An exceptionally negative mass-balance of a small Alpine glacier

Abstract

On Weißbrunnferner/Ghiacciaio di Fontana Bianca in the Ortles-Cevedale group, mass balance studies have been made since 1983/84 with a three-year interruption. In 1997/98, the mass balance reached its negative record with -1610 kg m², being about 1.5 times the former record. Neither the temperature recorded at nearby weather stations nor particular accumulation deficits can offer an explanation for the exceptional process. Yet, compared to the other years, the vertical mass balance profile was markedly different, indicating distinctly increased ablation in the glacier's higher zones. This can be explained by the consumption of almost the entire firn body over the last several years when the annual equilibrium line remained above the highest peaks. As a consequence, dust accumulated over many years became concentrated on an impermeable layer, changing the surface albedo distinctly. The lack of summer snowfall may be an additional reason for increased ablation. A 0.1 to 0.15 decrease in albedo can explain the increased ablation in the former firn zone of the glacier. Such sudden changes of surface properties can be expected during any period of strong glacier retreat and can lead to markedly wrong conclusions when deducing a previous climate from glacier fluctuations.