Margaret Darrow, a professor of geological engineering at University of Alaska Fairbanks, listens to community members as they recall details from the night of last November's deadly landslides. Darrow and her team have been in town for five days to examine the slide area. They talked with residents Saturday evening at the Nolan Center.
A team of experts has been conducting research in Wrangell this week, hoping to pinpoint the cause of last November's landslides. As a part of its visit, the group gave a well-attended presentation on Saturday evening at the Nolan Center to keep the community informed on their findings.
The team's research is funded by a National Science Foundation rapid response research grant, known as RAPID.
Led by Margaret Darrow, a professor in geological engineering at the University of Alaska Fairbanks, the RAPID team has already scheduled a second visit to Wrangell in the late fall where they will share some preliminary findings. University of Oregon geomorphologist Josh Roering is also helping to lead the project. Roering helped develop the Sitka landslide warning online dashboard in the aftermath of a deadly 2015 slide in that community.
Data collection for the Wrangell slide is not straightforward.
At the time of the Nov. 20 slide, the nearest weather data collection station was located over 11 miles away at the airport. Because of this, the RAPID team felt that to truly understand what caused the slide, they needed to walk the slide area. Darrow, Roering and the rest of the experts spent five days collecting data and surveying the landslide "scar."
In addition to the more scientific data collection, the RAPID team is heavily reliant on eyewitness accounts. During the presentation, Roering asked community members to offer anything they noticed that could have been related to the slide.
Audience members who live near the area shared several anecdotes, ranging from how a backyard stream's depth changed in the aftermath of the landslide to the level of noise caused by the slide itself. Meanwhile, Roering and the team wrote everything down.
The research conducted by RAPID comes after a team of three state geologists released a February report about the Wrangell slides. According to the report, excessive amounts of rain in a short period of time eventually led to the large-scale slides, the largest of which killed six people in their homes near 12-Mile.
Aaron Jacobs, the National Weather Service meteorologist working with the RAPID team, realizes the landslides would have been impossible without such heavy levels of rain, but he hopes the team can understand the other factors that led to the severity of the slides.
During the presentation at the Nolan Center, Jacobs noted that the amount of rain collected at the airport weather station did not meet the threshold of 4 to 4.5 inches of rain in 24 hours that can trigger landslides. However, this station was far from the slide, and community members recalled water "shooting off the cliffs" in areas closer to the landslide.
The team of experts is looking to fill in the other pieces of the puzzle to determine all contributing factors. One of which is something many audience members recalled from the night of the slide: severe wind.
Wind, according to the team, does not directly lead to landslides. But when it causes large trees to sway back and forth, the trees' root systems shift too. These massive root systems stir up the ground around them, making the ground weaker and more prone to slides.
Another contributing factor, according to Roering, is the geological formation of Wrangell's mountainsides.
They resemble stairs, with flat areas of thick soil alternating between steep bedrock cliffs. According to Roering, thick soil - which can take thousands of years to form - steep slopes and high levels of soil saturation often come together in the form of a landslide.
Roering also noted that while the rainfall numbers may not have been enough to cause a landslide, the rainfall coupled with the quickly melting snow caused the soil to saturate rapidly - something that often directly contributes to a landslide.
"The fact that the materials on the bedrock benches were so saturated is what allowed the landslide to expand to 20 times the size of the initiation point," Roering explained.
He hopes the research on the ground can help determine which of these contributing factors was most responsible.
As for their future plans, the RAPID team wants to help set up a landslide warning dashboard similar to the one in Sitka. The team is also installing stream water monitoring systems to help understand soil saturation levels, though it often takes multiple years to collect and analyze such data.
"Our goals are to use science and translate it to be useful for communities," Roering said.
Reader Comments(0)