In Skagway, at the height of summer, hundreds of tourists wait in line – some patiently, some less so – to return to their cruise ships. But they can’t get there on foot. Instead, they wait for shuttles or small, orange boats.
Jeff Jarvie, of Riverside, California, experienced the rigmarole this week.
“It’s disappointing, because it’s a ship with so many people,” he said. “The water taxi takes a whole, like, process.”
But that process is in place for good reason. Skagway’s largest cruise ship dock, known as the Railroad Dock, has been off-limits to pedestrians since the summer of 2022. That’s when multiple rock slides tumbled toward the dock from a ridge to the east.
No one was injured. But the slides damaged infrastructure and resulted in dock closures that took a major toll on the local economy. An assessment by an engineering firm later concluded the entire slide area would eventually collapse, which it said would be “catastrophic in nature.”
That fueled widespread concern in the community.
“We know that we have this one spot that’s active,” said Reuben Cash, the environmental program coordinator for the Skagway Traditional Council, a local tribe. “Where else? Where else can we expect to see these geohazards show up?”
That question is the driving force behind an ongoing research project that aims to study rockslide risk along the rest of that ridge and elsewhere in Skagway. The initiative is part of a regional effort that aims to help seven tribal governments understand and respond to local geohazards.
In Skagway specifically, the issue is rooted in the fact that the area for thousands of years was under miles of ice. Those glaciers retreated long ago. When that happened, they exposed the now slide-prone ridgeline.
“There’s no longer that support,” said Cash. “These valley faces, these slope faces, are beginning to topple because they don’t have anything holding them up.”
A landscape of wiggly rocks and leaning columns
That toppling effect is what brought Josh Roering, a University of Oregon geologist, to Southeast earlier this summer. He’s been visiting the area for research since 2022.
While out on a day-long hike along the town’s most prominent ridgeline in June, he said the project has a few main components.
First, mapping when and where rockfalls have happened before, modeling where they could happen later, and simulating where rocks would end up if they did fall. That work included analyzing hundreds of rockfall events in Skagway between 2005 and 2022.
“We identify that there are parts of this valley that are much more susceptible to rockfall runout than others,” Roering said.
That means some slopes are both rockslide-prone and oriented in a way that could put people and infrastructure in harm’s way.
Another key component is gauging the ridge’s stability – and the extent to which rocks along it respond to everything from wind, frost and rain to trucks, trains and cruise ships. The researchers did that by placing 38 seismometers, which measure movement, in the area for about a month, two years ago. They’re now analyzing that data.
“The more wiggly these rocks are, the more sort of decoupled they are from the underlying mountain,” Roering said. “And so that is a relative measure of how potentially unstable they may be.”
Roering spent several days this summer going back to those sites and gathering more information. Along the way, he and another team member used photos and GPS data to pinpoint exactly where the sensors were placed. Then they mapped the geology around those sites and measured the angle of various rock faces.
During that hike in June, Roering stopped periodically to point out deep, vertical gashes in earth – some of which could fit a human. The ridgeline is covered in them.
Roering explained that the mountain – like others in Skagway – is largely made up of upstanding sheets of granite that are peeling apart, absent support from glaciers. That process speeds up when rocks, trees and other debris fall into the fractures, wedging them open. Then they start bending toward Skagway down below.
“Once you sort of got a big column of rock leaning this far over, it starts to become difficult for it not to flip over,” he said.
For Skagway, no “time bomb just waiting to happen”
The research has generated some good news so far. The ridge above town does not seem to be prone to a deep-seated landslide, like the one that killed two people in Haines in 2020.
“We know that we don’t have a time bomb just waiting to happen,” said Cash, of the Skagway Traditional Council.
That doesn’t mean there’s no risk at all. Right now, rockslide activity that could threaten life or property is concentrated in a handful of areas in the valley, including two main spots along the ridge that towers above the cruise ship dock.
But Roering said it’s clear the instability isn’t limited to those specific areas. It’s also present along the rest of the ridge and elsewhere in Skagway. As a result, he said, it’s likely the toppling effect will continue to ripple across the region far into the future.
A major remaining question is what actually triggers that instability and sparks rockslides. So far, Roering said, it’s not totally clear. But there seems to be more activity during spring, as temperatures warm.
“This was a surprising finding for us because it shows that the timing of thaw is way more important than rainfall for triggering these rockfalls,” Roering wrote in an email this week.
The ongoing research is set to wind down by 2027. It won’t remedy the gargantuan slide in the harbor that has already damaged infrastructure, threatened public safety, and inconvenienced visitors like Jarvie, the cruise ship passenger from California.
But the effort ideally will provide the community the information it needs to better understand the risks it faces – and to prepare accordingly.
“It’s not going to tell you exactly where rocks will fall,” said Cash. “But it tells us the higher risk areas where it’s more likely to happen.”
