Alaska fjord mega‑tsunami reaches 480 m after mountain collapse tied to glacier melt

On 9 August 2025 the cruise ship Hanse Explorer sailed through the South Sawyer Glacier fjord in remote Alaska. Twelve hours later a large section of an adjacent mountain flank gave way, plunging millions of tonnes of rock into the water. The impact generated the second‑largest recorded tsunami, with a run‑up of 481 m – a wall of water that swept the opposite cliff face entirely.

Scientists say the event illustrates a growing hazard as rapid glacier retreat weakens natural buttresses that stabilize fjord‑side mountains. Similar mega‑landslides have recently struck Norway and Greenland. Researchers propose a three‑tier seismic‑alert system (yellow, orange, red) to warn ships and nearby communities when precursor tremors are detected, aiming to prevent future loss of life as climate‑driven instability accelerates.