Pulsed carbon export from mountains by earthquake-triggered landslides explored in a reduced-complexity model

Abstract

Abstract. In mountain ranges, earthquakes can trigger widespread landsliding and mobilize large amounts of organic carbon by eroding soil and vegetation from hillslopes. Following a major earthquake, the landslide-mobilized organic carbon can be exported from river catchments by physical sediment transport processes or stored within the landscape where it may be degraded by heterotrophic respiration. The competition between these physical and biogeochemical processes governs a net transfer of carbon between the atmosphere and sedimentary organic matter, yet their relative importance following a large landslide-triggering earthquake remains poorly constrained. Here, we propose a model framework to quantify the post-seismic redistribution of soil-derived organic carbon. The approach combines predictions based on empirical observations of co-seismic sediment mobilization with a description of the physical and biogeochemical processes involved after an earthquake. Earthquake-triggered landslide populations are generated by randomly sampling a landslide area distribution, a proportion of which is initially connected to the fluvial network. Initially disconnected landslide deposits are transported downslope and connected to rivers at a constant velocity in the post-seismic period. Disconnected landslide deposits lose organic carbon by heterotrophic oxidation, while connected deposits lose organic carbon synchronously by both oxidation and river export. The modeling approach is numerically efficient and allows us to explore a large range of parameter values that exert a control on the fate of organic carbon in the upland erosional system. We explore the role of the climatic context (in terms of mean annual runoff and runoff variability) and rates of organic matter degradation using single pool and multi-pool models. Our results highlight the fact that the redistribution of organic carbon is strongly controlled by the annual runoff and the extent of landslide connection, but less so by the choice of organic matter degradation model. In the context of mountain ranges typical of the southwestern Pacific region, we find that model configurations allow more than 90 % of the landslide-mobilized carbon to be exported from mountain catchments. A simulation of earthquake cycles suggests efficient transfer of organic carbon out of a mountain range during the first decade of the post-seismic period. Pulsed erosion of organic matter by earthquake-triggered landslides is therefore an effective process to promote carbon sequestration in sedimentary deposits over thousands of years.

Measuring the grain‐size distributions of mass movement deposits

“…The methodological uncertainties associated with comparing GSDs and percentiles obtained using different methods can have consequences for accurate process interpretation. For example, the factor of two difference in grain-size percentile estimates from survey tape counts relative to sieving for a fine deposit could shift the D 50 value from suspended load to bedload, which would have implications for estimates of sediment export rates and onward transport (Croissant et al, 2021;Marc et al, 2021). Similarly, by excluding up to 20% by weight of the finest grains, all non-sieving methods are unable to find evidence for processes where the proportion of sand and silt is influential (de Haas et al, 2015;Kaitna et al, 2016;Makris et al, 2020).…”

“…The rates and calibre of hillslope sediment supply to channels have also been used increasingly to drive landscape evolution and fluvial modelling (Attal et al, 2015;Croissant et al, 2021;Egholm et al, 2013;Roda-Boluda et al, 2018). Given that mass movementderived sediment is an essential component in these problems (Sklar & Dietrich, 2006), improvements are needed in our ability to characterize this material to provide robust conclusions about the timescales and rates of bedrock incision and sediment transport.…”

Landslide-Induced Weathering in Tectonically Active Mountains: Evidence From Dissolved Radiogenic Uranium Isotopes

“…Thus, landslide-induced weathering may represent an under-appreciated weathering mechanism with global-scale impacts. Resolving landslide-induced weathering fluxes relies on the development of process-based models (e.g., Lebedeva et al, 2007;Ferrier and Kirchner, 2008;Hilley et al, 2010;West, 2012;Croissant et al, 2021;Li and Moon, 2021) and effective tracers such as the dissolved uranium isotopes presented in this study. Future studies are needed to better understand how weathering rates respond to landslide activities across different conditions and to separate contributions from soils versus landslides, as well as from different lithologies (e.g., carbonates and silicates), in weathering budgets.…”

“…In seismically active regions, the seismic ground motion also induces landslides that erode topography and counteract seismic uplift (Keefer, 1994;Parker et al, 2011;Marc et al, 2016;Li G. et al, 2019). As a legacy of tectonic uplift, landslides have profound influences on Earth's surface environments, from generating hazards to exporting sediment and organic carbon fluxes (Fan et al, 2019;Croissant et al, 2021). Besides these recognitions, major research efforts have been devoted to studying how landslides impact chemical weathering-a key process governing the exchange of carbon between the atmosphere and lithosphere (Emberson et al, 2016;Jin et al, 2016;Emberson et al, 2017;Emberson et al, 2018).…”

Coseismic Debris Remains in the Orogen Despite a Decade of Enhanced Landsliding

“…However, quantitative evaluations of landslide patterns and trends after major earthquakes are still lacking, and quantifications of sediment transfers along the slopes and through the hydrographic network have not been attempted. Such evaluations are critical for assessing earthquake-induced geohazard chains and understanding the impact of earthquakes on landscape evolution and carbon fluxes (Croissant et al, 2021;Fan, Scaringi, Korup, et al, 2019;Hilton & West, 2020). Here, by analysing 12 years of mass wasting in the epicentral region of the Wenchuan earthquake (∼471 km 2 ) together with fluvial sediment data, we show spatio-temporal changes in landslide characteristics, quantify the migration and evacuation of debris, and discuss long-term sediment budget estimates.…”