Ancient very large and giant landslides on the eastern margin of the Qinghai–Tibet Plateau, China

Abstract

The migration of massifs on the eastern margin of the Qinghai–Tibet Plateau (QTP) in the middle to late Cenozoic and the collision with stable blocks on the northwestern margin of the Yangtze Plate governed the rapid rock uplift and erosion of local surfaces, leading to the widespread occurrence of various types of large-scale landslides. An anomalously high concentration of very large and giant landslides (VLGLs) is found around the Bailongjiang block on the eastern margin of the QTP. While these landslides are commonly attributed to active faults, the diversity of landslide types and complex spatial relationships prompt further investigation into the tectonic mechanisms influencing their formation and evolution. In this study, we identify and validate 140 ancient VLGLs, each with an area ≥ 1 km², in the Bailong River Basin. We analyse the spatial distributions, geomorphological characteristics, and necessary controlling and triggering factors of various landslide types in the region. On the basis of limited chronological data, we infer potential periods of landslide formation by examining these controlling and triggering conditions. The results suggest that the primary driver of VLGLs development was the collision between the Bailongjiang block and the Bikou massif. Earthflows along the eastern margin of the Bailongjiang block are influenced mainly by faults, lithology, uplift, and river downcutting and are induced by rainfalls. The current landslide landscapes likely formed during the last interglacial period, following the onset of the Gonghe movement. The southern margin of the Bailongjiang block is characterized by compression uplift and degradation of the rock mass strength, and earthquakes act as triggers for debris slides. The coupling of these three factors indicates the potential for periodic patterns in landslide development within this region.