The unsettling sound began after 5:30 a.m. on August 10, 2025, rousing Sasha Calvey from her sleeping bag on a remote Southeast Alaska island. She and two friends were 74 days into an ambitious sea kayaking expedition from Washington, camping amidst the quiet grandeur of spruce and hemlocks. Overnight rain had softened the landscape, but an alarming, deep rumble, akin to a colossal waterfall rapidly approaching, jolted Calvey from her slumber. The sound intensified, growing closer until it vibrated through the very ground beneath their tent, compelling her to investigate.

Emerging from their shelter, the trio discovered 15-foot waves had surged ashore, inundating the forest where they had camped. Seaweed lay scattered across the mossy ground beside their tent, a stark testament to the ocean’s sudden intrusion. Water, draining back towards the gravel beach, revealed a devastating scene: half of their meticulously stored food and gear had vanished, one kayak was wedged precariously in a tree, another dangled from a bluff, and the third bobbed in the distance. Their expedition, meticulously planned and bravely undertaken, was abruptly halted.

The trio’s survival was a matter of timing; had the tsunami arrived just three hours earlier, when the tide was significantly higher, the inundating waters could have surged through their campsite, uprooting trees and sweeping them, trapped within their tent, into the churning sea. For hours, the water remained chaotic, characterized by powerful swells and disorienting whirlpools, as Calvey later recounted. Faced with the loss of essential supplies, they radioed for rescue, bringing their journey to an unexpected and dramatic end.

Investigations revealed the cause of this formidable wave: a massive landslide approximately 30 miles away at the end of Tracy Arm fjord, a dramatic channel carving through mountains south of Juneau. This colossal slide occurred in an area where the South Sawyer Glacier is actively retreating, a phenomenon scientists increasingly link to slope instability. The sheer scale of the landslide was evident in the subsequent measurements, with the tsunami’s run-up reaching an astonishing 1,580 feet up the adjacent mountainsides, stripping away trees, brush, and soil in its path. This event registered as the second-largest run-up ever recorded, a terrifying indicator of the immense energy released. As the tsunami propagated outward from the slide, it scoured the steep shorelines of the 30-mile-long fjord, with its remnants ultimately reaching Calvey’s remote beach.

This incident in Tracy Arm is not an isolated event; evidence suggests a concerning increase in landslide-generated tsunamis across Alaska in recent years. In 2015, a similar landslide in Taan Fjord, located about 400 miles northwest of Tracy Arm, generated a staggering 630-foot wave run-up. Compounding these concerns, a slow-moving landslide near the Barry Glacier in Prince William Sound is closely monitored, with scientists warning it has the potential to unleash a tsunami even larger than the one that struck Tracy Arm.

This escalating hazard is prompting urgent action from scientists, land managers, and the tourism industry. The specter of more frequent and potentially larger landslides looms as glaciers continue their global retreat. These climate-driven events pose a significant threat to coastal communities, vital infrastructure, and the multitude of vessels that ply Alaska’s waters, including the large cruise ships that annually bring nearly two million visitors to the state.

Sasha Calvey, while researching her expedition, had encountered warnings about tsunamis in Alaska’s fjords, but these were typically attributed to seismic activity, such as the infamous 1958 earthquake that triggered a massive landslide and a 1,720-foot run-up in Lituya Bay. The concept of colossal, tsunami-inducing landslides directly linked to retreating glaciers was largely absent from her research. Her harrowing experience, however, has brought this under-recognized danger to the forefront, underscoring the urgent need for increased awareness and scientific investigation.

The sheer luck involved in the Tracy Arm event is difficult to overstate, especially considering the fjord’s popularity. Each summer, over 200 cruise ships navigate its waters, bringing eager travelers to witness the majestic South Sawyer and Sawyer glaciers as they meet the ocean. This part of the Tongass National Forest attracts an estimated 500,000 boat-based visitors annually. While dozens of vessels were present in the area in the days preceding the landslide, the early morning timing of the collapse meant that the most heavily trafficked zones were not immediately impacted. The closest known 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. Had the landslide occurred just a few hours later, the Venture would have been closer to the glacier, where passengers often disembark onto skiffs for close-up views, potentially exposing them to waves exceeding 100 feet high, laden with icebergs and debris.

Christine and Jeffrey Smith, owners of the 65-foot tour boat David B, also experienced a near miss. They had planned to anchor their vessel, carrying six guests, within five miles of the South Sawyer Glacier the evening before the landslide. The tsunami would have struck them minutes after the slide occurred. However, due to unfavorable weather, they had relocated their anchorage to the neighboring Endicott Arm, 45 miles away. "We’re definitely feeling our mortality," Christine Smith later reflected, struggling to comprehend the chaotic forces that could have engulfed them. Even in Endicott Arm, the tsunami’s effects were felt; Smith witnessed 10-foot swells suddenly surge over a shoal and observed an 80-foot vessel battling an unusually strong current while she was preparing breakfast.

It was a satellite text message from the Smiths to their geologist friend, Jackie Caplan-Auerbach in Washington, that provided the first indication of the Tracy Arm tsunami to the outside world. Caplan-Auerbach, a seismologist and professor at Western Washington University, was in the midst of her morning routine when the message arrived. She immediately pivoted to examining seismic data from stations near the David B’s reported location. While much seismic data is publicly accessible, the sparse network of seismometers in the vast and remote region of Southeast Alaska presented a challenge.

However, a sensor located in Angoon, a Tlingit village approximately 60 miles west of the David B, revealed a telltale seismic signal indicative of a nearby landslide. This observation, shared with colleagues, quickly led to the pinpointing of the event’s epicenter in Tracy Arm. "This is a big deal," Caplan-Auerbach recalled thinking, recognizing that the immense volume of water displaced by such a significant landslide was necessary to generate a tsunami that could travel 45 miles.

Further analysis of the seismic data from Angoon also revealed subtle, low-amplitude signals in the hours preceding the main landslide event. Caplan-Auerbach described these as "tiny" signals, noting that they likely would have gone unnoticed had the larger landslide not occurred. Geologists later identified similar precursory signals on other seismometers, which ceased abruptly once the mountainside failed. Caplan-Auerbach has dedicated nearly two decades to studying these "precursory" signals, pondering their potential role in a future landslide warning system. However, she cautions that such a system remains a distant prospect, as "landslides are notoriously difficult to anticipate" due to complex factors like rock type, precipitation, and other variables. Moreover, 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 of this article journeyed by packraft along the rugged shores of Portage Lake, an hour southeast of Anchorage and 500 miles from Tracy Arm. Higman’s objective was to check sensors installed on a slow-moving landslide situated above the Portage Glacier at the lake’s far end. A dense fog blanketed the water, and as they paddled towards the glacier, the distant rumble of a rockslide high in the mist served as a potent reminder of the ever-present geological forces at play. Higman, with a boyish curiosity, cocked his head towards the sound, his interest piqued.

In May 2020, Higman and over a dozen other scientists had issued an open letter to The New York Times, warning of a potentially catastrophic creeping landslide near the retreating Barry Glacier in Prince William Sound. The resulting national media coverage sparked considerable concern among locals, who expressed a preference for official announcements over potentially alarming media reports preceding the tourism season. The Barry Arm landslide, located 40 miles north of Portage Lake, presents a formidable hazard. During summer, rocks cascade down its gravelly surface, creating dust plumes and splashing into the ocean, while the nearby Barry Glacier actively calves ice. Models indicate that a complete collapse of the slope could trigger a massive tsunami, threatening boats, cabins, campsites, and everyone within a broad area. Even a diminished but still powerful 6-foot wave could impact the small city of Whittier, located 30 miles away, endangering those along its low-lying shores.

Shortly after the scientists’ open letter, state and federal agencies deployed a comprehensive array of high-tech 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. Crucially, research conducted using the Barry Arm instruments has significantly enhanced scientists’ ability to detect more distant landslides, including the event at Tracy Arm. This extensive project represents a substantial investment of millions of dollars in state and federal funding.

As they paddled across Portage Lake, their reflections clear on the water’s surface, Higman elaborated on the factors that make certain Alaskan glaciers, particularly those experiencing retreat, such significant hazards. The primary ingredients, he explained, are visibly unstable slopes situated above thinning ice, a sufficiently large body of water to generate a tsunami, and proximity to human populations and infrastructure. Portage Lake possesses all these characteristics. A Chugach National Forest visitor center located lakeside bustles with up to 1,000 visitors daily during the summer, many of whom board the 140-passenger Ptarmigan tour boat that traverses the lake. Nearby, a road, railroad, campgrounds, and hiking trails all lie within the potential path of a tsunami.

They landed their packrafts on a narrow strip of shore, securing them to a cliff face to deter any curious bears, and shouldered their packs. As they hiked upward through thick alder brush and then across steep, green tundra, the fog began to dissipate, revealing the Portage Glacier—a vast river of ice cradled between imposing mountains. Icebergs dotted the lake where the glacier met the water, but along its edges, rubble-streaked ice receded from the mountain walls, giving the glacier a visibly diminished appearance. This phenomenon, Higman explained, could be an example of "debuttressing." Healthy glaciers typically erode adjacent mountains, steepening or even undercutting their walls, but they also exert outward pressure, providing support.

When a glacier thins, as is happening globally due to climate change, this buttressing effect diminishes. This can lead to the collapse of steepened slopes. Climate change also contributes to the thawing of alpine permafrost and exacerbates extreme rainfall events, both of which can trigger landslides related to debuttressing. However, the precise mechanisms that dictate whether or when a slope will fail remain unclear. Landslides do not always occur immediately after glacial retreat, and sometimes they do not happen at all. While the Barry Glacier has pulled away from the base of its unstable slope over the past decade or more, the slope itself has not yet slid. "It’s frustrating that we don’t know more about how these systems work," Higman remarked, gazing down at the wasting glacier meeting Portage Lake.

As they ascended higher above the glacier, Higman pointed out thin cracks in the ground, tangible evidence of the slope’s instability. These fissures had opened so recently that living heather still clung to their edges, its desiccated roots dangling in the air. More cracks appeared as they continued their ascent, 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 zone. Stretching above, below, and across an area as wide as a football field, the slope was a chaotic jumble of upturned rock and soil, characterized by leaning spires, shattered boulders, and deep, gravelly sinkholes. The occasional hard knock of tumbling rocks echoed through the air. Higman estimated that the entire mass was slumping toward the glacier by several meters annually, attributing this movement primarily to the thinning glacier having debuttressed the entire slope.

Higman and other researchers are concerned that the slope could collapse catastrophically into the lake in the coming years as the glacier recedes further. This scenario mirrors what occurred at Tracy Arm, where satellite imagery revealed that the South Sawyer Glacier had rapidly withdrawn from beneath the doomed mountainside in the weeks and days leading up to its collapse. Higman, Caplan-Auerbach, and several other scientists, led by University of Calgary researcher Dan Shugar, recently published a paper in the journal Science detailing how the glacier’s retreat primed the slope for the landslide and subsequent tsunami.

However, Dennis Staley, the U.S. Geological Survey scientist overseeing the multi-agency effort at Barry Arm, acknowledges that numerous factors can contribute to landslides, including weather patterns and inherent slope weaknesses. While the recent research intensifies the focus on the connection between retreating glaciers and landslide-induced tsunamis, Staley noted that "it’s hard to know a specific trigger." Higman concurred, choosing his words carefully: "There could be many causes" for the Tracy Arm slide, but he described the timing of the glacier’s rapid retreat as an "extraordinary coincidence" that heightened immediate concerns for Portage.

They traversed the steep, barren slide, carefully navigating around wobbly boulders many times their size, with dirt and scree sloughing downward beneath their boots. Eventually, Higman reached over the edge of a sheer rock column to retrieve an extensometer, a compact metal and glass canister smaller than a water bottle that he had previously anchored into the rock. "It’s like an electronic tape measure," he explained, using a drill to open its casing and replace its battery. Throughout the day, this device meticulously records the rock’s movement. While still experimental, Higman expressed hope that its data could eventually be accessed online by researchers or visitor center staff, particularly during periods of heavy rain or accelerated glacial retreat. Ideally, Higman envisioned a denser network of more precise instruments on the Portage slide, similar to the array at Barry Arm. These instruments would be linked to satellites and a government agency, enabling someone to "push a red button" to alert the public if movement accelerates. Such an array could also detect any potentially critical precursory signals. Higman highlighted the cost-effectiveness of his small, grassroots efforts, which allow for more instruments in more locations. However, these rudimentary sensors must be precisely placed "at just the right crack" to capture meaningful data, and for now, they represent the sole monitoring presence at Portage. They continued to ascend, traversing the slope to reach other sensors, each serving as an "eye" on what Higman hoped were the most critical fissures.

A few weeks after the Tracy Arm tsunami, on a drizzly evening, Staley drove to Whittier for a public meeting. Whittier, a town that serves as a launch point for numerous boat and kayak tours into Prince William Sound, hosted dozens of tour operators, guides, officials, and local residents aboard a spacious tour boat moored in the harbor. They gathered to hear Staley provide an update on the Barry Arm landslide. Staley’s brief presentation was followed by an open forum for discussion. As low clouds and darkness descended over the calm harbor, operators posed questions and shared their evolving strategies for safely guiding visitors to the glaciers that sustain their businesses. While many operators had ceased visiting Barry Arm in 2020, following Higman’s initial warning, some had resumed operations after monitoring equipment was installed. Now, in the wake of the Tracy Arm event and a 2024 landslide and minor tsunami at the Surprise Glacier near Barry Arm, some were once again avoiding the area. This pattern of approach and withdrawal has become increasingly familiar to those who work near Alaska’s rapidly melting glaciers.

Later, 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 retreating Pedersen Glacier in Kenai Fjords National Park, located 60 miles south of Portage. The landslide struck a lagoon during a night of heavy rain, generating a tsunami that reached heights of 50 feet or more on nearby slopes. Further away, at the company’s backcountry lodge, a 3-foot wave inundated 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 slide, engaging in sober discussions about safety and revising their anchoring practices. They intend to continue visiting glaciers but will adapt their operations based on changing conditions, ideally informed by further research.

Major cruise lines, including Carnival, Holland America, and Royal Caribbean, have also taken note of the evolving risks. In early April, nearly all major cruise companies operating in Alaska announced they would bypass Tracy Arm in 2026, rerouting over 300 scheduled visits to the neighboring Endicott Arm, a similar fjord where the Dawes Glacier is also 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, voiced her concerns about the growing hazards. Yakutat, a village of approximately 600 residents situated between Southeast Alaska and Prince William Sound, lies near the massive Hubbard Glacier. Lekanof recently coordinated a community workshop, attended by Higman and other scientists, as part of the Átl’ḵa Geohazards Project. This initiative integrates Indigenous knowledge with Western science to enhance the understanding of landslide risks. "We have a lot to learn about our changing landscape," Lekanof stated, referring to the increasing frequency of landslides and glacial melt.

While cruise ships do not dock in Yakutat, they frequently pass the village en route to the Hubbard Glacier in Disenchantment Bay. Scientific models predict the potential for a landslide and a subsequent destructive wave along this route. Lekanof expressed concern that a lack of coordinated emergency planning among cruise ship companies, state agencies, and other entities would place the burden of disaster response on the small village. She fears that a cruise ship accident could result in loss of life or environmental damage to areas vital for her people’s fishing, hunting, and cultural practices. Lekanof also advocates for a monitoring array similar to the one at Barry Arm to be established in Disenchantment Bay, a project that would necessitate funding beyond the levels that have faced proposed cuts. Traditional teachings, passed down through millennia, reflect her ancestors’ deep understanding of glaciers and tsunamis, emphasizing respect for the natural environment. "We were taught to not be loud, we were taught to not damage the landscape, to be careful where you go," Lekanof said, contrasting these teachings with the observed practice of cruise ships blasting their horns near glaciers, which she finds spiritually disruptive and concerning for the local wildlife.

A month prior to visiting Portage Lake, the captain of the Ptarmigan tour boat had captured photographs of fresh debris at the base of the slow-moving landslide in an area recently uncovered by the receding Portage Glacier. She shared these images with visitor center staff, who subsequently consulted with Higman. A subsequent multiday storm brought 8 inches of rain, prompting the Forest Service to evacuate a school group and staff from the visitor center due to the increased landslide and tsunami risk, as stated by the agency. The Ptarmigan also canceled its tours, citing the same concerns. This demonstrated adaptability may signal a nascent shift in operational practices around Alaska’s melting glaciers.

While this adaptability offers a glimmer of hope, Higman pointed out that the Tracy Arm event raises critical questions about how scientists prioritize monitoring efforts. Visible signs of slope movement, such as those observed at Portage and Barry Arm, are important indicators, but so is the process of glacial retreat itself. Higman and his colleagues have gathered preliminary data suggesting a correlation between the duration a slope has been exposed after glacial retreat and its likelihood of sliding. He believes that other busy fjords south of Tracy Arm, such as Endicott Arm and LeConte Bay, warrant thorough investigation. The Tracy Arm landslide occurred on a seemingly stable mountainside, lacking the overt warning signs present at Portage, and crucially, without any monitoring sensors. "As scientists, we need to own up to having totally missed the ball on that one," Higman admitted.