Fiber-optic cable reveals hidden crevasses within the ice
ETH Zurich
image:
ETH researcher Thomas Hudson camped overnight beside the Gorner Glacier, with Monte Rosa and the Dufourspitze (4,634 m) visible in the background.
view moreCredit: Thomas Hudson / ETH Zurich
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.
Crevasses are crucial to the stability of glaciers, not only those that satellites and drones can detect on the surface but also those hidden within the ice. This is because meltwater can deepen them and accelerate the collapse of glaciers and ice sheets.
Researchers use seismic techniques to explore the inner workings of glaciers. Microearthquakes occur when crevasses open within the ice, and seismometers can detect them to pinpoint their sources. However, these measurements lack high spatial resolution, and deploying many seismometers is challenging due to high costs and the difficulty of installing them on a glacier ridden with crevasses.
One cable replaces hundreds of measuring instruments
ETH researchers led by Assistant Professor Thomas Hudson from the Environmental and Exploration Geophysics Group have demonstrated in a new study published in Science Advances that this can be done more simply, cost-effectively and with significantly higher spatial resolution.
For testing, the researchers laid a single fibre-optic cable on the surface of the Gorner Glacier in Valais. This enabled them to explore the glacier’s internal structure down to a depth of 25 metres. “A single fibre-optic cable replaces hundreds of seismometers,” emphasises Hudson.
The cable simply needs to be connected to what is known as an interrogator, which injects a light signal into the fibre and records the scattered light signals that are reflected back. Seismic waves are generated when a microearthquake occurs, such as a crevasse opening up in the ice. These waves cause a slight local deformation as they hit the fibre, leading to changes in how the injected light is deflected and reflected. This results in a change in the baseline signal, alerting researchers to the location and depth of a crevasse.
Using computational methods, the researchers can determine the structure of the ice and gain an insight into its internal composition, similar to an ultrasound scan performed by a doctor. Analysing the data is computationally demanding due to the vast amount of data generated. The researchers use an algorithm to assist with this.
Employing this method on the Gorner Glacier, the wave physicists uncovered a surprisingly large number of hidden crevasses, which accounted for more than eight percent of the ice volume at the measurement site. “That’s far more than we expected,” says Hudson. The crevasses contained water or air, while the rest of the ice ؎ 92 percent – remained undisturbed.
Not all crevasses are visible from the air. Hudson emphasises that they greatly impact the glacier’s stability. “Laypeople often assume that large, visible surface crevasses indicate whether a glacier is stable or not. However, scientists pay more attention to internal cracks and crevasses inside the ice,” he explains. Consequently, analysing these internal fractures is essential for researchers when determining whether a glacier is at risk of calving.
Measurement method proves its worth
The researcher states, “We are very pleased with the test runs on the Gorner Glacier. The method has proven its worth.” In future, it could assist in monitoring unstable glaciers and providing early warnings of calving events at glacier fronts. This would improve our ability to evaluate the risk of major calving events.
The researchers could extend their mapping of crevasses to other glaciers in the Alps and the ice sheets of Greenland or Antarctica to better understand their stability. Data collected from within the glaciers could complement satellite surface observations.
How crevasses affect sea level
The ETH researchers plan to further test their technique on other glaciers across the Swiss Alps and on polar ice sheets. They aim to understand the development of crevasses over time and space, as well as the connection between surface crevasses and those deeper within the ice. Glacier crevasses influence more than just the glacier – they alter its overall behaviour. Water that enters these crevasses acts as a lubricant at the glacier’s base, potentially accelerating its movement. This effect is globally significant, especially for the gigantic ice sheets of Greenland and Antarctica, which greatly impact sea levels. “Our method could therefore help to predict changes in the ice sheets and sea levels,” Hudson explains.
Reference
Hudson T, Walter F, Noe S et al.: Quantifying subsurface fracture damage in glaciers using fiber-optic seismology, Science Advances 2026. 12: eaef1107, DOI: 10.1126/sciadv.aef1107
ETH researcher Thomas Hudson camped overnight beside the Gorner Glacier, with Monte Rosa and the Dufourspitze (4,634 m) visible in the background.
Credit
Thomas Hudson / ETH Zurich
Journal
Science Advances
Article Title
Quantifying subsurface fracture damage in glaciers using fiber-optic seismology
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