A 481-meter-high landslide-tsunami in a cruise ship–frequented Alaska fjord.
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| Title: | A 481-meter-high landslide-tsunami in a cruise ship–frequented Alaska fjord. |
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| Authors: | Shugar, Dan H. (AUTHOR), Barnhart, Katherine R. (AUTHOR), Berdahl, Mira (AUTHOR), Caplan-Auerbach, Jacqueline (AUTHOR), Ekström, Göran (AUTHOR), Fathian, Aram (AUTHOR), Geertsema, Marten (AUTHOR), Hicks, Stephen P. (AUTHOR), Higman, Bretwood (AUTHOR), Jensen, Erin K. (AUTHOR), Karasözen, Ezgi (AUTHOR), Lynett, Patrick (AUTHOR), Lyons, John (AUTHOR), Monahan, Thomas (AUTHOR), Roe, Gerard (AUTHOR), Svennevig, Kristian (AUTHOR), Toney, Liam (AUTHOR), Van Wyk de Vries, Maximillian (AUTHOR), West, Michael E. (AUTHOR) |
| Source: | Science. 6/11/2026, Vol. 392 Issue 6803, p1-12. 12p. |
| Subjects: | Landslides, Tsunamis, Climate change, Induced seismicity, Fjords, Cruise ships, Glacial melting |
| Geographic Terms: | Alaska |
| Abstract: | Early in the morning of 10 August 2025, a >64 × 106–cubic meter landslide struck Tracy Arm fjord in Alaska. The landslide was preconditioned by glacial retreat caused by climate change. The resulting 481-meter runup megatsunami followed an initial 100-meter-high breaking wave traveling at >70 meters per second. The landslide was preceded by several days of microseismicity, which increased in rate and magnitude until ~1 hour before failure. The landslide produced globally observed long-period seismic waves equivalent in size to a moment magnitude 5.4 earthquake. A long-period (~66 second) global seismic signal, produced by a landslide-induced seiche trapped within the fjord, persisted for up to 36 hours, the second time a days-long seiche had thus been observed. With fjord regions increasingly visited by cruise ships, and climate change making similar events more likely, this unanticipated, near-miss event highlights the growing risk from landslides and tsunamis in coastal environments. Editor's summary: Retreat of coastal glaciers may be exposing these regions to increasing risk of landslide-triggered tsunamis. Shugar et al. report on the 10 August 2025 landslide in Tracy Arm fjord that caused a tsunami with runup as high as 480 meters. The landslide-tsunami occurred early in the morning, before the arrival of tour cruises, which during the summer can include six vessels and thousands of passengers each day. Pre- and postevent seismic and satellite data revealed precursory microseismicity, global long-period waves and a days-long, globally recorded standing wave in the fjord. The analysis highlights the potential for monitoring and risk mitigation along warming coastlines. —Angela Hessler INTRODUCTION: At 5:26 a.m. Alaska Daylight Time on 10 August 2025 (13:26 UTC), a large landslide (>64 × 106 m3) collapsed one vertical kilometer onto South Sawyer Glacier and into Tracy Arm fjord in southeast Alaska, after several hundred meters of glacier retreat at the base of the slope in the preceding months. The resulting tsunami ran up the opposing fjord wall 1.6 km away to a height of 481 m above sea level and propagated out of the fjord and into Stephens Passage and Endicott Arm to the south. An hour later, a ≥0.4-m-high wave was registered on a tide gauge ~130 km away, in Juneau, Alaska. The runup from this tsunami was the second highest ever recorded, approaching the record 530 m from the 1958 landslide-generated tsunami in Lituya Bay, Alaska. The Tracy Arm event also produced a days-long seiche, only the second ever to have produced an observable global seismic signal. In summer, Tracy Arm is frequented, on average, by three cruise ships per day, plus an unknown number of other vessels that travel within a few kilometers of the location of the landslide. The Tracy Arm landslide and tsunami occurred early in the day when vessels had not yet arrived in the upper fjord. The tsunami could have caused fatalities if it had hit a ship in the upper fjord, and the timing of future events could potentially result in higher exposure and substantial consequences. RATIONALE: Glacier retreat, including at Tracy Arm, is increasing the risk of hazard cascades. The large landslide in an area not previously assessed for slope instability in a fjord with extensive cruise ship activity highlights the risk of landslide-generated tsunamis (referred to here as landslide-tsunamis) and underscores how enhanced monitoring and continued research can help mitigate the effects of these hazards. RESULTS: The initial >64 × 106 m3 landslide was a rock wedge failure that transitioned into a rock avalanche as it traveled down the slope. Simulations of the resulting tsunami indicate an impulsive and violent generation, with a 100-m-high breaking wave impacting the opposite shoreline and reaching 481 m in elevation, with flow speeds exceeding 70 m s−1. The event was preceded by several days of precursory seismicity identified retrospectively, with small [up to moment magnitude (Mw) 2.1] earthquakes becoming increasingly frequent over time. The landslide itself produced globally observed long-period seismic waves equivalent in size to those of a Mw 5.4 earthquake. Long-period multichromatic seismic signals emerged from the landslide signal, with a mode at a 66-s period traveling globally and persisting for up to 36 hours, consistent with a landslide-induced seiche trapped in the fjord and confirmed by tsunami simulations and satellite observations. CONCLUSION: Glacier retreat in an Alaska fjord led to a rearrangement of landscape elements such that a large landslide was able to trigger a tsunami that ran up 481 m on the opposite fjord wall. Without the rapid glacier retreat, the landslide would not likely have resulted in such a wave because it would have collapsed entirely onto glacier ice or might not even have occurred at all. As the tsunami traveled out of the fjord, it stripped the walls of vegetation up to elevations of a hundred meters and produced a >36-hour-long seiche. Despite the magnitude of this event, no fatalities occurred during the Tracy Arm landslide and tsunami. With continued warming of cold regions, hazards from these events are growing alongside increasing exposure as a result of the expansion of infrastructure and cruise-ship tourism. Similar hazard cascades could result in future disasters. Landslide-tsunami in Tracy Arm, Alaska.: Simulations of a >64 × 106 m3 landslide into Tracy Arm at times (t) 0, 30, and 60 s (left) and an aerial photo of the tsunami runup observed directly across the fjord from the landslide (right; the dashed red line indicates approximate wave runup elevation, but maximum runup is out of frame to the left). Note the height of the runup relative to the ocean level on the right side of the photo. [PHOTO CREDIT: J. LYONS US GEOLOGICAL SURVEY] [ABSTRACT FROM AUTHOR] |
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| Database: | Psychology and Behavioral Sciences Collection |
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| Abstract: | Early in the morning of 10 August 2025, a >64 × 106–cubic meter landslide struck Tracy Arm fjord in Alaska. The landslide was preconditioned by glacial retreat caused by climate change. The resulting 481-meter runup megatsunami followed an initial 100-meter-high breaking wave traveling at >70 meters per second. The landslide was preceded by several days of microseismicity, which increased in rate and magnitude until ~1 hour before failure. The landslide produced globally observed long-period seismic waves equivalent in size to a moment magnitude 5.4 earthquake. A long-period (~66 second) global seismic signal, produced by a landslide-induced seiche trapped within the fjord, persisted for up to 36 hours, the second time a days-long seiche had thus been observed. With fjord regions increasingly visited by cruise ships, and climate change making similar events more likely, this unanticipated, near-miss event highlights the growing risk from landslides and tsunamis in coastal environments. Editor's summary: Retreat of coastal glaciers may be exposing these regions to increasing risk of landslide-triggered tsunamis. Shugar et al. report on the 10 August 2025 landslide in Tracy Arm fjord that caused a tsunami with runup as high as 480 meters. The landslide-tsunami occurred early in the morning, before the arrival of tour cruises, which during the summer can include six vessels and thousands of passengers each day. Pre- and postevent seismic and satellite data revealed precursory microseismicity, global long-period waves and a days-long, globally recorded standing wave in the fjord. The analysis highlights the potential for monitoring and risk mitigation along warming coastlines. —Angela Hessler INTRODUCTION: At 5:26 a.m. Alaska Daylight Time on 10 August 2025 (13:26 UTC), a large landslide (>64 × 106 m3) collapsed one vertical kilometer onto South Sawyer Glacier and into Tracy Arm fjord in southeast Alaska, after several hundred meters of glacier retreat at the base of the slope in the preceding months. The resulting tsunami ran up the opposing fjord wall 1.6 km away to a height of 481 m above sea level and propagated out of the fjord and into Stephens Passage and Endicott Arm to the south. An hour later, a ≥0.4-m-high wave was registered on a tide gauge ~130 km away, in Juneau, Alaska. The runup from this tsunami was the second highest ever recorded, approaching the record 530 m from the 1958 landslide-generated tsunami in Lituya Bay, Alaska. The Tracy Arm event also produced a days-long seiche, only the second ever to have produced an observable global seismic signal. In summer, Tracy Arm is frequented, on average, by three cruise ships per day, plus an unknown number of other vessels that travel within a few kilometers of the location of the landslide. The Tracy Arm landslide and tsunami occurred early in the day when vessels had not yet arrived in the upper fjord. The tsunami could have caused fatalities if it had hit a ship in the upper fjord, and the timing of future events could potentially result in higher exposure and substantial consequences. RATIONALE: Glacier retreat, including at Tracy Arm, is increasing the risk of hazard cascades. The large landslide in an area not previously assessed for slope instability in a fjord with extensive cruise ship activity highlights the risk of landslide-generated tsunamis (referred to here as landslide-tsunamis) and underscores how enhanced monitoring and continued research can help mitigate the effects of these hazards. RESULTS: The initial >64 × 106 m3 landslide was a rock wedge failure that transitioned into a rock avalanche as it traveled down the slope. Simulations of the resulting tsunami indicate an impulsive and violent generation, with a 100-m-high breaking wave impacting the opposite shoreline and reaching 481 m in elevation, with flow speeds exceeding 70 m s−1. The event was preceded by several days of precursory seismicity identified retrospectively, with small [up to moment magnitude (Mw) 2.1] earthquakes becoming increasingly frequent over time. The landslide itself produced globally observed long-period seismic waves equivalent in size to those of a Mw 5.4 earthquake. Long-period multichromatic seismic signals emerged from the landslide signal, with a mode at a 66-s period traveling globally and persisting for up to 36 hours, consistent with a landslide-induced seiche trapped in the fjord and confirmed by tsunami simulations and satellite observations. CONCLUSION: Glacier retreat in an Alaska fjord led to a rearrangement of landscape elements such that a large landslide was able to trigger a tsunami that ran up 481 m on the opposite fjord wall. Without the rapid glacier retreat, the landslide would not likely have resulted in such a wave because it would have collapsed entirely onto glacier ice or might not even have occurred at all. As the tsunami traveled out of the fjord, it stripped the walls of vegetation up to elevations of a hundred meters and produced a >36-hour-long seiche. Despite the magnitude of this event, no fatalities occurred during the Tracy Arm landslide and tsunami. With continued warming of cold regions, hazards from these events are growing alongside increasing exposure as a result of the expansion of infrastructure and cruise-ship tourism. Similar hazard cascades could result in future disasters. Landslide-tsunami in Tracy Arm, Alaska.: Simulations of a >64 × 106 m3 landslide into Tracy Arm at times (t) 0, 30, and 60 s (left) and an aerial photo of the tsunami runup observed directly across the fjord from the landslide (right; the dashed red line indicates approximate wave runup elevation, but maximum runup is out of frame to the left). Note the height of the runup relative to the ocean level on the right side of the photo. [PHOTO CREDIT: J. LYONS US GEOLOGICAL SURVEY] [ABSTRACT FROM AUTHOR] |
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| ISSN: | 00368075 |
| DOI: | 10.1126/science.aec3187 |
