Sasha Calvey and two friends were 74 days into a remote sea kayaking expedition in Southeast Alaska when the sound of the approaching tsunami jolted them awake before dawn on August 10, 2025. What began as the familiar roar of waves against the shore transformed into an alarming, deep rumble that grew rapidly, shaking the very ground beneath their campsite on a secluded island. "Everything in my gut told me to check outside," Calvey recounted, her voice still tinged with the memory of that terrifying morning.

Emerging from their tent, the trio discovered that 15-foot waves had already surged inland, inundating the forest floor where their campsite was established. Seaweed lay scattered among the moss, a stark indicator of the ocean’s unexpected reach. Half of their essential gear and food, stowed on the gravel beach, had been swept away, and their kayaks were found precariously wedged against trees or floating in the distance. The friends recognized their immense luck; had the tsunami arrived just three hours earlier, during the higher tide, the forest could have been completely submerged, potentially sweeping them away while they were still inside their tent. For hours, the water remained chaotic, marked by powerful swells and disorienting whirlpools, prompting Calvey and her companions to radio for rescue and end their expedition prematurely.

Later, they learned the cause of the dramatic inundation: a massive landslide approximately 30 miles away at the terminus of Tracy Arm fjord, a dramatic, narrow channel winding between mountainous terrain south of Juneau. Scientists attribute the landslide to the ongoing retreat of the South Sawyer Glacier, a phenomenon where receding ice can destabilize surrounding slopes, leading to catastrophic collapses. The landslide created a scar on the mountainside visible even from satellite imagery, a stark testament to the immense geological forces unleashed.

The resulting tsunami achieved an astonishing run-up of 1,580 feet on nearby mountainsides, stripping away trees, brush, and soil in its wake, marking it as the second-largest run-up ever recorded. As the wave propagated outward from the slide, it scoured the steep fjord shorelines before its remnants reached Calvey’s beach, located beyond the fjord’s mouth. This event is part of a concerning trend, with evidence suggesting a significant increase in landslide-generated tsunamis in Alaska over the past decade. In 2015, a landslide in Taan Fjord, over 400 miles northwest of Tracy Arm, generated a 630-foot run-up. Furthermore, a creeping landslide near Barry Glacier in Prince William Sound poses a potential threat of generating a tsunami even larger than the one observed in Tracy Arm.

This emerging hazard, directly linked to climate change and glacial retreat, is prompting urgent action from scientists, land managers, and tour operators. The implications are far-reaching, threatening coastal communities, vital infrastructure, and the numerous vessels that navigate Alaska’s waters, including the large cruise ships that annually bring nearly two million visitors to the state. Calvey herself had encountered warnings about tsunamis in Alaskan fjords during her trip research, but these were typically associated with seismic activity, such as the infamous 1958 event in Lituya Bay that caused a landslide and a staggering 1,720-foot run-up. The possibility of giant, tsunami-generating landslides triggered by retreating glaciers, however, was not widely publicized, a gap she hopes will be addressed in light of recent events.

The sheer scale of the Tracy Arm landslide’s impact underscores the good fortune of those who were in the area on August 10, 2025, particularly given the fjord’s immense popularity. Tracy Arm, a jewel within the Tongass National Forest, attracts over 200 cruise ship visits each summer, with passengers eager to witness the dramatic flow of the Sawyer and South Sawyer glaciers into the ocean. An estimated 500,000 boat-based visitors explore the fjord annually. While numerous vessels were present in the days leading up to the landslide, the early morning timing of the collapse meant that most were either in deep water or far from the immediate vicinity of the slide.

The closest large vessel, the over-100-passenger National Geographic Venture, was in Tracy Arm and en route to the glaciers. Fortunately, it was still approximately 20 miles from South Sawyer when the mountain gave way, and its deep-water location shielded it from the tsunami’s direct impact. Had the landslide occurred just a few hours later, the Venture would have been closer to the glaciers, where passengers often disembark onto smaller skiffs for close-up views. In that scenario, waves exceeding 100 feet, laden with icebergs and debris, could have wreaked havoc on the tour boat and any deployed skiffs.

Christine and Jeffrey Smith, owners of the 65-foot tour boat David B, also experienced a narrow escape. They had planned to anchor their vessel, carrying six guests, within five miles of South Sawyer Glacier the evening before the landslide. The tsunami would have reached them mere minutes after the collapse. However, adverse stormy weather prompted them to seek shelter 45 miles away in the neighboring Endicott Arm. Even in Endicott Arm, the tsunami’s effects were felt; Smith recounted observing 10-foot swells suddenly surge over a shoal and an 80-foot vessel struggling against an unusually strong current.

It was the Smiths who first alerted the outside world to the unusual event, sending a satellite text to their geologist friend, Jackie Caplan-Auerbach, in Washington, asking her to check seismic stations for signs of a landslide. Caplan-Auerbach, a seismologist and professor at Western Washington University, was in the midst of her morning routine when the message arrived. She immediately began analyzing 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 60 miles west of the David B, provided a crucial clue: a distinct seismic signature indicative of a nearby landslide. This finding prompted Caplan-Auerbach to contact colleagues, and a collaborative effort soon pinpointed the landslide’s origin in Tracy Arm. "This is a big deal," she recalled thinking, recognizing that the immense volume of water displaced by such a large landslide would be necessary to generate a tsunami capable of traveling 45 miles to reach the David B.

Further analysis of the seismic data from Angoon revealed subtle, precursory signals emanating from the slope for hours before the main landslide event. "They’re tiny," Caplan-Auerbach noted, emphasizing that these faint tremors would likely have gone unnoticed without the subsequent catastrophic slide. Geologists later identified similar signals on other seismometers, all of which ceased abruptly with the mountain’s collapse. Caplan-Auerbach has dedicated nearly two decades to studying these "precursory" signals, exploring their potential for developing future landslide warning systems. However, she acknowledges the significant challenges involved, stating, "Landslides are notoriously difficult to anticipate," due to complex factors like rock composition, precipitation, and other variables. Moreover, these precursory signals do not precede every landslide, adding another layer of uncertainty.

In October, geologist Bretwood "Hig" Higman and the author navigated the fog-laden waters of Portage Lake in small packrafts, heading towards Portage Glacier, located about an hour southeast of Anchorage and some 500 miles from Tracy Arm. Higman, an independent geologist working with his nonprofit Ground Truth Alaska, was on a mission to inspect sensors deployed on a slow-moving landslide above the glacier. As they paddled towards the ice, the rumble of a rockslide from the mist-shrouded mountains above served as a potent reminder of the inherent geological instability of the region.

Higman, along with more than a dozen other scientists, had gained national attention in May 2020 for 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. This unorthodox approach, while raising public awareness, also drew criticism from some locals who felt they should have been informed through official channels rather than national media coverage that generated apprehension before the peak tourism season. The Barry Arm landslide, situated about 40 miles north of Portage Lake, presents a formidable hazard. Each summer, rocks cascade down its gravelly surface, and the Barry Glacier actively calves ice into the ocean. Modeling indicates that a complete slope failure could trigger a massive tsunami, threatening boats, cabins, campsites, and all occupants within a wide area. Even a diminished but still powerful 6-foot wave could impact the nearby city of Whittier, located 30 miles away, posing a risk to those along its low-lying shores.

In response to the scientists’ warning, state and federal agencies invested millions of dollars in deploying a comprehensive array of high-tech instruments in Barry Arm fjord. This network 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 alert Whittier officials and boaters via VHF radio. Furthermore, research conducted using the Barry Arm instruments has significantly enhanced the ability to detect more distant landslides, including the one in Tracy Arm, demonstrating the project’s crucial role in advancing hazard assessment capabilities.

As their reflections shimmered on the calm waters of Portage Lake, Higman explained the critical factors that make certain Alaskan glaciers, particularly those experiencing retreat, potential sources of significant hazards. These include 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 exhibits all these characteristics. The Chugach National Forest visitor center on its shores bustles with up to 1,000 visitors daily during the summer, many of whom board the 140-passenger Ptarmigan tour boat for excursions across the lake. The area also features a nearby road, railroad, campgrounds, and trails, all potentially vulnerable to tsunamis.

Upon landing on a narrow stretch of shore, they secured their packrafts to a cliff to deter any curious bears. Shouldering their packs, they hiked through dense alder brush and up steep, green tundra. The fog eventually dissipated, revealing the Portage Glacier, a colossal river of ice flowing between imposing mountains. Icebergs dotted the lake where the glacier’s face met the water, but along its edges, rubble-streaked ice receded from the mountain walls, giving the glacier a visibly diminished appearance.

Higman described this phenomenon as "debuttressing," where healthy glaciers, through their erosive action, sculpt and support adjacent mountain slopes. However, as glaciers thin, a process accelerated by global climate change, this crucial buttressing effect diminishes. This loss of support can lead to the collapse of steepened slopes. Climate change also contributes to thawing alpine permafrost and exacerbates extreme rainfall events, both of which can further trigger landslides related to debuttressing. Despite these contributing factors, the precise mechanisms that dictate when and if a slope will fail remain elusive. Landslides do not always immediately follow glacial retreat, and sometimes they do not occur at all. The Barry Glacier has receded from its unstable slope’s base over the past decade or more, yet the slope has not yet slid.

"It’s frustrating that we don’t know more about how these systems work," Higman remarked, gazing at the wasting glacier meeting Portage Lake. As they ascended higher above the glacier, Higman pointed out thin cracks in the ground, evidence of the slope’s ongoing disintegration. These cracks were so recent that living heather still bridged them, its desiccated roots dangling in the air. More cracks appeared as they advanced, leading them to navigate around seemingly bottomless chasms several feet wide. Below, the Portage Glacier thundered as it calved icebergs into the lake.

The tundra abruptly gave way to the landslide’s most active edge. Stretching above and below, and spanning 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 sharp crack of tumbling rocks echoed through the air. Higman estimated that the entire mass was slumping towards the glacier by several meters annually, attributing this movement primarily to the thinning glacier’s debuttressing effect on the slope. He and other researchers fear that the slope could collapse catastrophically into the lake in the coming years as the glacier continues to recede from beneath it, mirroring the sequence of events that occurred at Tracy Arm, where satellite imagery revealed the South Sawyer Glacier’s rapid withdrawal in the weeks and days preceding the mountainside’s collapse.

Higman, Caplan-Auerbach, and 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 had primed the slope for the landslide and subsequent tsunami. However, Dennis Staley, the U.S. Geological Survey scientist overseeing the multi-agency monitoring effort at Barry Arm, cautioned that numerous factors, including weather and slope stability, contribute to landslides. While the recent research highlights the connection between retreating glaciers and large, tsunami-generating landslides, Staley acknowledged, "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 about the similar conditions at Portage.

Side-hilling across the steep, barren slide, dirt and scree sloughed away beneath their boots as they navigated around precariously balanced boulders. Higman retrieved an extensometer, a small device previously drilled into the rock, from the edge of a sheer column. "It’s like an electronic tape measure," he explained, using a drill to access its casing and replace its battery. This instrument continuously measures the rock’s movement, providing crucial data. While still experimental, Higman expressed hope that this data could eventually be accessible online, allowing for real-time monitoring by visitor center staff, particularly during periods of heavy rain or rapid glacial retreat.

Ideally, Higman envisioned a denser network of precise instruments on the Portage slide, similar to the comprehensive array deployed at Barry Arm. Such a system, linked to satellites and a government agency, could enable officials to "push a red button" to alert the public if movement accelerates, and potentially detect critical precursory signals. Despite the rudimentary nature of his current sensors, Higman highlighted the benefits of his low-cost approach, enabling wider deployment. However, he stressed that these basic sensors must be strategically placed "at just the right crack" to effectively capture movement, acknowledging that for now, they represent the sole monitoring presence at Portage. They continued traversing the slope, each sensor serving as an observation point 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. The town, a hub for numerous companies offering boat and kayak tours into Prince William Sound, hosted dozens of tour operators, officials, and local residents aboard a moored tour boat. They gathered to receive an update on the Barry Arm landslide. Staley delivered a concise briefing before opening the floor for discussion. As low clouds and darkness enveloped the calm harbor, operators inquired about evolving strategies for safely conducting glacier tours amidst changing conditions. Many 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, a number of operators were once again avoiding the area, a cyclical pattern becoming increasingly familiar to those working near Alaska’s melting glaciers.

Jeff Pedersen, operations manager for Alaska Wildland Adventures in nearby Girdwood, described this ongoing situation as a continuous assessment. In 2024, his company experienced minor damage from a significant landslide near the retreating Pedersen Glacier in Kenai Fjords National Park, located about 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 nearby slopes. Further inland, 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 slide, engaging in sober discussions about safety and revising their anchoring practices. While they intend to continue visiting glaciers, their operational procedures will adapt to evolving conditions, ideally informed by further research. Major cruise lines, including Carnival, Holland America, and Royal Caribbean, have also responded to the escalating concerns. In early April, nearly all major cruise ship companies operating in Alaska announced they would bypass Tracy Arm in 2026, rerouting over 300 scheduled visits to the neighboring Endicott Arm, a comparable fjord where the Dawes Glacier is receding from beneath steep mountainsides. None of the large cruise companies contacted for this report provided interviews.

Melenda Lekanof, secretary and treasurer of the Yakutat Tlingit Tribe Council, voiced her own concerns. Yakutat, a village of approximately 600 residents situated between Southeast Alaska and Prince William Sound, lies near the immense Hubbard Glacier. Lekanof recently coordinated a community workshop, attended by Higman and other scientists, as part of the Áak’w Xát’x’ Geohazards Project. This initiative aims to integrate Indigenous knowledge and Western scientific methods 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 the accelerating rate of glacial melt.

Although cruise ships do not dock in Yakutat, they frequently pass the village en route to the Hubbard Glacier in Disenchantment Bay. Scientific models predict a potential landslide and 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 could place the burden of disaster response on the small village. Furthermore, a cruise ship incident could result in loss of life or environmental damage in areas crucial 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 require sustained funding, especially in light of past attempts by the Trump administration to reduce resources for tsunami warning centers.

Traditional teachings regarding glaciers and tsunamis, Lekanof explained, encapsulate millennia of ancestral wisdom. "We were taught to not be loud, we were taught to not damage the landscape, to be careful where you go," she said, contrasting these teachings with the practice of cruise ships blasting their horns near glaciers, which she finds "spiritually disruptive and concerning for the birds and mammals there."

A month prior to the author’s visit to Portage Lake, the captain of the Ptarmigan tour boat documented fresh debris at the base of the slow-moving landslide in an area recently exposed by the receding Portage Glacier. She shared these photographs with visitor center staff, who then consulted with Higman. Subsequently, an intense multi-day storm delivered eight inches of rain. Considering the elevated risks, the Forest Service evacuated a school group and staff from the visitor center, according to an agency statement. The Ptarmigan also canceled its tours, citing landslide and tsunami concerns. This demonstrated adaptability may signify a nascent shift in operational practices around Alaska’s rapidly changing glacial landscapes.

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 slope movement, as observed at Portage and Barry Arm, is significant, but so is the rate of glacial retreat. Higman and his colleagues have gathered preliminary data suggesting a correlation between the duration a slope has been covered by a glacier and its subsequent likelihood of sliding once exposed. He believes that Endicott Arm and LeConte Bay, two heavily trafficked fjords south of Tracy Arm, warrant thorough investigation. After all, the Tracy Arm mountain appeared solid, exhibiting none of the overt warning signs evident at Portage, and crucially, lacked any monitoring sensors. "As scientists, we need to own up to having totally missed the ball on that one," Higman admitted.