OUT OF EDEN WALK

Shortly after dawn on a foggy morning last August, a mountain cracked apart in southeast Alaska and toppled a vertical kilometer into a beautiful fjord.

The mass of rock dislodged by the colossal landslide—estimated at 64 million cubic meters, or a volume of stone sufficient to build 25 pyramids of Giza—slammed into the green-blue tidewaters at the toe of the South Sawyer Glacier. Colonies of harbor seals typically doze on icebergs there. Did they jerk awake at the apocalyptic roar? Did the armadas of terns and gulls patrolling the fjord teeter onto their wingtips from the shock of impact? Nobody knows. No humans were present at the remote site of the disaster, nor did anyone directly witness what happened next: A wave rocketed up the fjord’s walls to almost incomprehensible heights—at least 481 meters, or tall enough to swamp the Empire State Building under nearly a hundred meters of water.

The Tracy Arm tsunami has entered history books as the second largest wave ever recorded by science. Wary of further geological instability and monster waves, few people venture today up the scenic waterway in the Tongass National Forest. But over three days last October, I joined the first scientific expedition to survey, up close and in sobering detail, the aftermath of the historic cataclysm.

What we found beggared belief.

Looking up from our small boat, we beheld a trimline or “bathtub ring” scoured by a tsunami that had shot-gunned down the fjord’s narrow channel at speeds up to 160 kilometers an hour. Even 10 kilometers downstream from the landslide, that raw scar stood out crisply some hundred meters above the usual sea level waterline of the granite cliffs. All life below it—a temperate rainforest composed of Sitka spruce, western hemlock, willow, and alder, inhabited by brown and black bears, wolves, and deer—was smashed, sodden, buried in muck. In places, both the soil and vegetation, ranging from grandmother trees to ankle-deep moss, was blasted entirely away as if by a gigantic fire hose. I placed my hand on the newly exposed bedrock, trying to sense a trembling hint of the dreadful power of what seemed, to me, like ecological suicide bombing. My awe was mixed with remorse, for humans had helped light the fuse.

“We keep seeing these tsunamis generated by landslides,” said Patrick Lynett, an environmental engineer at the University of Southern California and a senior researcher on the expedition. “They are becoming more and more relevant hazards. So they need to be understood.”

Landslides and tsunamis have reshaped the Earth’s surface through erosion, of course, for uncounted millennia.

But as human-caused climate change accelerates, and the Arctic and subarctic in particular warm at historically unprecedented rates, such geo-hazards are multiplying. Coastal glaciers are in drastic retreat. As their ancient ice melts, the surrounding mountains lose frozen buttresses that have propped up the lower slopes since the last Ice Age. An older, colder world is now literally crumbling away.

Alaska has become a focus of concern because its human populations are often squeezed along the frontier state’s narrow, craggy shorelines and now face growing prospects of falling mountains and the resulting titanic waves.

The largest known landslide tsunami in the world occurred 250 kilometers northwest of Tracy Arm, in isolated Lituya Bay, Alaska, in 1958. That wave surged an astounding 530 meters high and killed two people. Tracy Arm is the second-biggest wave on record. Miraculously, no people were harmed there, despite the scenic fjord being a popular sightseeing stop on Alaska’s cruise ship circuit. Vessels carrying more than 5,000 people often lumbered up Tracy Arm. By blind luck, and thanks to the timing of the catastrophe—5:26 a.m. on August 10 last year, a sleepy Sunday—no boats were nearby when the landslide collapsed at the foot of South Sawyer Glacier. Today, the cruise industry avoids the place.

For similar reasons, the scientific survey anchored 45 kilometers downstream from the disaster site as a safety precaution, on a 30-meter yacht named, appropriately, Dauntless.

Geologist Bretwood “Hig” Higman from the nonprofit (Ground Truth Alaska) project joined Lynett, an affable New Jerseyan who’d become intrigued by tsunamis after growing up near the overbuilt beaches of his home state. I had reported earlier last year on Higman, when he’d chivvied me up a scarp abutting Portage Glacier near Whittier, Alaska, to report on another landslide threat. I described him back then as a ferociously dedicated researcher-outdoorsman, and on encountering him again, found him wearing the same tattered Bolivian wool cap, and intense as ever.

“We’re trying to see where, exactly, the edge of the water reached,” Higman explained matter-of-factly, as he rock-climbed the high, slick, near-vertical bedrock walls stripped clean by the tsunami. “I don’t want to be where I don’t really believe my own data. Or where someone else doesn’t believe our data.”

Each overcast morning, we played the odds and motored to the head of the ravaged fjord. We used a smaller, 22-foot utility vessel, whose aluminum hull was better suited to thread a sprawling, perilous minefield of floating ice. The landslide had exploded close enough to the terminus of South Sawyer Glacier to blast off fragments ranging in size from pulverized slush to bergs larger than two-story houses. The crew took turns muscling the frozen debris away from the boat’s bow with a long pole. In the final kilometers, under rare flashes of amber sunlight, Higman and drone operator Bill Billmeier attempted to paddle tiny pack rafts through the icy maze but were thwarted by bergs piling up into jagged walls.

Again and again, the team deployed laser surveying instruments, logging hundreds of data points that computed the height of the tsunami’s trimline.

It struck me, privately, as funereal work.

I once had been a war correspondent. I was familiar with the hazardous silences that can haunt battlefields. And so, it was hard not to liken the terrible cruelties we inflict upon each other with the senseless devastation we wreak on nature. Tracy Arm wasn’t as clear-cut a moral link as, say, personally emptying the oceans of fish. (I once worked as a commercial fisherman too.) Nor was it as detached or impersonal as observing, with curiosity, the carcass of a rainforest elephant in the Democratic Republic of Congo embedded, mal chance, in a volcano’s lava flow. (Nature is incapable of mercy.) Instead, the vast ruins of the subarctic fjord settled, gloomily, into a strangely heavier middle ground: collective responsibility.

As much of the world wearily knows, from the beginning of the Industrial Revolution in 1750, the United States has pumped nearly a quarter of humankind’s planet-warming carbon dioxide emissions into the atmosphere. Since 2016, the country has withdrawn, twice, from the global Paris Agreement limiting such pollutants.

And so, the misery of Tracy Arm.

Under the cold spatter of rain, we worked briskly with one eye on the threatening walls above us, moving like dazed stretcher bearers among nature’s casualties, both atoning for and responsible for the boggling scale of violence around us.

Ultimately, the results of the field survey, coupled with analyses of satellite imagery, seismology, and advanced computer modeling, have enabled scientists to accurately recreate what happened in Tracy Arm almost exactly one year ago:

Months of rapid melting of the South Sawyer Glacier is pegged as a major factor in the disaster. Nobody may have seen the actual landslide, but at the grey dawn of ground zero, a seiche or huge standing wave was recorded by faraway seismometers. It began sloshing back and forth inside the fjord for more than a day.

Three and a half minutes after the mountainside’s collapse, and nine kilometers downstream, the tsunami rolled over Sawyer Island, an outcrop inside the fjord. The frothing wall of water, towering as high as a football field is long, scalped off all but a tuft of the island’s topmost trees.

Roughly 20 minutes later, hurtling up the outside walls of the fjord’s bends like a massive toboggan, the tsunami ricocheted into Williams Cove, a frequently used anchorage. The wave was slowing now, but its height still reached about 30 meters. Spruces with trunks a meter thick were shoved over like blades of grass. Some fallen trees surfed 50 meters into the flooded forest. Survivor trees had bark chewed off 20 meters above their base. The tsunami carried away the cove’s beaches, revealing the fjord’s rocky bottom.

By 6 a.m., or about half an hour after the landslide, the wave crashed into Harbor Island, just outside the fjord’s mouth some 50 kilometers downstream. Though still losing height and speed, the first humans to actually experience the event began reporting a strange passing swell three to five meters high. A group of camped kayakers awoke to seawater swirling about their tents. One of their beached boats was snatched away by the wave. Another was deposited in a tree. (“I’m really glad we went back in the woods,” one of them told the media at the time. “We definitely would’ve died if we hadn’t.”)

The Tracy Arm tsunami then radiated into the open waters of Alaska’s Inside Passage. Pods of humpback whales must have ridden its pulse of passing water and continued mildly on their migrations. An hour after the landslide, the diminishing wave nudged up tidal gauges upward by half a meter in Juneau, Alaska’s capital, some 140 kilometers away. Fishing boats and pleasure craft bobbed at their moorings. Few people were awake to notice.

Two months later, we too left Tracy Arm, and in haste.

A low-pressure front was building into a small craft advisory. With gusting winds and heavy swells barreling towards the Alaskan coast, the survey team retreated to the Dauntless and made for the ship’s home of Petersburg.

The master of the expedition’s utility boat, a goateed salt named Greg Chaney, decided to race the storm back to his home in Juneau. Safety protocol required a second hand on board, so I joined him. We chugged through the waves on a night so black that Chaney, double-checking his navigational instruments, resorted to peering steadily backward at the receding deck lights of fishing boats to maintain his course in the lightless Endicott Arm. It seemed an apt metaphor for the blind advance by Homo sapiens into this age of emergency. The biggest danger to our bobbing little craft lay in tearing our hull against unseen floating logs, including, conceivably, those spat out by the Tracy Arm tsunami. Through tense hours we hoped, however undeservedly, to make it to safe harbor.

Reporting for this story was supported by the Pulitzer Center.