SUBGLACIAL TOPOGRAPHY IMPLIED FROM DIGITAL ANALYSIS OF AERIAL IMAGES, EASTERN SECTOR, BERING GLACIER, ALASKA

The historic record suggests that Bering Glacier’s surges fade rapidly following loss of subglacial water during outburst events (jokulhlaups). The ice front outlet of an eastern sector conduit system, seen in Austin Post's 9/2/66 aerial photos, feeding the outburst during the 1966-67 surge, persisted for decades to also provide discharge during the 7/27/94 outburst that stalled the 1993-95 surge. Enhanced by techniques of Adobe Photoshop® digital analysis and image manipulation, the conduit system outlet may be traced during decades of retreat to occupy a common, stable ice front position, thus suggesting persistent subglacial drainage conditions.

The distribution of surge-related, ice surface domes and troughs observed during surge events are interpreted to represent adjustments to rapid basal sliding across subglacial topographic irregularities with endurance attributed to bedrock resistance. Mapping of such features and ice front processes is facilitated by digital techniques utilizing layered components of the glacial setting during and between surge events. Adobe Photoshop® superposition of glacial and geomorphic features, mapped in the field and on standard aerial photo and satellite images, provides a temporal sequence that is referenced to GPS-controlled maps. Implementation of various Adobe Photoshop® transformations provided accurate spatial alignment of related features and processes. The association of surface features only present during surge events with ice front processes leads to an interpretation of subglacial topography and conditions ascribed to bedrock control.