Assessing the rate of ice fracture using co-located geophysical surveys on the Brunt Ice Shelf, Antarctica

The rate of fracture-induced ice instability is an important factor contributing to uncertainties in sea level projections used for global flood mitigation planning. While the occurrence of ice fracturing at critical stress thresholds is well-documented, the detailed mechanisms controlling fracture timing, rate, and orientation are not fully understood. This gap is particularly evident in differences in fracture behaviour across varying ice types, such as meteoric ice and ice mlange. Observations on the Brunt Ice Shelf reveal a unique behaviour, where rifts deviate from the pathway predicted by the principal stresses to avoid thick blocks of meteoric ice. Their growth rate is significantly reduced when required to cross through these blocks. This stands in contrast to observations on other ice shelves, such as Larsen C, where rift propagation is slower in marine ice bands. Here we use co-located geophysical methods, seismic and ground-penetrating radar (GPR), to assess the fracture pattern and dynamics and the relationship to ice properties at the leading edge of two active rifts, Halloween Crack and Chasm 2, on the Brunt Ice Shelf. By determining the depth of seismic events using P to Rayleigh wave amplitude ratios, we estimate a theoretical maximum dry crevasse depththe depth at which fracturing can occur without the presence of englacial water. Additionally, GPR data are used to precisely locate rift terminations and identify refrozen layers associated with seawater intrusion into the firn layer. Combining these data, we provide new insight into the mechanisms controlling fracture propagation within the Brunt Ice shelf. The synthesis of observations from Chasm 2 and Halloween Crack contributes to a comprehensive understanding of fracture mechanics, enhancing our knowledge of regional-scale ice dynamics.