FEATURE TRACKING AND DIMENSIONAL ANALYSIS OF WAVE-OGIVES ON THE VAUGHAN LEWIS ICEFALL, ALASKA USING SATELLITE IMAGERY

Wave ogives are three-dimensional wave features that form annually at the bottom of some icefalls and persist with decreasing amplitude as the glacier flows down-valley. Exactly one crest and one trough are formed each year. In most glaciers, wave ogives turn to band ogives as they advance. This study focused on the wave ogives of the Vaughan Lewis Icefall on the Gilkey Glacier, Juneau Icefield in Alaska. Using Quantum Geographic Information System and Landsat panchromatic images (15m spatial resolution) from 1999 to 2009, the location and dimensions of each visible ogive were tracked (the last visible ogive dates to 1942). This information was then used to calculate the flow velocity of the Gilkey Glacier. In addition, GPS data were used to measure the elevation of certain crests. The ogives were tracked by tracing the border between each crest and trough on every distinct ogive on each image. The central flowline was used as a baseline to compare flow. To measure ogive aspect angles, the lateral moraines and center points were used. Two methods were used to determine the glacier velocity. First, because exactly one crest and one trough form each year, the length of one crest and one trough represents the distance the glacier has flowed in one year’s time. Second, the same ogive was identified in two separate images and the offset was measured to determine velocity. Results showed that the glacier moves at an average speed of 158.9 meters per year. The results were close but not uniform, probably due to the moderate spatial resolution and image quality (Landsat partially malfunctioned in 2000). It was also found that the angles of the ogives decrease as they move down the trench, as does the amplitude of each wave crest.