A case of rapid rock riverbed incision in a coseismic uplift reach and its implications

Ming Wan Huang, Yii-Wen Pan*, Jyh-Jong Liao

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

26 Scopus citations

Abstract

During the 1999 Chi-Chi earthquake (Mw=7.6) in Taiwan, the coseismic displacement induced fault scarps and a pop-up structure in the Taan River. The fault scarps across the river experienced maximum vertical slip of 10m, which disturbed the dynamic equilibrium of the fluvial system. As a result, rapid incision in the weak bedrock, with a maximum depth of 20m, was activated within a decade after its armor layer was removed. This case provides an excellent opportunity for closely tracking and recording the progressive evolution of river morphology that is subjected to coseismic uplift. Based on multistaged orthophotographs and digital elevation model (DEM) data, the process of morphology evolution in the uplift reach was divided into four consecutive stages. Plucking is the dominant mechanism of bedrock erosion associated with channel incision and knickpoint migration. The astonishingly high rate of knickpoint retreat (KPR), as rapid as a few hundred meters per year, may be responsible for the rapid incision in the main channel. The reasons for the high rate of KPR are discussed in depth. The total length of the river affected by the coseismic uplift is 5km: 1km in the uplift reach and 4km in the downstream reach. The downstream reach was affected by a reduction in sediment supply and increase in stream power. The KPR cut through the uplift reach within roughly a decade; further significant flooding in the future will mainly cause widening instead of deepening of the channel.

Original languageEnglish
Pages (from-to)98-110
Number of pages13
JournalGeomorphology
Volume184
DOIs
StatePublished - 1 Jan 2013

Keywords

  • Chi-Chi earthquake
  • Coseismic uplift
  • Incision rate
  • Taan River
  • Taiwan

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