Dry gas vents ('mazuku') in Goma region (North-Kivu, Democratic Republic of Congo): Formation and risk assessment

摘要

The word "mazuku" in Swahili means "evil wind". It corresponds to lowland (depressions) where carbon dioxide is released and, being heavier than air, accumulates at high - often lethal - concentrations (10 vol.% of CO_2 in atmosphere can be considered as the deadly threshold, even for a short time exposure). Mazuku are abundant in Goma and surrounding areas and particularly in the area south of the large volcanic edifices of Nyiragongo and Nyamulagira volcanoes located in the most eastern part of DR Congo, W branch of the East African Rift System (EARS). Our extensive field surveys have indicated that mazuku are concentrated within to and around the densely populated city of Goma close to the N shores of Lake Kivu, mainly near fault or fissure networks. At a more local scale, depressions allowing CO_2-rich gas accumulation are created by lava flow superposition, lava tunnels or cavity collapses, or directly associated with open fractures. People are killed by mazuku every year. Given political and social unrest coupled with the current important demographic and urban growths around Goma, the risks associated to mazuku are increasing accordingly. Mazuku are currently the most important natural risk in terms of human loss for the area and there is an urgent need for further research, more systematic mapping and monitoring of mazuku and for appropriate risk management to be implemented. This paper summarizes the current scientific knowledge on mazuku as well as new advances and a preliminary risk assessment performed recently in the frame of the GORISK project.