GSA QUATERNARY GEOLOGY AND GEOMORPHOLOGY DIVISION KIRK BRYAN AWARD: FLUVIAL RESPONSE TO COSEISMIC PERTURBATION - INSIGHTS INTO BEDROCK EROSION FROM THE FORMATION AND EVOLUTION OF THE DAAN RIVER GORGE (Invited Presentation)

Twenty years ago, on Sept 21, 1999, the M 7.6 Chi-Chi earthquake struck western Taiwan. At the northern end of the rupture zone, the earthquake activated an anticline that cuts across the Daan River, resulting in up to 10 m of uplift of the riverbed. This perturbation kicked off a unique natural experiment, and observations of the channel over the subsequent twenty years allow us to directly observe the formation and evolution of a bedrock gorge. This has yielded insight into a range of fluvial bedrock erosion processes, including gorge formation, knickpoint migration, braidplain incision, lateral erosion and widening, and the newly identified process of downstream sweep erosion. Ten years of detailed monitoring enable us to explore the factors that drive these processes, particularly the role of bedload transport and event-scale forcing, including both inter- and intra-event variability. Our observations highlight the efficiency, over different timescales, of both climatological and seismic events in driving fluvial erosion in this setting.