Linking Landslide Patterns to Transient Landscapes in the Northern Colombian Andes

Abstract

Landslides are among the most recognizable evidence of hillslope erosion in tectonically active mountains. Yet, how much of the distribution of landslides of different ages relates to, or is inherited from, the pattern of topographic metrics of landscape evolution remains partially unresolved, and especially so in tropical areas. We derive such metrics for 650 catchments of ${10}^1$-${10}^2$ ${\text{km}}^2$ in size, including their mean hypsometric integral, local relief, geological lineament density, and steepness variations and knickpoint density of river channels as proxies of tectonic activity. We test how these proxies match with, if not explain, the distribution of some 14,000 prehistoric and modern landslides in the northern Colombian Andes. A $K$-means cluster analysis of catchment hypsometry reveals four distinct groups of catchments. We interpret these groups to reflect different states of transience with clear contrasts in mean local relief, average hillslope inclination, channel steepness, and landslide density. We propose that tectonic uplift, base-level changes, and passing waves of incision control these different states of transience. Yet, we find that landslides occur widely without much spatial association to, or amassing near, major channel knickpoints. This observation reflects what we would expect from a threshold landscape in which landslides abound irrespective of contrasts in local river incision rates. Still, we notice a pronounced amassing of landslides near transient divides, where prehistoric landslides are preferentially preserved. In summary, we infer that, in our study area at least, differences in catchment hypsometry might be more useful to track potential tectonic controls on landslide patterns than comparing these to knickpoint distributions or channel metrics.