A Single Fiber-Optic Cable Reveals Hidden Crevasses That Could Destabilize Glaciers

Researchers at ETH Zurich, led by Assistant Professor Thomas Hudson of the Environmental and Exploration Geophysics Group, have demonstrated a new way to detect the hidden crevasses inside glaciers that can accelerate their collapse, using a single fiber-optic cable rather than a network of costly seismometers. The study was published in the journal Science Advances.

Crevasses that open within the ice generate microearthquakes, which seismometers can detect, but deploying many seismometers across a glacier riddled with cracks is expensive and difficult. The ETH team instead laid a single fiber-optic cable on the surface of the Gorner Glacier in Valais, Switzerland, and connected it to an interrogator device that sends a light signal down the cable and records the light scattered back. Seismic waves from a microearthquake deform the fiber slightly, changing how the light is reflected, which lets researchers pinpoint the location and depth of a crevasse.

Using the method, the researchers explored the glacier's internal structure to a depth of 25 meters and found that hidden crevasses, filled with water or air, accounted for more than 8% of the ice volume at the measurement site — an amount Hudson said was far more than expected. The remaining 92% of the ice was undisturbed. Hudson noted that visible surface crevasses do not necessarily indicate whether a glacier is stable; internal cracks matter more.

The technique follows recent glacier collapses in the Alps, including the 2023 Marmolada glacier collapse in the Dolomites that killed seven mountaineers, and the 2025 collapse of the Birch Glacier above Blatten. The ETH team plans to test the method on other glaciers in the Alps and on the polar ice sheets of Greenland and Antarctica, saying it could eventually help provide early warning of calving events and improve predictions of how melting glaciers affect sea levels.