DENUDATION AND UPLIFT IN THE WESTERN HIMALAYA

Complex western Himalaya topography represents integration of climatic, surface and tectonic processes but understanding polygenetic landscape evolution is difficult, and controversy surrounds issues of processes, relief production and quantitative characterization of unloading and uplift. In Nanga Parbat and Karakoram Himalaya, we determine process roles and relief production and seek relationships between polygenetic evolution and denudational unloading. We use advanced remote sensing, geographic information science, landscape simulation models, and field assessments, as well as: (1) terrain analysis and geomorphological mapping of mass movement, glacial, and fluvial processes; (2) glaciology; (3) cosmogenic and luminecence dating; and (4) paleoclimate simulations using advanced spectral Global Climate Model. Hypsometric analyses reveal 74% of Karakoram landscape between 3000-5000 m altitude, with mean elevation of 5,140 m. The K2 hypsometric curve is similar to Nanga Parbat, known as a region of strong, denudationally focused uplift in an upfaulted, tectonic-aneurysm, caused by the capture of the Indus River in late Cenozoic. The K2 hypsometric integral is 0.44, more than the 0.38 of Nanga Parbat, perhaps because of the greater ice at K2. Semivariogram analysis reveals that, in the absence of the large Indus River at Nanga Parbat, variation in relief at K2 is dramatically reduced. Slope-altitude functions are non-linear, and relatively low slope angles at high altitudes document erosion and redistribution of material by glaciers up to ~6000 m (i.e., high-altitude erosion surfaces). Glaciation profoundly affects relief production and other surface processes. Climate simulations support results and indicate paleoclimate conditions favorable for glacial advances could erode more rock debris. Ice depths determined from radio-echo sounding and feature-tracking for velocity using multi-date satellite imagery reveal potential for alpine glaciers to dominate unloading. Glacial undercutting and buttress removal in deglacial fluctuations appear related to sackung of rock ridges and extensive rock-avalanche deposits. Climate forcing thus appears to control such denudational unloading.