Erosion of an active mountain belt

The aim of this thesis is to quantify controls on erosion rates in the Taiwan mountain belt across a range of time-scales. Erosion rates in the Taiwan orogen are estimated from modern river sediment loads. Holocene river incision rates, and the thermochronometry on a million-year time-scale. Erosion rates within the actively deforming mountains are high (3-6 mm yr-1) on all time-scales, but the pattern of erosion has changed over time in response to the migration of localized tectonic deformation. Modern, decadal erosion rates correlate with historical seismicity and storm-driven runoff variability. The highest erosion rates are found where rapid deformation, high storm frequency and weak substrates coincide, despite low topographic relief. The geomorphic impact of individual earthquakes and typhoons is analysed through the natural experiment provided by the 1999 Mw 7.6 Chi-Chi earthquake and subsequent typhoon storms. Following the Chi-Chi earthquake, a 2-4-fold increase in sediment concentration was observed in rivers draining the epicentre region. Sediment was transferred from hillslopes to rivers in a cascade of processes. The earthquake triggered widespread landsliding on hillcrests and left large amounts of debris stored on hillslopes. Subsequent typhoons reworked this material and triggered new landslides in bedrock that had been weakened by co-seismic ground motion. Rivers draining the Taiwan mountain belt delivered 384 Mt yr-1 of suspended sediment to the ocean between 1970-1998. This amount represents 1.9% of estimated global suspended sediment discharge, yet is derived from only 0.024% of the Earth’s subaerial surface. Much of this sediment (30-42%) is delivered in hyperpycnal river plumes that sink to the sea-bed and may deposit turbidites. The rate of turbidite deposition increased by approximately 4 times following the Chi-Chi earthquake.EThOS - Electronic Theses Online ServiceGBUnited Kingdo