Climate-driven rockfall activity over the last 10 ka in the Rwenzori Mountains (Uganda): Insights from 10Be dating

Constraining the timing of landslides is crucial for deciphering their triggering mechanisms. Recent years have seen a high number of landslides in tropical regions emphasizing the need to explore the links between climate and slope instability over longer timescales. While considerable data exists for alpine, arctic, and arid regions, limited preservation of geomorphological features accounts for the lack of data in tropical environments (e.g., Pánek, 2019). The Rwenzori Mountains in Uganda offer a natural laboratory for such a study. The upper part of the range features multiple rockfall deposits that disrupt the glacially sculpted landscape, while the lower elevations are characterized by recent debris flows and active landslides. However, no chronological data currently exist for the major rockfall deposits in the Rwenzori Mountains. To address this gap, we used in-situ produced ¹⁰Be dating to establish the chronology for seven individual rockfall deposits. The concentrations of ¹⁰Be are relatively consistent, ranging from 1.61 ± 0.11 × 10⁴ to 2.96 ± 0.08 × 10⁵ atoms per gram of quartz. The resulting ¹⁰Be ages range from 0.8 ± 0.1 ka to 9.2 ± 0.6 ka, clustering during three distinct periods: 9–8 ka, 6–4.5 ka, and 2–1 ka. The 9–8 ka and 6–4.5 ka clusters correspond to periods of enhanced precipitation during the African Humid Period (~10–5 ka; Mason et al., 2024). They specifically align with the onset of warmer temperatures and a temperature optimum based on local lake records (Garelick et al., 2022). The more recent cluster (2–1 ka) aligns with a brief temperature increase (Garelick et al., 2022). These findings suggest that increased temperatures and precipitation create favourable conditions for triggering rockfall in the Rwenzori Mountains, highlighting the interplay between climate and slope instability in tropical glacial landscapes.