Measuring snow weak layer collapse propagation with distributed fiber-optic sensing

The propagation distance of snow weak layer collapse, colloquially referred to as a "whumpf", is important to understand slab avalanche size. We present findings from Greenland with weak layer collapse propagation distances of up to 800 m. The observed weak layer collapses occurred in exceptionally flat terrain on the North East Greenland Ice Stream, near the EastGRIP field station. Here we can expect pure anticrack propagation. Geophone arrays measure the arrival of the anticrack and provide a direct measurement of the crack tip. Additionally, using distributed fiber-optic sensing, we recorded the seismic signal created by the propagating anticrack. We can use this as an indirect measurement of the crack tip and reconstruct its propagation distance and speed. Applying a simple point source model and assuming radial propagation, we derive propagation speeds between 25-35 m/s. Based on the anticrack model, we can therefore also infer weak layer and slab properties. Improved understanding of the wavefield generated by a whumpf can contribute to our understanding of crack propagation in weak layers; propagation can be reconstructed without placing arrays in the collapsing area. Fiber optic seismology is a promising method for direct and indirect crack measurements and should be applied next in steep terrain.