Ripples in the Ice: Employing ogives to deduce glacier behavior

Arcuate glacier structures known as ogives are common to valley glaciers flowing below large icefalls and form annually. Long sequences comprising tens of ogives are often preserved on glacier surfaces. We explore their utility as unique sources of information about glacier behavior. Our investigation concentrates on two main objectives: (1) to assess any correlation between an ogive train and a climate time series, and (2) to evaluate what an ogive-derived velocity profile can reveal about the distribution of ice thickness beneath an ogive field. Using ArcGIS software, we analyze high-resolution satellite imagery of the Gates Glacier ogive sequence in southeastern Alaska to document ogive wavelengths, and to produce down-glacier surface velocity and strain profiles. A comparison of ogive wavelengths with the recent climate history from local weather stations suggests a complex relationship between annual temperature, meltwater inputs, basal sliding, and ogive formation. Finally, we employ surface velocity derived from ogive positions on a sequence of images, and a centerline slope profile (acquired from a digital elevation raster), to invert Glen's flow law for an estimate of ice thickness. The calculated ice thickness is then translated to a centerline bed profile and ultimately used to construct a three dimensional view of the Gates Glacier valley geometry.