Synthetic aperture radar (SAR) images acquired by the European Space Agency satellite ERS-1 were employed to observe the 1993-'94 surge of Bering Glacier, in the St. Elias and Chugach Mountains of Southcentral Alaska. Bering Glacier—which is the largest glacier in North America, and in the world outside Antarctica and Greenland—descends 180 km from an ice divide north of Mt. St. Elias to the Gulf of Alaska coast, where it calves icebergs into proglacial Vitus Lake. The total area of this massive glacier system, including tributaries, is 5,200 km2. The width of the main trunk is about 8-12 km. The mean thickness, estimated from the surface slopes (using U.S. Geological Survey [USGS] radar spot measurements of depth to bedrock on the lower glacier for control), appears to be approximately 600-700 m. Near the coast the glacier expands laterally into a broad, 47 km-wide piedmont lobe.

The developing surge was confirmed in the field on 11 June 1993 by Austin Post, of the USGS, and observed by glaciologists from the State University of New York, the USGS, Scripps Institution of Oceanography, and the University of Alaska Geophysical Institute during a June field program near the terminus. Subsequent examination at the Geophysical Institute of SAR imagery acquired by ERS-1 revealed that the surge was in progress by April 30, and may have been in its preliminary stages as early as March 26.

A time-lapse movie of the surge was constructed by James Roush and Richard Guritz, using subscenes of the lower glacier from sequential SAR images. The subscenes were terrain corrected using the USGS 90 m digital elevation model (DEM) of Alaska, which was interpolated onto a 30 m grid to match the nominal resolution of the imagery. The terrain-correction procedure also resulted in geocoding (rotation to a standard orientation, i.e., such that north was 'up'), and referencing of the pixels to geographic coordinates (latitude/longitude and universal transverse mercator). The terrain-corrected subscenes were co-registered, as a result of being registered to the same underlying DEM. A slight additional adjustment was necessary for co-registration in some cases.

Measurements made with the sequential subscenes used to construct the time-lapse movie show that the surge front propagated down-glacier at a mean velocity of 90 m/day between 19 May and 25 August 1993, reaching most of the broad perimeter of the terminus by and shortly after 25 August. Subsequently the calving terminus advanced rapidly into Vitus Lake, at a maximum rate in its central area of 19 m/day between 9 August and 18 October. The mean rate of advance across the entire width of the terminus was 11 m/day during the same time period. The advancing surge front consisted of a distributed region of undulations and elongated bulges on the glacier having heights— estimated from the SAR data—of 40 to 110 m and widths (in the radar 'look direction', approximately transverse to the direction of glacier flow) varying from about 0.7 to 1.5 km.

NASA Grant NAGW-2827: Scientific personnel; C.S. Lingle, W.D. Harrison, J.J. Roush and R.M. Guritz.

Please visit these links to image pair showing surge progression and an animation of the surging glacier in MPEG movie format.