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Earthquakes play a fundamental role in the evolution of Earth's topography through co-seismic uplift and subsidence, as well as erosion through widespread landslides induced by ground motion. Earthquake-induced landslides can result in exceptional increases in the transfer of mass from landscapes, supplying sediment to rivers where impacts can last for decades or longer. Landslides can also erode vegetation and soils, in addition to exposing freshly ground rock mass, which can both result in regionally significant carbon transfers. Recent work has sought to quantify the fluxes, rates, and temporal patterns of the impacts on earth surface processes generated by these tectonic events. In this review, we focus on the impacts of earthquake-induced landslides on erosion and sediment flux, river water chemistry, and carbon export through the lens of the well-studied 2008 Wenchuan earthquake. We then discuss these themes in the context of works from the 1999 Taiwan Chi-Chi earthquake, 2015 Nepalese Gorkha earthquake, and New Zealand historical earthquakes, altogether highlighting an important role of earthquake-induced landslides in erosion and weathering along tectonically active mountain ranges. We suggest that more monitoring, geochemical tracing, paleo-records, and/or modelling studies are needed to compare the processes and fluxes of catchment erosion and weathering before and after earthquake events, which will help to deepen our understanding not only of the impacts of earthquake-induced landslides on earth surface processes, but also the linkage among high magnitude events, continental erosion and weathering, and the long-term global carbon cycle. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

ABSTRACT In humid, forested mountain belts, bedrock landslides can harvest organic carbon from above ground biomass and soil (OCmodern) while acting to refresh the landscape surface and turnover forest ecosystems. Here the impact of landslides on organic carbon cycling in 13 river catchments spanning the length of the western Southern Alps, New Zealand is assessed over four decades. Spatial and temporal landslide maps are combined with the observed distribution and measured variability of hillslope OCmodern stocks. On average, it is estimated that landslides mobilized 7.6 ± 2.9 tC km−2 yr−1 of OCmodern, ~30% of which was delivered to river channels. Comparison with published estimates of OCmodern export in river suspended load suggests additional erosion of OCmodern by small, shallow landslides or overland flow in catchments. The exported OCmodern may contribute to geological carbon sequestration if buried in sedimentary deposits. Landslides may have also contributed to carbon sequestration over shorter timescales (<100 years). 5.4 ± 3.0 tC km−2 yr−1 of the eroded OCmodern was retained on hillslopes, representing a net-carbon sink following re-vegetation of scar surfaces. In addition, it was found that landslides caused rapid turnover of the landscape, with rates of 0.3% of the surface area per decade. High rates of net ecosystem productivity were measured in this forest of 94 ± 11 tC km−2 yr−1, which is consistent with rapid landscape turnover suppressing ecosystem retrogression. Landslide-OCmodern yields and rates of turnover vary between river catchments and appear to be controlled by gradients in climate (precipitation) and geomorphology (rock exhumation rate, topographic slope). Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We investigate the routing and transfer of particulate organic carbon (POC) from the western Southern Alps, New Zealand, using organic carbon (Corg) and nitrogen (Norg) concentrations and stable carbon isotopes (δ13Corg). In this active mountain belt, sediment discharge is dominated by landslide-derived material. Landsliding acts to homogenize the geochemically diverse hillslope POC, mixing POC from the standing biomass and soil with the fossil POC from bedrock. As a result, the POC in river sediment at the mountain front is a binary mixture of fossil and nonfossil carbon sourced from many landslide deposits. We calculate that nonfossil biogenic POC makes up 63 ± 7% of the total POC in the suspended load of rivers draining the western Southern Alps. The erosional flux of biogenic POC from these catchments represents a transfer of 39 tC km-2 a-1 of atmospheric CO2 averaged over the west flank of the mountain belt. If more than 10% of this POC is preserved in sediments on geological timescales, then this process is the most significant way in which the Southern Alps and similar, tectonically active mountain belts with restricted alluvial aprons consume atmospheric CO2. [ABSTRACT FROM AUTHOR]

On geological time scales, the erosion of carbon from the terrestrial biosphere and its burial in sediments can counter CO2 emissions from the solid Earth. Earthquakes may increase the erosion of this biospheric carbon and supply it to mountain rivers by triggering landslides, which rapidly strip hillslopes of vegetation and soil. Over the long term, elevated river sediment loads may promote more efficient carbon burial. However, riverine export of earthquakemobilized carbon has remained poorly constrained. Here we quantify biospheric carbon discharge by the Zagunao River following a large earthquake with a unique set of samples collected before and after the A.D. 2008 Mw 7.9 Wenchuan (China) earthquake. Radioactive and stable carbon isotopes are used to isolate the biospheric carbon, accounting for rock-derived organic carbon inputs. River discharge of biospheric carbon doubled in the downstream reaches, characterized by moderate landslide impact, following the earthquake. The rapid export of carbon from earthquake-triggered landslides appears to outpace its degradation on hillslopes while sediment loads are elevated. This means that enhanced river discharge of biospheric carbon following large earthquakes can link active tectonics to CO2 drawdown. [ABSTRACT FROM AUTHOR]

Large earthquakes in active mountain belts can trigger landslides, which mobilize large volumes of clastic sediment. Delivery of this material to river channels may result in aggradation and flooding, while sediment residing on hillslopes may increase the likelihood of subsequent landslides and debris flows. Despite recognition of these processes, the controls on the residence time of coseismic landslide sediment in river catchments remain poorly understood. Here we assess the residence time of fine-grained (<0.25 mm) landslide sediment mobilized by the C.E. 2008 Mw 7.9 Wenchuan earthquake, China, using daily suspended sediment discharge measured in 16 river catchments from 2006-2012. Following the earthquake, suspended sediment discharge was elevated 3-7x compared to 2006-2007. However, the total 2008-2012 export (92.5 ± 9.3 Mt from 68,719 km²) was much less than estimates of fine-grained sediment input by coseismic landslides (480 +350/-338 Mt) determined by landslide area-volume scaling and deposit grain-size distributions. We estimate the residence time of fine-grained sediment in the affected river catchments using the post-earthquake rate of sediment export, and find that it ranges from one year to over a century. The first-order variability in fine-sediment residence time is proportional to the areal extent of coseismic landsliding, and is inversely proportional to the frequency of intense runoff events (>5 mm day-1). Together with previous observations from the C.E. 1999 Chi-Chi earthquake in Taiwan, our results demonstrate the importance of landslide density and runoff intensity in setting the duration of earthquake-triggered landslide impacts on river systems. [ABSTRACT FROM AUTHOR]

The article discusses on long-term patterns of hillslope erosion by earthquake-induced landslides shape mountain landscapes. Topics discusses include information on erosion provenance using a novel combination of the isotopic and molecular composition of organic matter in Lake Paringa, New Zealand; shift in erosion provenance after four large earthquakes over 1000 years; and role of repeated large earthquakes in erosion at high elevations.

In tectonically active mountain ranges, landslides triggered by earthquakes mobilise large volumes of sediment that affect river dynamics. This sediment delivery can cause downstream changes in river geometry and transport capacity that affect the river efficiency to export this sediment out of the epicentre area. The subsequent propagation of landslide deposits in the fluvial network has implications for the management of hazards downstream and for the long-term evolution of topography over multiple seismic cycles. A full understanding of the processes and time scales associated with the removal of landslide sediment by rivers following earthquakes however, is still lacking. Here, we propose a nested numerical approach to investigate the processes controlling the post-seismic sediment evacuation at the mountain range scale, informed by results from a reach scale model. First, we explore the river morphodynamic response to a landslide cascade at the reach-scale using a 2D modelling approach. The results are then used to describe empirically the evacuation of a landslide volume which avoids using a computationally extensive model in catchments which may have thousands of co-seismic landslides. Second, we propose a reduced-complexity model to quantify evacuation times of earthquake-triggered landslide clusters at the scale of a mountain range, examining the hypothetical case of a M w 7.9 earthquake and its aftershocks occurring on the Alpine Fault, New Zealand. Our approach combines an empirical description of co-seismic landslide clusters with the sediment export processes involved during the post-seismic phase. Our results show that the inter-seismic capacity of the mountain range to evacuate co-seismic sediment is critical to assess the sediment budget of large earthquakes, over one to several seismic cycles. We show that sediment evacuation is controlled by two timescales, 1. the transfer time of material from hillslopes to channels and 2. the evacuation time of the landslide deposits once it has reached the fluvial network. In turn, post-seismic sediment evacuation can either be connectivity-limited, when sediment delivery along hillslopes is the main limiting process, or transport-limited, when the transport by rivers is the limiting process. Despite high values of runoff, we suggest that the Southern Alps of New Zealand are likely to be in connectivity-limited conditions, for connection velocities <10 m.yr−1. Connection velocities >2 m.yr−1 are sufficient to allow most of co-seismic sediments to be mobilised and potentially exported out of the range within less than one seismic cycle. Because of the poorly-constrained rate of sediment transfer along hillslopes, our results potentially raise the issue of co-seismic sediment accumulation within mountain ranges over several seismic cycles and of the imbalance between tectonic inputs and sediment export. We, therefore, call for renewed observational efforts to better describe and quantify the physical processes responsible for the redistribution and mobilization of sediment from landslide scars and deposits. [ABSTRACT FROM AUTHOR]

Abstract: The concentration of 10Be in detrital quartz (10Beqtz) from river sediments is now widely used to quantify catchment-wide denudation rates but may also be sensitive to inputs from bedrock landslides that deliver sediment with low 10Beqtz. Major landslide-triggering events can provide large amounts of low-concentration material to rivers in mountain catchments, but changes in river sediment 10Beqtz due to such events have not yet been measured directly. Here we examine the impact of widespread landslides triggered by the 2008 Wenchuan earthquake on 10Beqtz in sediment samples from the Min Jiang river basin, in Sichuan, China. Landslide deposit material associated with the Wenchuan earthquake has consistently lower 10Beqtz than in river sediment prior to the earthquake. River sediment 10Beqtz decreased significantly following the earthquake downstream of areas of high coseismic landslide occurrence (i.e., with greater than ∼0.3% of the upstream catchment area affected by landslides), because of input of the 10Be-depleted landslide material, but showed no systematic changes where landslide occurrence was low. Changes in river sediment 10Beqtz concentration were largest in small first-order catchments but were still significant in large river basins with areas of . Spatial and temporal variability in river sediment 10Beqtz has important implications for inferring representative denudation rates in tectonically active, landslide-dominated environments, even in large basins. Although the dilution of 10Beqtz in river sediment by landslide inputs may complicate interpretation of denudation rates, it also may provide a possible opportunity to track the transport of landslide sediment. The associated uncertainties are large, but in the Wenchuan case, calculations based on 10Be mixing proportions suggest that river sediment fluxes in the 2–3 years following the earthquake increased by a similar order of magnitude in the 0.25–1 mm and the <0.25 mm size fractions, as determined from 10Beqtz mixing calculations and hydrological gauging, respectively. Such information could provide new insight into sediment transfer, with implications for secondary sediment-related hazards and for understanding the removal of mass from mountains. [Copyright &y& Elsevier]