Passive seismology uses natural (as opposed to man-made) sources of seismic energy to study Earth structures. Glaciers play host to a symphony of seismic sources, from low rumbles created by moulins, to high-pitched squeaks and bangs associated with the glacier moving along its bed.
These sounds can be recorded using a network of geophones placed on top of the glacier. Variations in the number, timing, frequency content and source location of the seismic events can lend useful insights into the dynamics of glaciers and how they vary with the seasons. For example, it has been shown that the pitch and length of tremors heard near moulins vary with the supply of water into them (Röösli et al., 2014). Likewise, the number and location of sudden microseismic slip events at the base of the glacier can inform us about the frictional conditions at the base of the glacier.
A substantial advantage of using passive seismology to study glaciers is the ability to observe a large 3D volume of the glacier for an extended amount of time. This constitutes a valuable addition to the detailed surface measurements provided by UAV and GPS techniques, and the vertical resolution offered by borehole data.
Store Glacier provides a challenging environment for passive seismology, which requires the design of seismic stations to be adapted from those used for solid-earth applications. The effort is rewarded, though, as the fast flow of the glacier creates a large number of seismic sounds to analyse. After two busy field campaigns in 2018, work is now underway to make sense of the many noises recorded at our network of 12 surface and 3 borehole geophones.