Rapid present-day knickpoint migrations of the Taiwan orogenic belt following the 1999 Chi-Chi earthquake
Abstract
The 1999 Chi-Chi earthquake (Mw =7.6) in central Taiwan created an approximately 100-km-long surface rupture along the north-south-trending Chelungpu fault. The surface rupture was about 1-10 meter heights across many east-west trending rivers in central Taiwan, generating knickpoints as waterfalls. Knickpoint, which is the precise point in the long profile where the maximum change rate of channel gradient, usually forms in bedrock channel in response to an abrupt base-level fall or a change in the resistance of bedrock. With the passage of time, knickpoints migrate upstream through fluvial processes. Since the Choushui River is the largest river in Taiwan with very large stream power, along with the fact that the surface rupture across the Choushui River is around 3 meter based on field observations, it is an opportunity to examine how the knickpoint evolves along the Choushui River and what controls the knickpoint migration in such large initial condition and rapid processes. In order to evaluate the migration history and processes of knickpoint within the Taiwan orogen, we construct DSMs derived from aerial photos by using the SfM-MVS method and evaluate yearly topography changes since 1999. According the longitudinal profiles and transverse sections of Choushui River derived from the DSMs, the knickpoint recession rate is not spatially and temporally steady. There is no significant migration between 2005 to 2011 and 1000 meters of migration from 2011 to 2016. There is 5-9 meters of incision between 2008 to 2016, which is more than coseismic uplift. Based on our results, Choushui River currently has two knickpoints with different migration rate along this section. In addition, we observe knickpoints turn into knickzone during the migration processes, possibly controlled by lithology.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMEP33D2450L
- Keywords:
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- 1824 Geomorphology: general;
- HYDROLOGYDE: 1825 Geomorphology: fluvial;
- HYDROLOGYDE: 1856 River channels;
- HYDROLOGYDE: 5419 Hydrology and fluvial processes;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS