Sasha Calvey awoke to an ominous roar on August 10, 2025, a sound that defied explanation and instilled immediate dread. Camped with two friends on a remote island in Southeast Alaska, 74 days into a sea kayaking expedition from Washington, Calvey was jolted from her sleeping bag not by the expected sounds of a coastal storm, but by a deep, resonant rumble that grew alarmingly louder and closer. The sound, likened to a colossal waterfall, intensified until it vibrated through the very ground beneath their tent, compelling Calvey to investigate.

Emerging into the pre-dawn light, the trio discovered a scene of utter devastation wrought by 15-foot waves that had just surged inland, inundating the forest bordering their campsite. Seaweed lay scattered across the mossy ground near their tent, a stark indicator of the ocean’s violent intrusion. Their meticulously stored food and gear, stashed on the gravel beach, were partially swept away, with one kayak impaled on a tree and another precariously lodged on a bluff. A third vessel was spotted adrift in the distance. Reflecting on their narrow escape, Calvey noted their immense luck, realizing that had the tsunami struck just three hours earlier, during the higher tide, the water could have easily breached their campsite, potentially sweeping them away. For hours, the water remained violently chaotic, characterized by powerful swells and disorienting whirlpools, prompting the group to radio for rescue and abandon their arduous journey.

Later, the cause of the astonishing wave was identified as a massive landslide occurring approximately 30 miles away, at the terminus of Tracy Arm fjord, a dramatic waterway carving through the mountains south of Juneau. Scientists believe the landslide was linked to the ongoing retreat of the South Sawyer Glacier, a phenomenon increasingly contributing to geological instability in the region. The immense scale of the event was evident in the scar left on the mountainside, a dramatic testament to the sheer volume of rock and soil that had cascaded into the fjord.

The tsunami generated by the slide exhibited an extraordinary run-up of 1,580 feet on the adjacent mountainsides, stripping vegetation and soil as it ascended. This figure represents the second-largest run-up ever recorded, underscoring the catastrophic power of the event. As the initial wave surged away from the impact zone, it scoured the steep fjord walls, its residual energy reaching Calvey’s remote beach beyond the fjord’s mouth.

This incident is not an isolated occurrence; evidence suggests a significant increase in landslide-generated tsunamis across Alaska in recent years. In 2015, a landslide in Taan Fjord, located about 400 miles northwest of Tracy Arm, produced a wave with a staggering 630-foot run-up. Compounding these concerns, a slow-moving landslide near the Barry Glacier in Prince William Sound is currently being monitored, with projections indicating the potential for a tsunami even larger than the one witnessed at Tracy Arm.

The escalating frequency of these events has prompted an urgent response from scientists, land managers, and tourism operators who are grappling with understanding and mitigating this emerging climate-related hazard. As glaciers continue their global retreat, the risk of such landslides, and the tsunamis they trigger, is expected to rise, posing a significant threat to coastal communities, vital infrastructure, and the vast maritime traffic that frequents Alaskan waters, including the nearly two million annual visitors arriving on cruise ships.

While researching her expedition, Calvey had encountered warnings about tsunamis in Alaskan fjords, but these were predominantly linked to seismic activity, such as the 1958 earthquake that caused the record-breaking 1,720-foot run-up in Lituya Bay. The notion of massive, tsunami-generating landslides triggered by receding glaciers was largely absent from her preparedness information. She now hopes that the severity of the Tracy Arm event will bring this critical, and potentially underestimated, geological hazard to the forefront of public and scientific attention.

The sheer luck involved in the Tracy Arm incident is difficult to overstate, given the fjord’s immense popularity. During the summer months, Tracy Arm welcomes over 200 visits from large cruise ships, whose passengers eagerly seek close-up views of the magnificent Sawyer and South Sawyer glaciers as they meet the ocean. This part of the Tongass National Forest attracts an estimated 500,000 boat-based visitors annually. Although numerous vessels were present in the area in the days preceding the landslide, the incident occurred in the early morning, a period of lower maritime traffic. The closest observed vessel, the over-100-passenger National Geographic Venture, was approximately 20 miles from the South Sawyer Glacier and in deep water when the mountain gave way, thus remaining unharmed by the tsunami.

Had the landslide occurred just a few hours later, the National Geographic Venture would have been near the glaciers, a location where passengers often disembark onto skiffs to explore the ice formations up close. In that scenario, the vessel and any deployed skiffs would have faced the immense danger of over 100-foot whitewater waves laden with icebergs and debris, potentially leading to catastrophic destruction.

Similarly, Christine and Jeffrey Smith, owners of the 65-foot tour boat David B, narrowly avoided disaster. They had planned to anchor for the night within five miles of the South Sawyer Glacier with six guests aboard, placing them directly in the path of the tsunami. However, due to prevailing stormy weather, they opted to anchor in the neighboring Endicott Arm, 45 miles away. Even at this distance, the tsunami’s impact was felt. While preparing breakfast, Christine Smith witnessed 10-foot swells suddenly surge over a shoal and observed an 80-foot vessel struggling against an unusually powerful current.

The Smiths promptly sent a satellite text message to their geologist friend, Jackie Caplan-Auerbach, in Washington, requesting her to check nearby seismic stations for evidence of a landslide. This message served as the initial alert of the Tracy Arm tsunami reaching the outside world. Caplan-Auerbach, a seismologist and professor at Western Washington University, was in the midst of her morning routine when the urgent text arrived. She immediately began analyzing seismic data from stations near the David B’s location, utilizing publicly accessible data streams. However, the scarcity of seismometers in the vast and remote region of Southeast Alaska, where monitoring infrastructure is expensive, presented a challenge.

A sensor located in the Tlingit village of Angoon, approximately 60 miles west of the David B, provided Caplan-Auerbach with a definitive seismic signature indicating a nearby landslide. Subsequent collaboration with colleagues quickly pinpointed the event’s origin to Tracy Arm. Caplan-Auerbach recognized the immense scale of the landslide, estimating that such a colossal displacement of water would be necessary to generate a tsunami that could travel 45 miles to the David B.

Further analysis of the seismic data from Angoon revealed subtle signals emanating from the slope for several hours preceding the main landslide. Caplan-Auerbach described these as "tiny" signals, emphasizing that they would likely have gone unnoticed had the major landslide not occurred. Geologists later identified similar precursory signals on other seismometers, which ceased abruptly with the mountain’s collapse. Caplan-Auerbach has dedicated nearly two decades to studying these "precursory" signals, exploring their potential role in developing future landslide warning systems. However, she acknowledges that predicting landslides remains an immensely complex challenge, influenced by numerous factors including rock type, precipitation, and geological conditions, and that these precursory signals do not precede every landslide event.

In October, Bretwood "Hig" Higman, an independent geologist working with his nonprofit Ground Truth Alaska, and the author navigated the fog-shrouded waters of Portage Lake, about an hour southeast of Anchorage and 500 miles from Tracy Arm. Their objective was to inspect sensors installed on a slow-moving landslide above the Portage Glacier. As they paddled towards the glacier, the distant rumble of a rockslide echoed through the mist, a stark reminder of the precarious terrain. Higman, characterized by his wire-rimmed glasses and well-worn cap, displayed a keen, almost boyish, interest in the sound.

In May 2020, Higman and a dozen other scientists gained national attention by publishing an open letter in The New York Times, warning of a potentially catastrophic creeping landslide near the receding Barry Glacier in Prince William Sound. This unconventional approach, while raising awareness, also drew criticism from some locals who felt they should have been informed through official channels rather than national media coverage that caused unease prior to the peak tourism season. The Barry Arm landslide, situated 40 miles north of Portage Lake, is a formidable geological feature. During the summer months, rocks periodically cascade down its gravelly surface, kicking up dust or splashing into the ocean. Nearby, the Barry Glacier actively sheds ice with resounding booms. Scientific modeling suggests that a complete collapse of the slope could trigger a massive tsunami, endangering boats, cabins, campsites, and any occupants within a wide area. Even a diminished, but still powerful, 6-foot wave could impact the small city of Whittier, located 30 miles away, posing a threat to those along its low-lying shores.

Following the researchers’ open letter, state and federal agencies responded by deploying an array of sophisticated monitoring instruments throughout Barry Arm fjord. This included weather stations, seismometers, live-feed cameras, radio repeaters, and ground-based radar, all designed to provide real-time observations of the unstable slope. An experimental tsunami warning system was also established, enabling scientists to notify Whittier officials and alert boaters via VHF radio. Furthermore, research conducted using the Barry Arm instruments has significantly enhanced the ability to pinpoint more distant landslides, including the event at Tracy Arm. The comprehensive project represents a substantial investment of millions of dollars from both state and federal sources.

As they paddled across Portage Lake, Higman explained the critical factors that make certain of Alaska’s thousands of receding glaciers particularly hazardous. These include visibly unstable slopes situated above thinning ice, a sufficiently large body of water to generate a tsunami, and proximity to populated areas and infrastructure. Portage Lake exhibits all these characteristics. A Chugach National Forest visitor center is located lakeside and attracts up to 1,000 visitors daily during the summer, many of whom board the 140-passenger Ptarmigan tour boat, which circumnavigates the lake. The area also includes a nearby road, railroad, campgrounds, and trails, all potentially within the path of a tsunami.

Upon landing at a narrow section of the shore, they secured their packrafts to a cliff, hoping to deter curious bears. Shouldering their packs, they ascended through dense alder brush and then onto steep, green tundra. The fog gradually dissipated below, revealing the Portage Glacier, a massive river of ice cradled between imposing mountains. Icebergs floated where the glacier’s face met the lake, but along its edges, rubble-darkened ice visibly receded from the mountain walls, giving the glacier a diminished appearance.

Higman described this phenomenon as "debuttressing." Healthy glaciers, he explained, naturally erode and sculpt adjacent mountains, often steepening or undercutting their walls, while simultaneously providing support through their immense mass. However, as glaciers thin, a process accelerated globally by climate change, this buttressing effect diminishes. This loss of support can lead to the collapse of steepened slopes. Climate change also contributes by thawing alpine permafrost and exacerbating extreme rainfall events, both of which can trigger landslides linked to debuttressing.

Despite these contributing factors, the precise mechanisms that determine when or if a slope will fail remain elusive. Landslides do not invariably follow glacial retreat, and in some instances, they do not occur at all. For over a decade, the Barry Glacier has been receding from its unstable slope’s base, yet the slope itself has not yet slid. Higman expressed frustration at the limited understanding of these complex systems, gazing down at the wasting glacier meeting Portage Lake.

As they ascended higher above the glacier, Higman pointed out thin cracks in the ground, visible evidence of the slope’s instability. These cracks had formed so recently that living heather still spanned them, its desiccated roots dangling in the air. More cracks appeared as they progressed, leading them to navigate around seemingly bottomless chasms several feet wide. Far below, the Portage Glacier thundered as it calved icebergs into the lake. The tundra abruptly gave way to the landslide’s most active edge, a chaotic expanse of upturned rock and soil stretching as wide as a football field. Leaning spires, shattered boulders, and deep, gravelly sinkholes characterized the landscape. The occasional sharp crack of tumbling rocks underscored the inherent instability. Higman noted that the entire mass was slumping toward the glacier by several meters annually, attributing this movement primarily to the thinning glacier having "debuttressed" the slope.

Higman and other researchers are concerned that the slope could collapse catastrophically into the lake in the coming years as the glacier continues its retreat. This scenario mirrors the events at Tracy Arm, where satellite imagery reveals that the South Sawyer Glacier rapidly withdrew from beneath the doomed mountainside in the critical weeks and days preceding its collapse.

Higman, Caplan-Auerbach, and several other scientists, led by Dan Shugar of the University of Calgary, recently published a paper in the journal Science detailing how the glacier’s retreat created the conditions for the landslide and subsequent tsunami. However, Dennis Staley, a U.S. Geological Survey scientist overseeing the multi-agency monitoring effort at Barry Arm, emphasized that numerous factors can contribute to landslides, including weather patterns and inherent slope weakness. While the recent research highlights the connection between retreating glaciers and large, tsunami-generating landslides, Staley acknowledged the difficulty in identifying a specific trigger. Higman concurred, cautiously suggesting that while multiple causes might exist for the Tracy Arm slide, the timing of the glacier’s rapid retreat presented an "extraordinary coincidence" that amplified concerns regarding Portage.

Traversing the steep, barren slide, where dirt and scree sloughed downward with each step, they navigated around precariously balanced boulders. Higman retrieved an extensometer, a compact instrument previously drilled into the rock, describing it as an "electronic tape measure" that continuously records the rock’s movement. While still experimental, he expressed hope that this data could eventually be accessed online, potentially by visitor center staff, providing crucial information during periods of heavy rain or accelerated glacial retreat. Ideally, Higman envisioned a more extensive network of precise instruments at Portage, similar to the Barry Arm installation, linked to satellites and a central government office capable of issuing public alerts if movement accelerates. Such a system could also detect critical precursory signals. Higman highlighted the cost-effectiveness of his grassroots efforts, enabling more sensors in more locations, though he admitted the rudimentary nature of these sensors necessitates precise placement within "just the right crack" to effectively measure movement. For now, these remain the sole sensors at Portage.

The researchers continued to ascend, reaching the crown of the slide and returning to more stable tundra. They spent an hour traversing the slope to examine other sensors, each serving as an observation point for what Higman hoped were the most indicative cracks.

A few weeks after the Tracy Arm tsunami, on a drizzly evening, Staley, the lead scientist for Barry Arm monitoring, drove to Whittier for a public meeting. Whittier, a hub for numerous companies operating boat and kayak tours in Prince William Sound, hosted dozens of tour operators, guides, officials, and local residents aboard a spacious tour boat. The gathering aimed to provide an update on the Barry Arm landslide. Staley delivered a concise presentation, followed by an open forum for discussion. As low clouds enveloped the calm harbor, operators inquired about safety protocols and shared their evolving strategies for safely guiding visitors to the glaciers that sustain their businesses. Many operators had ceased visiting Barry Arm in 2020 following Higman’s initial warning. However, the installation of monitoring equipment had led some to return in subsequent years. Now, in the wake of the Tracy Arm incident and a 2024 landslide and minor tsunami at Surprise Glacier near Barry Arm, a cautious return to avoiding the area was observed. This pattern of fluctuating access has become increasingly familiar to those operating near Alaska’s melting glaciers.

Jeff Pedersen, operations manager for Alaska Wildland Adventures in nearby Girdwood, described the situation as an ongoing assessment. In 2024, his company experienced minor damage from a significant landslide near the receding Pedersen Glacier in Kenai Fjords National Park, approximately 60 miles south of Portage. The landslide struck a lagoon during a night of heavy rainfall, generating a tsunami that reached heights of 50 feet or more on adjacent slopes. Further away, at the company’s backcountry lodge, a 3-foot wave overran boardwalks near a cabin where guests were sleeping. Staff reviewed their safety protocols and now avoid that particular glacier.

Christine and Jeffrey Smith of the David B adopted a similar cautious approach following the Tracy Arm landslide, engaging in sober discussions about safety and revising their anchoring practices. While they intend to continue visiting glaciers, their operations will adapt to changing conditions, ideally informed by further research. Major cruise lines, including Carnival, Holland America, and Royal Caribbean, have also taken notice. In early April, nearly all major cruise ship companies operating in Alaska announced they would reroute over 300 planned visits to Tracy Arm in 2026, redirecting them to the neighboring Endicott Arm, a similar fjord where the Dawes Glacier is receding from beneath steep mountainsides. None of the large cruise companies contacted for this report responded to interview requests.

Melenda Lekanof, secretary and treasurer of the Yakutat Tlingit Tribe Council, expressed her concerns. Yakutat, a village of 600 residents situated between Southeast Alaska and Prince William Sound, lies in proximity to the vast Hubbard Glacier. Lekanof recently coordinated a community workshop attended by Higman and other scientists as part of the Áut Geohazards Project, an initiative combining Indigenous knowledge and Western science to enhance understanding of landslide risks. "We have a lot to learn about our changing landscape," Lekanof stated, referring to the increasing incidence of landslides and melting glaciers.

Although cruise ships do not dock in Yakutat, they frequently pass the village en route to Hubbard Glacier in Disenchantment Bay. Scientific models predict the potential for a significant landslide and destructive wave along this route. Lekanof voiced concerns that a lack of coordinated emergency planning among cruise ship companies, state agencies, and other stakeholders could place an undue burden on the small village in the event of a disaster. She also worried that a cruise ship accident could result in loss of life or environmental damage to areas vital for fishing, hunting, and cultural practices. Lekanof advocates for a monitoring array similar to the one at Barry Arm to be established in Disenchantment Bay, a project that would necessitate expanded funding, particularly in light of past efforts by the Trump administration to reduce such resources.

Lekanof highlighted the wisdom of traditional teachings concerning glaciers and tsunamis, passed down through millennia. "We were taught to not be loud, we were taught to not damage the landscape, to be careful where you go," she explained. She expressed dismay at observing cruise ships blasting their horns near the glacier, finding such actions "spiritually disruptive and concerning" for the local wildlife.

A month prior to visiting Portage Lake, the captain of the Ptarmigan tour boat captured photographs of fresh debris at the base of the slow-moving landslide, in an area recently exposed by the Portage Glacier’s retreat. She shared these images with visitor center staff, who subsequently consulted with Higman. A subsequent multi-day storm brought 8 inches of rain, prompting the Forest Service to evacuate a school group and staff from the visitor center due to concerns over landslide and tsunami risk, as stated in an agency release. The Ptarmigan also canceled tours, citing similar safety concerns. This adaptive response may signify a evolving operational approach in areas surrounding Alaska’s receding glaciers.

Higman noted that while such adaptability offers a measure of hope, the Tracy Arm incident raises critical questions about how scientists prioritize monitoring efforts. While visible slope movement, as observed at Portage and Barry Arm, is a significant indicator, glacial retreat itself is equally crucial. Higman and his colleagues have gathered preliminary data suggesting a correlation between the duration a slope has been covered by a glacier and its propensity to slide once exposed. He proposed that fjords such as Endicott Arm and LeConte Bay, popular tourist destinations south of Tracy Arm, warrant thorough investigation. The Tracy Arm landslide occurred on a seemingly solid mountainside with none of the visible warning signs present at Portage and no prior sensor data, underscoring the unpredictable nature of these events. Higman candidly admitted, "As scientists, we need to own up to having totally missed the ball on that one."