HR: 17:15h
AN: T34B-06 INVITED     [Abstracts]
TI: Dynamics of Monsoonal Forcing, Tectonics and Erosion Processes Along the Southern Himalaya, Sutlej Valley, NW India
AU: * Strecker, M R
EM: strecker@geo.uni-potsdam.de
AF: Universitaet Potsdam, Inst. f. Geowissenschaften PO 601553, Potsdam, 14415 Germany
AU: Bookhagen, B
EM: bodo@geo.uni-potsdam.de
AF: Universitaet Potsdam, Inst. f. Geowissenschaften PO 601553, Potsdam, 14415 Germany
AU: Thiede, R
EM: thiede@geo.uni-potsdam.de
AF: Universitaet Potsdam, Inst. f. Geowissenschaften PO 601553, Potsdam, 14415 Germany
AB: Under present-day conditions the interplay between topography and Indian Summer Monsoon (ISM) circulation controls precipitation, sediment transport, and river discharge along the Southern Himalayan Mountain Front (SHF). Precipitation measurements derived from passive microwave analysis (SSM/I) show that monsoonal vortexes draw moisture from the Bay of Bengal, move northwestward and result in heavy rainfall when colliding with the mountain front. The end of the monsoonal conveyer belt is near the Sutlej Valley of NW India and corresponds to a climatic transition sensitive to changes in ISM strength. For example, during the 2002 and previous abnormal monsoon years, violent rainstorms penetrated far into otherwise arid regions in the NW Himalaya at elevations > 3000 m, while rainfall amounts in lower-elevation sectors were not significantly increased. Farther moisture transport into the orogen also enhanced fluvial sediment flux and emphasizes the importance of these short-lived events in the modern ISM variability for geomorphic processes. On centennial time scales the Sutlej region also shows a close link between monsoon oscillation, sediment flux and relief production. The onset of the strengthened ISM in early Holocene time was accompanied by deposition of massive conglomerate deposits in low-gradient sectors of the Sutlej. Sculpted into this 120-m-thick valley fill were six fluvial terraces at successively lower elevations, cut between 9 and 2.5 ka (Bookhagen et al., this session). Channel abandonment and terrace formation correlate with reduced moisture during centennial oscillations of the Indian monsoonal system, which have resulted in lower sediment supply, allowing flux-undersaturated rivers to incise episodically and evacuate material to foreland areas. At the level of millennial ISM oscillations clusters of exceptionally large bedrock landslides were generated in the high-elevation sectors of the orogen during protracted intensified monsoon phases at about 27 and 6 ka. These episodes also correlate with significantly increased sediment-flux rates and are inferred to correspond to higher precipitation, lateral undercutting of rivers, and higher pore pressures, related to moisture penetration far into the arid parts of the orogen. Over much longer time spans, involving hundred thousands to millions of years, late Pliocene to Quaternary apatite fission track cooling ages reveal a coincidence between rapid erosion and exhumation focused in an up to 70-km-wide sector of the SHF (Thiede et al., this session). This sector of the orogenic wedge currently receives more than 80% of precipitation related to moisture-bearing winds impinging on the SHF. This concentrated loss of material is compensated by an area of pervasive brittle deformation, suggesting that protracted climatically controlled surface processes may localize deformation in the internal part of the Himalaya.
DE: 9320 Asia
DE: 8102 Continental contractional orogenic belts
DE: 1833 Hydroclimatology
DE: 1035 Geochronology
DE: 1625 Geomorphology and weathering (1824, 1886)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting