​Listen to the Harmonic Hum of a Glacier

Scientists have recorded the eerie radio emissions of Saturn, the sounds of interstellar space, and the acoustic blasts of earthquakes. Now, a team of geologists based out of the University of California San Diego has eavesdropped on the harmonic humming of the Gorner Glacier, or "Gornergletscher," a valley glacier located in the Swiss Alps. Take a listen.

An audio/video representation of a glacier's hum. Credit: Heeszel/Walter/Kilb.

The sound is almost like a crackling fire, and the work that went into the recording yields fresh insights into the internal dynamics of glaciers. It could also lead to more accurate predictions of the hazardous floods resulting from glacial lake outbursts, which can be very sudden, and sometimes fatal. The team recently published their findings in the journal Geology.

"We hypothesize that the observed humming is due to changes in crack geometry within the glacier," lead author David Heeszel told me. "As water moves through a network of cracks and fractures inside Gornergletscher, the shape, length, width, etc., of these cracks is constantly changing due to changes in internal stress, water levels, and a number of other processes."

The ambient hum emitted by the glacier's dynamic crack geometry was captured with eight borehole seismometers, one of which was implanted 120 meters below the glacial surface. The team then sped up the resulting seismogram 250 times, in order to better assess the subsonic frequency.

"This has the added benefit of turning a process that occurred over a period of more than 21 hours into a five minute movie," Heeszel said. "If we speed the seismogram up too much, all of the interesting changes that occur over hours are squished into only a second or so, but if we speed it up just a little, then the movie is incredibly long."

It's important to note that the authors do not mean "harmonic" in the traditional musical sense, which is why the glacier's song seems so static. "What we mean is that there is a particular peak in the frequency content of the data and that this peak is repeated at higher frequencies with regular intervals," explained Heeszel.

"I kind of think of this like having air in your water pipes," he continued. "When you first turn on the water, it sounds like the house is going to shake apart, but as the air escapes, the sound gets higher and higher in pitch. In this case the 'pipes' are getting longer, so the pitch goes down instead of up."

This seismic analysis also gave the researchers a chance to overhear some of the glacier's more exotic rumblings, including crackly icequakes, which appear on the video as bright vertical lines.

The team's technique could be a boon for both scientific research and emergency flood preparation, and it also helps contextualize the internal mechanics of crucial freshwater repositories. And on top of all that, the study provides yet another opportunity to listen to the otherworldly sounds of a natural object. Gornergletscher may not sing in tune, but its icy hum speaks volumes about the complex inner world of glaciers.