Sequential photos were acquired showing retreat of the transient snow line to its late-summer position on Black Rapids Glacier, which is a 45 km-long surge-type glacier located in the Alaska Range about 170 km SE of Fairbanks. The photos were acquired using an automatic camera, which was mounted on a rock outcrop overlooking the area of the equilibrium line during a spring 1993 program of field measurements. The camera and film were retrieved in spring 1994. Photos showing the maximum late-summer position of the snow line were acquired on 30 July and 7 August 1993. The 1993 ablation season ended when a snow storm occurred on 8 August. The position of the late-summer snow line shown in the photos was subsequently reduced to geographic coordinates by Mikkel Tamstorf—an exchange student from Copenhagen—during summer 1994, and plotted on a map of the glacier made from recent survey data. The late-summer position of the snow line, identified in the photographs, was found to be approximately in agreement with the position of the late-summer snow line on Black Rapids Glacier identified in a winter SAR image acquired by the European Space Agency satellite ERS-1 on 5 December 1993.

Winter SAR images showing the positions of late-summer snow lines on a large number of glaciers in Alaska and the Yukon Territory were located by Kristina Ahlnäs in the archive of the Alaska SAR Facility.

NASA Grant NAGW-2827: Scientific personnel; W.D. Harrison, C.S. Lingle, K. Ahlnäs and T. Heinric