When Mountains Fall into the Sea

As glaciers melt, unstable slopes are being exposed and are on the precipice of collapse.

photo:The downside of this Norwegian fjord’s attractive features—sheer mountainsides and deep waters—is that they’re ideal for creating localized tsunamis from landslides. Photo by Adam Machowiak/Alamy Stock Photo

Howard Ulrich and his eight-year-old son had just fallen asleep in their salmon troller when a sudden barrage of waves nearly knocked them out of their bunks. Their boat, the Edrie, was anchored in an uninhabited Alaskan inlet called Lituya Bay. Ulrich ran onto the jolting deck half dressed and heard a rumbling from the mountains at the head of the bay. His boy, Sonny, clambered onto the deck with him, and as the boat pitched and tugged at its anchor chain, they watched the 2,000-meter-high mountain peaks shudder and convulse, sending clouds of snow billowing into the air. Then it happened: “a mighty seismic disturbance … exploded with a deafening crash,” Ulrich recalled in an Alaska Sportsman magazine article. It was followed by a massive landslide.

The Ulrichs had anchored in the wrong place at the wrong time: ground zero for the strongest earthquake in Alaska in 60 years. It lasted over a minute, and the tremors were felt as far south as Seattle. The landslide it triggered was not a gradual tumbling of individual boulders. Rather, 82 million tonnes of rock and ice—the weight of 240 Empire State Buildings—hit the water as a slab. The impact was like an asteroid strike. Dropped from more than 900 meters, the slab sent up an instant, towering displacement wave that tore into the forested mountainside directly across the northern end of the inlet.

It was, and is, the largest wave ever recorded: 524 meters high. The initial splashdown kicked out a second, smaller, wave that sped across the inlet at over 150 kilometers per hour, shearing trees off the surrounding hills as it went. That wave was headed directly for the Edrie.

Ulrich shook off his awe, threw his son a life preserver, and told him to start praying. Though his anchor was stuck on the bottom—possibly pinned by newly shifted boulders—Ulrich managed to steer the boat toward the oncoming wall of water and climb it, snapping the anchor chain like fishing line as he did. The wave had reduced to about 20 meters high by the time it reached the Edrie, and after cresting it, Ulrich was able, barely, to ride out the ensuing chaos of refraction waves and log debris and exit the bay.