Fractures in glaciers — Crack tips and their stress fields by observation and modeling

High‐resolution optical camera systems are opening new opportunities to study fractures in ice. Here, we present data obtained from the Modular Aerial Camera System camera system operated onboard of Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI) polar aircraft in northeast Greenland in 2022. In addition, we are using optical and radar satellite imagery. The study area is the 79°N Glacier (Nioghalvfjerdsbræ, 79NG), an outlet glacier of the Northeast Greenland Ice Stream. We found that crack tips are exhibiting additional isolated cracks ahead of the main crack. Subsequent crack propagation is starting from those isolated cracks, leading to an advance of the crack, with bridges between crack faces. The bridges provide information of the episodic crack propagation. Fractures have typically a length scale of kilometers and the distance of crack faces is in the order of meters to tenths of meters. Fracture modes will be inferred from stress fields computed by an inverse modeling approach using the Ice Sheet and Sea Level System Model. To this end, a surface velocity field derived from satellite remote sensing is used for the optimal control method that constrains model parameters, for example, basal friction coefficient or rheology.