Sasha Calvey heard the tsunami coming, a deep, rumbling roar like an approaching waterfall that intensified as it neared, shaking the very ground beneath her tent. It was just after 5:30 a.m. on August 10, 2025, and Calvey, along with two friends, were 74 days into a challenging sea kayaking expedition from Washington, camped on a remote island in Southeast Alaska. Overnight rain and strong winds had buffeted the surrounding spruce and hemlocks, but it was this new, alarming sound that jolted them awake. "Everything in my gut told me to check outside," Calvey recounted.

Emerging from their tent, the trio discovered 15-foot waves had violently crashed onto the beach, inundating the nearby forest. Seaweed lay scattered on the moss beside their campsite, a stark indicator of the surge’s power. Just a few steps away, water was draining from the woods back to the gravel beach where they had stored their provisions and gear; half of it was now gone. One kayak was wedged against a tree, another dangled precariously from a bluff, and the third was spotted floating in the distance. They were incredibly fortunate; had the tsunami struck just three hours earlier, when the tide was a full 10 feet higher, the water could have swept through their location, toppling trees and potentially dragging them, trapped within their tent, into the ocean. "The water was chaotic for hours," Calvey recalled, describing powerful swells and immense whirlpools. With so much of their essential equipment lost, they activated their radio for a rescue, abruptly ending their ambitious journey.

Their ordeal was later attributed to a massive landslide approximately 30 miles away, at the terminus of Tracy Arm fjord, a narrow channel winding between mountains south of Juneau. The slide occurred as the South Sawyer Glacier recedes, a phenomenon scientists believe can destabilize the surrounding landscape and contribute to such catastrophic events. The immense scale of the landslide was evident in the resulting tsunami’s run-up, which reached an astonishing 1,580 feet on nearby mountainsides, stripping away trees, brush, and soil. This measurement marks it as the second-largest run-up ever recorded. As the colossal wave propagated outward from the slide, it scoured the steep shorelines along the 30-mile fjord, with its diminished but still powerful remnants reaching Calvey’s beach, located beyond the fjord’s mouth.

Evidence suggests a concerning upward trend in landslide-generated tsunamis across Alaska over the past decade. In 2015, a similar event at Taan Fjord, located 400 miles northwest of Tracy Arm, generated a wave with a 630-foot run-up. More recently, a slow-moving landslide near the Barry Glacier in Prince William Sound poses a threat of triggering a tsunami potentially even larger than the one observed at Tracy Arm. This emerging hazard, exacerbated by climate change, is prompting scientists, land managers, and tour operators to urgently seek solutions and anticipate further instability as glaciers continue their retreat. The implications are far-reaching, threatening coastal communities, vital infrastructure, and the myriad of boats operating in Alaskan waters, including the large cruise ships that transport nearly two million visitors to the state annually.

While researching her kayaking trip, Calvey had encountered warnings about tsunamis in Alaska’s fjords, but these were predominantly linked to seismic activity, such as the 1958 earthquake that triggered a landslide and a staggering 1,720-foot run-up in Lituya Bay, Glacier Bay National Park. She found no prior mention of giant, tsunami-inducing landslides directly caused by retreating glaciers. Her experience, however, underscores the urgent need for greater awareness and research into this specific type of natural disaster.

The sheer luck of the timing for Calvey and her companions cannot be overstated, particularly given Tracy Arm’s popularity. Each summer, this majestic fjord, situated within the Tongass National Forest, hosts over 200 visits from large cruise ships. These vessels bring a constant stream of visitors eager to witness the awe-inspiring spectacle of the massive Sawyer and South Sawyer glaciers meeting the ocean. The fjord attracts an estimated 500,000 boat-based visitors annually. While numerous vessels were navigating the area in the days preceding the landslide, the early morning hour of the event meant traffic was significantly lighter. The closest known vessel was the over-100-passenger expedition ship National Geographic Venture, which was in Tracy Arm, heading toward the glaciers. Fortunately, it was in deep water and approximately 20 miles from the South Sawyer Glacier when the mountain gave way, thus remaining unharmed by the tsunami. Had the landslide occurred a few hours later, the Venture would have been positioned near the glacier, where passengers disembark onto smaller skiffs for close-up viewing. In that scenario, the potential for 100-foot-high whitewater waves, laden with icebergs and debris, could have devastatingly impacted the tour boat and any deployed skiffs.

Christine and Jeffrey Smith, owners of the 65-foot tour boat David B, also experienced a near miss. The previous evening, with six guests aboard, they had planned to anchor overnight just five miles from the South Sawyer Glacier, directly in the path of the impending tsunami. However, unfavorable stormy weather prompted them to anchor instead in the neighboring Endicott Arm, a decision that ultimately saved them. "We’re definitely feeling our mortality," Christine Smith shared later, reflecting on the sheer terror of contemplating survival amidst such chaos. Even in Endicott Arm, the tsunami’s effects were felt; while preparing breakfast, Smith witnessed 10-foot swells suddenly surge over a shoal, forcing an 80-foot vessel to contend with an unusually powerful current. The Smiths immediately sent a satellite text to Jackie Caplan-Auerbach, a geologist friend in Washington, requesting she check nearby seismic stations for any signs of landslides, marking the first report 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 coffee and Wordle game when the Smiths’ urgent text arrived. She swiftly shifted her focus to examining seismic data from stations near the David B‘s location, leveraging the publicly accessible data from many stations, though acknowledging the sparse seismometer coverage in the vast and remote Southeast Alaska region, where monitoring is costly. A sensor in the Tlingit village of Angoon, about 60 miles west of the David B, revealed a distinct seismic signature indicative of a nearby landslide. Caplan-Auerbach quickly alerted colleagues, and through a collaborative effort, scientists began to pinpoint the landslide’s location in Tracy Arm. "This is a big deal," she recalled thinking, recognizing the immense volume of water that must have been displaced to generate a tsunami capable of traveling 45 miles to reach the David B.

Intriguingly, Caplan-Auerbach also noted that for several hours preceding the landslide, the Angoon seismometer had been detecting faint seismic signals originating from the slope. "They’re tiny," she commented, adding that these subtle tremors would likely have gone unnoticed had the major landslide not occurred. 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, and she, along with other researchers, contemplates their potential role in a future landslide warning system. However, the development of such a system faces significant hurdles, as Caplan-Auerbach explained, "Landslides are notoriously difficult to anticipate," citing the complex interplay of factors such as rock type, precipitation, and other variables that complicate predictive models. Furthermore, she noted that precursory signals do not precede every landslide event.

In October, Bretwood "Hig" Higman, an independent geologist working with his nonprofit Ground Truth Alaska, and I navigated the cliff-lined shores of Portage Lake, an hour southeast of Anchorage and roughly 500 miles from Tracy Arm. Higman’s objective was to inspect sensors installed on a slow-moving landslide situated above the Portage Glacier at the lake’s far end. A thick fog blanketed the water, and as we paddled towards the glacier, the distant rumble of a rockslide somewhere high in the mist served as a potent reminder of the unstable mountains looming overhead. Higman, identifiable by his wire-rimmed glasses and well-worn ballcap, tilted his head with a keen, almost boyish interest toward the sound.

In May 2020, Higman and more than a dozen other scientists made headlines with 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 public warning, while raising awareness, drew some criticism from local residents who felt they should have received official notification rather than learning of the danger through national media coverage that caused anxiety just before the peak tourism season. The Barry Arm landslide, located 40 miles north of Portage Lake, is a formidable feature. During the summer months, rocks cascade down its gravelly surface, kicking up dust or splashing into the ocean, while nearby, the Barry Glacier periodically booms as it sheds ice. Predictive modeling suggests that a complete collapse of the slope could unleash a massive tsunami, threatening boats, cabins, campsites, and all occupants across 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 significant risk to anyone along its low-lying shores.

In the wake of the scientists’ open letter, state and federal agencies swiftly 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 has also been established, enabling scientists to notify Whittier officials or alert boaters via VHF radio. Furthermore, research conducted using the Barry Arm instruments has significantly enhanced scientists’ ability to detect and locate more distant landslides, including the event at Tracy Arm. The entire Barry Arm project represents a substantial investment of millions of dollars in state and federal funding.

As we paddled across Portage Lake, our reflections mirroring the calm water, Higman elaborated on why certain glaciers among Alaska’s thousands, particularly those in retreat, stand out as potential hazards. The critical factors, he explained, 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, much like Barry Arm, possesses all these attributes. A Chugach National Forest visitor center is located lakeside, bustling with up to 1,000 visitors daily during the summer season. Many of these visitors board the 140-passenger Ptarmigan tour boat, which regularly traverses the lake. Additionally, a nearby road, railroad, campgrounds, and trails all lie within the potential path of a tsunami.

We landed on a narrow strip of shore and secured our packrafts to a cliff face, a precaution against curious bears. Shouldering our packs in the cool, crisp air, we hiked upwards through dense alder brush, transitioning to steep, green tundra. Far below, the dissipating fog revealed the Portage Glacier, a magnificent river of ice winding between imposing mountains. Icebergs floated where its face met the lake, but along its edges, rubble-streaked ice was visibly receding from the mountain walls, giving the glacier a seemingly unhealthy appearance.

"It could be an example of ‘debuttressing’," Higman explained, referring to a process where healthy glaciers erode adjacent mountains, steepening or undercutting their walls, while simultaneously exerting outward pressure that supports the slopes. However, as glaciers thin globally due to climate change, this buttressing effect diminishes, potentially leading 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. The precise mechanisms that determine when or if a slope will fail remain elusive. Landslides do not always immediately follow glacial retreat, and in some cases, they may not occur at all. For over a decade, the Barry Glacier has pulled away from the base of its unstable slope, yet the slope has not yet slid. "It’s frustrating that we don’t know more about how these systems work," Higman mused, gazing down at the wasting glacier meeting Portage Lake.

As we ascended higher above the glacier, Higman pointed out thin cracks in the ground, clear indicators of the slope’s instability. These cracks were so recent that living heather still straddled them, its desiccated roots dangling in the air. More cracks appeared as we progressed, leading us 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. Stretching above, below, and across a width comparable to a football field, the slope presented 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 toward the glacier by several meters annually, attributing this movement primarily to the thinning glacier’s loss of support for the slope.

Higman and other researchers harbor concerns that the slope could collapse catastrophically into the lake in the coming years as the glacier continues to recede from beneath it, a scenario mirroring the events at Tracy Arm. Satellite imagery clearly shows that the South Sawyer Glacier rapidly withdrew from beneath the unstable mountainside in the critical 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 critically destabilized the slope, paving the way for the landslide and subsequent tsunami. However, Dennis Staley, a U.S. Geological Survey scientist overseeing the multi-agency effort at Barry Arm, emphasized that numerous factors can contribute to landslides, including weather patterns and inherent slope weakness. While the recent research intensifies the focus on the connection between retreating glaciers and large, tsunami-generating landslides, Staley noted, "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 Lake.

We traversed the steep, barren landslide zone, navigating around wobbly boulders many times our size, with dirt and scree sloughing downward beneath our 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. This device continuously measures the rock’s movement. While still experimental, Higman expressed hope that in the future, he or even visitor center staff could access its data online, particularly during periods of heavy rain or accelerated glacial retreat. Ideally, Higman envisioned a more extensive network of precise instruments deployed on the Portage slide, akin to the monitoring system at Barry Arm. These instruments would connect to satellites and a government agency, empowering someone to "push a red button" and alert the public if movement accelerates, while also detecting any potentially critical precursory signals. Higman acknowledged the cost-effectiveness of his current "homegrown" efforts, allowing for more sensors in more locations. However, these rudimentary sensors must be strategically placed "at just the right crack" to effectively measure movement, and for now, they represent the sole monitoring presence at Portage. We continued our ascent to the crown of the slide and then onto more stable tundra, spending an hour traversing the slope to examine other sensors, each acting as an "eye" on what Higman believed were the most critical fissures.

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 town that serves as a launching point for numerous boat and kayak tours into Prince William Sound, hosted dozens of tour operators, captains, guides, officials, and concerned locals. Gathered aboard a spacious tour boat moored in the harbor, the attendees enjoyed pizza while listening to Staley provide an update on the Barry Arm landslide. Staley delivered a brief presentation before opening the floor for discussion. As low clouds and gathering darkness enveloped 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. However, following the Tracy Arm event and a 2024 landslide and minor tsunami at Surprise Glacier near Barry Arm, some companies were again avoiding the area. This ebb and flow of operational decisions has become a familiar reality for those working 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 about 60 miles south of Portage. The landslide plunged into a lagoon during a night of heavy rainfall, generating a tsunami that reached heights of 50 feet or more on nearby slopes. Further from the slide, at the company’s backcountry lodge, a 3-foot wave overran boardwalks adjacent to a cabin where guests were sleeping. In response, staff reviewed their safety protocols and have since ceased visiting that particular glacier. Christine and Jeffrey Smith of the David B adopted a similar cautious approach following the Tracy Arm slide, engaging in serious discussions about safety and revising their anchoring practices. While they intend to continue visiting glaciers, they acknowledge their operations will need to adapt to changing environmental conditions, ideally informed by ongoing research. Major cruise lines, including Carnival, Holland America, and Royal Caribbean, have also taken note of these developing risks. In early April, nearly all major cruise 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 receding from beneath steep mountainsides. None of the large cruise companies contacted for this report responded to requests for interviews.

Melenda Lekanof, secretary and treasurer of the Yakutat Tlingit Tribe Council, also expressed deep concern. Yakutat, a village of approximately 600 residents, is situated between Southeast Alaska and Prince William Sound, not far from the massive Hubbard Glacier. Lekanof recently coordinated a community workshop attended by Higman and other scientists, as part of the ‘á¹€ut’í Geohazards Project. This initiative aims to integrate Indigenous knowledge and Western science to enhance understanding of landslide risks. "We have a lot to learn about our changing landscape," Lekanof stated, referencing the increasing frequency of landslides and the accelerating pace of glacial melt. While cruise ships do not dock in Yakutat, they frequently pass the village en route to Hubbard Glacier in Disenchantment Bay. Scientific models predict the possibility of a landslide and a subsequent destructive wave along this popular route. Lekanof voiced concerns that a lack of coordinated emergency planning among cruise ship companies, state authorities, and other entities could place an undue burden on the small village in the event of a disaster. Furthermore, a cruise ship incident could result in loss of life or environmental damage to areas vital for fishing, hunting, and cultural practices. Lekanof also advocated for a monitoring array similar to the one at Barry Arm to be established in Disenchantment Bay, a project that would necessitate expanding funding, particularly in light of past efforts by the Trump administration to curtail such programs. Traditional teachings regarding glaciers and tsunamis embody the accumulated wisdom of her ancestors over millennia, Lekanof explained. "We were taught to not be loud, we were taught to not damage the landscape, to be careful where you go," she said, contrasting this with the practice of some cruise ships blasting their horns near glaciers. "Spiritually, for the birds and mammals there, I find that to be disruptive and concerning."

A month prior to my visit to Portage Lake, the captain of the Ptarmigan tour boat captured photographs of fresh debris at the base of the slow-moving landslide, an area recently exposed 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 heightened landslide and tsunami risk, according to an agency statement. The Ptarmigan also canceled its tours, citing these concerns. This adaptive response may signify a new operational paradigm for navigating the evolving landscape 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 and select slopes for monitoring. Visible slope movement, as observed at Portage and Barry Arm, is undeniably important, but so is the process of glacial retreat itself. Higman and his colleagues have gathered preliminary data suggesting that the longer a newly exposed slope remained buried beneath a glacier, the greater its propensity for future sliding. He indicated that Endicott Arm and LeConte Bay, two bustling fjords south of Tracy Arm, warrant thorough investigation, especially considering that the Tracy Arm mountain appeared outwardly stable, lacking the visible warning signs evident at Portage, and crucially, had no sensors in place. "As scientists, we need to own up to having totally missed the ball on that one," Higman conceded.