Sasha Calvey awoke to an ominous sound on August 10, 2025, a deep rumble that vibrated through her tent and her very core, signaling a force far more powerful than the heavy rain and wind battering their remote Southeast Alaska campsite. Seventy-four days into a sea kayaking expedition, Calvey and her two companions were camped on a secluded island when an unfamiliar, intensifying roar, likened to a colossal waterfall, drew them from their sleeping bags. Their immediate scramble outside revealed a terrifying reality: fifteen-foot waves had surged inland, inundating the forest and scattering seaweed amongst the moss beside their tent, a stark testament to nature’s sudden fury.

The chaotic aftermath saw half their essential supplies vanish, one kayak lodged precariously in a spruce tree, another suspended from a bluff, and the third drifting in the distance, a chilling testament to the tsunami’s power. The trio narrowly escaped a far graver fate; had the surge arrived just three hours earlier, with the tide at its peak, the water could have swept through their campsite, tearing through trees and pulling them into the ocean while they were still sheltered within their tent. For hours, the water remained violently turbulent, characterized by powerful swells and disorienting whirlpools, ultimately compelling them to radio for rescue and prematurely end their ambitious journey.

The cause of this devastating inundation was later identified as a massive landslide, occurring approximately 30 miles away at the terminus of Tracy Arm fjord, a dramatic, serpentine channel carving through mountains south of Juneau. This colossal slide originated near the South Sawyer Glacier, a region where receding glacial ice is increasingly implicated in destabilizing surrounding slopes. The immense volume of displaced earth and rock triggered a significant tsunami, its effects dramatically observed on the surrounding mountainsides, where the wave’s "run-up" – the highest point reached by the water – was measured at an astonishing 1,580 feet. This immense inundation stripped vegetation and soil from steep inclines, marking the second-largest run-up ever officially recorded. As the tsunami propagated outward from the slide’s origin, it scoured the fjord’s steep shores before its diminished, yet still formidable, remnants reached Calvey’s remote beach.

This event is not an isolated incident; evidence points to a concerning rise in landslide-generated tsunamis within Alaska over the past decade. A similar, though less severe, event occurred in 2015 at Taan Fjord, approximately 400 miles northwest of Tracy Arm, resulting in a 630-foot run-up. More alarmingly, a creeping landslide near the Barry Glacier in Prince William Sound poses a continuous threat, with scientists warning it could potentially generate a tsunami even larger than the one that struck Tracy Arm. This escalating hazard has galvanized scientists, land managers, and tourism operators, all grappling with the implications of increased geological instability, exacerbated by the ongoing retreat of glaciers worldwide.

The implications extend far beyond remote campsites. The burgeoning threat of climate-related geological hazards endangers coastal communities, vital infrastructure, and the diverse array of maritime vessels operating in Alaskan waters, including the large cruise ships that ferry nearly two million visitors to the state annually. While researching her trip, Calvey had encountered warnings about tsunamis in Alaska’s fjords, but these were predominantly linked to seismic activity, such as the infamous 1958 earthquake that caused a colossal landslide and a 1,720-foot run-up in Lituya Bay, Glacier Bay National Park. The prospect of giant, tsunami-inducing landslides triggered by receding glaciers, however, was not widely documented, a gap in knowledge Calvey hopes will be rectified by such recent, impactful events.

The sheer scale of the Tracy Arm landslide and its subsequent tsunami underscores the immense luck of the kayakers, particularly given the fjord’s popularity as a tourist destination. Tracy Arm is a summer highlight for over 200 cruise ship visits annually, with hundreds of thousands of visitors drawn to witness the dramatic spectacle of the Sawyer and South Sawyer glaciers meeting the ocean. While the area experiences significant daytime traffic, the early morning hours of August 10, 2025, were comparatively quiet, a factor that likely mitigated potential casualties.

The closest documented vessel, the over-100-passenger National Geographic Venture, was navigating Tracy Arm, heading towards the glaciers. Fortunately, it was in deep water and approximately 20 miles from the South Sawyer Glacier when the mountain gave way, remaining unharmed by the tsunami’s direct impact. Had the landslide occurred just a few hours later, the Venture would have been in close proximity to the glaciers, where passengers disembark onto skiffs for up-close viewing. In that scenario, the tsunami, manifesting as whitewater waves exceeding 100 feet and laden with icebergs and debris, could have easily overwhelmed the tour boat and any deployed skiffs.

Christine and Jeffrey Smith, proprietors of the 65-foot tour vessel David B, also experienced a fortunate turn of events. The previous evening, with six guests aboard, they had intended to anchor for the night within five miles of South Sawyer Glacier, placing them directly in the path of the tsunami. However, adverse weather conditions led them to seek refuge 45 miles away in the neighboring Endicott Arm. Despite the distance, the tsunami’s reach extended even there. While preparing breakfast, Christine Smith witnessed 10-foot swells unexpectedly surge over a shoal and observed an 80-foot vessel battling an unusually strong current.

It was from Endicott Arm that the Smiths sent a satellite text to Jackie Caplan-Auerbach, a geologist friend in Washington, requesting she check nearby seismic stations for signs of landslides. This message marked the first notification of the Tracy Arm tsunami to the outside world. Caplan-Auerbach, a seismologist and professor at Western Washington University, immediately shifted her attention from her morning routine to analyzing seismic data from stations near the David B. While much of this data is publicly accessible, the scarcity of seismometers in the vast and remote Southeast Alaska region presents a challenge for comprehensive monitoring.

At a sensor located in Angoon, a Tlingit village 60 miles west of the David B, Caplan-Auerbach detected a distinct seismic signature indicative of a nearby landslide. This discovery prompted her to contact colleagues, and through their collective efforts, the landslide’s precise location in Tracy Arm was rapidly pinpointed. Caplan-Auerbach recognized the magnitude of the event, noting that the tsunami’s significant travel distance to reach the David B implied an enormous volume of water displaced by the landslide.

Further analysis of the seismic data from Angoon revealed subtle signals emanating from the slope for several hours preceding the main landslide event. Caplan-Auerbach described these as "tiny" signals, likely to have gone unnoticed without the subsequent major event. Geologists later identified similar precursory signals on other seismometers, which ceased abruptly once the mountainside collapsed. Caplan-Auerbach has dedicated nearly two decades to studying these "precursory" signals, exploring their potential role in future landslide warning systems. However, the development of such a system faces considerable hurdles, as she explained, "Landslides are notoriously difficult to anticipate," citing the complex interplay of factors such as rock composition, precipitation patterns, and other variables that complicate predictive models. Furthermore, she cautioned that these precursory signals do not consistently precede every landslide event.

In October, Bretwood “Hig” Higman, an independent geologist working with his nonprofit Ground Truth Alaska, and this author navigated the fog-laden waters of Portage Lake, an hour southeast of Anchorage and approximately 500 miles from Tracy Arm. Higman’s mission was to inspect sensors installed on a slowly moving landslide above Portage Glacier at the lake’s far end. As they paddled towards the glacier, the muffled rumble of a rockslide high in the mist served as a stark reminder of the unstable terrain surrounding them. Higman, with an air of boyish curiosity, cocked his head towards the sound, his keen interest in geological phenomena palpable.

This is not the first time such concerns have been raised. In May 2020, Higman, along with over a dozen other scientists, published an open letter in The New York Times, warning of a potentially catastrophic creeping landslide near the retreating Barry Glacier in Prince William Sound. While the letter aimed to raise awareness, some local residents expressed a preference for receiving such critical information through official channels rather than national media, which had inadvertently triggered public anxiety prior to the peak tourism season.

The Barry Arm landslide, situated 40 miles north of Portage Lake, presents a formidable hazard. During the summer months, rocks frequently cascade down its gravelly surface, creating plumes of dust and splashing into the ocean, while the nearby Barry Glacier audibly booms as it sheds ice. Scientific modeling suggests that a complete collapse of the slope could unleash a massive tsunami, endangering boats, cabins, campsites, and the people within them across a wide area. Even a diminished yet still powerful 6-foot wave could impact the small city of Whittier, located 30 miles away, posing a threat to anyone along its low-lying shores.

In response to the researchers’ open letter, state and federal agencies swiftly deployed a comprehensive network of high-tech instruments throughout Barry Arm fjord. This array includes weather stations, seismometers, live-feed cameras, radio repeaters, and ground-based radar, collectively providing real-time observations of the unstable slope. An experimental tsunami warning system has also been established, enabling scientists to alert Whittier officials and notify boaters via VHF radio. The research conducted using these instruments has significantly enhanced scientists’ ability to pinpoint distant landslides, including the recent event in Tracy Arm, representing a substantial investment of millions of dollars in state and federal funding.

As their reflections shimmered on the calm surface of Portage Lake, Higman elaborated on the specific factors that render certain Alaskan glaciers, particularly those experiencing retreat, significant hazards. The critical elements, he explained, are visibly unstable slopes perched above thinning ice, a sufficiently large body of water to generate a tsunami, and proximity to human populations and infrastructure. Portage Lake embodies these conditions. The Chugach National Forest visitor center, a hub of activity for up to 1,000 visitors daily during the summer, is situated lakeside. Many visitors board the 140-passenger Ptarmigan tour boat, which regularly circumnavigates the lake. The area also includes a nearby road, railroad, campgrounds, and trails, all situated within the potential path of a tsunami.

Upon landing their packrafts on a narrow strip of shore, they secured their vessels to a cliff to deter curious bears before shouldering their packs and hiking into the cool air. The ascent took them through dense alder brush and up steep, green tundra slopes. As the fog began to dissipate below, revealing the expansive Portage Glacier, a colossal river of ice nestled between imposing mountains, icebergs floated where its face met the lake. However, along its edges, ice darkened with rubble receded from the mountain walls, presenting a somber image of a glacier in decline.

Higman explained this phenomenon as a potential example of "debuttressing." Healthy glaciers, through their erosive action, sculpt and can even undercut adjacent mountains, but they also exert outward pressure, providing support to the slopes. As glaciers thin, a process accelerated globally by climate change, this crucial buttressing effect diminishes, potentially leading to the collapse of steepened slopes. Compounding this instability are the thawing of alpine permafrost and an increase in extreme rainfall events, both linked to climate change, which can further trigger debuttressing-related landslides.

However, the precise mechanisms governing slope failure remain an area of active research. Landslides do not invariably follow glacial retreat, and in some instances, they may not occur at all. While the Barry Glacier has receded from the base of its unstable slope over the past decade or more, the slope itself has not yet experienced a major slide. "It’s frustrating that we don’t know more about how these systems work," Higman remarked, gazing at the wasting glacier meeting Portage Lake.

The ascent continued, leading them to the landslide’s most active edge. Stretching above and below, and extending as wide as a football field, the slope was a chaotic landscape 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 loss of buttressing support. He and other researchers are concerned that the slope could collapse catastrophically into the lake in the coming years, mirroring the events at Tracy Arm, where satellite imagery indicated a rapid glacial retreat from beneath the doomed mountainside in the days and weeks preceding its collapse.

During their hike across the steep, barren slide, dirt and scree shifted underfoot as they carefully navigated around precariously balanced boulders. Higman reached over the edge of a sheer column to retrieve an extensometer, a compact instrument previously drilled into the rock. Describing it as an "electronic tape measure," he used a drill to access its casing and replace its battery, explaining that it continuously records the rock’s movement. While still experimental, Higman expressed hope that this data could eventually be accessed online by himself or visitor center staff, particularly during periods of heavy rain or rapid glacial retreat.

Ideally, Higman envisioned a more extensive network of precise instruments deployed across the Portage slide, similar to the comprehensive monitoring at Barry Arm. Such a system would be linked to satellites and a government agency, enabling a rapid "red button" alert to the public in the event of accelerating movement and the detection of any critical precursory signals. He acknowledged the limitations of his current low-cost, homegrown efforts, which, while enabling more instruments to be placed in more locations, require precise placement to accurately capture movement. For now, these rudimentary sensors represent the sole monitoring presence at Portage.

As they scrambled further up the slope, traversing to other sensor locations, each acting as an "eye" on potentially critical fractures, Higman emphasized the benefits of his ongoing research, particularly its cost-effectiveness, which allows for broader deployment. However, the rudimentary nature of these sensors necessitates careful placement in precisely the right locations to yield meaningful data.

A few weeks after the Tracy Arm tsunami, amidst a drizzling evening, Dennis Staley, the U.S. Geological Survey scientist leading the multi-agency effort at Barry Arm, drove to Whittier for a public meeting. The town, a hub for numerous companies operating boat and kayak tours in Prince William Sound, hosted dozens of captains, guides, officials, and locals aboard a spacious tour boat docked in the harbor. Amidst conversation and pizza, Staley provided an update on the Barry Arm landslide. He spoke briefly before opening the floor for discussion. As low clouds descended and darkness enveloped the calm harbor, operators posed questions and shared their evolving strategies for safely navigating tourists to the glaciers that sustain their businesses. While many operators ceased visiting Barry Arm in 2020, following Higman’s initial warning, some had resumed operations after the installation of monitoring equipment. However, following the Tracy Arm event and a 2024 landslide and minor tsunami at the Surprise Glacier near Barry Arm, some operators have once again opted to avoid the area, a recurring pattern for those working near Alaska’s rapidly melting glaciers.

Jeff Pedersen, operations manager for Alaska Wildland Adventures in nearby Girdwood, described the situation as an ongoing assessment. In 2024, his company sustained 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 night of heavy rainfall, triggering a tsunami that reached heights of 50 feet or more on nearby slopes. Further from the landslide’s epicenter, at the company’s backcountry lodge, a 3-foot wave inundated boardwalks near a cabin where guests were sleeping. In response, staff reviewed their safety protocols and have since ceased visits to that glacier.

Similarly, Christine and Jeffrey Smith of the David B engaged in sober discussions about safety and revised their anchoring practices following the Tracy Arm slide. While they intend to continue visiting glaciers, their operational approach will adapt to changing conditions, ideally informed by further research. Major cruise lines, including Carnival, Holland America, and Royal Caribbean, have also taken note. In early April, the majority of large cruise ship companies operating in Alaska announced their decision to bypass Tracy Arm in 2026, rerouting over 300 scheduled visits to the neighboring Endicott Arm, a comparable fjord where the Dawes Glacier is retreating 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, also expressed significant concern. Yakutat, a village of approximately 600 residents, is situated between Southeast Alaska and Prince William Sound, not far from the immense Hubbard Glacier. Lekanof recently coordinated a community workshop, attended by Higman and other scientists, as part of the Átl’kū Geohazards Project. This initiative integrates Indigenous and Western scientific knowledge to enhance 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 ongoing melting of glaciers.

Although cruise ships do not make direct calls in Yakutat, they frequently pass the village en route to the Hubbard Glacier in Disenchantment Bay. Scientific models indicate a potential for a landslide and a subsequent destructive wave along this route. Lekanof voiced concerns 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 potential for a cruise ship accident, she warned, could lead to loss of life or environmental damage in areas crucial for her people’s 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, a project requiring expanded funding, particularly in light of recent efforts to reduce such programs. Traditional teachings regarding glaciers and tsunamis, Lekanof explained, embody the wisdom passed down by her ancestors over millennia. "We were taught to not be loud, we were taught to not damage the landscape, to be careful where you go," she recounted. She has, however, observed cruise ships sounding their horns near the glacier, an action she finds "spiritually disruptive and concerning for the birds and mammals there."

A month prior to visiting Portage Lake, the captain of the Ptarmigan tour boat photographed fresh debris at the base of a slow-moving landslide, an area recently exposed by the receding Portage Glacier. She shared these images with visitor center staff, who then consulted with Higman. Subsequently, an intense multi-day storm delivered eight inches of rain. Weighing the potential risks, 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 risks. This proactive adaptability may signify a evolving operational paradigm for navigating the challenges posed by Alaska’s retreating 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 slope movement, evident at Portage and Barry Arm, is undoubtedly significant, but the extent of glacial retreat also plays a crucial role. Higman and his colleagues have gathered preliminary data suggesting that the longer a newly exposed slope remained covered by a glacier, the greater its potential susceptibility to sliding. He believes that Endicott Arm and LeConte Bay, two busy fjords south of Tracy Arm, warrant thorough investigation. After all, the Tracy Arm mountainside appeared solid, lacking the overt warning signs observed at Portage and without the benefit of any monitoring sensors. "As scientists, we need to own up to having totally missed the ball on that one," Higman conceded.