Rockfall hazard gains popularity nowadays among researchers in different scientific fields, decision-makers and urban planners. The assessment of rockfall hazard requires detection, mapping and estimating the maximum travel distance that rock boulders may reach, commonly known as “rockfall runout”. This latter can change significantly under the effects of different triggering factors such as soil conditions, chemical, physical and geological rock properties. However, comparing and analyzing these different effects represents, to the best of our knowledge, one of the newest scientific challenges that need to be addressed. This paper presents a complete methodologic approach aiming to assess the rockfall hazard through runout estimation in three different conditions: (i) gravity, (ii) earthquakes, and (iii) the presence of moisture along the slope. The “Mtein” Village and its surrounding areas in the Mount Lebanon region were chosen as the study area because there have been numerous historic rockfalls and various-sized rocks, such as cobbles and boulders, scattered throughout the area. Thus, three-dimensional simulations were conducted using the Rockyfor3D software and aerial photos for the year 1999 to assess the rockfall runout, the energy curves, and the number of deposited rocks. The results reveal that earthquakes have the highest triggering effect on rockfall and that moisture has a damping effect on RFs by decreasing the kinetic energy. The study shows the importance of taking into consideration the influence of triggering factors as well as rock density on rockfall runout and hazard.
Cet article a pour objet l'étude spéléogénique de la grotte de Kanaan (Metn, Liban) située en rive gauche de la basse vallée du nahr Antélias au nord-est de Beyrouth. La diversité des morphologies et des remplissages présents dans cette cavité permet de retracer sa genèse et son évolution et, au-delà, de poser des jalons dans l'évolution géomorphologique du rebord occidental du Mont Liban. Ce dernier est recoupé par une série de petits fleuves côtiers, comme les nahr Beyrouth, Antélias, El Khab. Cet article présente les différentes étapes spéléogéniques qui ont pu être extraites de la cartographie géomorphologique. La carte présentée en hors-texte constitue la première carte géomorphologique souterraine d'une caverne libanaise. Les implications géomorphologiques et géologiques issues de la reconstitution spéléogénique sont développées au terme de cet article. Cet article est également l'expression des travaux qui sont actuellement menés sur les cavités libanaises afin de mettre en avant la richesse des informations paléogéographiques et paléoenvironnementales qui y sont contenues. Ces travaux ont permis de mettre en évidence une paléozone noyée karstique liée à un ancien niveau d'enfoncement du nahr Antélias. Il est intéressant de relever qu'on retrouve, dans la vallée voisine du nahr El Khab au niveau de la grotte de Jeita, une paléozone noyée karstique à une altitude similaire à celle relevée dans la grotte de Kanaan. Les conditions de l'enfoncement postérieur du nahr Antélias jusqu'à son niveau actuel sont discutées.
Beirut faced with climatic aridificationBeirut, the capital of Lebanon, is currently undergoing a significant deterioration of its air quality. At the same time, water resources appear to be a crucial challenge, especially in late summer. These two environmental problems simultaneously related to regional climatic characteristics, urban planning and anthropogenic activities, are likely to worsen in the middle term. Indeed, the country is starting to feel the early impacts of the climatic developments observed in the Near and Middle East: desertification is spreading, the length of the dry season increasing, rainfall patterns changing, and temperature rising significantly. However, no management policy has yet been implemented in response to such environmental constraints. Quite on the contrary, private initiatives are developing and putting human pressure on resources already under strain: urbanization is becoming vertically and horizontally denser, illegal wells are being multiplied, thus increasing the scarcity of water and pollutant emissions due to road traffic are suffocating the town. In the end, early signs of aridification combined with the lack of environmental management are threatening, especially in terms of water resources, the thus-far privileged position of Lebanon in the arid or semi-arid context.
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