Les corridors de lahars du volcan Merapi (Java, Indonésie) : des espaces entre risque et ressource. Contribution à la géographie des risques au Merapi.

Abstract : This PhD dissertation focuses on lahar-prone areas on the slopes of Merapi volcano, where boulders and sand mining in recent volcaniclastic deposits takes place. The method combines different approaches: fieldwork (mapping of the deposits and sampling of volcaniclastic sediments, interviews and questionnaire-based surveys), laboratory (sedimentology) and remote sensing. The dissertation first describes the 240 lahars which occurred during the 2010-2011 monsoon after the 2010 VEI-4 eruption of Merapi. Their recurrence and the main events are detailed. Then, the geomorphic processes generating lahar corridors are described, and their consequences on the houses, the crops and the road network are quantified and mapped. Moreover, hazard perception survey realized in many villages around the volcano helps to better localize lahar-related risk areas. Finally, volcaniclastic deposits are analyzed: different lithofacies are described, and special attention is paid to the sandy matrix. The second part of the dissertation focuses on sand mining in volcaniclastic deposits at Merapi volcano, which has never been studied before despite its great economic importance for local communities. It aims to quantify the extracted volumes and the main evolutions of the activity. The consequences of the 2010 eruption are analyzed and the risk for workers is assessed: quarries need to be considered as dangerous areas, and must not be forgotten in risk studies on Merapi. Indeed, livelihoods are valuable hints of social vulnerability. The dissertation reveals the vulnerability, the capacity and the resilience of local communities at Merapi: the last section of the manuscript presents a systemic risk analysis chart in which sand mining plays an important role. To conclude, this dissertation explores many different aspects of lahars from the hazard to the livelihood. It contributes to a better and systemic understanding of risk at Merapi volcano, and shows what are the main strategies developed by people living in such a dangerous areas in order to cope with disasters.
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Edouard de Belizal. Les corridors de lahars du volcan Merapi (Java, Indonésie) : des espaces entre risque et ressource. Contribution à la géographie des risques au Merapi.. Géographie. Université Panthéon-Sorbonne - Paris I, 2012. Français. ⟨tel-00931862⟩

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