Spectral mixture analysis of Landsat thematic mapper images applied to thedetection of the transient snowline on tropical Andean glaciers

The tropical glaciers in the central Andes are sensitive indicators of clim atic variability. They are an important water resource, but are presently i n a state of rapid retreat. Spectral mixture analysis using Landsat Themati c Mapper (TM) images was used to identify the ablation and accumulation zon es and the transient snowline at two tropical sites: Zongo Glacier in the C ordillera Real, Bolivia, and the Quelccaya Ice Cap in Peru. Delineation of the accumulation and ablation zones is relatively insensitive to the endmem bers selected to represent each zone. Endmembers selected from Zongo Glacie r were successfully used to delineate accumulation and ablation zones on th e Quelccaya Ice Cap. Spectral mixture analysis was found to be superior to a single band image or the TM4/TM5 ratio in discriminating the accumulation and ablation zones on these small tropical glaciers. The altitude of the t ransient snowline identified on Zongo Glacier at the end of the ablation se ason is consistent with the altitude of the equilibrium line determined fro m mass balance studies. This suggests that in the tropics, as in mid-latitu des, the highest altitude reached by the transient snowline during a hydrol ogical year can be used as a proxy for the altitude of the equilibrium line . (C) 1999 Elsevier Science B.V. All rights reserved.