Spatial patterns of landslides in a modest topography of the Ozark and Ouachita Mountains, USA

Abstract

Controls on landslides vary as a function of landscape and regional activity. For example, low-relief, woodland regions have slope gradients, soil types, and substrate lithologies that contrast with steeper mountainous regions prone to rock fall and debris flows. Similarly, regional variations in precipitation, earthquakes, and other impacts on landslide surfaces create regional variations in landslide properties. While the controls on landslide characteristics have been extensively studied for high-relief coastal and tectonically active regions, controls on low-relief landslides have received comparatively less attention. We focus here on a part of the Ozark and Ouachita Mountains in the US southern mid-continent to explore such characteristics of landslides and potential controls in low-relief regions. The area exhibits frequent landslides in soil-covered low-relief forested hillslopes. We evaluated the frequency-size scaling of landslides occurred during periods of different earthquake frequency and precipitation amount (pre- and post-2005). We also produced maps of landslide susceptibility based on random forest machine learning applied to remotely sensed data. We found that landslides are clustered mostly in upland hillslopes, and that small landslides dominate the area, quantified by a landslide frequency-size distribution fitting a double Pareto curve. Additionally, the overall landslide frequency, and potentially the porportion of smaller landslides relative to the larger ones, significantly increased after 2005, the period during which the area also experienced increased induced seismicity and extreme storm events. Approximately 94 % of historical landslides were within random-forest-classified high-landslide probability (probability > 0.5) zones, coinciding with moderate to steep (18° ± 9°) and convergent upland slopes underlain by shale and sandstone. Anomalously high frequency landslides appear to result from triggering by extreme weather, human-induced earthquake activity, and human-induced hillslope modification.