Constraining landslide timing in a data-scarce context: from recent to very old processes in the tropical environment of the North Tanganyika-Kivu Rift region

Dewitte, Olivier; Dille, Antoine; Depicker, Arthur; Kubwimana, Désiré; Mateso, Jean-Claude Maki; Bibentyo, Toussaint Mugaruka; Uwihirwe, Judith; Monsieurs, Elise

doi:10.1007/s10346-020-01452-0

Cited by 28 publications

(66 citation statements)

References 107 publications

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“…In addition , it must be noted that the estimated erosion rate due to shallow landsliding is most likely an underestimation. First, we did not observe earthquakeinduced landslide events, which are rare but may lead to catastrophic landslide erosion (Marc et al, 2015;Dewitte et al, 2020). Second, the landslide inventory used to calculate the erosion rate is incomplete due to limitations in © Google Earth coverage.…”

Section: A New Approach For Calculating Landslides Erosion Rates?mentioning

confidence: 94%

“…There are not enough observations to make two separate consistent plots for rejuvenated and relict landscapes (Fig. A1) triggering earthquakes occurred (Dewitte et al, 2020). The absence of such events suggests that our window of observation is too short to capture the direct impact of large earthquakes on landslide erosion within the rejuvenated NTK Rift.…”

Section: Interactions Between Deforestation Rejuvenation and Landslmentioning

confidence: 96%

“…The majority of observed recent shallow landslides in the NTK Rift are rainfall-triggered (Monsieurs et al, 2018a;Depicker et al, 2020;Dewitte et al, 2020). To explore any relationship between rejuvenation and rainfall, we analyze two metrics: the average annual rainfall and the number of times where accumulated rainfall was sufficiently large to trigger landsliding.…”

Section: Rainfallmentioning

confidence: 99%

“…Deforestation, mainly driven by agriculture, is widespread and a result of the fastgrowing population (from 89 inhabitants per km 2 in 1975 to 241 inhabitants per km 2 in 2015) (Hansen et al, 2013;JRC and CIESIN, 2015;Musumba Teso et al, 2019). Furthermore, the area is characterized by frequent landsliding, mostly triggered by rainfall (Monsieurs et al, 2018a;Depicker et al, 2020;Dewitte et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

“…2 mm/yr (Saria et al, 2014). Due to this setting, there is widespread seismic activity, active volcanism, and uplift initiating landscape rejuvenation through knickpoint retreat (Smets et al, 2015;Delvaux et al, 2017;Dewitte et al, 2020). Adding to the geological complexity of the NTK Rift is the wide variability in age and strength of rock formations.…”

Section: Introductionmentioning

confidence: 99%

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Interactions between deforestation, landscape rejuvenation, and shallow landslides in the North Tanganyika – Kivu Rift region, Africa

Depicker¹,

Govers²,

Jacobs³

et al. 2020

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Abstract. Deforestation increases landslide activity over short, contemporary timescales. However, over longer timescales the location and timing of landsliding is controlled by the interaction between uplift and fluvial incision. Yet, the interaction between (human-induced) deforestation and landscape evolution has hitherto not been explicitly considered. We address this issue in the North Tanganyika-Kivu Rift region (East African Rift). In recent decades, the regional population has grown exponentially and the associated expansion of cultivated and urban land has resulted in widespread deforestation. On a much longer time scale, tectonic uplift has forged two parallel mountainous Rift shoulders that are continuously rejuvenated through knickpoint retreat, enforcing topographic steepening. In order to link deforestation and rejuvenation to landslide erosion, we compiled an inventory of nearly 8,000 recent shallow landslides in Google Earth© imagery from 2000–2019. To accurately calculate landslide erosion rates, we developed a new methodology to remediate inventory biases linked to the spatial and temporal inconsistency of this satellite imagery. We find that erosion rates in rejuvenated landscapes are roughly 40 % higher than in the surrounding relict landscapes, upstream of retreating knickpoints and outside of the Rift shoulders. This difference is due to the generally steeper relief in rejuvenated landscapes which more than compensates for the fact that rejuvenated slopes, when compared to similarly angled slopes in relict zones, often display a somewhat lower landslide erosion rate. These lower rates in the rejuvenated landscapes could be the result of a drier climate, the omission of earthquake-induced landslide events in our landslide inventory, and potentially a smaller regolith stock. More frequent extreme rainfall events in the relict zones, and possibly the presence of a thicker regolith, cause a stronger landslide response to deforestation compared to rejuvenated landscapes. Overall, deforestation initiates a landslide peak that lasts approximately 15 years and increases landslide erosion by a factor 2 to 8. Eventually, landslide erosion in deforested land falls back to a level similar to that observed under forest conditions, most likely due to the depletion of the most unstable regolith. Landslides are not only more abundant in rejuvenated landscapes but are also smaller in size, which may be a consequence of the seismic activity that fractures the bedrock and reduces the minimal critical area for slope failure. With this paper, we highlight the importance of considering the geomorphological context when studying the impact of recent land use changes on landslide activity.

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Section: A New Approach For Calculating Landslides Erosion Rates?mentioning

confidence: 94%

Section: Interactions Between Deforestation Rejuvenation and Landslmentioning

confidence: 96%