Fibre optics on glaciers open new frontiers for natural disaster predictions

The May 28 collapse of the Birch glacier in the Swiss Alps made headlines around the world. A huge landslide of ice, mud and debris buried the evacuated village of Blatten in one of the worst natural disasters in recent Swiss history.

Although such events are rare, they may be more common than previously thought, according to a studyExternal link that analysed evidence of previous glacial collapse in the Andes, Caucasus and other mountainous regions. There is no straightforward way to predict where they might occur, but some conditions such as the surface slope of the glacier may help determine if a glacier detachment can occur in a specific area, according to the study.

Ice and rock landslides can have different causes, often attributable to geological conditions and land topography. But climate change can increase the likelihood of a collapse: rising temperatures accelerate ice melt, promote the formation of cracks in glaciers, and make mountain slopes more unstable.

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This heightens the need to monitor at-risk areas to protect villages and infrastructure from natural hazards. Satellite images, cameras and radar make it possible to track the evolution and movement of glaciers, as was the case at Blatten. But this technology provides limited information about what is going on inside the glaciers.

Researchers in Switzerland and in other mountainous areas such as Alaska think they have found a solution: fibre-optic cables that detect micro-vibrations and other early signs of instability in glaciers.

“Fiber optics allow us to detect extremely small seismic events, which other technologies could not measure. That could help refine glacier monitoring systems,” Thomas Hudson, a seismologist at the federal technology institute ETH Zurich tells Swissinfo. He recently presented the results of his experiments on a Swiss glacier to the Seismological Society of AmericaExternal link.

Fibre optics on Alpine glaciers

In 2023 the institute’s research team installed 1.2 kilometres of fibre-optic cables on the Gorner GlacierExternal link in Switzerland. Connected to these was a device called an interrogator, which sends laser pulses through the fibre.

Seismic waves in the glacier cause the cables to stretch or compress, which then alters the laser pulse. This method, known as Distributed Acoustic Sensing (DAS), turns the optical fibre into a strip of hundreds of seismic sensors.

Some of the seismic waves (or icequakes) come from fractures that form in the glacier. These cracks could compromise the glacier’s stability because they allow meltwater to infiltrate, which increases the risk of detachments and accelerates the downstream movement of the glacier.

>>The Birch glacier collapse above Blatten, canton Valais, in southern Switzerland (May 28, 2025):

A technology to monitor entire glaciers

Thomas Hudson has recorded up to a thousand seismic waves per day on the glacier. He does not yet know the exact significance of this seismic activity and cannot say if it’s an anomaly capable of triggering a collapse, or an average measurement, since the experiment is in its early stages. But in the future, after Hudson has taken more measurements and observed the glacier’s movement, these vibrations could provide clues to changes within the ice. “A sudden increase in seismic activity could signal an impending collapse. These are signals that other devices would not detect,” Hudson says.

Fibre optics also provide information about the structure and composition of the ice. Compared to traditional seismic sensors, which are placed at specific locations, fibre-optic cables can be more easily installed over a large area, says Fabian Walter, a mass movement expert at the Federal Research Institute for Forest, Snow and Landscape (WSL).

If deployed more widely, the technology would make it possible to monitor entire glaciers, even in hard-to-access areas, according to Walter, who is among the first researchers to test the use of fibre optics on a glacier. In 2019 he had identified new types of seismic waves in the Rhone GlacierExternal link, also in Switzerland.

Andreas Max Kääb, professor of physical geography and hydrology at the University of Oslo and author of a study on large-volume detachments of mountain glaciersExternal link, also thinks this approach is promising. “It is certainly a good idea. The acceleration of rock faces or glaciers is often accompanied by increased vibrations,” he told Swissinfo via e-mail.

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The next step, he says, will be to understand the signals recorded through fibre-optic measurement. “But I have no doubt that fibre optics will be able, at least in some cases, to provide crucial information on the invisible processes behind the acceleration of glacier movement,” Max Kääb says.

Earthquakes, avalanches and debris flows

Detection of seismic activity using fibre optics is not new. DAS technology has long been used in undersea fibre-optic cables to locate oceanic earthquakes and volcanic activity. It is only in recent years, however, that its use has been extended to other natural hazards, and in this regard “Switzerland is among the pioneer countries,” Fabian Walter says.

In 2022, optical fibre was used for the first time to detect snow avalanches in SwitzerlandExternal link. Fibre optics also made it possible to measure the small rock detachments that preceded the large landslide that fell near the village of BrienzExternal link, canton Graubünden, in 2023.

Research in Switzerland and other countries focuses particularly on monitoring debris flows, one of the most common and potentially catastrophic natural hazards on the planet.

Walter notes that fibre-optic cables for telecommunications already exist underground along roads, railroads and near some infrastructure. There are about four billion kilometresExternal link deployed around the world.

It would be easy, he says, to connect the DAS interrogator to the end of an unused filament or “dark fibre” (a fibre-optic cable contains numerous filaments, but not all of them are operational). The device would send laser pulses along the whole length of the fibre optic, transforming it into a monitoring system that spans tens of kilometres.

This means that unlike radar, which only monitors part of the mountain, fibre-optic cables can detect material movement along the entire valley. This makes them particularly useful in areas where a specific high-risk zone has not yet been identified.

“Our experiences show that all it takes is for the fibre optics to be within a kilometre of the unstable slope,” Walter says.

A technology suitable for developing countries

The current challenge is to develop an artificial intelligence-based algorithm that can automatically recognise relevant signals to distinguish, for example, the movement of a rock from that of an animal.

If the system detects considerable movement that could lead to a landslide or glacier collapse, it can trigger an early warning, giving people time to react before disaster occurs, says Madhubhashitha Herath of Uva Wellassa University in Sri Lanka, author of a review on the use of fibre optics in natural hazard monitoringExternal link.

Fibre-optic cable itself is relatively inexpensive and carries low operating and maintenance costs, Herath says. “This makes the technology suitable for both developed and developing countries,” he says in an e-mail to Swissinfo.

Monitoring the most dangerous glaciers with fibre optics

Thomas Hudson from ETH Zurich believes that kilometres of fibre optics could be rolled out on the most unstable glaciers in the future. “It would be enough to cover the front of the hanging glaciers, that is, the part most exposed to the risk of collapse.”

The system will have to be calibrated for each glacier, however, because “every glacier is unique,” Hudson says. “What is the critical number of fractures beyond which a collapse becomes likely? We don’t know yet,” he stresses.

Fibre optics would complement the array of existing monitoring technologies, such as satellite imagery and radar devices. “By combining observations of changes at the surface with those at depth, we could improve monitoring of the most dangerous glaciers,” he says.

Edited by Gabe Bullard/vdv/ds