A half-billion cubic meters of fractured rock above Alaska’s Barry Arm fjord is sending out strange seismic signals, a kind of subterranean heartbeat beneath a slope that could, in the worst case, generate a megatsunami. The signals are subtle, but the stakes are not, because the unstable mass sits directly over a narrow inlet lined with fishing boats, cruise routes, and coastal communities that have already seen how violently steep Alaskan terrain can fail.
As researchers tune in to these low rumblings, they are trying to answer two intertwined questions: what exactly is moving inside this enormous block of rock, and how much warning it might give before a catastrophic slide. The emerging picture is a story of hidden fractures, evolving technology, and a race to read the signals of a hazard that has been flagged as both plausible and urgent.
The unstable giant above Barry Arm
The potential disaster zone begins with a single, enormous rock mass perched above Barry Arm, a fjord in Prince William Sound in Alaska. Scientists estimate that roughly 500 million cubic meters of material is draped across a steep slope that was left over-steepened and weakened after a retreating glacier pulled back from the valley wall, leaving a cliff-like face and a jumbled interior of broken rock. That combination of volume, height and structural weakness is what makes Barry Arm stand out among the many landslide-prone slopes in coastal Alaska.
Researchers monitoring this unstable Barry slope have documented that the rock is not quiet, but instead produces a pattern of unusual seismic activity that does not match ordinary earthquakes. The signals, described as mysterious seismic signals beneath a potential megatsunami zone, are tied directly to the mass of rock above Barry Arm and have become the focus of a dedicated monitoring effort that treats the entire slope as a single, restless body rather than a series of small, isolated failures, a distinction that matters when the volume in question is measured in hundreds of millions of cubic meters.
Strange seismic signals and what they might mean
The most intriguing clue to what is happening inside this 500 million cubic meter block is a set of repeating, low-level tremors that do not behave like typical tectonic earthquakes. Instead of sharp jolts, instruments are picking up longer, more drawn-out vibrations that suggest slow movement or internal cracking within the rock mass itself. These mysterious seismic signals beneath a potential megatsunami zone have raised the possibility that the slope is creeping, deforming in ways that are too subtle to see at the surface but large enough to leave a fingerprint in the seismic record.
Scientists working on this problem are careful not to over-interpret the data, but they are equally clear that the signals are real and persistent. The pattern points to a complex interaction between gravity, groundwater, and the fractured architecture of the slope, with the rock mass behaving less like a solid wall and more like a stack of blocks that can grind, slip, and occasionally lurch. The fact that these signals are coming from directly beneath the unstable Barry rock mass has turned them into a central piece of evidence in efforts to understand whether the slope is slowly stabilizing or edging closer to failure.
How a megatsunami could form in Barry Arm
The reason this particular slope has drawn global attention is not only its size but its position above deep, confined water. If a large portion of the 500 million cubic meters of rock were to detach rapidly and plunge into Barry Arm fjord, the displacement of water could generate a wave hundreds of meters high near the source. In a narrow inlet, that wave would have little room to spread out, so the initial wall of water could be extraordinarily tall before it begins to decay as it races down Prince William Sound.
Earlier analysis of Barry Arm has warned that the area in Barry Arm fjord will be destroyed if a major collapse occurs, with flying rocks and water expected to sever trees and scour the shoreline. Anyone in the vicinity will likely be killed by the direct impact of debris and the violent surge of water, a scenario that has led experts to describe Barry Arm as an urgent hazard for nearby communities and maritime traffic. The combination of a towering initial wave, confined geography, and short travel times to populated areas is what turns a slope failure into a potential megatsunami rather than a localized landslide.
Listening posts on the fjord walls
To move beyond worst-case scenarios and into measurable risk, researchers have spent the past several years wiring Barry Arm with instruments designed to catch the earliest signs of accelerating movement. Since 2020, researchers have equipped the unstable Barry slope with seismic sensors and other monitoring tools that can detect subtle changes in vibration patterns, shifts in the timing of tremors, and any uptick in the rate at which the rock mass deforms. The goal is to build a continuous record of the slope’s behavior, so that any departure from its baseline can be recognized quickly.
This network of instruments is not just listening for a single, dramatic crack, but for the quieter precursors that often precede large landslides. By tracking how the seismic signals evolve as the slope becomes unstable, scientists hope to identify a set of warning signs that could be used to trigger alerts or evacuations. The work at Barry Arm is part of a broader effort to understand how unstable slopes talk through the ground, and how those signals can be translated into actionable information before a catastrophic failure sends rock and water surging through Prince William Sound.
Decoding the seismic fingerprints of slope failure
One of the most promising developments in this field is the use of detailed seismic analysis to search for landslide clues in the noise that constantly ripples through the Earth. A recent study focused on seismic signals from Alaska’s Barry Arm has treated the slope as a natural laboratory, examining how different types of tremors correlate with small movements and changes in the rock mass. By comparing these patterns over time, researchers are beginning to distinguish between background activity and the more ominous signatures of accelerating slope movement.
The study searches for landslide clues in seismic signals from Alaska’s Barry Arm by looking for specific frequencies, durations, and waveforms that might indicate internal cracking or the slow glide of large rock blocks. The researchers note that certain patterns appear to be tied directly to slope movement, suggesting that with enough data, it may be possible to recognize when the system is transitioning from a relatively stable state to one that is primed for failure. This kind of seismic fingerprinting is still in its early stages, but it offers a path toward turning the strange signals under Barry Arm into a practical early warning tool.
Recent Alaskan slides and the scale of the threat
The danger at Barry Arm does not exist in isolation, and recent events elsewhere in Alaska have underscored how destructive slope failures can be when they intersect with water. Earlier this year, a tsunami-causing slide in Alaska was identified as larger than anything in the past decade in Alaska, a benchmark that came from detailed analysis by the Alaska Earthquake Center. Alaska Earthquake Center Director Michael West described that event as a reminder of how much energy can be released when a large volume of rock suddenly collapses into a body of water.
In that case, the slide-generated tsunami was powerful enough to be recorded across a wide area, and it has been used as a real-world example of the processes that could play out on an even larger scale at Barry Arm. The Alaska Earthquake Center Director Michael West has also referred to the ability to monitor such hazards in real time as the Holy Grail of hazard monitoring, a phrase that captures both the ambition and the difficulty of predicting when a slope will finally give way. The Barry Arm monitoring effort is, in many ways, an attempt to move closer to that goal by learning from every available slide and its seismic signature.
Rock mass quality in Prince William Sound
Understanding why Barry Arm is so unstable requires zooming out to the broader geology of Prince William Sound, where glaciers, tectonics, and coastal erosion have carved steep, fractured slopes along the fjords. Multiple subaerial landslides adjacent to Prince William Sound, Alaska, have been documented in recent years, including events in western and eastern Prince William Sound that involved large rock masses detaching from over-steepened valley walls. These failures are not random; they tend to occur where rock mass quality is poor, with extensive fracturing, weak layers, and complex structural geology.
Detailed rock mass quality and structural geology observations in Prince William Sound, Alaska, have shown that many slopes share similar weaknesses, including the presence of old glacial scars, zones of crushed rock, and discontinuities that can act as sliding surfaces. Studies that reference Dai and others and Higman and others have highlighted how these structural features can predispose a slope to failure once external triggers such as heavy rainfall, rapid snowmelt, or seismic shaking are added. Barry Arm fits squarely within this pattern, with its 500 million cubic meters of rock resting on a foundation that has been heavily modified by past glaciation and ongoing coastal processes.
Why Barry Arm is labeled an “urgent hazard”
Long before the latest seismic signals were cataloged, experts had already singled out Barry Arm as a uniquely dangerous combination of unstable geology and human exposure. Analyses of the fjord have warned that the area in Barry Arm fjord will be destroyed if a major slope collapse occurs, with flying rocks and water projected to sever trees and strip the shoreline. Anyone in the vicinity will likely be killed by the direct impact of debris and the force of the wave, a stark assessment that has led specialists to describe Barry Arm as an urgent hazard that demands close monitoring and contingency planning.
The concern is not limited to the immediate impact zone. A large wave generated in Barry Arm could propagate through Prince William Sound, affecting fishing communities, ports, and shipping lanes that are central to the regional economy. The combination of a 500 million cubic meter rock mass, a confined fjord, and the potential for flying debris and extreme wave heights has pushed Barry Arm to the top of the list of coastal hazards in Alaska, prompting calls for better evacuation planning, real-time monitoring, and clear communication with residents and mariners who could be in the path of a slide-generated tsunami.
Megatsunami physics and the 500 meter benchmark
To grasp the scale of what is at stake, it helps to look at how scientists and educators describe megatsunamis in general. In a widely viewed explanation of a 500 meter tall megatsunami in Alaska, a video released in Oct walks through the physics of how an enormous wave can form when a large mass of rock suddenly enters a confined body of water. The discussion emphasizes that megatsunamis are not typical ocean-wide tsunamis generated by distant earthquakes, but highly localized events where wave heights near the source can reach hundreds of meters before rapidly diminishing with distance.
In that context, the 500 million cubic meter rock mass above Barry Arm becomes more than an abstract number. If even a fraction of that volume were to fail rapidly, the initial wave in the fjord could approach the extreme heights described in the 500 meter tall megatsunami scenario, at least near the impact zone. The Oct discussion underscores that the key ingredients are a large, fast-moving landslide, deep water, and a narrow basin, all of which are present at Barry Arm. While the exact height of any future wave cannot be predicted with precision, the physics make clear that the combination of volume and geometry is capable of producing a truly extraordinary surge.
Comparing Barry Arm’s signals with volcanic tremor
One of the puzzles facing scientists at Barry Arm is how to interpret the unusual seismic signals coming from beneath the slope, and here comparisons with other natural systems can be instructive. According to Ingibjörg Andrea Bergþórsdóttir, a natural hazards specialist at the IMO, tremors detected near Grjótárvatn in Iceland are not typical earthquakes but rather low-frequency rumbles associated with volcanic systems. These signals, which have been linked to deep-seated magma movement detected near Grjótárvatn, show how different physical processes can produce distinct seismic signatures that depart from the sharp jolts of tectonic quakes.
The Barry Arm signals are not being attributed to magma, but the analogy helps illustrate why researchers are paying close attention to their frequency content and duration. Just as the low-frequency rumbles near Grjótárvatn reveal the slow movement of magma, the longer, more drawn-out vibrations beneath Barry Arm may be revealing the slow deformation of rock. By comparing these patterns with known examples from volcanic and landslide settings, scientists hope to refine their interpretation of what the 500 million cubic meter rock mass is doing at depth, and whether its internal movements are accelerating in a way that would warrant heightened concern.
From strange signals to practical warning
For communities and mariners in Prince William Sound, the key question is not whether the rock above Barry Arm is moving at all, but whether the strange signals it emits can be turned into a reliable warning system. The work to study landslide clues in seismic signals from Alaska’s Barry Arm, combined with the broader monitoring network that has been in place since 2020, is aimed at building exactly that bridge between scientific insight and public safety. The hope is that by cataloging how the seismic fingerprints of the slope change over time, it will be possible to recognize when the system is entering a more dangerous phase.
There are limits to what any monitoring system can promise, and no one is suggesting that the 500 million cubic meter rock mass can be predicted to the day or hour. Yet the combination of continuous seismic listening, detailed rock mass quality assessments in Prince William Sound, and lessons from other Alaskan slides and volcanic tremor studies is steadily improving the odds that a major change in behavior would be noticed in time to act. For now, the giant above Barry Arm continues to murmur rather than roar, but the instruments are listening, and the strange signals beneath this potential megatsunami zone are no longer passing unnoticed in the deep.
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