DIFFERENT MORPHODYNAMIC PROCESSES AND GLACIER VARIATIONS AS A CONSEQUENCE OF PETROGRAPHICAL AND TECTONICAL STRUCTURE VARIATIONS FIRST OBSERVATIONS ON GEOMORPHOLOGICAL PROCESS BOUNDARIES IN THE UPPER & MIDDLE NAR-PHU-KHOLA (DAMODAR-HIMALAYA, NEPAL)

In 2007 a four-week expedition to the Damodar Himalaya was carried out with the aim to work out first geomorphologic and quarternary geological results on the yet unworked-on higher catchment areas of Nar-Phu Valley. The author focussed on the altitudinal zonation of geomorphological processes. Two facts turned out to be determinating for the detectability of altitudinal limits apart from climate: first the existence or abstinence of late quarternary moraine-deposits and secondly the orographic divide within the catchment area, specially the petrographical change with Mesozoic Tethys-sediments in the western part and the tectonically uplifted Palaeozoic Manaslu-crystalline as a part of the Himalaya Main Ridge in the eastern part of the drainage basin.

The petrographical change causes significantly higher erosion rates in the crystalline area due to the higher elevation and steeper flanks. As a result the quarternary debris-material is almost completely excavated and plain rock surfaces have been building out the flanks. The lack of debris-deposits in which geomorphological processes could create evident key forms for altitude zones or limits (i.e rock glaciers as indicators of permafrost) are missing and due to that a differentiated zonation of processes and altitude-limits cannot be made.

In contradiction to that in the western, less morphodynamically active Tethys-Sediment-area an almost complete zonation of periglacial process-limits has been proven by geomorphological evidence.

A second unambiguous difference caused by the petrographical and tectonical variation is the extent of glaciation. The catchment area of the glaciers in the crystalline area is bigger due to higher altitude with the consequence of the glacier-termini reaching more than 500 m further down than in the less high sediment zone in the western part of the catchment area. ELA-calculations show a 100 m snowline depression for the W-exposed glaciers of the crystalline catchment area compared to the ELA-exposition middle of 5623 m in the whole research area.

In summary there can be proven a significant E-W division in the organisation of geomorphological and glacial processes and altitude belts reducible to tecto-petroragphic variations.