Numerical and analytical models of cosmogenic radionuclide dynamics in landslide‐dominated drainage basins

Abstract

[1] In many tectonically active regions on Earth, landslides dominate sediment delivery to channels. While cosmogenic radionuclides (CRN) represent a valuable tool to document basin-averaged erosion rates, a better understanding of CRN dynamics in these systems is required before erosion rates can be reliably inferred from CRN concentrations. The stochastic nature of landslides results in variability of CRN concentrations in both alluvial and hillslope samples that is both difficult to document and poorly understood. To guide sampling strategies, we developed a 2-D plan view model to simulate the influence of landslides on CRN dynamics. We employ a sediment mixing model, in which concentrations of CRNs from material eroded by both landslides and steady processes are combined to evaluate how best to infer erosion rates from CRN concentrations. This model is further used to test a new analytical solution for the distribution of CRN concentrations on hillslopes in a landslide-prone system. Results suggest that for landscapes dominated by deep (>5 m) landslides, only large drainage basins (!100 km 2 ) provide consistently reliable estimates of erosion rates from CRN concentrations. For landscapes dominated by shallow landslides (0.7-2 m), smaller basins can produce reliable estimates. Results further suggest that the distribution of concentrations from hillslope samples could be used to deduce the relative contribution of material derived from landslide and steady processes. These findings underscore the need to consider carefully the sources of natural variability in sampling and analyzing CRNs; if properly done, the variability can reveal useful information about geomorphic processes in landslide-prone areas.Citation: Yanites, B. J., G. E. Tucker, and R. S. Anderson (2009), Numerical and analytical models of cosmogenic radionuclide dynamics in landslide-dominated drainage basins,

Cosmogenic nuclide budgeting of floodplain sediment transfer

“…Our approach differs considerably from the way Yanites et al (2009) assess the effect of storage of land slide-derived material in a river basin. In their model, Yanites et al (2009) consider the effects of sediment storage on cosmogenic 10 Be nuclide concentrations in erosional settings, where landslide material is usually prone to storage before it is removed by rivers and in the process is mixed with material from source area erosion processes.…”

“…In their model, Yanites et al (2009) consider the effects of sediment storage on cosmogenic 10 Be nuclide concentrations in erosional settings, where landslide material is usually prone to storage before it is removed by rivers and in the process is mixed with material from source area erosion processes. In contrast to the Yanites et al study, which addresses storage effects near the sediment source in very small catchments, the focus of our analysis is on sediment reworking by lateral channel migration.…”

Cosmogenic nuclide‐derived rates of diffusive and episodic erosion in the glacially sculpted upper Rhone Valley, Swiss Alps

“…These estimates are subject to large uncertainty due in part to the narrow grain size range investigated here. Many authors (Brown et al, 1995;Belmont et al, 2008;Niemi et al, 2005) have suggested that stochastic processes such as the large-scale rockfalls and debris flows produce different grain size distributions and potentially different cosmogenic nuclide concentrations than in creep-dominated landscapes (Yanites et al, 2009). However, the large difference between the denudation rates recorded for the landslide dominated basins vs. the soil creep dominated basins suggests that our grain size fractions do include this signal.…”

“…Finally, modern landslides in the Goms occur within the thin soil mantled zone. Therefore, the perturbations to denudation rates due to the occurrence of deep-seated landslides should not be a significant factor here (Niemi et al, 2005;Yanites et al, 2009).…”

<sup>10</sup>Be systematics in the Tsangpo-Brahmaputra catchment: the cosmogenic nuclide legacy of the eastern Himalayan syntaxis

“…However, it is also increasingly recognized that CWDRs are affected by a number of site-specific biases and limitations that prevent us from simply reading denudation rates from a bag of sand. Amongst others, landsliding, a dominant erosion process in actively eroding landscapes, violates the steadystate denudation assumption and may thus lead to biases in the CWDR (Niemi et al, 2005;Yanites et al, 2009). The stochastic nature of sediment supply to the channels and hydrology within the river network may also perturb the TCN signal over a range of timescales and limits our ability to use a single sediment sample as a representative and accurate representative of upstream erosion products (Kober et al, 2012;Lupker et al, 2012;West et al, 2014;Foster and Anderson, 2016).…”