This article originally appeared on Hakai Magazine, an online publication about science and society in coastal ecosystems. Read more stories like this hakimagazine.com.
In 2015, 76 million cubic meters of rock fell from the rugged cliffs above a southeastern fjord in Alaska into the water below. The landslide caused a nearly 200-meter-high wave that swept through the narrow Taan Fiord 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. Higman looked up from his work and saw a gigantic cruise ship crossing the mouth of the fjord. He was stunned.
“It never occurred to me that a cruise ship would enter Icy Bay,” Higman says. An image of tsunami-tossed ships stuck in the rocky passage filled his mind. “There are a lot of ways that could turn out very badly.” He couldn't get the image out of his head.
Landslide-induced tsunamis are low-probability, high-consequence events. But as rising temperatures cause glaciers to melt, the steep slopes of southeastern Alaska are created Many fjords are becoming increasingly unstable. Many exposed cliffs, once supported by ice, now stand without support and are at risk of collapsing as the glaciers that once held them up are rapidly retreating. Heavier rainfall and thawing permafrost further increase the dangers. And with tourists flocking to the rugged coast of Alaska“There are now huge concentrations of people going straight to the highest risk areas,” Higman said. We have increased our vulnerability to disasters, and we have increased the probability, he says. This risk increases in coastal areas around the world that share Alaska's conditions, such as Greenland, Chile, Norway and New Zealand.
Unlike tsunamis caused by earthquakes far offshore, which take time to hit coastal communities, tsunamis caused by landslides appear suddenly and can produce significantly higher waves, Higman says. That poses a greater threat to people in boats.
The growing threat is gnawing at Amanda Bauer, who has been organizing day cruises for 17 years and navigating the narrow channels around Alaska's Prince William Sound, including in the Barry Arm fjord, where a 500 million cubic meter chunk of unstable terrain teeters above the retreating Barry Glacier. “I think about it a lot when I'm there: What would I do?” says Bauer. “Sometimes I sit there, surrounded by ice; If I wanted to, I couldn't go further than two knots. That's different from having open water where I can turn around and get sunburned if I see something happening.”
Concerned about how captains should respond to such an extreme threat, Higman delved into the existing scientific literature on how ships can brave tsunami waves. Focusing only on research related to landslide-induced tsunamis, his search yielded little beyond a few one-off case studies and eyewitness accounts of historical events, such as the time in 1958 when a wave nearly leveled the CN Tower in Toronto capsized. two boats in Lituya Bay, Alaska, killing two people. Scientific efforts to model landslide-induced tsunamis and their effects on ships are only just beginning, meaning there is little data to provide guidance.
Higman found that official guidelines from the United States National Tsunami Hazard Mitigation Program are also missing. That advice, based on the effects of marine tsunamis on California ports, essentially boils down to three points: For moored ships, abandon ship and walk to higher ground. For vessels in deep water – between 300 and 600 feet deep – go to even deeper water. And for ships that are close to shore, you can choose to beach the boat and run away, or flee to deeper water. This one-size-fits-all advice is for 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, Higman says the captains he spoke to would never choose to deliberately beach (and possibly destroy) their ship and try to evacuate with passengers and man a rugged Alaska. coastline without even knowing when the wave will arrive or how far it will flow along the coast.
While it is currently impossible to predict in advance the arrival time or size of a landslide-induced tsunami, Higman says guidelines can explain how tsunamis work in general. Tsunami waves are fundamentally different from the wind waves that sailors are used to navigating, he says, and which can disrupt a captain's intuition. For starters, tsunami waves increase in deeper water and become significantly larger in shallow water. Because the depths of Alaska's fjords can vary greatly, a captain might think he has ample time to outrun a tsunami, only for the wave to overtake him and break on top.
Tsunamis confined to the fjords also tend to slosh around like water in a bathtub, creating unpredictable currents of more than 60 miles per hour. These three points of guidance don't address these nuances of tsunamis' interactions with Alaska's complex coastline, Higman says. By oversimplifying tsunami science so much, he says the guidelines also underestimate the expertise of ship operators, who are used to making quick decisions in dangerous conditions.
Elena Suleimani, a tsunami modeler for the Alaska Earthquake Center and co-author of the existing guidelines, admits they are imperfect. Although she has created port-specific maps that show where the water is deep enough for a ship to safely weather a tsunami, Suleimani is uncomfortable giving advice to ship operators: “I have no idea how to use boats management,” she says.
So, on a mission to give captains the best possible advice, Higman is hosting a workshop with the Prince William Sound Regional Citizens' Advisory Council (RCAC) in Valdez, Alaska in June 2024. The event will bring together tsunami scientists and ship operators. for the first time to pool their knowledge and, hopefully, develop some more practical recommendations.
At this point, Higman cannot say exactly what the right guidance should be. But while the workshop will focus on improving advice for captains of small vessels, Chad Hults, a geologist with the National Park Service (NPS), says operators of larger vessels, such as cruise ships, should consider the threat of landslides. tsunamis too. Hults says the NPS is eager to begin discussions with the cruise lines that visit Glacier Bay, where a dozen pieces of land could slip away at any time.
During the tourist season, Hults says, “we have 260 cruise ships – two cruise ships a day – coming into Glacier Bay. There is no other place in the park system where we have 4,000 people on a boat and there is a pretty clear hazard that could cause some damage.”
Likewise, says Alan Sorum, the maritime operations project manager for the Prince William Sound RCAC, there are no official tsunami hazard guidelines for the oil tankers visiting Valdez, Alaska, the terminus of the Trans-Alaska Pipeline. “If you capsize a ship that big,” Sorum says, “it would be a big problem to clean it up.”
So far, Alaska's sailors have managed to avoid the worst. In Alaska, a tsunami has not caused an oil spill or killed anyone on board a boat in 60 years. “Despite all my efforts, there's a little voice in the back of my head that says, 'Maybe it's not that bad, maybe I'm wasting my time,'” Higman says.
But then he thinks of Barry Arm, Lituya Bay and the cruise ship he saw sailing past the mouth of Taan Fiord. He lists the dozens of unstable slopes known to lurk throughout Alaska, all waiting to collapse into bays and fjords. “And I think at some point [the situation] is going to explode.”
This article first appeared in Hakai Magazine and is republished here with permission.
