Methodological advances in mountain research

Abstract/Description

Time-lapse gravimetry (TLG) is a non-invasive, integrative, geophysical/geodetic method in which changes in g can be measured to parts-per-billion precision. Measured gravity changes are, in part, the result of water/ice storage changes. Thus, TLG can be a powerful tool for the monitoring of the two hydrological components of alpine systems that are the most difficult to quantify: ground ice and groundwater.

We recently carried out the first periglacial application of TLG. At the well-known Murtèl rock glacier (Graubünden, Switzerland), we measured seasonal gravity changes in the July to September period and used UAV photogrammetry to correct for the effect of snow mass. Our results reveal spatial variations in active layer thaw (11 to 64 cm water equivalent) that would be challenging to observe directly. Comparison of our high precision data with a historic gravimetry survey also suggests the occurrence of permafrost degradation over the past three decades.

At other Alpine sites, we have employed TLG to monitor groundwater storage recession during the summer/autumn snow-free period. The gravimetry data provide quantitative insights into groundwater storage that would typically require extensive borehole infrastructure to obtain. TLG is a unique and effective method for quantifying subsurface storage variations and is particularly well-suited for alpine regions due to their pronounced annual hydrological variability and insufficient subsurface monitoring.

Abstract/Description

Debris-covered glaciers present acute challenges for fieldwork due to the presence of rocky debris and steep slopes. Consequently, the spatial distribution of surficial debris layers and the processes governing debris-covered glacier evolution remain understudied. Recent advances in drone-based remote sensing have improved our observation abilities for debris-covered glaciers, including ground-penetrating radar (GPR) and thermal infrared imagery. We present research that integrates thermal infrared imagery with airborne GPR to improve investigations of supraglacial debris. Data for this study was collected in the summer of 2024 on a debris-covered glacier in the Shár Shaw Tagà (also known as Grizzly Creek) watershed in Kluane National Park and Reserve, Yukon, Canada.

While airborne GPR provides unprecedented spatial coverage, it is limited in the minimum debris thickness that can be measured (approximately 1/4 the wavelength, or 0.37 m for the 200 MHz GPR radar). As a result of this limitation, we present a novel technique to measure a range of debris thicknesses by combining airborne GPR and thermal infrared photogrammetry surveys. In locations where debris is thin (< 0.5 m), thermal imaging enables debris thickness estimation where the radar would be unable to distinguish the surface and the ice/debris interface. Conversely, where debris thicknesses is greater, the GPR can more effectively evaluate debris thickness when empirical relationships of thickness and temperature become less precise. Combining these two techniques allows the debris thickness to be accurately assessed across varied debris thicknesses over the 0.5 ha study site. This new technique for debris mapping has applications for larger areas, where varied supraglacial debris thicknesses prevent estimations using a single technique.