As on all Peruvian Cordilleras, the glaciers on the eastern slopes of the Cordil lera Blanca extend to generally lower elevations than those on the western slope s. The mountain range of Santa Cruz - Pucahirca possesses the largest E-W extens ion within the Cordillera Blanca. A significant retreat of the glaciers between two quasistationary situations around 1930 and around 1950 was reconstructed fro m air photographs. The derived ELAs as well as the (ELA(1930 - 1950) show spatia l diversities. The pattern of the ELAs is caused by differences in both accumula tion and effective global radiation. The change in ELAs(1930-1950) is partly due to a spatially uniform increase in air temperature. The remaining rise of the e quilibrium line, which varies within different parts of the investigation area, has to be related to changes in precipitation and effective global radiation. Bo th correspond to changes in air humidity which is suggested to be an important f actor on tropical glacier fluctuations. A model of superposed typical tropical c irculation patterns of different scales and ELA-climate model based approaches i s presented.