataset through validated computer hydrodynamic models to calculate the precise wave height, propagation speed, and energy profile. The study notes that because the fjord is remote and uninhabited, no human casualties resulted from the event. However, a research team monitoring the area remotely happened to have slope-instability sensors active in the vicinity and recorded anomalous ground movement data in the hours before the collapse, though not in time to issue a formal alert.
Lead author Dr. Priya Narayanan said the findings highlight an accelerating pattern of mass-wasting events in glaciated mountain environments directly attributable to ice loss. As glaciers thin and retreat, they withdraw the lateral and basal mechanical support they have historically provided to adjacent valley walls, exposing rock slopes that in many cases have been frozen and buttressed for thousands of years. Once that support is removed, the underlying geology — in many areas fractured, saturated, and subject to freeze-thaw cycles over millennia — becomes prone to sudden and catastrophic failure. She said her team’s rate of identifying high-risk slopes in Alaska, British Columbia, and Greenland through remote-sensing analysis has grown substantially over the past decade as the pace of glacial retreat has accelerated.
Coastal geographers and maritime safety specialists not involved in the study said the research raises important questions about risk protocols in high-latitude regions where settlement is sparse but marine traffic is significant. Commercial fishing fleets, research vessels, and cruise ships regularly navigate fjord and inlet systems in coastal Alaska and neighbouring Canadian waters that could be exposed to future events of this type. One specialist said that existing hazard assessment frameworks for these corridors were largely developed before the current rate of glacial retreat was anticipated and may require substantial revision.
Alaska’s Division of Geological and Geophysical Surveys said it is expanding an early-warning monitoring network developed after a previous Alaskan fjord event to include additional slope-stability sensors at six high-risk sites identified in the supplementary risk assessment appended to the new study. The division confirmed it is in active coordination with maritime safety authorities and the national parks service to review whether navigation advisories for the most at-risk coastal corridors should be updated in light of the findings.