ANCHORAGE, Alaska (KTUU) – Scientists and officials with Kenai Fjords National Park are advising people staying in an area near Seward to be cautious after they say a heavy rain event earlier this month in Pedersen Lagoon caused an estimated 2.6 million cubic yards of land to slide and trigger a tsunami.
The massive landslide occurred on August 7 at around 5 a.m.
Calls for caution around the fjords of southcentral and southeast Alaska, where glaciers have receded, are not new, especially since the Barry Arm landslide was discovered.
Preliminary data show that the wave reached a height of at least 56 feet in the upper part of the lagoon.
Chad Hults, Alaska regional geologist with the National Park Service (NPS), said the landslide occurred across the rapidly receding Pedersen Glacier and carved a trench in the ice as it made its way into the lagoon, creating a wave there.
“When the tsunami swept across the lagoon, it climbed some mountain slopes on the opposite side of the lagoon and destroyed some forests,” Hults said.
Hults heard that the tsunami wave near the cabin was about a meter high and that a wooden walkway was damaged.
He says a steel bear container at a campsite was also moved 20 feet.
According to scientists, no one was injured.
Geologist Bretwood “Hig” Higman said the danger in such situations is not over just because the landslide has occurred. He warned that one landslide could bring with it the possibility of another landslide.
Hults said people in the area do not necessarily need to worry, but should be aware of the danger when doing anything in the Pedersen Lagoon area, such as boating or deciding where to camp.
He said it was important to know the warning signs of a tsunami and when to move to higher ground.
Hults said a fellow scientist has since advised against conducting research in the lagoon area at this time of year.
“In August, the slopes seem to become more unstable,” Hults said. “This is because summer is over, the permafrost at high altitudes is thawing, and then the rains start in August.”
He said rain could cause cracks in the rock, making the slope unstable.
“When there is heavy rainfall, you definitely have to be prepared for possible landslides, and landslides generate tsunamis,” he said.
Interestingly, when the Kenai Fjords Glacier Lodge alerted scientists to the nearby landmass, they warned them of a possible tsunami. They had already realized that it was likely unstable and had planned field work.
“It was actually scheduled for about the same time that the landslide started,” Hults said. “So we had it planned. We wanted to do it. We had a flight scheduled the week before to measure tidewater glaciers, but we had a technical issue that prevented us from continuing the operation that day, so we couldn’t capture it before the landslide started.”
The USGS and Park Service are collaborating on numerous projects in southcentral and southeast Alaska, he said, trying to identify unstable slopes and model possible tsunamis from landslides.
He said this event will be a really good test case for this research.
“We’ve identified some unstable slopes that are above retreating glaciers. Just like this one, they could break off and land on the glacier and then flow down the glacier before they reach the water,” Hults said. “So this is a really good test case where we can collect a lot of good data.”
This is not the only region in Alaska where the same danger exists.
“In southern Alaska, there are very steep slopes that are potentially unstable, just like this one. Being aware of this danger is important in your decisions,” Hults said.
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