Toward the Acoustic Detection of Two‐Phase Flow Patterns and Helmholtz Resonators in Englacial Drainage Systems

• Published in: Geophysical research letters Vol. 47; no. 6
• Main Author: Podolskiy, Evgeny A.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 28.03.2020
• Subjects: Acoustic noise; Acoustic resonance; Acoustics; Air-water interactions; bubble burst; Bubbling; Cracks; crevasse; Crevasses; Drainage systems; Ear; Ears; Flow distribution; Flow pattern; glacier; Glaciers; Glaciohydrology; Greenland; Helmholtz resonators; Ice calving; intermittent flow; Microphones; Overwintering; Records; Resonance; Sonar detection; Sound detecting and ranging; Sound sources; Tidewater; Water
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2020GL086951

Passive acoustic monitoring has revolutionized the characterization of industrial processes and the acoustic wavefield in various environments. However, cryospheric acoustic phenomena remain largely unknown, especially at medium and small scales. Furthermore, the englacial drainage system is poorly documented, even though it is fundamental for understanding water routing through the glacier body. Here I present the first‐of‐its‐kind in situ records of periodic or sustained acoustic signals generated by water drainage through crevasses at the calving front of a glacier, in this case a Greenlandic tidewater glacier. The generative mechanisms of gurgling and bubbling noise are explained as flow‐induced sounds that are excited by intermittent air‐water two‐phase flow and Helmholtz resonance, respectively. This paper demonstrates that there is the tremendous potential to study near‐surface glacier systems using acoustic methods and detect different flow patterns in englacial conduits from their acoustic signatures, both of which can significantly advance our understanding of glaciological processes. Plain Language Summary The glacier surface is full of various audible sounds. While early polar explorers have documented this noisy glacier environment, these qualitative observations have never been supported by measurements. For example, Nansen (1897), wrote, “I can hear reports from the glacier… whenever it turns cold–it writhes horribly, and crevice after crevice appears in the huge body; there is a noise like the discharge of guns, and the sky and the earth tremble so that I can feel the ground that I am lying on quake” while wintering in Franz Josef Land, and Baldwin (1896) described his crossing of Bowdoin Glacier, which is the subject of this study, as follows: “…shrieking sounds frightful enough, came…to our ears, seeming to vibrate through…our very bodies, spitefully shouting in our ears: Why, presumptuous man, hast thou set disturbing foot upon my chaste bosom?” Here I analyze the first acoustic records that were directly acquired on a glacier, in Greenland, which reveal previously unknown repetitive or continuous sound sources. It appears that different patterns in air‐water interactions give rise to interesting acoustic phenomena, such as bubble resonance and unstable flow in cracks. Future glaciological investigations could consider using microphones to better understand englacial water drainage. Key Points This is the first report of repeating and continuous acoustic radiators in a near‐surface englacial drainage system Water‐air phase interactions in the drainage system hold the key to understanding self‐excited flow pulses and bubble bursts There is tremendous potential in acquiring passive acoustic observations to characterize glaciological processes