Chemical weathering in active mountain belts controlled by stochastic bedrock landsliding

Abstract

In active mountain belts, erosion is driven by bedrock landsliding. River water chemistry in New Zealand’s Southern Alps suggests that stochastic mass wasting processes also enhance chemical weathering in such environments. A link between chemical weathering and physical erosion exists at the catchment scale over a wide range of erosion rates1,2. However, in mountain environments, where erosion rates are highest, weathering may be kinetically limited3,4,5 and therefore decoupled from erosion. In active mountain belts, erosion is driven by bedrock landsliding6 at rates that depend strongly on the occurrence of extreme rainfall or seismicity7. Although landslides affect only a small proportion of the landscape, bedrock landsliding can promote the collection and slow percolation of surface runoff in highly fragmented rock debris and create favourable conditions for weathering. Here we show from analysis of surface water chemistry in the Southern Alps of New Zealand that weathering in bedrock landslides controls the variability in solute load of these mountain rivers. We find that systematic patterns in surface water chemistry are strongly associated with landslide occurrence at scales from a single hillslope to an entire mountain belt, and that landslides boost weathering rates and river solute loads over decades. We conclude that landslides couple erosion and weathering in fast-eroding uplands and, thus, mountain weathering is a stochastic process that is sensitive to climatic and tectonic controls on mass wasting processes.