A fibre-optic cable recorded the sounds of a melting glacier in the Swiss Alps across its entire length. This marks the first time that researchers were able to capture such sounds across an entire glacier.
鈥淭he fact that you can just spool out a fibre on the surface of a glacier and let it get snowed in and then use that as a sensor, that鈥檚 revolutionary,鈥� says at the University of Washington in Seattle.
Lipovsky and his colleagues laid out a 9-kilometre fibre-optic cable on Switzerland鈥檚 Rhone glacier in the summer of 2020. Over a period of one month, the cable continuously recorded both acoustic and seismic vibrations by sending laser pulses and analysing the signals that bounced back.
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The team was most interested in identifying sounds that can help measure the amount of glacier melt as the Rhone glacier and others shrink in the face of heatwaves and global warming. Melting ice creates streams of water that pour into crevasses, which produces higher-frequency sounds, while water moving beneath the glacier can emit low-frequency rumbling sounds. It also produces sounds that are more familiar to human ears, such as the rushing or trickling of falling water.
鈥淭he signals that we look at are generally in the range of 100 to 500 Hertz, and so that鈥檚 kind of below a middle C on a piano,鈥� says Lipovsky. 鈥淚t鈥檚 right in the middle of the piano range.鈥�
The team collected 20 terabytes of glacier sounds, which is the data storage equivalent of several hundred thousand songs.
This sound-based approach proved to be as accurate as other methods of measuring streams of meltwater, says Lipovsky. He described the fibre-optic cable as much more resilient than traditional seismometers or acoustic sensors that can tip over or experience other accidents. It is also capable of continuously monitoring melt events from across the entire glacier, as opposed to more labour-intensive efforts that involve flying drones for short surveys or drilling holes in the ice to place 10-metre measurement sticks.
The researchers at the fall meeting of the American Geophysical Union in Chicago on 13 December.
