A huge landslide in Alaska’s Tracy Arm fjord generated a towering tsunami and seiche that lingered for 36 hours.
A tsunami measured in hundreds of metres erupted inside Alaska’s Tracy Arm fjord after a massive landslide, underscoring how quickly hazards can escalate in steep coastal terrain.
Misryoum reports that detailed reconstructions indicate the wave reached more than 480 metres in height within the fjord, making it among the largest tsunamis ever recorded. The event occurred at about 5:26am, when the fjord’s deep, narrow geography helped funnel the energy and intensify the surge.
Meanwhile, the tsunami did not simply pass. It swept through the fjord at speeds of at least 70 metres per second and triggered a seiche, a wave that reflects and sloshes back and forth in an enclosed water body, persisting for roughly 36 hours.
This matters because the danger from such events is not only the initial surge, but also the prolonged oscillations that can keep conditions volatile long after the first wave.
Misryoum says researchers pieced together what happened using a combination of satellite observations. seismic records. accounts from people in the region. and computer modeling.. Their analysis points to a destabilization process in the Tracy Arm area: as a glacier retreated and thinned over time. it likely undermined surrounding terrain until a large portion of rock collapsed into the fjord.
Crucially, investigators found little obvious warning immediately before the failure, though smaller tremors were detected in the days leading up to the landslide. The first direct sign came when kayakers camping far from the impact zone woke up to find their campsite inundated and swept away.
Misryoum notes that the timeline of discovery shaped how quickly the scale of the event could be assessed. After the landslide triggered a seismic signal, a dedicated research visit to the area did not occur until weeks later, limiting early on-the-ground documentation.
At the same time, the absence of nearby vessels during the worst moments proved fortunate.. With cruise and tourism activity common in nearby fjord landscapes. the timing meant that the most severe part of the wave may have struck when no ships were positioned near the upper fjord where survival would have been particularly unlikely.
The broader lesson, as Misryoum emphasizes, is that such tsunamis are often not linked to a single direct trigger.. Instead. they can reflect indirect pathways in which changing ice and coastal slopes alter the likelihood of extreme failures. creating hazards that may be underestimated even where people know fjords and glaciers well.
In this context, policymakers and local planners face a clear challenge: designing risk awareness and emergency preparation for events that can arrive suddenly in terrain where the scale of potential wave amplification is easy to overlook.