Sasha Calvey heard the tsunami coming. It was after 5:30 a.m. on August 10, 2025, and she was camped with two friends on a remote island in Southeast Alaska, 74 days into a sea kayaking trip from Washington. Heavy rain had fallen overnight, with gusts swaying the spruce and hemlocks overhead, but an alarming new sound roused Calvey from her sleeping bag: a deep, rumbling roar like a waterfall, growing louder and closer until it seemed to shake the very ground. "Everything in my gut told me to check outside," Calvey recounted.

The trio scrambled out to discover that 15-foot waves had just slammed into the nearby beach, inundating the forest. Seaweed lay scattered on the moss beside their tent, and water drained from the woods back to the gravel beach where their food and gear had been stowed; half of it was gone, one kayak was wedged against a tree, another hung precariously from a bluff, and the third floated in the distance. They were fortunate; had the tsunami arrived just three hours earlier, when the tide was 10 feet higher, the surging water could have swept through their campsite, toppling trees and potentially engulfing them in their tent. "The water was chaotic for hours," Calvey recalled, describing powerful swells and giant whirlpools, ultimately prompting them to radio for rescue and end their ambitious expedition.

Later, they learned the immense wave was generated by a massive landslide approximately 30 miles away, at the terminus of Tracy Arm fjord, a narrow channel snaking between mountains south of Juneau. The slide occurred where the South Sawyer Glacier is retreating, a phenomenon scientists believe can destabilize surrounding mountainsides. The landslide carved a significant scar into the bedrock above the glacier, creating a wave that achieved an astonishing 1,580-foot run-up on nearby mountainsides, stripping away trees, brush, and soil – the second-largest run-up ever recorded. As the tsunami propagated from the slide, it scoured the steep shorelines along the 30-mile fjord, with its remnants reaching Calvey’s beach beyond the fjord’s mouth.

Evidence suggests a marked increase in landslide-generated tsunamis in Alaska over the past decade. In 2015, a landslide in Taan Fjord, roughly 400 miles northwest of Tracy Arm, resulted in a 630-foot wave run-up. Furthermore, in Prince William Sound, a slow-moving landslide near the Barry Glacier poses a threat of generating a tsunami potentially even larger than the one at Tracy Arm. Scientists, land managers, and tour operators are urgently seeking solutions, anticipating more slides as glaciers continue their retreat. This escalating, climate-related hazard poses a significant risk to coastal communities, vital infrastructure, and vessels of all sizes, including the large 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 typically linked to seismic events, such as the 1958 earthquake that triggered a landslide and a record-setting 1,720-foot run-up in Lituya Bay, Glacier Bay National Park. She found no prior mention of large, tsunami-generating landslides caused by receding glaciers. Her experience, however, underscores the urgent need for greater awareness and research into this emerging geohazard.

The sheer luck of the Tracy Arm incident is difficult to overstate, given the area’s popularity. Each summer, Tracy Arm, located within the Tongass National Forest, welcomes over 200 visits from cruise ships whose passengers hope to witness the dramatic flow of the Sawyer and South Sawyer glaciers into the ocean. The fjord attracts an estimated 500,000 boat-based visitors annually. While numerous vessels were present in the fjord in the days leading up to the slide, traffic was lighter in the early morning hours when the mountain gave way. The closest known vessel, the over-100-passenger National Geographic Venture, was in Tracy Arm but approximately 20 miles from the South Sawyer Glacier when the landslide occurred. Traveling in deep water, it remained unharmed by the tsunami. Had the landslide occurred just a few hours later, the Venture would have been near the glacier, where passengers often board smaller skiffs to get a closer look. In that zone, waves exceeding 100 feet, laden with icebergs and debris, could have easily destroyed 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 South Sawyer Glacier, putting them directly in the path of the tsunami. However, due to stormy weather, they rerouted to the neighboring Endicott Arm, anchoring 45 miles away. "We’re definitely feeling our mortality," Christine Smith later stated, finding it hard to comprehend surviving such a chaotic event. Even in Endicott Arm, the tsunami made its presence known; while cooking breakfast, Smith witnessed 10-foot swells suddenly surge over a shoal, forcing an 80-foot vessel to battle an unusually strong current.

The Smiths immediately sent a satellite text to Jackie Caplan-Auerbach, a geologist friend in Washington, asking her to check nearby seismic stations for signs of a landslide. This message provided the first indication of the Tracy Arm tsunami to the outside world. Caplan-Auerbach, a seismologist and professor at Western Washington University, was alerted by the text while having coffee. She quickly accessed publicly available seismic data from stations near the David B’s location. Southeast Alaska, however, is a vast and remote region with sparse seismic monitoring due to the high cost of installation and maintenance. At a sensor located in the Tlingit village of Angoon, about 60 miles west of the David B, Caplan-Auerbach detected a characteristic seismic signal indicating a nearby landslide. She alerted colleagues, and collaboratively, scientists pinpointed the event’s origin in Tracy Arm. "This is a big deal," she recalled thinking, recognizing that the landslide must have displaced a colossal volume of water for the tsunami to travel 45 miles and be felt by the David B.

Intriguingly, Caplan-Auerbach also noted that for several hours preceding the main landslide event, the Angoon seismometer had been registering subtle, low-frequency signals originating from the slope. "They’re tiny," she explained, adding that these signals would likely have gone unnoticed without the subsequent catastrophic failure. Geologists later identified similar precursory signals on other seismometers, which ceased abruptly once the mountainside collapsed. Caplan-Auerbach has spent nearly two decades studying these "precursory" signals, pondering their potential to inform future landslide warning systems. However, she acknowledges that such systems are still a distant prospect, as "landslides are notoriously difficult to anticipate" due to a complex interplay of factors like rock type, precipitation, and geological conditions. Moreover, she cautioned that 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, paddled packrafts along the shores of Portage Lake, about an hour southeast of Anchorage and 500 miles from Tracy Arm. Their objective was to check sensors on a slow-moving landslide situated above the Portage Glacier at the lake’s far end. Dense fog shrouded the water, and as they approached the glacier, a rockslide rumbled in the mist, a stark reminder of the unstable mountains surrounding them. Higman, a geologist with a keen, boyish interest in the natural world, cocked his head towards the sound.

In May 2020, Higman and over a dozen other scientists had issued a public warning about a potentially catastrophic creeping landslide near the retreating Barry Glacier in Prince William Sound through an open letter to The New York Times, which published a story detailing the risks. This unorthodox approach drew criticism from some locals who felt they should have received official notification rather than learning about the danger from national media coverage that caused concern just before the peak tourism season. The Barry Arm landslide, located 40 miles north of Portage Lake, is a significant geological feature. During the summer, rocks continuously tumble down its gravelly surface, creating dust plumes and splashing into the ocean. Nearby, the Barry Glacier calves ice with booming sounds. Computer modeling suggests that if the entire slope were to fail, it could trigger a massive tsunami, endangering boats, cabins, campsites, and all occupants within a broad area. A diminished, yet still powerful, 6-foot wave could impact the small city of Whittier, 30 miles away, threatening anyone along its low-lying shores.

Following the researchers’ 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. Furthermore, research conducted using the Barry Arm instruments has significantly enhanced scientists’ ability to pinpoint more distant landslides, including the Tracy Arm event, representing millions of dollars in state and federal investment.

As they paddled across Portage Lake, Higman explained why certain of Alaska’s thousands of retreating glaciers pose particular hazards. The key ingredients are visibly unstable slopes situated above thinning ice, a body of water large enough to generate a tsunami, and proximity to human populations and infrastructure. Like Barry Arm, Portage Lake possesses all these elements. A Chugach National Forest visitor center sits lakeside and bustles with up to 1,000 visitors daily during the summer. Many board the 140-passenger Ptarmigan tour boat, which circulates the lake throughout the day. Additionally, a nearby road, railroad, campgrounds, and trails are all situated within the potential path of a tsunami.

They landed at a small inlet and secured their boats to a cliff face, hoping to deter curious bears. Shouldering their packs in the cool air, they hiked up through dense alder brush and then onto steep, green tundra. Far below, the fog dissipated, revealing the Portage Glacier, a vast river of ice nestled between bulging mountains. Icebergs floated where its face met the lake, but along its edges, rubble-darkened ice had receded from the mountain walls, giving the glacier a sickly appearance. Higman explained this phenomenon as "debuttressing," where healthy glaciers typically erode and support adjacent mountainsides. However, as glaciers thin, a process exacerbated globally by climate change, this buttressing effect diminishes, potentially leading to the collapse of steepened slopes. Climate change also contributes by thawing alpine permafrost and intensifying extreme rainfall events, both of which can trigger debuttressing-related landslides.

However, the precise mechanisms that dictate whether and when a slope will fail remain elusive. Landslides do not always immediately follow glacial retreat, and sometimes they do 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 slid. "It’s frustrating that we don’t know more about how these systems work," Higman commented, gazing down 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 instability. These cracks had opened so recently that living heather still clung to their edges, with desiccated roots dangling in the air. More cracks appeared as they moved upward, 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 landscape of upturned rock and soil, featuring leaning spires, shattered boulders, and deep, gravelly sinkholes. They occasionally heard the sharp crack of tumbling rocks. The entire mass was slumping toward the glacier by several meters annually, Higman stated, attributing it to the thinning glacier’s removal of support.

Higman and other researchers, led by Dan Shugar of the University of Calgary, recently published a paper in the journal Science detailing how the glacier’s retreat primed the slope for the landslide and subsequent tsunami. Nevertheless, Dennis Staley, the U.S. Geological Survey scientist overseeing the multi-agency effort at Barry Arm, noted that numerous factors, including weather and slope characteristics, can contribute to landslides. While the recent research highlights the connection between retreating glaciers and tsunami-generating landslides, Staley admitted that "it’s hard to know a specific trigger." Higman concurred, carefully choosing his words: "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 raised immediate concerns about Portage.

They traversed the steep, barren slide, with dirt and scree sloughing downward beneath their boots as they navigated around wobbly boulders many times their size. Eventually, Higman reached over the edge of a sheer column to retrieve an extensometer, a metal and glass canister smaller than a water bottle that he had previously drilled 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, it captures precise measurements of the rock’s movement. Though still experimental, Higman hoped that someday, either he or visitor center staff could access its data online, particularly during periods of heavy rain or accelerated glacial retreat. Ideally, Higman envisioned a dense network of more precise instruments on the Portage slide, similar to the array at Barry Arm, linked to satellites and a government office capable of activating an alert system if movement accelerated. Such a network could also detect any critical precursory signals.

While his current setup is rudimentary, Higman highlighted the benefits of his low-cost, homegrown effort, enabling more sensors in more locations. However, these basic sensors must be placed "at just the right crack" to effectively monitor movement, and for now, they are the sole sensors at Portage. They continued scrambling upward to the crown of the slide and back onto firm tundra, spending an hour traversing the slope to reach other sensors, each serving as an observation point for what Higman hoped were the crucial fissures.

On a drizzly evening a few weeks after the Tracy Arm tsunami, Staley drove to Whittier for a public meeting. Dozens of companies launching boat and kayak tours into Prince William Sound operate from Whittier. Captains, guides, officials, and local residents gathered aboard a spacious tour boat moored in the harbor, enjoying pizza while Staley provided an update on the Barry Arm landslide. Staley spoke briefly before opening the floor for discussion. As low clouds and darkness settled over the calm harbor, operators posed questions or shared their evolving strategies for safely guiding visitors to the glaciers that support their businesses. While many operators had ceased visiting Barry Arm in 2020 after Higman’s initial warning, some had resumed operations after monitoring equipment was installed. Now, following the Tracy Arm event and a 2024 landslide and small tsunami at Surprise Glacier near Barry Arm, some were again avoiding the area, a pattern of caution becoming familiar to 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 large landslide near the retreating Pedersen Glacier in Kenai Fjords National Park, approximately 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 overran boardwalks near a cabin where guests were sleeping. Staff reviewed their safety protocols and have since stopped visiting that particular glacier. Christine and Jeffrey Smith of the David B also responded to the Tracy Arm slide with sober discussions about safety and revised anchoring practices. They intend to continue visiting glaciers but will adapt their operations based on changing conditions and, ideally, more research.

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

Melenda Lekanof, secretary and treasurer of the Yakutat Tlingit Tribe Council, also expressed concern. Yakutat, a village of 600 residents situated between Southeast Alaska and Prince William Sound, is located near the massive Hubbard Glacier. Lekanof recently coordinated a community workshop attended by Higman and other scientists, as part of the Áak’w Hwáan Geohazards Project, which integrates Indigenous and Western scientific knowledge to better understand landslide risks. "We have a lot to learn about our changing landscape," Lekanof stated, acknowledging the increasing frequency of landslides and melting glaciers. Although cruise ships do not dock in Yakutat, they frequently pass the village en route to the Hubbard Glacier in Disenchantment Bay. Scientific models indicate a potential landslide and destructive wave along this route. Lekanof worries 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, and 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 installed in Disenchantment Bay, a project that would require expanding funding that has faced potential cuts. Traditional teachings about glaciers and tsunamis reflect lessons learned by 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 has, however, observed cruise ships blasting their horns near the glacier, which she finds "spiritually disruptive and concerning for the birds and mammals there."

A month before visiting Portage Lake, the captain of the Ptarmigan tour boat photographed fresh debris at the base of the slow-moving landslide, in an area recently exposed by the Portage Glacier’s retreat. She shared these images with visitor center staff, who consulted Higman. Subsequently, an eight-inch rainfall event occurred over several days. Weighing the potential risks, the Forest Service evacuated a school group and staff from the visitor center, according to an agency statement. The Ptarmigan also canceled tours, citing landslide and tsunami risks. This kind of adaptive response may signify a new operational paradigm for navigating Alaska’s changing glacial environments.

While this adaptability offers a glimmer of hope, Higman pointed out that the Tracy Arm incident raises critical questions about how scientists prioritize slopes for monitoring. Visible slope movement, as observed at Portage and Barry Arm, is important, but so is the extent of glacial retreat. Higman and other researchers have gathered preliminary data suggesting that the longer a newly exposed slope was covered by a glacier, the greater its potential likelihood of sliding. Higman suggested that Endicott Arm and LeConte Bay, two busy fjords south of Tracy Arm, warrant thorough investigation, especially considering that the Tracy Arm mountain appeared stable with no visible warning signs and lacked any monitoring sensors. "As scientists, we need to own up to having totally missed the ball on that one," Higman concluded.