Fiber-optic cable reveals hidden crevasses that could destabilize glaciers
In recent years, the Alps have experienced devastating glacier collapses: In September 2023, a section of the Marmolada glacier in the Dolomites collapsed, resulting in the deaths of seven mountaineers. Just over a year and a half later, in May 2025, the Birch Glacier above Blatten collapsed, keeping Switzerland and the entire world in suspense.
Recent years have seen devastating collapses of glaciers in the Alps, including the tragic loss of seven mountaineers in September 2023 when the Marmolada glacier in the Dolomites collapsed. In May 2025, the Birch Glacier above Blatten also collapsed, causing significant concern worldwide. Understanding the stability of glaciers is crucial, as hidden crevasses within the ice can destabilize them.
Researchers have long struggled to detect these hidden crevasses due to their deep nature and the high costs and logistical challenges of deploying numerous seismometers.
However, a groundbreaking study led by Assistant Professor Thomas Hudson from the Environmental and Exploration Geophysics Group at ETH has demonstrated a more economical and precise method. They utilized a single fiber-optic cable laid on the surface of the Gorner Glacier in Valais to map the internal structure of the glacier to a depth of 25 meters.
The fiber-optic cable functions similarly to a network of seismometers, capturing seismic waves generated when microearthquakes occur as crevasses open within the ice. These waves cause slight deformations in the fiber, altering the reflection of the injected light signal. By analyzing these changes, researchers can determine the location and depth of crevasses, akin to an ultrasound scan.
The results were surprising, revealing that hidden crevasses comprised more than 8% of the ice volume at the measurement site, far exceeding expectations. While these crevasses contained water or air, the remaining 92% of the ice remained undisturbed. The researchers emphasize that not all crevasses are visible from the air; many are internal and significantly impact the glacier's stability. This discovery underscores the importance of analyzing internal fractures in determining a glacier's risk of calving.
Hudson and his team are optimistic about the potential of this method to enhance monitoring of unstable glaciers, providing early warnings of calving events at glacier fronts. This capability would improve the evaluation of risks associated with major calving events. The researchers plan to extend their use of this technique to other glaciers in the Alps and the ice sheets of Greenland or Antarctica, aiming to better understand glacier stability and its impact on sea levels.
The increased understanding of glacier crevasses could also aid in predicting changes in ice sheets and their contribution to global sea level rise.
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