It turns out that an enormous tsunami in Alaska last summer was one of the biggest in history. Researchers say a mountainside collapse in August sent 64 million cubic meters of rock crashing into Tracy Arm fjord near Juneau, driving water up the fjord's walls to about 1,578 feet, reports New Scientist. Only the 1958 Lituya Bay event, also in Alaska, is known to have been higher. The wave raced along at an estimated 156mph and set off a seiche, a sloshing rebound that disturbed the fjord for a day and a half. The timing—5:26am—meant cruise ships and tour boats weren't nearby. Kayakers camping some 30 miles away reported flooding at their site.
"We know that there were people that were very nearly in the wrong place," says Alaskan geologist Bretwood Higman, per the BBC. 'I'm quite terrified that we're not going to be so lucky in the future." Writing in Science, researchers say the wave was unleashed by a sudden, massive landslide and was likely driven by climate change: As glaciers in the region have shrunk by about 13% since the mid-1980s, once-frozen slopes have been destabilized. Unlike many large rock avalanches that creep and crack for months, this one offered virtually no warning, notes the New York Times, which features a simulation of the giant wave. Seismic rumblings were so faint they went unnoticed.
Using NASA's new Surface Water Ocean Topography satellite along with seismic data and modeling, scientists were able to "see" the tsunami after the fact—and warn that similar, highly localized waves could wind up larger than quake-driven tsunamis. The USGS and study authors urge closer monitoring of glacier-lined fjords. Several cruise lines, meanwhile, have already rerouted 2026 Alaska itineraries away from Tracy Arm.
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