THE TRANSGLACIAL DEBRIS LANDSCAPE IN HIGH ASIA: ARE TALUS CONES A KEY FORM OF THE PERIGLACIAL LANDSCAPE ASSEMBLAGE?

In the classical view of geomorphology, talus cones are considered to be part of the periglacial landscape assemblage. Frost weathering processes were identified as one the main processes of rock desintegration in high mountain areas. However, new research investigations in High Asia proved, that the genesis of a major part of debris accumulations is glacial-induced (ITURRIZAGA 1999, 2002). The extent of glaciation during the Last Glacial Maximum and the Late Glacial, with its glacial valley shaping and legacy of glacial sediments, may be considered the most important supraregional geoparameter in the distribution of debris accumulations. The debris supply areas consist of high-lying, late glacial moraine deposits, which cover the valley flanks over 1000 m above the valley floor. They are transformed by postsedimentary processes into transglacial debris accumulations. These transglacial landforms show often convergent forms to pure slope accumulations and can be easily mistaken for weathering landforms. Erratic and rounded boulders, the high clay content and their position-specific topographical relationship to the corresponding stages of glaciation indicate among other factors their glacial origin. The widespread distribution of talus cones and talus slopes ranging over a vertical distance of up to 4000 m already implies that these landscape forms do not represent climatic-controlled geomorphological features. Moreover, the transition from an "oversteepened ice-age debris accumulation landscape" to a Postglacial "adjustment debris accumulation landscape" results in various polygenetic collapse debris accumulations. The presentation will focus on representative case examples of semi-arid high mountain areas in the Hindukush and Karakorum, including especially the Shimshal, Hispar, Chogolungma, Braldu, Karambar, Chapursan and Mastuj valleys.

Iturrizaga, L. (1999): Typical debris accumulation forms and formations in High Asia. A glacial-history-based concept of the origin of Postglacial debris accumulation landscapes in subtropical high mountains with selected examples from the Hindu Kush, the Karakoram and the Himalayas. In: GeoJournal (M. Kuhle, ed.), Tibet and High Asia V, vol. 47, nos 1-2, 277-339.

Iturrizaga, L. (2002): Transglacial landforms in the Karakoram (Pakistan). In: Karakoram in Transition: The Hunza Valley (in press).