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Characteristics and causes of natural and human-induced landslides in a tropical mountainous region: the rift flank west of Lake Kivu (Democratic Republic of the Congo)
Get PDFTropical mountainous regions are often identified as landslide hotspots with growing population pressure. Anthropogenic factors are assumed to play a role in the occurrence of landslides in these densely populated regions, yet the relative importance of these human-induced factors remains poorly documented. In this work, we aim to explore the impact of forest cover dynamics, roads and mining activities on the characteristics and causes of landslides in the rift flank west of Lake Kivu in the Democratic Republic of the Congo (DR Congo). To do so, we compile a comprehensive multi-temporal inventory of 2730 landslides. The landslides are of different types and are grouped into five categories that are adapted to study the impact of human activities on slope stability: old (pre-1950s) and recent (post-1950s) deep-seated landslides, shallow landslides, landslides associated with mining and landslides associated with road construction. We analyse the landslides according to this classification protocol via frequency area statistics, frequency ratio distribution and logistic regression susceptibility assessment. We find that natural factors contributing to the cause of recent and old deep-seated landslides were either different or changed over time. Under similar topographic conditions, shallow landslides are more frequent, but of a smaller size, in areas where deforestation has occurred since the 1950s. We attribute this size reduction to the decrease in regolith cohesion due to forest loss, which allows for a smaller minimum critical area for landsliding. In areas that were already deforested in the 1950s, shallow landslides are less frequent, larger and occur on less steep slopes. This suggests a combined role between regolith availability and soil management practices that influence erosion and water infiltration. Mining activities increase the odds of landsliding. Landslides associated with mining and roads are larger than shallow landslides but smaller than the recent deep-seated instabilities, and they are controlled by environmental factors that are not present under natural conditions. Our analysis demonstrates the role of human activities on the occurrence of landslides in the Lake Kivu region. Overall, it highlights the need to consider this context when studying hillslope instability characteristics and distribution patterns in regions under anthropogenic pressure. Our work also highlights the importance of using landslide classification criteria adapted to the context of the Anthropocene
A Microphysics Model of Multicomponent Venus' Clouds With a High-Accuracy Condensation Scheme
Get PDFAccurate modeling of the Venusian cloud structure remains challenging due to its complex microphysical properties. Condensation primarily determines the cloud particle size distribution within the various cloud layers. However, existing Venus microphysics models mainly use a full-stationary bin scheme, which may be prone to numerical diffusion during condensation. To address this, we developed a new microphysics model, the Simulator of Particle Evolution, Composition, and Kinetics (SPECK), which incorporates a moving-center bin scheme designed to minimize numerical diffusion. Furthermore, SPECK can accommodate any number of size distributions with multiple components, enabling versatile applications for more complex cloud systems. The 0-D simulations demonstrated that this microphysics framework is a reliable tool for modeling cloud microphysics under Venusian atmospheric conditions, particularly in capturing condensation and evaporation processes. We further validated SPECK against recent Venus microphysics models in 1-D simulations. The moving-center scheme is shown to exhibit less numerical diffusion compared to an existing model based on a full-stationary bin scheme, allowing for more accurate calculations of microphysical processes. Furthermore, SPECK reproduces the cloud structure observed by the Pioneer Venus Large Probe, using the same computational settings adopted in the latest microphysical model study. Thanks to the suppressed numerical diffusion, SPECK achieves high accuracy at half the typical resolution while reducing computational time sixfold, making it a promising tool for future 3-D modeling. This microphysics framework will be useful for the upcoming EnVision mission and is applicable to other planetary atmospheres, including those of Mars, Titan, gas giants, and exoplanets
Du nouveau à propos de la typo-chronologie des charpentes médiévales en région Bruxelles-Capitale (RBC)
No full textComparative study of the body proportions in Elephantidae and other large herbivorous mammals
No full textIn this study, we aimed to achieve three objectives: (1) to precisely characterize the body plans of Elephantidae and other large herbivorous mammals; (2) based on this analysis, to determine whether the body plans of the extinct woolly mammoth (Mammuthus primigenius) and steppe mammoth (M. trogontherii) differ from those of modern-day Elephantidae: the Asian elephant (Elephas maximus), the African bush (Loxodonta africana), and forest (L. cyclotis) elephants; (3) to analyze how the body plans have changed in extant perissodactyls and proboscideans compared with their Paleogene ancestors. To accomplish this, we studied mammoth skeletons from the collections of Russian museums and compared this data with a large number of skeletons of extant elephantids, odd-toed, and even-toed ungulates, as well as their extinct relatives. We showed that three genera of Elephantidae are characterized by a homogeneous body plan, which is markedly different from other large herbivores. Elephantids break the interrelationship, that exists in artiodactyls and perissodactyls, between the total length of the head and neck on one side and the limb's segments on the other. Their limbs are very tall (inferior in this regard among large ungulates only to the giraffe), and, contrary to the other large herbivorous mammals, elongated due to the length of the proximal segments. This allows them to effectively utilize the principle of inverted pendulum (straight-legged walking) in locomotion. The biggest differences in the body plan of mammoths compared with extant elephants are a markedly larger pelvis, elongated fore- and hindlimbs (due to the increased relative length of their proximal segments), and different proportions of the skull. The body plans of plesiomorphic Paleogene proboscideans and perissodactyls differed markedly from their descendants in every body part; these differences are related, on the one hand, to the allometric growth, and on the other hand, to the advancement of the locomotor apparatus in the course of their evolution. The most notable difference in the body plan between Paleogene proboscidean Moeritherium and extant Elephantidae is the ~2-fold increase in relative limb height
Technical Expertise Report ref. exp-114, 18/6/2015 - Applicant: Lesley Bone, Fine Arts Museum of San Francisco, Golden Gate Park, 50 Hagiwara Tea Garden Drive, San Francisco CA 94118, USA, 16/3/2015
No full textA regenerated chelicera in an African tarantula, <i>Anoploscelus lesserti</i> Laurent, 1946 (Araneae: Theraphosidae)
Get PDFAn adult male of Anoploscelus lesserti Laurent, 1946 from Burundi, deposited in the Royal Museum for Central Africa (RMCA) with a regenerated right chelicera is illustrated and discussed. Simultaneously, this constitutes the first record of the genus Anoploscelus Pocock, 1897 for Burundi
Vertebral morphology and intracolumnar variation of the iconic African viperid snake Atheris (Serpentes, Viperidae)
No full textWe here provide a detailed description of the vertebral morphology of the African arboreal viperid snakes of the genus Atheris. Vertebrae of three different species of the genus, i.e., Atheris desaixi, Atheris hispida, and Atheris katangensis, were investigated via the aid of μCT (micro‐computed tomography) scanning. We describe several vertebrae from different regions of the vertebral column for all three species, starting from the atlas‐axis complex to the caudal tip, in order to demonstrate important differences regarding the intracolumnar variation. Comparison of these three species shows an overall similar general morphology of the trunk vertebrae among the Atheris species. We extensively compare Atheris with other known viperids. As the sole arboreal genus of Viperinae the prehensile nature of the tail of Atheris is reflected in its caudal vertebral morphology, which is characterized by a high number of caudal vertebrae but also robust and anteroventrally oriented pleurapophyses as a skeletal adaptation, linked with the myology of the tail, to an arboreal lifestyle. We anticipate that the extensive figuring of these viperid specimens will also aid identifications in paleontology
