THE IMPACTS OF LANDSLIDES TRIGGERED BY THE 2009 TYPHOON MORAKOT ON LANDSCAPE EVOLUTION: A MASS BALANCE APPROACH

Research focusing on the possibility of climatically driven tectonics remains centered on long-term (10³ -10⁶ year) geologic and climatic signals. The geomorphic change at the core of any climate-tectonic coupling is enacted through the compounding effects of small-scale events. The relative rarity of single events with the power to change topography, however, has led to less emphasis being placed on the dynamics of these processes at an event-scale. We use remote sensing techniques and field investigation to quantify production, deposition, and transport of landslide sediments resulting from the 2009 Typhoon Morakot in Southern Taiwan. Typhoon Morakot delivered record-breaking rainfall, triggering more than 22,000 landslides distributed across 7800km² of the southern Taiwan orogen. An annual landslide catalog allows an analysis of landslide area-volume scaling to estimate volume of landslide material distributed across a strong northward gradient in tectonic uplift in Southern Taiwan. Landslide volume and frequency exhibit similarly positive trends with distance from the southern tip of the orogen. Next, we exploit a wealth of publicly available imagery and elevation data to map sediment aggradation throughout ten drainage basins. Preliminary results suggest widespread sediment aggradation of 10’s of meters, with localized aggradation exceeding 100 meters. Finally, the timescale over which the excess sediment will be removed from channels and ultimately delivered to the ocean is calculated using coupled suspended sediment and water discharge in the Sandimen watershed combined with empirical models of bedload transport. Initial estimates indicate that the effects of this event may be present for 100’s of years. Analysis of spatio-temporal patterns of sediment aggradation and removal provide new insight into the ways in which effects of a single, large event can propagate through a landscape, and the degree to which these effects are bound to regional tectonic processes.