For Glaciar Santa Rosa, in the Cordillera Raura, Peru, the extent and volume are determined for 1980 and 1961 from topographic mapping, and for two undated earlier stages LME and MAX from moraines. The regime of the glacier in terms of ice flow and mass balance is evaluated for the 1977–83 period. More than half of the water discharge from the glacier is not renewed by precipitation but supplied by the ice thinning. The rate of surface lowering of 2 m a−1 liquid-water equivalent corresponds to an energy amount for melting of 22 W m−2. Sensitivity analyses of Glaciar Yanamarey in the nearby Cordillera Blanca show that such a decrease of energy available for melting could be produced by a cloudiness increase of one-tenth, an air temperature decrease of more than 2°C, a decrease in specific humidity of 1 g kg−1, or some combination of heat-budget processes. Such changes in the atmospheric environment would be required to stabilize the glacier at its recent volume. As another indication of the recent imbalance, the maximum volume flux is found about 100 m below the equilibrium-line altitude. Under continuation of recent climatic conditions, the glacier may disappear within a few decades. These inferences coorroborate a recent assessment for the neighboring Cordillera Blanca.