11:15 〜 11:30
[HGM02-08] Coupling Relationship between Co-Seismic Landslides and Landscape Evolution in an Active Orogenic Belt
キーワード：Cosmogenic nuclides、Erosion rate、Morphometric parameters、Co-seismic landslides、Tibetan plateau
In modern geomorphology, existed a common view that erosion rate is linearly coupling with topography in gentle landscapes, then gradually break the linear relationship with increasing the local relief and finally decoupled when close to a “critical state”.
Concentration of 10Be in detrital quartz from river sediments is widely used to quantify catchment-wide denudation rates and reconstruct tectonic history during this three decades. This method basically presumes a steady state in the removal of surface materials. However, in active orogenic belts, co-seismic landslides occur widely and significantly dilute the 10Be concentration in river sand, causing overestimation in the erosion rates. This dilution effect thus exhibits an illusion of unlimited growing of the apparent erosion rates around the threshold gradient in such high-relief landscapes. Establishing a model to predict the authentic erosion rates beyond the critical state is essential for the quantitative test of landform evolution theories and for addressing questions about potential response of the geomorphic systems to the tectonic forcing.
The eastern margin of the Tibetan Plateau, a typical active orogenic zone, is characterized by unique crustal movements and representative steep topography, resulting in widely-distributed landslides especially after the 2008 Mw 8.0 earthquake. Deposits from bedrock landslides may dilute the 10Be concentration in river sediments then caused an “accelerated” erosion rate. However, previous studies in this area have focused on apparent 10Be-derived erosion rates and topographic indices to reveal: 1) channel steepness is a more reliable topographic metric than mean hillslope gradient for erosion rate; 2) fault system exerts a first-order control on denudation and acts as an important geomorphic boundary between the highly dissected margin and the low-relief plateau; 3) topographic metrics are the best predictors of the variations in these millennial-scale denudation rates and that fault activity strongly regulates surface erosion across the plateau margin, which, these apparent “accelerated” 10Be-derived erosion rate may not be appropriate for quantitatively evaluating the interactions between erosion processes and topographic evolution beyond the threshold geomorphic condition under intense tectonic forcing.
Therefore, in this work, we combined GIS-based geometry analysis and a series of detrital 10Be concentrations for catchments after 2008 earthquake, to establish an empirical model for evaluating the authentic erosion rates in the active orogenic belt using a function including distribution of co-seismic landslides and background erosion rates constrained by local topography. Based on the model fitting, we reconstructed the relationships between the occurrence of landslides, gross erosion rates, and catchment geometry. This study provided new insights into the dynamic interactions between mountain topography with erosional processes in a landslide-dominated zone, with implications for understanding the contribution of the catastrophic landslides in the total mass removal from steep mountainous landscapes.
Concentration of 10Be in detrital quartz from river sediments is widely used to quantify catchment-wide denudation rates and reconstruct tectonic history during this three decades. This method basically presumes a steady state in the removal of surface materials. However, in active orogenic belts, co-seismic landslides occur widely and significantly dilute the 10Be concentration in river sand, causing overestimation in the erosion rates. This dilution effect thus exhibits an illusion of unlimited growing of the apparent erosion rates around the threshold gradient in such high-relief landscapes. Establishing a model to predict the authentic erosion rates beyond the critical state is essential for the quantitative test of landform evolution theories and for addressing questions about potential response of the geomorphic systems to the tectonic forcing.
The eastern margin of the Tibetan Plateau, a typical active orogenic zone, is characterized by unique crustal movements and representative steep topography, resulting in widely-distributed landslides especially after the 2008 Mw 8.0 earthquake. Deposits from bedrock landslides may dilute the 10Be concentration in river sediments then caused an “accelerated” erosion rate. However, previous studies in this area have focused on apparent 10Be-derived erosion rates and topographic indices to reveal: 1) channel steepness is a more reliable topographic metric than mean hillslope gradient for erosion rate; 2) fault system exerts a first-order control on denudation and acts as an important geomorphic boundary between the highly dissected margin and the low-relief plateau; 3) topographic metrics are the best predictors of the variations in these millennial-scale denudation rates and that fault activity strongly regulates surface erosion across the plateau margin, which, these apparent “accelerated” 10Be-derived erosion rate may not be appropriate for quantitatively evaluating the interactions between erosion processes and topographic evolution beyond the threshold geomorphic condition under intense tectonic forcing.
Therefore, in this work, we combined GIS-based geometry analysis and a series of detrital 10Be concentrations for catchments after 2008 earthquake, to establish an empirical model for evaluating the authentic erosion rates in the active orogenic belt using a function including distribution of co-seismic landslides and background erosion rates constrained by local topography. Based on the model fitting, we reconstructed the relationships between the occurrence of landslides, gross erosion rates, and catchment geometry. This study provided new insights into the dynamic interactions between mountain topography with erosional processes in a landslide-dominated zone, with implications for understanding the contribution of the catastrophic landslides in the total mass removal from steep mountainous landscapes.