Wavering Ways Waves Work: Understanding glacier ogive formation using satellite and field observations combined with modelling

Wave ogives are among the most striking and least studied glacier surface features. They sometimes form at the bottom of icefalls, yet exactly how they form has eluded scientists for decades. On the Gilkey Glacier, below the Vaughan Lewis Icefall in the Juneau Icefield region of Alaska there is a well-developed series of wave ogives. Our study uses geophysical field observations of the Gilkey Glacier ogives combined with satellite data and modeling to better understand the formation process. Satellite-derived DEMs provide ogive amplitudes of 5-8 m and wavelengths of ~130 m. By combining Global Navigation Satellite System (GNSS), satellite, and timelapse camera-derived velocity observations, we found that the Vaughan Lewis Glacier is significantly slower than the Gilkey Glacier (60 m/yr compared to 130 m/yr), and the icefall is exceptionally fast (~2200 m/yr). We used the velocity and ogive characteristics to constrain parameters in a finite-difference numerical model that simulates ogive formation. Using this model, we tested the plausibility of the two formation mechanisms; i) seasonal mass balance variation; and ii) seasonal velocity variation of the lower glacier. Our results suggest that seasonal velocity variation of the lower glacier is the primary driver in wave ogive formation.