The impact of 63.5 million cubic meters of rock hitting the fjord released forces large enough to be registered globally. The seismic waves that cascaded across the planet were recorded by sensor stations worldwide and were equivalent in energy to a magnitude 5.4 earthquake. The sloshing water within the fjord established a 66-second long-period seiche, a standing wave, that reverberated back and forth for 36 hours.

“It could easily turn into a catastrophic disaster,” Fathian says. It could, because Tracy Arm is a highly frequented tourist destination.

A close call

During the summer, more than 20 boats navigate the Tracy and Endicott arms every day, including up to six large cruise ships. Had the landslide occurred a few hours later, in the middle of the tourist day, the outcome could have been tragic. But even at 5:26 in the morning, the tsunami was enough to terrify the few people present in the vicinity.

About 55 kilometers away on Harbor Island, a group of kayakers saw the water flowing past their tents 20 minutes after the landslide. The surging tide took away some of their gear and one of the kayaks. Nearby in No Name Bay, observers on a motor vessel reported a 2-2.5-meter cresting wave coming along the beach from the direction of Tracy Arm, followed by a secondary 1-meter wave.

Farther away, 85 kilometers from the source, the crew of the small cruise boat anchored in Fords Terror saw a surge of water pouring over a nearby sandbar; it then physically lifted their vessel three meters despite a falling tide. The surge, they reported, lasted until 11 am, only to leave their small skiff stranded on dry land a few minutes later as the water receded.

At the mouth of the fjord, a National Geographic Venture cruise ship carrying around 150 people was anchored in dense fog. The captain noted currents, white water, and a significant amount of ice and debris near the edges of the fjord. Because the jagged, shallow seabed near the fjord’s mouth acted like a speed bump that sapped the wave’s energy, people onboard the cruise ship came out of the event unscathed. “It was a miraculous kind of luck we had that nobody got hurt,” Fathian claims.