謝孟龍2006-07-252018-06-282006-07-252018-06-282004http://ntur.lib.ntu.edu.tw//handle/246246/11860Although over long term an orogen that has been actively deforming would maintain a theoretical steady state with erosion balancing rock uplift, the short-term evolution of the orogen is strongly dictated by climatic forcing and other environmental perturbations such as seismic or rainfall events. The data from the Li-wu River in eastern Taiwan shows that the response of these short-term environmental changes can be quick and drastic. Based on radiocarbon dates of fill terraces, the river had aggraded during ca. 4-2 ka, starting at the river mouth and transferring to the upstream direction, with the maximum thickness of deposition of 350 m. The subsequent incision cut locally through bedrock (marble/schist) where the channel had shifted laterally away from its original position during or after the aggradation. The rate of this bedrock incision is up to > 10 mm/yr (and likely > 20 mm/yr). Even considering only the net incision of bedrock since the time before the aggradation, the rate obtained in the upper part of the river is much higher than the long-term rock uplift rate of 3-6 mm/yr. The observed aggradation corresponds to a relatively cool and dry climate recorded by palynological data. This suggests that lowering of tree line and enhancing of periglacial processes in the upper part of the catchment may have played important roles upon the excessive supply of the sediments that caused the aggradation. Alternatively, the aggradation may be simply triggered by some seismic or rainfall events. In any cases, given the capability of the river to incise bedrock, episodic deposition that temporarily retards or stops the incision is likely to be a norm for the river, such that over long term the incision and rock uplift can be mutually balanced.application/pdf1483751 bytesapplication/pdfzh-TW國立臺灣大學地質科學系暨研究所Landscape evolutionLiwu RiverClimate changeFill terraceBedrock incision[SDGs]SDG13reporthttp://ntur.lib.ntu.edu.tw/bitstream/246246/11860/1/932116M002007.pdf