Alaska 2025's glacier retreat linked to one of the tallest tsunamis ever recorded

A massive landslide in Alaska’s Tracy Arm Fjord generated one of the highest tsunami run-ups ever documented, according to new scientific analysis. The event occurred on 10 August 2025, when more than 64 million cubic metres of rock and debris collapsed from a mountainside near South Sawyer Glacier and plunged into the narrow fjord below.

The impact displaced a large volume of water and produced a megatsunami with a maximum run-up height of approximately 481 metres. This makes it the second-highest tsunami run-up documented in modern records, after the 1958 Lituya Bay event, also in Alaska.

The failure was preconditioned by glacier retreat. As South Sawyer Glacier pulled back, it reduced support for the steep valley wall, leaving the rock mass more vulnerable to collapse. When the slope failed, the confined geometry of the fjord amplified the tsunami, forcing water and debris high up the surrounding slopes and stripping vegetation from large areas.

No fatalities or injuries were reported, largely because the event occurred early in the morning before tourist vessels entered the fjord. Tracy Arm is a popular cruise and sightseeing destination, and researchers described the event as a near miss because vessels were expected in the area later that day.

The event highlights a growing geotechnical hazard in glaciated fjords. As warming temperatures contribute to glacier retreat and the destabilisation of steep rock slopes, landslide-generated tsunamis may become a more significant risk in Arctic and sub-Arctic regions. For engineers and hazard planners, the Alaska megatsunami shows that remote fjord landscapes can still pose direct risks to tourism, navigation, and coastal infrastructure.