Radar scattering in an alpine glacier: Evidence of seasonal development of temperate ice beneath ogives (vol 8, pg 1054, 2012)

Glacial ogives are transverse topographic, wave-like surface features that form below icefalls on some alpine glaciers. Ground-penetrating radar surveys from the Gorner glacier system in the Swiss Alps reveal an along-flow periodicity in scattering intensity that correlates with ogives. The scattering appears in the ablation zone and occurs at 5-20 m depth. The geometry of the scattering mimics that of the ogives, although exaggerated in amplitude. We interpret the scattering to represent lateral variations in water content. We propose that as glacial ice accelerated and stretched through the ice-fall, seasonal fluctuations occurred in water infiltration to crevasses during the summer and subsequent freezing of that water in the crevasses in the winter. This seasonally varying infilling and freezing locally altered the distribution of temperature, creating zones of temperate ice with water inclusions that preferentially scatter radar energy. In addition to the scattering pattern, highly reflective planar features associated with these periodic regions of temperate ice are interpreted as water-filled fractures. A three-dimensional rendering of the orientation of these planar features precludes a "fold-and-thrust" hypothesis for the formation of the ogives.