Abstract
Abstract. In this study, we assess the geomorphic role of a rare, large-magnitude landslide-triggering event and consider its effect on mountain forest ecosystems and the erosion of organic carbon in an Andean river catchment. Proximal triggers such as large rain storms are known to cause large numbers of landslides, but the relative effects of such low-frequency, high-magnitude events are not well known in the context of more regular, smaller events. We develop a 25-year duration, annual-resolution landslide inventory by mapping landslide occurrence in the Kosñipata Valley, Peru, from 1988 to 2012 using Landsat, QuickBird, and WorldView satellite images. Catchment-wide landslide rates were high, averaging 0.076 % yr−1 by area. As a result, landslides on average completely turn over hillslopes every ∼ 1320 years, although our data suggest that landslide occurrence varies spatially and temporally, such that turnover times are likely to be non-uniform. In total, landslides stripped 26 ± 4 tC km−2 yr−1 of organic carbon from soil (80 %) and vegetation (20 %) during the study period. A single rain storm in March 2010 accounted for 27 % of all landslide area observed during the 25-year study and accounted for 26 % of the landslide-associated organic carbon flux. An approximately linear magnitude–frequency relationship for annual landslide areas suggests that large storms contribute an equivalent landslide failure area to the sum of lower-frequency landslide events occurring over the same period. However, the spatial distribution of landslides associated with the 2010 storm is distinct. On the basis of precipitation statistics and landscape morphology, we hypothesise that focusing of storm-triggered landslide erosion at lower elevations in the Kosñipata catchment may be characteristic of longer-term patterns. These patterns may have implications for the source and composition of sediments and organic material supplied to river systems of the Amazon Basin, and, through focusing of regular ecological disturbance, for the species composition of forested ecosystems in the region.
Highlights
We evaluate the spatial distribution of landslides with respect to catchment topography and climatic factors that may act as potential longer-term forcing on the location of most active landslide erosion
Landsat images were processed with a standard terrain correction which consists of systematic radiometric and geometric processing using ground control points and a digital elevation model (DEM) for ortho-georectification (USGS, 2013b)
When considering carbon budgets at the landscape scale, the landslide-associated carbon fluxes we report here should be viewed in the context that other processes such as soil creep may contribute to the transfer of carbon from hillslopes to rivers (e.g. Yoo et al, 2005)
Summary
Landslides are major agents of topographic evolution (e.g. Li et al, 2014; Egholm et al, 2013; Ekström and Stark, 2013; Larsen and Montgomery, 2012; Roering et al, 2005; Hovius et al, 1997) and are increasingly recognised for their important biogeochemical and ecological role in mountainous environments because they drive erosion of carbon and nutrients (Pepin et al, 2013; Ramos Scharrón et al, 2012; Hilton et al, 2011; West et al, 2011; Stallard, 1985) and introduce regular cycles of disturbance to ecosystems (Restrepo et al, 2009; Bussmann et al, 2008). Landslides result when slope angles reach a failure threshold (Burbank et al, 1996; Schmidt and Montgomery, 1995; Selby, 1993), which is thought to occur in mountains as rivers incise their channels, leaving steepened hillslopes (Montgomery, 2001; Gilbert, 1877). Incision is climatically regulated (Ferrier et al, 2013), providing a mechanism connecting storm activity, erosion, and topographic evolution (e.g. Bilderback et al, 2015), and further linking to organic carbon removal from hillslopes and ecological processes across landscapes
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