Scientists propose new way to monitor glaciers using sound

Monitoring glacial runoff using acoustic signals presents a cost-effective and accessible alternative to existing methods. With glaciers melting rapidly and causing significant sea-level rise and outburst floods, it is crucial to track the meltwater contribution to oceans and freshwater resources worldwide, as well as monitor the risk of glacial flooding. However, glacio-hydrological monitoring can be financially burdensome for many countries, requiring either significant human effort or advanced technology with substantial data requirements.

To address these challenges, a team of scientists led by Evgeny A. Podolskiy from Hokkaido University has proposed a safe, affordable, and efficient approach for monitoring glacial discharge. Their method, published in the journal Geophysical Research Letters, offers several advantages. First, it is approximately 100 times cheaper than the most advanced methods currently available. Second, it is non-invasive, allowing for quick and easy deployment. Finally, it has the potential to serve as a long-term monitoring tool for glaciers.

Previous research, including studies conducted by this team, has established a connection between inaudible (infrasound) signals and glacial runoffs. These studies have identified daily variations in the recorded signals, with a peak occurring during the summer. The hypothesis is that these signals are generated by the propagation of air-pressure waves from glacial runoff. Based on this understanding, it has been suggested that glacier discharge can be measured by analyzing the audible sounds emitted by melting glaciers.

In summary, the utilization of acoustic signals for monitoring glacial runoff offers a promising solution. It is not only more cost-effective and accessible than existing methods but also provides a non-invasive, quick, and easily deployable approach for long-term glacier monitoring. By harnessing the power of sound, scientists can enhance their understanding of glacial dynamics and effectively address the challenges posed by glacial melt and associated hazards.

In the proposed method, an acoustic sensor is deployed in a sheltered location (red circle, bottom right, under the large rock) near the glacier to continuously record sounds; a much easier and simpler process. Credit: Evgeny Podolskiy

The researchers conducted their initial study near the Qaanaaq Glacier in Greenland, focusing on the area close to the source of glacial discharge. They discovered a direct relationship between the levels of acoustic noise and the proglacial discharge, which exhibited a distinct diurnal pattern that was easily detectable. According to Podolskiy, the ambient sound resembled the continuous roar of rushing water, a familiar experience for anyone near turbulent white water.

To capture the ambient soundscape, the team deployed a commercially available bird-song recorder near the terminus of the Qaanaaq Glacier. They estimated the proglacial discharge by measuring water depth and flow speed at a site where the proglacial stream intersected the road between Qaanaaq and the local airport. The collected acoustic data was then analyzed, and the results were cross-correlated with the discharge measurements to identify the frequency band that most accurately represented the proglacial stream.

The researchers discovered that the highest correlation occurred within the frequency range of 50-375 Hz. They also observed that the noise level closely mirrored the temporal variations in runoff. Additionally, they found that the acoustic signals were recorded approximately 50 minutes before corresponding changes in discharge were observed.

In summary, the team’s study at the Qaanaaq Glacier demonstrated that acoustic signals can effectively serve as a proxy for glacial discharge. The researchers successfully identified the frequency band that best represented the proglacial stream, showing a strong correlation between acoustic noise levels and runoff variations. The ability to detect changes in discharge through acoustic monitoring, even with a slight time advance, holds promise for improved glacial monitoring and understanding the dynamics of glacial runoff.

A graph showing the correlation between the acoustic signal (black) and the measured proglacial discharge (red). Credit: Geophysical Research Letters (2023). DOI: 10.1029/2023GL103235

The study showcased the effectiveness of using audible acoustic signals to remotely and continuously sense glacio-hydrological variations. This approach offers several advantages, including a reduced risk of instrument loss and the absence of complicated data processing techniques. While it may not provide the same level of spatial resolution as fiber-optic tools currently in use, it represents a significant step forward in terms of affordability and overall simplicity. Importantly, this method can be employed to establish early-warning systems capable of promptly detecting events such as glacier lake outbursts, thereby aiding in the mitigation of glacial flooding incidents.

The research team acknowledges the potential complexity of sound-discharge relationships in glaciated watersheds. To further enhance this methodology, future efforts should focus on long-term monitoring to gain a comprehensive understanding of the connection between audible and inaudible sounds. Additionally, it would be valuable to assess the potential interference effects of wind on the accuracy of acoustic measurements.

Overall, this study opens up new possibilities for cost-effective and accessible monitoring of glacial processes. By leveraging audible acoustic signals, researchers can contribute to the development of effective strategies for early detection and mitigation of glacial hazards, providing crucial support in safeguarding vulnerable areas from the impacts of glacial flooding.

Source: Hokkaido University

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