A slow-moving mountainside in southern Alaska has scientists and emergency planners tracking what could become one of the most destructive landslide-triggered tsunamis in modern history. The unstable slope at Barry Arm in Prince William Sound contains an estimated 455 million cubic meters of rock perched above a narrow fjord, and federal models show that a sudden collapse could send waves exceeding 200 meters near the source, with runup topping 500 meters on the opposite fjord wall. While no collapse is imminent, the threat extends well beyond Alaska, placing Hawaii and the broader West Coast in a widening zone of concern.
Barry Arm: The Scale of the Threat
The numbers behind the Barry Arm scenario are staggering by any measure. The U.S. Geological Survey’s Open-File Report 2021-1071 modeled what would happen if the estimated slide mass failed catastrophically into the fjord, with the technical details laid out in a dedicated tsunami modeling study. Modeled wave heights exceed 200 meters near the source, with runup exceeding 500 meters on the opposite fjord wall. Arrival times to southern Barry Arm and Harriman Fjord fall within 10 to 15 minutes, and waves would reach the port town of Whittier in approximately 20 minutes. For a community accessible only by tunnel or water, that window is razor thin and leaves little time for evacuation once a collapse is detected.
Those projections have driven a sustained federal monitoring effort. The USGS has created a focused Barry Arm research program to track surface movement, refine landslide volume estimates, and coordinate with state emergency managers. Geophysicists have also used the horizontal-to-vertical spectral ratio method to better estimate the landslide’s thickness, tightening the parameters that feed into wave simulations and improving confidence in worst-case and more moderate scenarios. Each refinement sharpens the picture of how much energy a collapse could release and how far the resulting waves would travel, informing everything from harbor design to evacuation signage in nearby communities.
Monitoring Gaps Across Prince William Sound
Barry Arm is not the only unstable slope in the region. A separate USGS assessment used satellite interferometry to identify moving slopes with tsunamigenic plausibility across Prince William Sound, an effort explicitly motivated by the Barry Arm discovery. That broader inventory suggests the hazard is not confined to a single fjord but is a regional characteristic of glacially steepened terrain now losing the ice that once buttressed it. As warming air and ocean temperatures accelerate glacier retreat, more slopes that were formerly frozen in place may transition into slow-moving, potentially unstable masses similar to Barry Arm.
Real-world validation of these concerns arrived in 2024, when landslides at Surprise Inlet, also in Prince William Sound, were detected by a prototype monitoring network designed to capture landslide-generated waves. The event confirmed that landslide-driven tsunamis threaten coastal Alaska and demonstrated the value of experimental sensor arrays that combine seismometers, pressure gauges, and other instruments. Yet the prototype covers only a fraction of the coastline, and no integrated system currently links local detection in fjords like Barry Arm to cross-Pacific warning chains for Hawaii or the West Coast. That gap matters because the speed of landslide-generated waves within confined waterways leaves almost no room for delayed alerts, especially for boaters, cruise ships, and small coastal communities that rely on rapid, automated warnings.
Reassessments and Remaining Uncertainty at Barry Arm
As of a February 2026 status update from the Alaska Division of Geological and Geophysical Surveys, the Barry Arm landslide shows no signs of large-scale active deformation, easing immediate fears of a sudden collapse. Newer modeling also suggests potentially less severe outcomes than earlier worst-case assumptions, according to archived state hazard communications that incorporate updated volume estimates and more realistic failure geometries. But “less severe” is relative when even reduced scenarios still threaten port infrastructure and vessel traffic in a region that handles cruise ships, commercial fishing fleets, and fuel shipments that supply coastal communities.
Scientists emphasize that uncertainty cuts both ways. The absence of rapid deformation now does not eliminate the possibility of future acceleration, particularly if intense rainfall, rapid snowmelt, or seismic shaking destabilize the slope. To narrow those uncertainties, agencies rely on a mix of remote sensing, in situ instruments, and numerical models, many of which are documented and distributed through official USGS data portals. These tools allow researchers and emergency planners to test evacuation routes, simulate harbor impacts, and explore how different trigger scenarios (such as a partial versus full-slope failure) would change the resulting tsunami. The central challenge is turning that evolving science into practical, community-level decisions about land use, critical infrastructure placement, and public education before a real emergency unfolds.
Hawaii and the West Coast Face Distinct Dangers
A Barry Arm collapse would primarily devastate Prince William Sound, but the broader tsunami threat to Hawaii and the Pacific coast stems from multiple sources that extend far beyond any single landslide. Hawaii, sitting in the middle of the Pacific “Ring of Fire,” is exposed to wave-generating earthquakes around the entire basin and is widely recognized as the U.S. state at greatest risk for tsunami impacts. The islands lie in the direct path of energy radiating from subduction zones in Alaska, Chile, Japan, and elsewhere, meaning that a major event almost anywhere along the Pacific margin can send waves toward Hawaiian shores within hours, challenging emergency managers to interpret distant seismic data and issue timely warnings.
Along the West Coast, the Cascadia Subduction Zone presents its own long-term hazard. The USGS maintains a comprehensive Cascadia database compiling locations of tsunami deposits, sites of coseismic land-level change, marine cores and turbidites, GNSS velocities, mapped faults, slip rates, and seismicity. That evidence base documents repeated great earthquakes over thousands of years, each capable of generating ocean-crossing waves that would strike northern California, Oregon, Washington, and British Columbia with little local warning. While a Barry Arm tsunami would be more localized in its most destructive phase, the Cascadia record underscores that the West Coast must prepare for a spectrum of tsunami sources, from distant megathrust ruptures to nearer submarine landslides and volcanic flank failures, that could arrive with different warning times and inundation patterns.
Learning From History and Building a Warning Chain
One of the most powerful tools for understanding what Barry Arm or a future Cascadia event might do is the historical record of past tsunamis. The National Centers for Environmental Information curate global tsunami data that catalog wave heights, arrival times, and damage from events spanning more than a century. These records show that landslide-generated tsunamis, while less frequent than earthquake-driven ones, can produce extreme local runup and unexpected damage patterns, as seen in Alaska’s own 1958 Lituya Bay event. By comparing modeled Barry Arm scenarios with observed impacts from historical analogs, scientists can better gauge which parts of Prince William Sound, Hawaii, or the West Coast might see dangerous currents, harbor resonance, or coastal flooding even when far from the slide itself.
Translating that knowledge into safety, however, depends on a functioning warning chain that connects sensors, analysts, and communities. For Barry Arm and similar fjord systems, that chain begins with ground-based and satellite monitoring that can detect accelerating slope movement or the signature of a collapse in real time. It then runs through regional tsunami centers, which must quickly decide whether a local event poses a broader oceanic threat, and ends with coastal residents who understand sirens, text alerts, and natural warning signs such as strong ground shaking or sudden water level changes. Integrating specialized landslide monitoring in Prince William Sound with basin-wide alert systems designed for subduction-zone earthquakes remains an unfinished task, but the science now on the books makes clear that the cost of inaction could be measured in lost lives and devastated coastal economies.
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*This article was researched with the help of AI, with human editors creating the final content.
