Temperature fluctuations controlled episodic rockfall activity in the Rwenzori Mountains (Uganda) during the Holocene

Abstract

Rockfalls and other gravitational mass movements are expected to become more frequent under ongoing global warming in temperate and cold mountainous regions. Tropical mountain ranges that have experienced past climatic warming, such as the Rwenzori Mountains (Uganda), provide natural laboratories for studying slope stability under warm and humid conditions. However, although rockfalls are frequently observed in these environments, their controls and evolution through Holocene climatic changes remain poorly understood. We used ¹⁰Be surface exposure dating to establish a chronology for seven rockfall deposits in the Rwenzori Mountains and assess the climatic conditions associated with slope destabilisation. The ¹⁰Be ages range from 13.6 ± 0.9 ka to 1.0 ± 0.1 ka and cluster into three distinct periods: 11–9 ka, 7–5 ka and ~2 ka. These periods correspond to local temperature fluctuations, suggesting that rockfalls occurred episodically in response to Holocene temperature variations. Early Holocene rockfall activity (~11–9 ka) likely reflects enhanced mechanical weathering and fracture propagation because of glacier retreat and freeze–thaw cycles. In contrast, mid-Holocene (7–5 ka) and late Holocene (~2 ka) rockfall activities coincide with warmer conditions that promoted chemical and biological weathering, fracture propagation and slope destabilisation. These results highlight the role of temperature as a key climatic control on progressive rock failure mechanisms in the Rwenzori Mountains. Rising temperatures enhance chemical and biological weathering, promoting slope destabilisation and rockfall activity in tropical mountain environments.