GLACIAL RETREAT AND ITS GEOMORPHOLOGIC EFFECTS ON MEXICO ACTIVE VOLCANOS, 1994-95

The northern slopes of Mexico's great, active stratovolcanoes, Popocat epetl (5450 m a.s.l.) and Pico de Orizaba (5700 m a.s.l.), are covered by glaciers. This paper analyzes the retreat of the glaciers between February 1994 and October 1995, and its geomorphological consequences. The results discussed are a continuation of research con ducted on th e volcanoes up to 1994. Although the glaciers retreated a great deal d uring the 1980s and early 1990s, the process accelerated from 1994 to 1995. The heavy erosion that had been observed on the deglaciated wall s of the volcanoes during these decades increased as the glaciers retr eated. Sediments originating from material loosened from the exposed l ateral walls added to the supraglacial layer. Temperature readings tak en from boreholes made in the glaciers indicated that ablation had bee n reduced as a result of the insulating effects of the debris mantle. This allowed widespread formation of deposits that buried ice in areas where the glacier had already disappeared. These results con firmed t he conclusions of earlier studies that deglaciation of stratovolcanoes has resulted in the acceleration of slope processes and the formation of buried ice deposits.