This article was originally published on Hakai Magazine, An online publication on science and society in coastal ecosystems. To read more articles like this Hakai Magazine.
In 2015, 76 million cubic meters of rock collapsed from a steep cliff above a fjord in southeast Alaska and spilled into the ocean. The landslide spawned a wave nearly 200 meters high that roared down the narrow Tern Fjord and into Icy Bay. No one witnessed the collapse, but a year later geologist Bretwood Higman visited the area to measure the tsunami’s effects in detail. During a break from his work, Higman looked up and saw a huge cruise ship sailing across the mouth of the fjord. He was shocked.
“I never thought about a cruise ship going into I.C. Bay,” Higman said. Images of a ship swept away by a tsunami and trapped in the rocky channel flashed through his mind. “There are so many things that could go really badly.” The image stuck in his mind.
Tsunamis caused by landslides have a low probability of occurring, but the damage they cause is great. However, rising temperatures are melting glaciers and causing steep slopes in southeastern Alaska to collapse. Many fjords are becoming increasingly unstableMany exposed cliffs that were once supported by ice now stand unsupported and are at risk of collapse as the glaciers that once supported them have retreated rapidly. Heavy rains and melting permafrost have exacerbated the risk. And tourists are flocking to them. Gather on Alaska’s rugged coast“People are now concentrated in the areas that are at the highest risk,” Higman said. This increases vulnerability to disasters and the likelihood of disasters, he said. This risk is heightened in coastal areas around the world that are in the same situation as Alaska, including Greenland, Chile, Norway and New Zealand.
Higman said tsunamis caused by offshore earthquakes take time to hit coastal areas, but those caused by coastal landslides can appear suddenly and produce much higher waves, which pose a bigger threat to people on boats.
The growing threat worries Amanda Bauer, who has run day cruises in the narrow waters around Alaska’s Prince William Sound for 17 years. Half a billion cubic metres of unstable rock teetering precariously on top of the retreating Barry Glacier.“When you’re out on the water, you often think about what you would do,” Bauer says. “You’re sitting surrounded by ice and you can’t go more than two knots even if you wanted to. It’s not like being out in open water where you can turn around and get away if you see something going on.”
Concerned about how ship captains should respond to such an extreme threat, Higman scoured the existing scientific literature on how ships can survive tsunamis. He focused exclusively on coastal landslide-induced tsunamis, but found little, apart from a few one-off case studies and eyewitness accounts of historical events, such as when a tsunami approaching the height of Toronto’s CN Tower capsized two ships in Littoral Bay, Alaska, in 1958, killing two people. Scientific efforts to model landslide-induced tsunamis and their effects on ships are just beginning, with little data to serve as guidelines.
Higman found official guidance from the US National Tsunami Hazard Mitigation Program to be similarly inadequate. Based on the impact of an offshore tsunami in a California port, the advice essentially boils down to three points: Vessels at anchor should abandon ship and make their way to higher ground on foot. Vessels in deeper waters, between 300 and 600 feet, should head for deeper waters. Vessels closer to shore should choose between beaching and escaping or retreating to deeper waters. This all-purpose advice applies to everything from kayaks to fishing boats to 150-passenger day cruisers.
Because landslide-induced tsunamis can strike before experts can detect them and issue warnings, the captains Higman spoke to said they would never choose to deliberately run their ships aground (or even wreck them) and attempt to evacuate with passengers and crew to Alaska’s rugged coastline, not knowing when a tsunami would arrive or how far upriver it would travel.
While it is currently impossible to predict the arrival time or size of a landslide-induced tsunami in advance, Higman says guidelines could explain how tsunamis generally work. Tsunamis are fundamentally different from the wind waves that sailors are accustomed to sailing through, which can throw off captains’ intuition, he says. First, tsunamis move faster in deeper waters and can be quite high in shallow areas. The depth of Alaskan fjords varies greatly, so even if a captain thinks he has enough time to escape a tsunami, it can catch up with him and crash right on top of him.
Tsunamis trapped in fjords tend to swell like water in a bathtub, creating unpredictable currents that can reach speeds of more than 100 kilometers per hour. The guidelines’ three bullet points don’t address the subtleties of how tsunamis interact with Alaska’s complex coastline, Higman says. By so oversimplifying tsunami science, he says, the guidelines underestimate the expertise of boat operators who are accustomed to making quick decisions in dangerous situations.
Elena Suleimani, a tsunami modeler at the Alaska Earthquake Center and co-author of the existing guidelines, acknowledges that they are incomplete. She has mapped out ports where water is deep enough for ships to safely weather a tsunami, but Suleimani isn’t comfortable advising ship operators. “We have no idea how to operate a ship,” she says.
So, on a mission to give ship captains the best advice possible, Higman will be co-hosting a workshop with the Prince William Sound Regional Citizens Advisory Council (RCAC) in June 2024 in Valdez, Alaska. The event will bring tsunami scientists and vessel operators together for the first time to pool their knowledge and develop more actionable recommendations.
At this point, Higman can’t say exactly what the appropriate guidance should be. But while the workshop will focus on improving advice for small-ship captains, National Park Service geologist Chad Hultz says operators of larger vessels, like cruise ships, also need to consider the threat of landslide tsunamis. Hultz says the NPS is eager to begin discussions with cruise lines that frequent Glacier Bay, where dozens of landslides could happen at any time.
During tourist season, “two cruise ships a day come into Glacier Bay, for a total of 260 ships. Nowhere else in the park system has there been such an obvious hazard with as many as 4,000 passengers on board that could cause harm,” Hults said.
Similarly, there are no official tsunami hazard guidelines for oil tankers visiting Valdez, Alaska, the terminus of the Trans-Alaska Pipeline, according to Alan Sorum, maritime operations project manager for the Prince William Sound RCAC. “If a ship that big were to capsize, the cleanup would be a massive undertaking,” Sorum said.
So far, Alaska’s sailors have avoided the worst: There have been no oil spills or shipboard fatalities from tsunamis in Alaska in the past 60 years. “Despite all the energy we’re putting into this, there’s always that voice in the back of your mind that says, ‘Maybe it’s not a big deal, maybe this is a waste of time,'” Higman says.
But then he thought about the cruise ships that sail through Barry Arm, Lituya Bay and the mouth of Taarn Fjord. He counted dozens of unstable slopes known to lurk across Alaska, all waiting to collapse into a bay or fjord. “And I thought, at some point, [the situation] It’s going to explode.”
This article was first Hakai Magazine Republished here with permission.
