Preprints
https://doi.org/10.5194/nhess-2021-205
https://doi.org/10.5194/nhess-2021-205

  02 Sep 2021

02 Sep 2021

Review status: this preprint is currently under review for the journal NHESS.

Hanging glacier monitoring with icequake repeaters and seismic coda wave interferometry: a case study of the Eiger hanging glacier

Małgorzata Chmiel1, Fabian Walter2, Lukas Preiswerk1,3, Martin Funk1, Lorenz Meier4, and Florent Brenguier5 Małgorzata Chmiel et al.
  • 1Laboratory of Hydraulics, Hydrology and Glaciology, ETH Zürich, Zürich, Switzerland
  • 2Swiss Federal Institute for Forest, Snow and Landscape Research, Zürich, Switzerland
  • 3Forensic Technology & Discovery Services, Ernst & Young, Zürich, Switzerland
  • 4Geoprevent AG, Technoparkstrasse 1, Zürich, Switzerland
  • 5Univ. Grenoble Alpes, Institut des Sciences de la Terre, Grenoble, France

Abstract. Driven by the force of gravity, hanging glacier instabilities can lead to catastrophic rupture events. Reliable forecasting remains a challenge as englacial damage leading to large-scale failure is masked from modern sensing technology focusing on the ice surface. The Eiger hanging glacier, located in the Swiss Alps, was intensely monitored between April and August 2016 before a moderate 15,000 m3 break-off event from the ice cliff. Among different instruments, such as an automatic camera and interferometric radar, four 3-component seismometers were installed on the glacier. A single seismometer operated throughout the whole monitoring period. It recorded over 200,000 repeating icequakes showing strong englacial seismic coda waves. We propose a novel approach for hanging glacier monitoring by combining repeating icequake analysis, coda wave interferometry, and attenuation measurements. Our results show a seasonal 0.1 % decrease in relative englacial seismic velocity dv/v and an increase in coda wave attenuation Qc−1 (Qc decreases from ~50 to ~30). Comparison of dv/v and Qc with air temperature suggests that these changes are driven by a seasonal increase in the glacier’s ice and firn pack temperature that might affect the top 20 m of the glacier. Diurnal cycles of Qc−1, repeating icequake activity, and the velocity of the glacier front shift from cosinusoidal to sinusoidal variations under the presence of meltwater. The proposed approach extends the monitoring of the hanging glacier beyond the ice surface and allows for a better understanding of the glacier’s response to time-dependent external forcing, which is an important step towards improved break-off forecasting systems.

Małgorzata Chmiel et al.

Status: open (until 14 Oct 2021)

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Małgorzata Chmiel et al.

Małgorzata Chmiel et al.

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Short summary
The hanging glacier on Switzerland’s Mount Eiger regularly produces ice avalanches which threaten tourist activity and nearby infrastructure. Reliable forecasting remains a challenge as physical processes leading to ice rupture are not fully understood yet. We propose a new method for hanging glacier monitoring using repeating englacial seismic signals. Our approach allows monitoring temperature and meltwater driven changes occurring in the hanging glacier at seasonal and diurnal timescales.
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