In the early morning of Aug. 10, 2025, only a few people are known to have been anywhere near Tracy Arm, just south of Juneau, when the forces of nature left a scar on the land.

The narrow fjord has two glaciers at the end of it, North Sawyer Glacier and South Sawyer Glacier. The glacier on the south side was forever altered that morning.

A large landslide, almost 3,300 feet by 2,000 feet, according to the U.S. Geological Survey, came crashing down from the northern wall of the fjord onto the toe of the glacier just before 5:30 that morning.

The sheer force of the land falling into a narrow, deepwater fjord pushed the water far up the wall across from the landslide and created a large tsunami.

There were kayakers camping on Harbor Island, near the mouth of Tracy Arm. USGS reports the wave swept their gear away. The kayakers were unharmed.

When the weather cleared, Cyrus Read, a geophysicist with USGS, was one of the first scientists to fly over the landslide and see the aftermath for himself, just days after it happened.

“I think we were the first ones to really kind of give an estimate for how high that splash had gone across the bay,” he said. “I think other people had flown around maybe earlier that day because it was the first good weather day and taken photos, but we hadn’t seen them yet. So, we were amongst the first people who had really been up there and looked carefully. We were probably the first to look carefully.”

With those attentive eyes, the crew saw how the energy from the landslide and tsunami profoundly changed the land’s anatomy.

“In my job with the Alaska Volcano Observatory for 20-something years, I’ve seen a lot of cool things from helicopters, and this was right up there with any of the coolest I’ve seen,” Read said.

His journey was exclusively in the air since the helicopter was unable to land.

At the head of Tracy Arm, Read explained, “You couldn’t miss the big chunk of the mountain that had fallen off and kind of landed mostly on the glacier and partially in the water,” he said of the northern side of the fjord.

He and the crew on the helicopter had an idea of what they would see on the northern side of the fjord where the land had let go from the rock beneath it, but Read said he had no idea what the southern side of the fjord would look like after the tsunami had hit.

“The wave had run up to 1,500-ish feet. And that, I think, kind of took us aback. We knew that there was likely a splash on the other side, but we didn’t realize how big it was,” he said. “That’s pretty unusual, I think. It doesn’t happen often.”

“We could see where the alders had all their bark peeled off. And so, we kind of got an estimate for how high up that splash on the opposite side of the landslide was. And that was a really cool thing to see,” Read said.

“You could see the trim line, where how high up the water had run, as you went down the fjord. And then it kind of disappeared toward the mouth of the fjord, except that around the corner in Williams Cove, it was like a bulldozer had gone through to about 80 feet above the sea level at the head of the cove,” he said.

“The way that the wave ran up in different places was really interesting. And the extent to which it ran up when it was even pretty far away from the source of the wave itself, that, too, was striking to me because I just didn’t expect that. I kind of thought the wave would be created and then slowly diminish in size. And that’s not how it works,” he said.

“I mean, I hope I don’t have to see it again. I think we really dodged a bullet here, right?” he said. “There are frequent cruise ships up in that area in Tracy Arm. And if one had been there at that time, it could have been a real problem.”

The concern of landslides over and near melting glaciers in Alaska has grown in recent years.

There’s no solid timeline on when those masses could fall into the water, and scientists don’t know whether it will be in a worst-case scenario. There’s been a push for more research over the past few years and could be considered a “young study” in some respects.

“I think it’s a really important topic, and it’s something that we’re going to continue to see,” he said of the large, deep-seated landslides like the one in Tracy Arm but also the shallow, smaller landslides like the deadly ones in Southeast Alaska over the past few years, which have often been triggered by rainfall.

He thinks the most important thing for scientists right now when it comes to landslides is hazard mapping.

“Knowing the history of where landslides have happened, to know where there’s risk is a very important aspect of this,” he said.

“The Tracy Arm landslide produced a series of small seismic events in advance of it happening that were recorded in Juneau and Sitka. So, it does seem like, perhaps, with a large event like this, you could detect it in advance if you had a density of seismometers and enough people watching,” he said.

“I think that we have a lot of work to do on the landslide side. There’s a lot to learn, but it’s also a difficult thing to instrument and alert in real time.”

Scientists have been working on a project that may possibly in the future detect landslides in real-time. The program is in a test phase but was expanded in fall of 2025 and continues to be in the works.