Glacier Bay’s geology reads kind of like a recipe for giant waves: It’s a recently glaciated area that’s still rebounding from ice cover. It freezes and thaws. There are steep slopes above deep water in an active fault zone.
In fact, the biggest wave ever recorded anywhere was on the park’s outer coast, in Lituya Bay in the 1950s. Geologists say the conditions that can lead to landslides are only getting more pronounced in Alaska.
“So this begs the question, you know, as temperatures continue to warm here, will we start seeing more of them or not?” asked Jeff Coe, who leads the U.S. Geological Survey team that’s working with the park.
Some really big slides in 2012 and 2016 are what piqued his interest.
“There was nothing like them in the historical record. They were two to five times larger than anything else that had happened in the historical record back to 1984,” he said.
Coe’s guess is that they’re related to degrading permafrost and rock. That’s because two big slides look like they’re associated with warm winter temperatures.
Landslides and tsunamis aren’t historically common in Glacier Bay, but because more than half a million visitors tour the park each year — most of them by cruise ship — park superintendent Philip Hooge wants a clearer picture of the risk. That way, he can take steps to keep visitors safe.
“I’d like to sleep better at night and know that I did what was right,” Hooge said.
Over the next several years, the park will refine its understanding of where landslides could happen, and which slides could generate tsunamis.
“You can’t prevent all hazards from happening in your visits to parks, but it just seemed like we needed to get a good handle on exactly what that potential was, especially with climate change and the potential for that increasing,” Hooge said.
So far, the park has taken precise, three-dimensional measurements of the park. Next, scientists will study the likelihood of any large landslides making it into the water, and what kinds of waves that might generate.
Hooge says the risk of a tsunami happening while a cruise ship is nearby isn’t zero, but it is a very small statistical probability. An initial study shows there are a handful of areas in the park where a landslide could hit the water and generate a wave that would affect boats.
“There’s a 90% chance of capsize if you have a wave that is the size of the beam of a ship,” Hooge said.
The beam of a ship is its width. The Majestic Princess, one of a few ships that visited the park this summer, has a 150-foot beam. The estimated wave from a landslide at Tidal Inlet is up to 250 feet high.
“Cruise ships can only go like 30 degrees, at the most, over,” Hooge said. “You know, they’re not built for tilting.”
But there’s a big difference between a wave hitting the bow or the side of a ship. Hooge has thought a lot about how to keep visitors safe while they’re observing this dynamic landscape. One solution is some kind of warning system. He says placing sensors around risk zones could give ships a chance to take the wave from an advantageous angle.
“Legs would break and swimming pools would empty, but they could potentially turn the boat,” he said.
That’s just a theoretical example, he said, and a warning system like that would be complicated and expensive to build. And again, the odds of a cruise ship passing Tidal Inlet at the exact moment of a landslide are really, really small.
For now, Jeff Coe with the USGS plans to monitor the area remotely. He says the landslide at Tidal Inlet has been a source of concern for a while, but so far, its movement looks pretty non-threatening.
This year was the agency’s first year of field study at Glacier Bay. Coe hopes to return next year and continue to study the area over the next six or seven years.
“I think with climate change the way it is, and warm temperatures continuing to warm, I think Alaska will be kind of the landslide research frontier,” he said.
The ultimate result will be a map showing how likely slides are in different areas of the park.