IMAGERY ANALYSIS OF ENIGMATIC DIFFERENTIAL ABLATION, BERING GLACIER, ALASKA

Conventional aerial photography, satellite imagery, and over-flight pictures of the eastern Bering piedmont glacier reveals a curious recurrence of lacunas leading to an interpretation of subglacial terrain.

The Lacuna Glacier of the Alaska Range takes its name from ablation hollows commonly distributed below the snowline. Although ubiquitous here, they are not commonly found on other glaciers. Unlike vertical shafts of isolated moulin or pitted debris laden stagnant ice, lacunas on Bering Glacier are confined to active, debris-free ice within a specific band (1.5 km wide and 5 km long) between convoluted debris bands on the eastern terminus of the extensive piedmont lobe. Here they appear as elongate, steeply-sided, flat-floored hollows ranging in size from 40 to 60 m wide, 80 to 120 m long, and 35 to 50 m in deep.

Two aspects challenge explanation. Although lacunas are clearly the product of differential ablation, why are they restricted to such a confined part of the piedmont lobe? Furthermore, and even more puzzling is that after being displace 2-4 km by two surges since the mid 60’s), they form again 4 to 6 years later in exactly the same location as prior to the surge. Factors pertinent to causes for differential ablation here and the curious question of recurrence location are the central topics for consideration.

For Austin Post, the Bering frequently challenged conventional thinking, of which lacunas are just one example.