Sailing in Alaska? Watch Out for Tsunamis

By Christian Elliott.

Tour boat operators and cruise ship captains face a growing hazard: tsunamis generated by collapsing cliffs. If disaster strikes, what should they do?

In 2015, 76 million cubic meters of rock crashed from the rugged cliffs above a southeastern Alaska fjord and into the water below. The landslide sparked a nearly 200-meter-tall wave that roared down the narrow Taan Fiord and out into Icy Bay. No one witnessed the collapse, but a year later, geologist Bretwood Higman was in the area taking detailed measurements of the tsunami’s effects. Looking up from his work, Higman saw a massive cruise ship crossing the fjord’s mouth. He was stunned.

“It’d never occurred to me that a cruise ship would go into Icy Bay,” Higman says. An image of tsunami-tossed ships trapped in the rocky passage filled his mind. “There are many ways in which that could work out really badly.” He couldn’t get the picture out of his head.

Landslide-generated tsunamis are low-probability, high-consequence events. But as rising temperatures cause glaciers to melt, the steep slopes of southeastern Alaska’s numerous fjords are becoming increasingly unstable. Once buttressed by ice, many exposed cliffs now stand unsupported and at risk of collapse as the glaciers that once held them up rapidly retreat. Heavier rains and thawing permafrost are further increasing the hazards. And with tourists flocking to Alaska’s rugged coast, “there are now these huge concentrations of people that are going right to the areas of highest risk,” Higman says. We’ve increased our vulnerability to disaster, and we’ve increased the probability, he says. This risk is rising in coastal regions around the world that share Alaska’s conditions, such as Greenland, Chile, Norway, and New Zealand.

Unlike tsunamis triggered by earthquakes far offshore, which take time to strike coastal communities, tsunamis triggered by coastal landslides appear suddenly and can cause significantly higher waves, Higman says.