Landslides, bedrock incision and human-induced environmental changes in an extremely rapidly formed tropical river gorge

Toussaint Mugaruka Bibentyo, Antoine Dille, Arthur Depicker, Benoît Smets, Matthias Vanmaercke, Charles Nzolang, Stijn Dewaele, Olivier Dewitte

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)

Abstract

Landslides are hillslope processes controlled by natural changing topographic conditions. Landslides are also influenced by human activities. Yet, understanding the space-time occurrence of landslides and their interactions with these typically long-term natural and short-term human-induced controls remains a key challenge in many regions, especially in tropical environments where data scarcity is commonplace. Here we decipher these dynamic processes in the Ruzizi Gorge located in the Kivu Rift (Central Africa), that is an exceptional geomorphological landmark whose origin is associated with the rerouting of >7000 km2 of drainage area from Lake Kivu during the Holocene. This bedrock river has also seen its landscape disturbed over the past decades by the development of the city of Bukavu (DR Congo). In this study, we combine detailed field observations, historical aerial photographs, archive analysis and satellite imagery to compile a multi-temporal inventory of 385 landslides and constrain their dynamics. We show that extremely high incision rates during the early stage of the formation of the gorge explain the space-time clustering of thousand-year-old large (up to ∼2 km2) landslides, independently from the lithological context. These landslides are currently non-active and poorly eroded. Their deposit areas partly cover the riverbed with boulders, armouring the channel and inhibiting further incision. The landslides that occurred over the last 60 years are shallower slope failures of smaller size and higher mobility. They tend to disappear rather quickly from the landscape, sometimes within a few years. Their distribution is primarily controlled by threshold slopes, lithology, and the past large landslides, the influence of the land use being less pronounced. Overall, the sediment mobilization rates associated with these high frequency landslides significantly outpace the extreme landslide erosion pulse associated with the gorge formation. Our results provide insight on interactions between channel-hillslope coupling and feedbacks among landslide processes and river gorge formation in a unique environment.

Original languageEnglish
Article number109046
Number of pages20
JournalGeomorphology
Volume449
DOIs
Publication statusPublished - 15 Mar 2024

Bibliographical note

Funding Information:
This research received financial support from the Directorate-General Development Cooperation and Humanitarian Aid of Belgium through the HARISSA (Natural Hazards, RISks and Society in Africa: developing knowledge and capacities; RMCA–DGD 2019–2024; https://georiska.africamuseum.be/en/activities/harissa, last accessed: 24 February 2023) project funded by Development Cooperation program of the Royal Museum for Central Africa. The research also benefited from the Belgian Science Policy Office (BELSPO) through the RESIST (Remote Sensing and In Situ Detection and Tracking of Geohazards; BELSPO STEREO III programme, contract no. SR/00/305) project, the MODUS (A Multi-sensOr approach to characterize ground Displacements in Urban Sprawling contexts; BELSPO STEREO III programme contract no. SR/00/358) project and the PAStECA (Historical Aerial Photographs and Archives to Assess Environmental Changes in Central Africa; BELSPO BRAIN-be programme, contract no. BR/165/A3/PASTECA) project. We thank Guy Ilombe Mawe and Espoir Mugisho Birhenjira from the Université Officielle de Bukavu for their support in the field. A special thank goes to François Kervyn for his support. Three anonymous reviewers and the editor are also gratefully acknowledged.

Funding Information:
This research received financial support from the Directorate-General Development Cooperation and Humanitarian Aid of Belgium through the HARISSA (Natural Hazards, RISks and Society in Africa: developing knowledge and capacities; RMCA–DGD 2019–2024; https://georiska.africamuseum.be/en/activities/harissa , last accessed: 24 February 2023) project funded by Development Cooperation program of the Royal Museum for Central Africa. The research also benefited from the Belgian Science Policy Office (BELSPO) through the RESIST (Remote Sensing and In Situ Detection and Tracking of Geohazards; BELSPO STEREO III programme, contract no. SR/00/305) project, the MODUS (A Multi-sensOr approach to characterize ground Displacements in Urban Sprawling contexts; BELSPO STEREO III programme contract no. SR/00/358) project and the PAStECA (Historical Aerial Photographs and Archives to Assess Environmental Changes in Central Africa; BELSPO BRAIN-be programme, contract no. BR/165/A3/PASTECA) project. We thank Guy Ilombe Mawe and Espoir Mugisho Birhenjira from the Université Officielle de Bukavu for their support in the field. A special thank goes to François Kervyn for his support. Three anonymous reviewers and the editor are also gratefully acknowledged.

Publisher Copyright:
© 2024 Elsevier B.V.

Keywords

  • Boulders
  • Channel-hillslope coupling
  • Landscape dynamics
  • Landslide inventory
  • River incision
  • Weathering

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