VALLEY FORMATION AND EROSION AT K2 IN THE KARAKORAM HIMALAYA

Understanding mountain landscape evolution is complicated by the coupling of climatic, tectonic, and surface processes. Empirically based research has yet to identify the complex nature of tectonic and climatic influences on surface processes, as the dominance of various controlling factors can vary. The high Karakoram Himalaya has topography whose origin is not well understood, and there is considerable debate concerning external forcing, erosive forces and relief production. The complex nature of polygenetic evolution is seen in the topography of the Karakoram and in valleys surrounding the K2 massif. Consequently, we examined the topography of the Karakoram and used numerical modeling to better understand the influences of surface processes. Computer simulations were used to estimate the magnitude of erosion and relief production in the Baltoro Valley at K2. Analysis of the topography revealed focused erosion zones that coincide with high-mountain peaks. Global climate simulation results and geomorphological mapping support the notion of deep glacier erosion in the past. Glacier erosion simulations indicate that valley incision rates can exceed 5 mm/yr and account for 2 km of relief. Down valley, hillslope erosion simulations reveal that valley erosion can be dominated by bedrock landsliding, where segments of the landscape are rapidly uplifting. Sackung failure is seen to be concentrated above zones of prior tectonic strain where rock strength may be decreased. This suggests robust mass movement denudation, the rock fragment portions of which are exported from the system by glaciers and rivers. Our results suggest that denudational unloading at K2 is strongly controlled by climate forcing, and that glaciation potentially regulates the influence of other erosional forces. These findings indicate that glacial events and mass-balance fluctuations significantly control denudational unloading and relief production. More sophisticated characterization and coupling of surface processes in numerical models is required to better understand the controlling factors that cause differential denudation and relief production.