Glacial retreat on rock slope monitoring

ShapeArray used to monitor rock damage next to retreating glacier

The Great Aletsch Glacier is currently the largest ice mass in the Swiss Alps. It has advanced and retreated many times since the beginning of the last Alpine glacial period approximately 70,000 years ago. Since the 1860s, it seemed that it was once again on a slow and steady retreat—but new observations made in the past ten years revealed a steady increase in the amount of ice being lost with every passing year. To monitor these rapid changes, the Swiss National Science Foundation funded the installation of a custom-designed ShapeArray monitoring system capable of tracking the glacier’s recession and its effects on adjacent rock formations in the Alps.

Because so much of the movement within glaciers takes place below the surface, the exact processes within retreating glaciers that result in rock damage and subsequent rock slope failure are difficult to observe. The Great Aletsch Glacier project utilizes ShapeArray to monitor the subsurface temperature, pore pressure, and stress of glacier-adjacent rock formations in order to observe these hidden processes. Over time, the data collected will allow for a comprehensive view of rock slope movement specific to the Great Aletsch Glacier, as well as for a greater understanding of the relationship between retreating glaciers and rock slope deformation in general.

Solexperts AG installed three SAAF ShapeArray in 50-metre-deep vertical boreholes to measure horizontal strain and temperature within the rock slope adjacent to the glacier. Each ShapeArray consists of a series of evenly spaced sensors that measure tilt relative to gravity as well as temperature sensors to monitor and collect the full range of geotechnical activity at the site. Also installed in each borehole are FGB sensors from Sylex Fiber Optics to measure axial strain. Together, these instruments give a comprehensive view of the level of rock stress caused by the glacial retreat. The three SAAF ShapeArray chains are connected via cabling to a local data logger paired with a GSM data transmission unit. Data is collected hourly and is automatically uploaded to an FTP server, allowing for immediate remote viewing and analysis.

With the exception of a few gaps in data caused by extreme environmental conditions or battery issues (which were immediately noted and promptly fixed), data has been collected continually since December 2017 and will continue to be collected long into the future as the glacier further recedes.

References: 

[1] “Würm glacial stage | geology,” Encyclopedia Britannica. https://www.britannica.com/science/Wurm-glacial-stage (accessed Apr. 23, 2021). 

[2] M. Hugentobler, S. Loew, J. Aaron, C. Roques, and N. Oestreicher, “Borehole monitoring of thermo-hydro-mechanical rock slope processes adjacent to an actively retreating glacier,” Geomorphology, vol. 362, p. 107190, Aug. 2020, doi: 10.1016/j.geomorph.2020.107190.