Sasha Calvey awoke to an unfamiliar, deeply resonant sound, unlike anything she had experienced during her 74-day sea kayaking expedition in Southeast Alaska. It was just after 5:30 a.m. on August 10, 2025, and the sound, initially like a distant waterfall, grew alarmingly louder and closer, a primal rumble that seemed to shake the very ground beneath her tent. Calvey, camped with two friends on a remote island, felt an instinctive urge to investigate. What they discovered was a terrifying scene: 15-foot waves had surged inland, inundating the beach where their gear and kayaks were stowed. Seaweed lay scattered among the mossy forest floor beside their campsite, and half of their essential supplies were missing, their kayaks tossed about like toys, one wedged against a tree, another precariously hanging from a bluff, and the third adrift. They were fortunate; had the tsunami arrived just three hours earlier, at high tide, the devastating surge could have swept them away. The chaotic waters, marked by powerful swells and disorienting whirlpools, persisted for hours, prompting the friends to radio for rescue and cut their expedition short.

Later, they learned that this immense wave had been triggered by a massive landslide approximately 30 miles away, at the terminus of Tracy Arm fjord, a dramatic channel winding between steep mountains south of Juneau. Scientists believe the landslide occurred in an area where the South Sawyer Glacier is rapidly retreating, a process that can destabilize the surrounding mountainsides. The scale of the event was staggering, with the tsunami’s run-up reaching an astonishing 1,580 feet up the adjacent mountain slopes, stripping away trees, vegetation, and soil. This marked the second-highest run-up ever recorded, underscoring the immense power unleashed. As the tsunami propagated outward from the slide, it scoured the fjord’s steep shorelines, with its diminishing but still formidable waves eventually reaching Calvey’s campsite beyond the fjord’s mouth.

This incident is not an isolated event; evidence suggests a concerning 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, generated a wave with a 630-foot run-up. More alarmingly, a slow-moving landslide near Barry Glacier in Prince William Sound is closely monitored, as it holds the potential to generate a tsunami even larger than the one at Tracy Arm. This emerging hazard, directly linked to a warming climate, poses a significant threat to coastal communities, vital infrastructure, and the myriad of vessels, from small fishing boats to the massive cruise ships that bring nearly two million visitors to Alaska annually. While researching her trip, Calvey had encountered warnings about tsunamis in Alaska’s fjords, but these were predominantly associated with seismic activity, such as the infamous 1958 event in Lituya Bay that caused a 1,720-foot run-up. The possibility of a glacier-retreat-induced landslide triggering such a catastrophic tsunami was not widely publicized, a gap in awareness that the Tracy Arm event has now starkly illuminated.

The sheer luck of the Tracy Arm incident cannot be overstated, especially considering the fjord’s immense popularity. Each summer, more than 200 large cruise ships navigate Tracy Arm, a key destination within the Tongass National Forest, carrying hundreds of thousands of visitors eager to witness the majestic South Sawyer and Sawyer Glaciers meeting the ocean. Despite the heavy daytime traffic, the early morning hours, when the landslide occurred, are relatively quiet. The closest known vessel at the time was the National Geographic Venture, a ship carrying over 100 passengers, which was in Tracy Arm but still approximately 20 miles from the South Sawyer Glacier when the mountain collapsed. In its deep-water position, it was unaffected by the initial tsunami. However, had the landslide occurred just a few hours later, the Venture would have been near the glacier, a popular spot for passengers to disembark onto skiffs for closer viewing. In that scenario, waves exceeding 100 feet, laden with icebergs and debris, could have annihilated the tour boat and any launched skiffs.

Christine and Jeffrey Smith, owners of the 65-foot tour boat David B, also experienced a close call. They had planned to anchor their vessel, carrying six guests, within five miles of South Sawyer Glacier the evening before the landslide, putting them directly in the path of the tsunami. However, due to unfavorable weather conditions, they opted to anchor 45 miles away in the neighboring Endicott Arm. Even at this distance, the tsunami’s reach was felt; Smith described observing 10-foot swells suddenly engulfing a shoal and an 80-foot vessel struggling against an unusually strong current while she was preparing breakfast. The Smiths were among the first to report the event, sending a satellite text to their geologist friend, Jackie Caplan-Auerbach in Washington, urging her to check seismic stations for signs of a landslide.

Caplan-Auerbach, a seismologist and professor at Western Washington University, was alerted to the unfolding crisis via the Smiths’ text message. She immediately began analyzing seismic data from stations near the David B’s location. While much seismic data is publicly available, the vast and remote region of Southeast Alaska has a limited number of seismometers, making comprehensive monitoring challenging and expensive. At a sensor located in Angoon, a Tlingit village approximately 60 miles west of the David B, Caplan-Auerbach detected a distinct seismic signature indicative of a nearby landslide. This initial data point, shared with colleagues, rapidly led to the pinpointing of the landslide’s origin in Tracy Arm. The magnitude of the event became apparent as scientists realized the colossal volume of water displaced to generate a tsunami that could travel 45 miles to reach the David B.

Intriguingly, Caplan-Auerbach also observed subtle seismic signals emanating from the slope in Angoon for several hours prior to the landslide. These "precursory" signals, though minute, were only recognized in hindsight due to the subsequent catastrophic event. Other seismometers also recorded these faint tremors, which ceased abruptly once the mountainside gave way. Caplan-Auerbach has dedicated nearly two decades to studying such precursory signals, and she and other researchers are exploring their potential for inclusion in future landslide warning systems. However, the inherent unpredictability of landslides, influenced by a complex interplay of geological factors, precipitation patterns, and other variables, presents a significant challenge to accurate forecasting. Furthermore, these precursory signals do not precede every landslide, making their predictive power limited.

In October, Bretwood “Hig” Higman, an independent geologist operating through his nonprofit Ground Truth Alaska, and the author, explored the shores of Portage Lake, about an hour southeast of Anchorage. Higman was investigating sensors deployed on a slow-moving landslide situated above the Portage Glacier at the lake’s far end. Dense fog obscured the water as they paddled towards the glacier, and the distant rumble of a rockslide served as a stark reminder of the unstable mountainous terrain. Higman, a keen observer, reacted to the sound with characteristic scientific curiosity.

This exploration brought to mind a significant event in May 2020, when Higman and over a dozen other scientists issued an open letter published in The New York Times, warning of a potentially catastrophic creeping landslide near the retreating Barry Glacier in Prince William Sound. While their intention was to raise awareness, the national media coverage before the peak tourism season caused significant concern among local residents, who felt they should have been alerted through official channels. The Barry Arm landslide, located roughly 40 miles north of Portage Lake, presents a formidable threat. In summer, rocks continuously cascade down its gravelly surface, creating dust plumes and splashing into the ocean, while the nearby Barry Glacier audibly sheds ice. Scientific modeling indicates that a complete collapse of the slope could trigger a massive tsunami, endangering vessels, cabins, campsites, and all occupants within a wide radius. Even a diminished yet still powerful wave, estimated at 6 feet, could reach the small city of Whittier, located 30 miles away, posing a risk to those along its low-lying shores.

Following the researchers’ open letter, state and federal agencies undertook a comprehensive deployment of advanced monitoring equipment in Barry Arm fjord. This array includes 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 has also been established, enabling scientists to notify Whittier officials and alert boaters via VHF radio. Crucially, research conducted using the Barry Arm instruments has significantly enhanced the scientific community’s ability to detect and analyze more distant landslides, including the recent event at Tracy Arm. This extensive project represents a substantial investment of millions of dollars in state and federal funding.

As Higman and the author paddled across Portage Lake, the reflections on the water mirroring the surrounding mountains, Higman elaborated on the specific factors that elevate the risk of landslide-generated tsunamis in certain Alaskan glacial environments. The primary ingredients, he explained, are visibly unstable slopes positioned above thinning ice, a sufficiently large body of water to amplify a tsunami, and proximity to human populations and infrastructure. Portage Lake exhibits all these characteristics. A Chugach National Forest visitor center situated lakeside attracts up to 1,000 visitors daily during the summer months. Many of these visitors board the 140-passenger Ptarmigan tour boat, which regularly traverses the lake. Furthermore, the area is served by a nearby road, a railroad, campgrounds, and hiking trails, all situated within the potential inundation zone of a landslide-induced tsunami.

Upon landing on a narrow strip of shore, they secured their packrafts to a cliff face, hoping to deter any curious bears. Equipped with their backpacks, they began their ascent through dense alder brush, transitioning to steep, verdant tundra. As they climbed higher, the fog that had blanketed the lake began to dissipate, revealing the Portage Glacier—a vast river of ice flanked by imposing mountains. Icebergs dotted the water where the glacier met the lake, but along its edges, rubble-streaked ice receded from the mountain walls, giving the glacier an unhealthy appearance.

Higman described this phenomenon as "debuttressing." He explained that healthy glaciers naturally erode and sculpt the adjacent mountains, often steepening or even undercutting their slopes. However, they also exert outward pressure, providing a buttressing effect that supports these slopes. As glaciers thin, a process accelerated globally by climate change, this crucial buttress diminishes. This loss of support 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 debuttressing-related landslides. Despite these contributing factors, the precise mechanisms that determine whether or when a slope will fail remain incompletely understood. Landslides do not invariably follow glacial retreat, and in many cases, they do not occur at all. For over a decade, the Barry Glacier has pulled away from the base of its unstable slope, yet 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 angled higher above the glacier, Higman pointed out thin cracks in the ground, visual evidence of the slope’s instability. These cracks had formed so recently that living heather plants still straddled them, their desiccated roots dangling precariously in the air. More cracks appeared as they ascended, 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 ended at the landslide’s most active edge, a chaotic expanse stretching above and below, as wide as a football field. The slope was a jumble of upturned rock and soil, characterized by leaning spires, shattered boulders, and deep, gravelly sinkholes. The occasional sharp crack of tumbling rocks echoed through the air. Higman noted that the entire mass was slumping towards the glacier by several meters annually, attributing this movement primarily to the thinning glacier debuttressing the slope. He and other researchers express concern that this slope could catastrophically collapse into the lake in the coming years as the glacier continues its retreat from beneath it, mirroring the sequence of events at Tracy Arm, where satellite imagery revealed the South Sawyer Glacier’s rapid withdrawal from beneath the doomed mountainside in the 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 ripe for the landslide and subsequent tsunami. However, Dennis Staley, a U.S. Geological Survey scientist leading the multi-agency monitoring effort at Barry Arm, emphasized that numerous factors can contribute to landslides, including weather and inherent slope weaknesses. While the recent research renews focus on the link between retreating glaciers and landslide-generated tsunamis, Staley acknowledged, "It’s hard to know a specific trigger." Higman concurred, carefully stating, "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 regarding Portage.

Navigating the steep, barren slide, where dirt and scree dislodged underfoot and wobbly boulders the size of small cars loomed, Higman retrieved an extensometer—a compact metal and glass canister he had previously drilled into the rock. This instrument functions as an "electronic tape measure," he explained, diligently recording the rock’s movement. Although still experimental, Higman expressed hope that its data could eventually be accessed online, perhaps by visitor center staff, allowing for real-time monitoring, particularly 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 deployment. These instruments would be linked to satellites and a government agency capable of activating an alert system with the push of a "red button" in the event of accelerated movement or the detection of critical precursory signals. While Higman’s current low-cost, homegrown effort allows for more sensors in more locations, their rudimentary nature necessitates precise placement in specific cracks to yield meaningful data.

On a drizzly evening a few weeks after the Tracy Arm tsunami, Staley drove to Whittier to attend a public meeting. Whittier, a hub for numerous companies operating boat and kayak tours in Prince William Sound, hosted dozens of tour operators, 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 voiced questions and shared their evolving strategies for safely guiding visitors to glaciers while managing the inherent risks. Many operators had ceased visiting Barry Arm in 2020, following Higman’s initial warning, but some had resumed operations after the installation of monitoring equipment. Now, following the Tracy Arm event and a 2024 landslide and minor tsunami at Surprise Glacier near Barry Arm, some operators were once again avoiding the area. This pattern of cautious withdrawal and hesitant return reflects a new operational reality for those working near Alaska’s rapidly melting glaciers.

Jeff Pedersen, operations manager for Alaska Wildland Adventures in nearby Girdwood, described this evolving 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, approximately 60 miles south of Portage. The landslide impacted a lagoon during a heavy rainstorm, 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 overran boardwalks near a cabin where guests were sleeping. In response, staff reviewed their safety protocols and now avoid that particular glacier. Christine and Jeffrey Smith of the David B also adopted a more cautious approach after the Tracy Arm incident, engaging in serious discussions about safety and revising their anchoring practices. They intend to continue visiting glaciers but acknowledge that their operations will need to adapt to changing conditions, ideally informed by further scientific research.

Major cruise lines, including Carnival, Holland America, and Royal Caribbean, have also taken note of the escalating risks. In early April, the majority of large cruise companies operating in Alaska announced they would bypass Tracy Arm in 2026, rerouting over 300 scheduled visits to the neighboring Endicott Arm, a similarly shaped fjord where the Dawes Glacier is also receding from beneath steep mountainsides. None of the major cruise companies contacted for this report responded to interview requests.

Melenda Lekanof, secretary and treasurer of the Yakutat Tlingit Tribe Council, expressed her concerns regarding the growing geohazard risks. Yakutat, a village of approximately 600 residents situated between Southeast Alaska and Prince William Sound, lies in proximity to the immense Hubbard Glacier. Lekanof recently coordinated a community workshop, attended by Higman and other scientists, as part of the Áak’u Geohazards Project. This initiative integrates Indigenous knowledge with Western scientific methods to enhance the understanding of landslide risks in the region. "We have a lot to learn about our changing landscape," Lekanof stated, referring to the increasing frequency of landslides and the ongoing 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 popular route. Lekanof voiced concern that a lack of coordinated emergency planning among cruise ship companies, state agencies, and other entities could place an undue burden on the small village in the event of a disaster. The possibility of a cruise ship accident, she noted, could result in loss of life or environmental damage to areas vital for fishing, hunting, and cultural practices. Lekanof also advocates for the establishment of a monitoring array similar to the one at Barry Arm in Disenchantment Bay, though she recognizes this would require sustained funding, a resource that has faced proposed cuts from previous administrations. Lekanof highlighted that traditional teachings passed down through generations offer profound lessons about glaciers and tsunamis, emphasizing respect for the environment. She lamented the practice of some cruise ships sounding their horns near the glacier, which she finds spiritually disruptive to 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. These images were shared with visitor center staff, who consulted with Higman. Subsequently, an intense multiday storm delivered eight inches of rain. In response to the heightened risk, the Forest Service evacuated a school group and staff from the visitor center, according to an agency statement. The Ptarmigan canceled its tours, citing landslide and tsunami concerns. This adaptive response may signify a new approach to operating in the vicinity of Alaska’s receding glaciers.

Higman, however, pointed out that 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 that the longer a newly exposed slope remained covered by ice, the greater its potential to slide. He believes 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 stable mountainside, devoid of the visible warning signs present at Portage, and lacked any monitoring sensors. "As scientists, we need to own up to having totally missed the ball on that one," Higman admitted.