Since 2020, scientists have installed monitoring instruments around the Barry Landslide in Alaska's Prince William Sound to closely track seismic activity in the area. Their goal is to detect warning signs early, before a sudden landslide could trigger a destructive tsunami.

By analyzing these seismic recordings, researchers identified a previously unrecognized type of signal. These events are marked by sharp, high-frequency pulses that become more common from late summer through mid-winter, then suddenly stop in late winter or early spring.

Strange Signals Linked to Freezing and Thawing Rock

Writing in Seismological Research Letters, Gabrielle Davy of the University of Alaska Fairbanks and her colleagues propose that the signals are caused by water freezing and thawing inside tiny cracks in the rock beneath the nearby Cascade Glacier. The research team is the first to carry out a systematic analysis of these short, impulsive seismic events near the Barry Landslide.

The scientists emphasize that these signals are not signs that the landslide itself is moving. However, they may still provide valuable insight into changes in underground water conditions behind the slope. Those changes could eventually play a role in triggering slope movement.

Why the Barry Landslide Poses a Serious Risk

Searching for seismic warning signs at Barry Arm is especially important because the landslide sits in a highly unstable setting. The slope is steep and underlain by weak, heavily fractured bedrock, making it prone to failure. It has also lost critical support from Barry Glacier, which has rapidly melted and retreated over the last century.

"What makes Barry Landslide especially concerning is the size of the landslide," Davy explained. "It's a large, slowly moving mass -- on the order of about 500 million cubic meters -- that has been creeping for decades."

"If a rapid collapse were to occur, the material would fall directly into the fjord, and that could generate a tsunami with potentially high wave heights," she added. "Barry Arm is visited by kayakers and cruise ships, and nearby communities such as Whittier could be affected, so understanding the hazard is important from both a scientific and a public-safety perspective."

Sorting Through a Year of Seismic Data

Because of these risks, the landslide area has been extensively instrumented since 2020. The study by Davy and her colleagues is among the first to carefully examine the large volume of seismic data collected by those instruments.

For this research, the team manually reviewed an entire year of continuous seismic waveform recordings. They searched for signals that might help determine when and where a landslide could occur.

This hands-on approach allowed the researchers to recognize the wide range of signals present in the data. These included vibrations from small earthquakes, glacier motion, slope deformation, and other sources of seismic background noise.