Observing subglacial bedload transport dynamics with on-ice seismic networks on Glacier d’Otemma, Switzerland

The manner by which glaciers evacuate the products of erosion is poorly known, especially for the coarser-sized sediments produced by plucking and quarrying, that is the bedload fraction. It has traditionally been assumed that bedload export from Alpine glaciers is relatively efficient. However, continuous, seismic measurements of bedload transport at glacier portals question this assumption as do the results of numerical modelling experiments. There are a number of possible hypotheses to explain such inefficiency, including the structure and geometry of subglacial channels, periodic variation in discharge due to diurnal melt cycles and near-ice margin effects. The problem remains, however, that there are no published datasets on subglacial bedload transport to investigate the effects, not surprising because of the challenges associated with measuring it. The aim of this research is to harness environmental seismology to quantify subglacial bedload transport rates for the first time using on-ice measurements.

In the first part of the project, we traced the location and development of two subglacial channels of Glacier d’Otemma, Valais, Switzerland. In this study, we investigate the discharge and sediment traveling in our identified channels. With the help of thirty seismic sensors on the glacier surface and at the glacial terminus, we record the seismic activity of Glacier d’Otemma during its melt season in 2024. We trace the path the sediment takes underneath the glacier with seismic beamforming techniques and relate it to the previously identified shape of the subglacial drainage system. A line of seismic sensors along the glacier was able to record waves of bedload as they travel underneath the ice. With the help of physical models, the spectral information of the ground motion data is translated into sediment transport and discharge quantities. The project contributes to reveal the interaction of sediment and the characteristics of subglacial drainage system in alpine glaciers, giving further insights into erosion mechanisms at play.