台灣山區五條河流現今岩盤下切速率的監測
Other Title
Late Holocene fluvial aggradation and bedrock incision in an active
mountain belt, Li-wu River, eastern Taiwan
mountain belt, Li-wu River, eastern Taiwan
Date Issued
2004
Date
2004
Author(s)
謝孟龍
DOI
932116M002007
Abstract
Although 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.
Subjects
Landscape evolution
Liwu River
Climate change
Fill terrace
Bedrock incision
SDGs
Publisher
臺北市：國立臺灣大學地質科學系暨研究所
Type
report
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