HR: 17:00h
AN: T34B-05    [Abstracts]
TI: Holocene Monsoonal Dynamics and Fluvial Terrace Formation in the NW Himalaya
AU: * Bookhagen, B
EM: bodo@geo.uni-potsdam.de
AF: Universit\"at Potsdam, Institut f\"ur Geowissenschaften, Potsdam, 14415 Germany
AU: Fleitmann, D
EM: fleitmann@pangea.stanford.edu
AF: Stanford University, Geological and Environmental Sciences, Stanford, CA 94305 United States
AU: Nishiizumi, K
EM: kuni@ssl.berkeley.edu
AF: University of California, Space Scienes Laboratory, Berkeley, CA 94720 United States
AU: Strecker, M R
EM: strecker@geo.uni-potsdam.de
AF: Universit\"at Potsdam, Institut f\"ur Geowissenschaften, Potsdam, 14415 Germany
AU: Thiede, R C
EM: thiede@geo.uni-potsdam.de
AF: Universit\"at Potsdam, Institut f\"ur Geowissenschaften, Potsdam, 14415 Germany
AB: Along the lower Sutlej Valley in the NW Indian Himalaya, cut and fill terraces reflect Holocene climatic variations that match known episodes of variable precipitation. We dated a flight of six fluvial terrace surfaces in conglomeratic valley fill using cosmogenic radionuclides (26Al, 10Be) to reveal the link between Holocene Indian Summer Monsoon (ISM) oscillations and fluvial processes. The onset of heavy precipitation and farther penetration of moisture into the orogen during the Holocene ISM optimum at approx. 10ka and coeval amplified sediment flux at higher elevations choked the wide, low-gradient valleys with debris along the southern Himalayan front. Sedimentation of the highest fluvial valley fill, 120m above the present-day river, occurred almost instantaneously at 9.7ka, when vast amounts of sediment from erosion off vegetation-free hillslopes and formerly lodged glacigenic deposits were deposited. Between 8.3 and 2.5ka, well preserved terraces sculpted into these deposits at successively lower elevations reflect short-term, transient episodes in river profile development. Incision and channel abandonment between ISM onset and today coincides with centennial-long, drier intervals in the oscillating monsoonal system. Contrary to common concepts linking fluvial incision of terrace systems to increased precipitation and runoff, we demonstrate that less moisture during centennial oscillations of the Indian monsoonal system results in lower sediment supply, allowing flux-undersaturated rivers to incise episodically.
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