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The risk of reactivated ancient landslides in the Sichuan–Tibet transportation corridor in China is significantly increasing, primarily driven by the intensification of engineering activities and the increased frequency of extreme weather events. This escalation has resulted in a considerable number of fatalities and extensive damage to critical engineering infrastructure. However, the factors contributing to the reactivation and modes of destruction of ancient landslides remain unknown. Therefore, it is imperative to systematically analyze the developmental characteristics and failure modes of reactivated ancient landslides to effectively mitigate disaster risks. Based on a combination of data collection, remote sensing interpretation, and field investigations, we delineated the developmental attributes of typical ancient landslides within the study area. These attributes encompass morphological and topographic aspects, material composition, and spatial structure of ancient landslides. Subsequently, we identified the key triggers for the reactivation of ancient landslides, including water infiltration, reservoir hydrodynamics, slope erosion, and excavation, by analyzing representative cases in the study area. Reactivation of ancient landslides is sometimes the result of the cumulative effects of multiple predisposing factors. Furthermore, our investigations revealed that the reactivation of these ancient landslides primarily led to local failures. However, over extended periods of dynamic action, the entire zone may experience gradual creep. We categorized the reactivation modes of ancient landslides into three distinct types based on the reactivation sequences: progressive retreat, backward thrusting, and forward pulling–backward thrusting. This study is of great significance for us to identify ancient landslides, deepen our understanding of the failure modes and risks of reactivated ancient landslides on the eastern margin of the Tibetan Plateau, and formulate effective disaster prevention and mitigation measures. [ABSTRACT FROM AUTHOR]

Toxic and major elements, such as As and Fe, in watersheds can significantly impact the surrounding water environment and ecosystem. Thus, in this study, we conducted an investigation into the origins and spatial distribution of typical toxic trace elements (As and Mn) and crustal major elements (Al, Fe, and Ti) in suspended particulate matter (SPM) across various glacial watersheds located at different elevations in the northeastern Tibetan Plateau (NETP) from June to July in 2017. The results revealed that the mean value of each element followed the order of abundance in the samples, with Al having the highest mean value at 21307 µg/L, followed by Fe at 13366 µg/L, Ti at 1520 µg/L, Mn at 245 µg/L, and As at 66.6 µg/L. Moreover, our study identified high content of these elements from the Dabanshan Snowpack, Laohugou Glacier No.12, and Yuzhufeng Glacier in the upper reaches of the basin, which were found to be 9.9, 10.2, and 19.4 times higher, respectively, than that of the upper reaches of the Heihe River. We found that As and Mn exhibited clear indications of anthropogenic influence on a local and regional scale. The calculated enrichment factor (EF) demonstrated a significant As enrichment (EF>100) in the Qiyi and Lenglongling Glaciers, possibly resulting in the release of upstream glacier melt and anthropogenic-derived As deposition. Our findings suggested that the upstream region was primarily linked to glacier meltwater discharge. In contrast, the middle and lower reaches of the basin exhibited a more pronounced influence from local human activities. Based on the findings, the water environment of the glacier watershed appears to be in good condition overall. However, the presence of elevated levels of As element in the water system can be traced back to both anthropogenic and natural factors. As a result, ensuring the safety of the water supply for nearby residents is a matter of utmost concern. This study provides a comprehensive examination of hydrochemical variations and the overall water environment of high-altitude glacier basins in the NETP, offering valuable insights into the topic. [Display omitted] • Elemental concentration indicated a increasing trend in HG, LG, and QG basins, while in DS, LG12, and YG inverse. • As was significantly enriched, probably affected by regional coal combustion and other anthropogenic sources. • Relationship between elemental composition and various sources in upstream and downstream were very different. [ABSTRACT FROM AUTHOR]