Le fluttuazioni dei ghiacciai del Ruwenzori (Africa Orientale) dalla spedizione del Duca degli Abruzzi (1906) sino agli anni ’90

Fluctuations of glaciers in the Ruwenzori Mountains (East-Africa) since the Duke of Abruzzi’s Expedition in 1906

Abstract

Whereas Kilimanjaro (5 896 m) and Mt. Kenya (5199 m) culminate in higher summits, the Ruwenzori Range (5 109 m, Margherita Peak, Mt. Stanley) forms the largest and the only nonvolcanic of the three ice-capped mountains on the African continent. The total surface of Ruwenzori glaciers (ca. 30) was determined as 4.43 km² from aerial photographs taken during 1952-1955 (OSMASTON, 1989, b). Speke Glacier of Mt. Speke and Elena Glacier of Mt. Stanley are the best studied glaciers of the range. ‘The glaciological observations carried out by the 1906 expedition led by the Duke of Abruzzi, results of various scientific expeditions in the fifties and data obtained by the authors’ visits in 1990 and 1991 allow the reconstruction of surface variations of the Glaciers Speke and Elena between 1906 and 1990/91. While Elena Glacier has lost almost 60% of its surface since 1906, the relatively minor recession of Speke Glacier (ca. — 50% since 1906) does not necessarily correlate with a minor loss of mass. Due to the local topography a certain significant loss of the tongue volume resulted in a less significant surface and length fluctuation. The behaviour of the two Ruwenzori glaciers highly corresponds to that of other tropical glaciers. A decreased atmospheric humidity is assumed to be the main reason for the recent significant recession of Ruwenzori glaciers. The decreased snow accumulation, significantly appearing in the highest parts of the glaciers, is normally associated with a decreased cloud cover. This leads to an increased amount of absorbed shortwave radiation and orographically less protected portions, like the western section of Speke Glacier, are exposed to higher ablation rates.